Lidé
doc. Ing. Lukáš Jelínek, Ph.D.
Všechny publikace
Characteristic Mode Decomposition of Polarizability Tensors
 Autoři: Escobar, A., Baena, J., doc. Ing. Lukáš Jelínek, Ph.D.,
 Publikace: Proceedings of IEEE International Symposium on Antennas and Propagation and USNCURSI Radio Science Meeting APS/URSI 2023. NEW YORK: The Institute of Electrical and Electronics Engineers, 2023. p. 839840. ISBN 9781665442282.
 Rok: 2023
 DOI: 10.1109/USNCURSI52151.2023.10238304
 Odkaz: https://doi.org/10.1109/USNCURSI52151.2023.10238304
 Pracoviště: Katedra elektromagnetického pole

Anotace:
This abstract presents a method for evaluating four polarizability tensors using characteristic mode decomposition and scattering description based on the method of moments formulation of field integral equations. The method's precision is confirmed by comparison with polarizabilities obtained from the sixwaves method.
Characteristic Mode Decomposition Using the Scattering Dyadic in Arbitrary FullWave Solvers
 Autoři: prof. Ing. Miloslav Čapek, Ph.D., Lundgren, J., Gustafsson, M., Schab, K., doc. Ing. Lukáš Jelínek, Ph.D.,
 Publikace: IEEE Transactions on Antennas and Propagation. 2023, 71(1), 830839. ISSN 0018926X.
 Rok: 2023
 DOI: 10.1109/TAP.2022.3213945
 Odkaz: https://doi.org/10.1109/TAP.2022.3213945
 Pracoviště: Katedra elektromagnetického pole

Anotace:
Characteristic modes are formulated using the scattering dyadic, which maps incident plane waves to scattered farfields generated by an object of arbitrary material composition. Numerical construction of the scattering dyadic using arbitrary fullwave electromagnetic solvers is demonstrated in examples involving a variety of dielectric and magnetic materials. Wrapper functions for computing characteristic modes in methodofmoments, finitedifference time domain, and finiteelement solvers are provided as Supplementary Material.
Characteristic Modes of FrequencySelective Surfaces and Metasurfaces from Sparameter Data
 Autoři: Schab, K., Chen, F., doc. Ing. Lukáš Jelínek, Ph.D., prof. Ing. Miloslav Čapek, Ph.D., Lundgren, J., Gustafsson, M.
 Publikace: IEEE Transactions on Antennas and Propagation. 2023, 71(12), 96969706. ISSN 0018926X.
 Rok: 2023
 DOI: 10.1109/TAP.2023.3324991
 Odkaz: https://doi.org/10.1109/TAP.2023.3324991
 Pracoviště: Katedra elektromagnetického pole

Anotace:
Characteristic modes of arbitrary twodimensional periodic systems are analyzed using scattering parameter data. This approach bypasses the need for periodic integral equations and allows for characteristic modes to be computed from generic simulation or measurement data. Example calculations demonstrate the efficacy of the method through comparison against a periodic method of moments formulation for a simple, singlelayer conducting unit cell. The effect of vertical structure and electrical size on the number of modes is studied and its discrete nature is verified with example calculations. A multiband polarizationselective surface and a beamsteering metasurface are presented as additional examples.
DensityBased Topology Optimization in Method of Moments: Qfactor Minimization
 Autoři: Ing. Jonáš Tuček, prof. Ing. Miloslav Čapek, Ph.D., doc. Ing. Lukáš Jelínek, Ph.D., Sigmund, O.
 Publikace: IEEE Transactions on Antennas and Propagation. 2023, 71(12), 97389751. ISSN 0018926X.
 Rok: 2023
 DOI: 10.1109/TAP.2023.3321373
 Odkaz: https://doi.org/10.1109/TAP.2023.3321373
 Pracoviště: Katedra elektromagnetického pole

Anotace:
Classical gradientbased density topology optimization is adapted for methodofmoments numerical modeling to design a conductorbased system attaining the minimal antenna Qfactor evaluated via an energy stored operator. Standard topology optimization features are discussed, e.g., interpolation scheme and density and projection filtering. The performance of the proposed technique is demonstrated in a few examples in terms of the realized Qfactor values and necessary computational time to obtain a design. The optimized designs are compared to the fundamental bound and wellknown empirical structures. The presented framework can provide a completely novel design, as presented in the second example.
Fundamental Bound on Maximum Antenna Gain as a Sum of Characteristic Modes
 Autoři: prof. Ing. Miloslav Čapek, Ph.D., doc. Ing. Lukáš Jelínek, Ph.D.,
 Publikace: 2023 17th European Conference on Antennas and Propagation. Bruxelles: The European Association on Antennas and Propagation, 2023. p. 14. ISBN 9781665475419.
 Rok: 2023
 DOI: 10.23919/EuCAP57121.2023.10133575
 Odkaz: https://doi.org/10.23919/EuCAP57121.2023.10133575
 Pracoviště: Katedra elektromagnetického pole

Anotace:
Characteristic mode theory for lossy obstacles is employed to show that the fundamental bound on maximal antenna gain can be composed of a simple sum of characteristic antenna gains. This connects traditional work on bounds proposed by Harrington and modern currentdensitybased approaches utilizing convex optimization. The developed theory helps to understand what the true performance bound of a design region is. The paper is accompanied by an example demonstrating the working principles and verifying the developed theory.
Iterative Calculation of Characteristic Modes Using Arbitrary FullWave Solvers
 Autoři: Lundgren, J., Schab, K., prof. Ing. Miloslav Čapek, Ph.D., Gustafsson, M., doc. Ing. Lukáš Jelínek, Ph.D.,
 Publikace: IEEE Antennas and Wireless Propagation Letters. 2023, 22(4), 799803. ISSN 15361225.
 Rok: 2023
 DOI: 10.1109/LAWP.2022.3225706
 Odkaz: https://doi.org/10.1109/LAWP.2022.3225706
 Pracoviště: Katedra elektromagnetického pole

Anotace:
An iterative algorithm is adopted to construct approximate representations of matrices describing the scattering properties of arbitrary objects. The method is based on the implicit evaluation of scattering responses from iteratively generated excitations. The method does not require explicit knowledge of any system matrices (e.g., stiffness or impedance matrices) and is wellsuited for use with matrixfree and iterative fullwave solvers, such as FDTD (Finitedifference timedomain method), FEM (Finite element method), and MLFMA (Multilevel Fast Multipole Algorithm). The proposed method allows for significant speedup compared to the direct construction of a full transition matrix or scattering dyadic. The method is applied to the characteristic mode decomposition of arbitrarily shaped obstacles of arbitrary material distribution. Examples demonstrating the speedup and complexity of the algorithm are studied with several commercial software packages.
Maximum Peak Radiation Intensity
 Autoři: Ing. Jakub Liška, doc. Ing. Lukáš Jelínek, Ph.D., prof. Ing. Miloslav Čapek, Ph.D.,
 Publikace: 2023 24th International Conference on Applied Electromagnetics and Communications (ICECOM). IEEE Xplore, 2023. ISBN 9798350313017.
 Rok: 2023
 DOI: 10.1109/ICECOM58258.2023.10367960
 Odkaz: https://doi.org/10.1109/ICECOM58258.2023.10367960
 Pracoviště: Katedra elektromagnetického pole

Anotace:
This paper presents a method for maximizing radiated power flux in a specified direction and timeframe while accounting for the radiation mechanism and impedance matching in a fullwave manner. The proposed approach leverages the formulation of field integral equations using the method of moments and employs convex optimization techniques. By considering the interplay between radiated power and impedance matching, the process enables the attainment of optimal power flux. Through rigorous analysis and simulation, this study unveils insights into the optimal performance of pulseradiating antennas.
Maximum Radiation Efficiency of an Implantable Antenna: The Role of HighOrder Modes
 Autoři: Ing. Jakub Liška, Gao, M., doc. Ing. Lukáš Jelínek, Ph.D., prof. Ing. Miloslav Čapek, Ph.D., Skrivervik, A.
 Publikace: 2023 17th European Conference on Antennas and Propagation. Bruxelles: The European Association on Antennas and Propagation, 2023. ISBN 9781665475419.
 Rok: 2023
 DOI: 10.23919/EuCAP57121.2023.10133397
 Odkaz: https://doi.org/10.23919/EuCAP57121.2023.10133397
 Pracoviště: Katedra elektromagnetického pole

Anotace:
A combination of two numerical techniques of computational electromagnetics, namely, method of moments and vector spherical wave expansion, is used to show performance limitations on the radiation efficiency of implantable antennas and to efficiently resolve computation difficulties imposed by the interaction of an electrically small radiator with its host body. The results computed for ideal and realistic radiation sources prove the significantly limited performance of implantable antennas. The role of substructure characteristic modes decomposition in the formulation of this fundamental limit is explained.
Minimization of Channel Correlation Between Antenna Clusters
 Autoři: Ing. Vojtěch Neuman, prof. Ing. Miloslav Čapek, Ph.D., doc. Ing. Lukáš Jelínek, Ph.D., Lehtovuori, A., Viikari, V.
 Publikace: 2023 17th European Conference on Antennas and Propagation. Bruxelles: The European Association on Antennas and Propagation, 2023. ISBN 9781665475419.
 Rok: 2023
 Pracoviště: Katedra elektromagnetického pole

Anotace:
An existing method for maximization of the total efficiency of antenna clusters is modified so that the correlation between the channels can be suppressed while maintaining good balance of powers in different channels. This is achieved by setting additional constraints based on matrix description which control the system radiated power by means of weighted feeding coefficients. The developed theory is demonstrated on the example of four parallel dipoles forming two antenna clusters.
Optimal Inverse Design Based on Memetic Algorithms  Part I: Theory and Implementation
 Autoři: prof. Ing. Miloslav Čapek, Ph.D., doc. Ing. Lukáš Jelínek, Ph.D., Kadlec, P., Gustafsson, M.
 Publikace: IEEE Transactions on Antennas and Propagation. 2023, 71(11), 88068816. ISSN 0018926X.
 Rok: 2023
 DOI: 10.1109/TAP.2023.3308587
 Odkaz: https://doi.org/10.1109/TAP.2023.3308587
 Pracoviště: Katedra elektromagnetického pole

Anotace:
A memetic framework for optimal inverse design is proposed by combining a local gradientbased procedure and a robust global scheme. The procedure is based on methodofmoment (MoM) matrices and does not demand full inversion of a system matrix. Fundamental bounds are evaluated for all optimized metrics in the same manner, providing natural stopping criteria and quality measures for realized devices. Compared to densitybased topology optimization, the proposed routine does not require filtering or thresholding. Compared to commonly used heuristics, the technique is significantly faster, still preserving a high level of versatility and robustness. This is a twopart article in which the first part is devoted to the theoretical background and properties, and the second part applies the method to examples of varying complexity.
Optimal Inverse Design Based on Memetic Algorithms  Part II: Examples and Properties
 Autoři: prof. Ing. Miloslav Čapek, Ph.D., doc. Ing. Lukáš Jelínek, Ph.D., Kadlec, P., Gustafsson, M.
 Publikace: IEEE Transactions on Antennas and Propagation. 2023, 71(11), 88178829. ISSN 0018926X.
 Rok: 2023
 DOI: 10.1109/TAP.2023.3308583
 Odkaz: https://doi.org/10.1109/TAP.2023.3308583
 Pracoviště: Katedra elektromagnetického pole

Anotace:
Optimal inverse design, including topology optimization and evaluation of fundamental bounds on performance, which was introduced in Part 1, is applied to various antenna design problems. A memetic scheme for topology optimization combines local and global techniques to accelerate convergence and maintain robustness. Methodofmoments (MoMs) matrices are used to evaluate objective functions and allow determination of fundamental bounds on performance. By applying the Shermann–Morrison–Woodbury identity, the repetitively performed structural update is inversionfree yet fullwave. The technique can easily be combined with additional features often required in practice, e.g., only a part of the structure is controllable, or evaluation of an objective function is required in a subdomain only. The memetic framework supports multifrequency and multiport optimization and offers many other advantages, such as an actual shape being known at every moment of the optimization. The performance of the method is assessed, including its convergence and computational cost.
Quality Factor Minimization of Electrically Small Antennas by Density Topology Optimization
 Autoři: Ing. Jonáš Tuček, prof. Ing. Miloslav Čapek, Ph.D., doc. Ing. Lukáš Jelínek, Ph.D., Sigmund, O.
 Publikace: 2023 17th European Conference on Antennas and Propagation. Bruxelles: The European Association on Antennas and Propagation, 2023. p. 15. ISBN 9781665475419.
 Rok: 2023
 DOI: 10.23919/EuCAP57121.2023.10133497
 Odkaz: https://doi.org/10.23919/EuCAP57121.2023.10133497
 Pracoviště: Katedra elektromagnetického pole

Anotace:
Densitybased deterministic topology optimization is formulated for methodofmoments numerical technique, and the corresponding stored energy operator is exploited to evaluate and optimize antenna Qfactor. The settings are briefly discussed, including material interpolation function, density filters, and projection filters. The proposed technique is used to improve fractional bandwidth, i.e., minimize the quality factor of a current density excited on a spherical shell. The results are compared with known fundamental bounds and with realized spherical helices.
Transducer and Radiation Efficiency Figures of a Multiport Antenna Array
 Autoři: prof. Ing. Miloslav Čapek, Ph.D., doc. Ing. Lukáš Jelínek, Ph.D.,
 Publikace: IEEE Transactions on Antennas and Propagation. 2023, 71(7), 61326137. ISSN 0018926X.
 Rok: 2023
 DOI: 10.1109/TAP.2023.3264834
 Odkaz: https://doi.org/10.1109/TAP.2023.3264834
 Pracoviště: Katedra elektromagnetického pole

Anotace:
Optimal performance of antennas used in MIMO systems is addressed in this paper with optimality being expressed in terms of the power radiated which is subject to realistic, yet unknown, excitation and fixed, however arbitrarily complicated, matching. It is shown that if excitation is not specified, the optimality of a MIMO radiating system has to be understood differently as compared to the case of a specified excitation. Consequently, two important figures of merits  transducer and radiation efficiency figures  are adopted to measure the quality of the MIMO radiating systems. The communication is accompanied by examples illustrating the theoretical concepts.
Upper Bound on Instantaneous Power Flux
 Autoři: doc. Ing. Lukáš Jelínek, Ph.D., Ing. Jakub Liška, prof. Ing. Miloslav Čapek, Ph.D.,
 Publikace: Proceedings of IEEE International Symposium on Antennas and Propagation and USNCURSI Radio Science Meeting APS/URSI 2023. NEW YORK: The Institute of Electrical and Electronics Engineers, 2023. p. 16031604. ISBN 9781665442282.
 Rok: 2023
 DOI: 10.1109/USNCURSI52151.2023.10237969
 Odkaz: https://doi.org/10.1109/USNCURSI52151.2023.10237969
 Pracoviště: Katedra elektromagnetického pole

Anotace:
This abstract presents a method for maximization of the radiation in a given direction and a given time. The radiation mechanism and the impedance matching are taken into account in a fullwave manner. The approach is based on the method of moments formulation of field integral equations and convex optimization.
Upper Bound on Transducer and Radiation Efficiencies of a Multiport Antenna Arrays
 Autoři: prof. Ing. Miloslav Čapek, Ph.D., doc. Ing. Lukáš Jelínek, Ph.D.,
 Publikace: Proceedings of IEEE International Symposium on Antennas and Propagation and USNCURSI Radio Science Meeting APS/URSI 2023. NEW YORK: The Institute of Electrical and Electronics Engineers, 2023. ISBN 9781665442282.
 Rok: 2023
 DOI: 10.1109/USNCURSI52151.2023.10238259
 Odkaz: https://doi.org/10.1109/USNCURSI52151.2023.10238259
 Pracoviště: Katedra elektromagnetického pole

Anotace:
The optimal performance of MIMO antennas is studied via the tools of convex optimization, utilizing two different concepts of power entering radiating systems: available and incident power. Two figures of merit – radiation and transducer figures – are defined as Rayleigh quotients over network system matrices and used to study several cases involving dipole antennas of various arrangements and balun transformers. It is concluded that the design strategy significantly differs depending on the amount of information known about the MIMO system and its excitation.
Characteristic Mode Decomposition of Scattering Dyadic
 Autoři: prof. Ing. Miloslav Čapek, Ph.D., Lundgren, J., Gustafsson, M., doc. Ing. Lukáš Jelínek, Ph.D., Schab, K.
 Publikace: Proceedings of IEEE International Symposium on Antennas and Propagation and USNCURSI Radio Science Meeting APS/URSI 2022. NEW YORK: The Institute of Electrical and Electronics Engineers, 2022. p. 12. ISBN 9781665496582.
 Rok: 2022
 DOI: 10.1109/APS/USNCURSI47032.2022.9886601
 Odkaz: https://doi.org/10.1109/APS/USNCURSI47032.2022.9886601
 Pracoviště: Katedra elektromagnetického pole

Anotace:
This abstract describes the decomposition of a matrix representing a scattering dyadic into characteristic modes. Scattering dyadic, as compared to conventionally used impedance matrices, are independent of numerical method used to compute them and the same characteristic mode formulation can be used for decomposition of composite and inhomogeneous materials. The utilization of scattering dyadic makes it possible to synthesize characteristic modes which are orthogonal over prescribed portions of the farfield sphere, or expost decomposition of measured data. The theory is demonstrated on a simple example and its features are discussed.
Cloaking Synthesis Based on Exact Reanalysis
 Autoři: prof. Ing. Miloslav Čapek, Ph.D., doc. Ing. Lukáš Jelínek, Ph.D., Gustafsson, M., Schab, K.
 Publikace: Proceedings of IEEE International Symposium on Antennas and Propagation and USNCURSI Radio Science Meeting APS/URSI 2022. NEW YORK: The Institute of Electrical and Electronics Engineers, 2022. p. 12. ISBN 9781665496582.
 Rok: 2022
 DOI: 10.1109/APS/USNCURSI47032.2022.9886332
 Odkaz: https://doi.org/10.1109/APS/USNCURSI47032.2022.9886332
 Pracoviště: Katedra elektromagnetického pole

Anotace:
A novel synthesizing procedure is introduced and employed to extract locallyoptimal cloaking devices. Their performance is compared with fundamental bounds found using a convex optimization approach. The optimization method is based on a methodofmoments paradigm utilizing rank1 updates of the structure iteratively performed based on a greedy algorithm. This approach produces locally optimal shapes and its incorporation into a global search strategy is described and applied. As compared to classical topology optimization schemes, no postprocessing is required. Two canonical problems are solved and presented.
Computation of Fundamental Bounds for Antennas
 Autoři: Ing. Jakub Liška, doc. Ing. Lukáš Jelínek, Ph.D., prof. Ing. Miloslav Čapek, Ph.D.,
 Publikace: Proceedings of 16th European Conference on Antennas and Propagation. Piscataway, NJ: IEEE, 2022. p. 14. ISBN 9788831299046.
 Rok: 2022
 DOI: 10.23919/EuCAP53622.2022.9769248
 Odkaz: https://doi.org/10.23919/EuCAP53622.2022.9769248
 Pracoviště: Katedra elektromagnetického pole

Anotace:
Fundamental bounds play an important role in antenna design. Using method of moments and electric field integral equation, this paper shows a formulation of fundamental bounds on antenna metrics based on optimal current density. This methodology is applied to two representative and challenging examples. The first example examines YagiUda antenna and compares it with performance limits on Qfactor, radiation efficiency, and directivity. The second example shows how to determine fundamental bounds when a designer has farfield constraints. In their entirety, the examples demonstrate variability and generality of this treatment and also recall the existence of an opensource computational package, which can be used for evaluation of fundamental bounds on various metrics including their mutual tradeoffs.
GradientBased Topology Optimization in Method of Moments with Black & White Material Elements
 Autoři: Ing. Jonáš Tuček, prof. Ing. Miloslav Čapek, Ph.D., doc. Ing. Lukáš Jelínek, Ph.D.,
 Publikace: Proceedings of 16th European Conference on Antennas and Propagation. Piscataway, NJ: IEEE, 2022. ISBN 9788831299046.
 Rok: 2022
 Pracoviště: Katedra elektromagnetického pole

Anotace:
A topology optimization technique based on exact reanalysis is proposed within methodofmoments formalism. The optimization is formulated over a fixed discretization grid by performing general block structural modification. The procedure is based on an inversionfree evaluation of topological sensitivities, constituting a gradientbased local step that is iteratively restarted by the genetic algorithm. The proposed method sacrifices structural resolution at the expense of lower computational time and direct manufacturability. The method's validity and effectiveness are demonstrated in two examples.
Method of Moments and Tmatrix Hybrid
 Autoři: Losenický, V., doc. Ing. Lukáš Jelínek, Ph.D., prof. Ing. Miloslav Čapek, Ph.D., Gustasfsson, M.
 Publikace: IEEE Transactions on Antennas and Propagation. 2022, 70(5), 35603574. ISSN 0018926X.
 Rok: 2022
 DOI: 10.1109/TAP.2021.3138265
 Odkaz: https://doi.org/10.1109/TAP.2021.3138265
 Pracoviště: Katedra elektromagnetického pole

Anotace:
Hybrid computational schemes combining the advantages of a method of moments formulation of a field integral equation and Tmatrix method are developed in this paper. The hybrid methods are particularly efficient when describing the interaction of electrically small complex objects and electrically large objects of canonical shapes such as spherical multilayered bodies where the Tmatrix method is reduced to the Mie series making the method an interesting alternative in the design of implantable antennas or exposure evaluations. Method performance is tested on a spherical multilayer model of the human head. Along with the hybrid method, an evaluation of the transition matrix of an arbitrarily shaped object is presented and the characteristic mode decomposition is performed, exhibiting fourfold numerical precision as compared to conventional approaches.
Performance bounds of magnetic traps for neutral particles
 Autoři: Ing. Jakub Liška, doc. Ing. Lukáš Jelínek, Ph.D., prof. Ing. Miloslav Čapek, Ph.D.,
 Publikace: PHYSICAL REVIEW A. 2022, 106 19. ISSN 24699926.
 Rok: 2022
 DOI: 10.1103/PhysRevA.106.053110
 Odkaz: https://doi.org/10.1103/PhysRevA.106.053110
 Pracoviště: Katedra elektromagnetického pole

Anotace:
Knowledge of the fundamental limitations on a magnetic trap for neutral particles is of paramount interest to designers as it allows for the rapid assessment of the feasibility of specific trap requirements or the quality of a given design. In this paper, performance limitations are defined for convexity of magnetic trapping potential and bias field using a local approximation in the trapping center. As an example, the fundamental bounds are computed for current supporting regions in the form of a spherical shell, a cylindrical region, and a box. A Paretooptimal set considering both objectives is found and compared with known designs of the baseball trap and IoffePritchard trap. The comparison reveals a significant gap in the performance of classical trap designs from fundamental limitations. This indicates a possibility of improved trap designs and modern techniques of shape synthesis are applied in order to prove their existence. The topologically optimized traps perform almost two times better as compared to conventional designs. Last, but not least, the developed framework might serve as a prototype for the formulation of fundamental limitations on plasma confinement in a wider sense.
Shape Regularization and Acceleration of Topology Optimization via Point Group Symmetries
 Autoři: prof. Ing. Miloslav Čapek, Ph.D., Ing. Vojtěch Neuman, Ing. Jonáš Tuček, doc. Ing. Lukáš Jelínek, Ph.D.,
 Publikace: Proceedings of 16th European Conference on Antennas and Propagation. Piscataway, NJ: IEEE, 2022. p. 14. ISBN 9788831299046.
 Rok: 2022
 DOI: 10.23919/EuCAP53622.2022.9769019
 Odkaz: https://doi.org/10.23919/EuCAP53622.2022.9769019
 Pracoviště: Katedra elektromagnetického pole

Anotace:
The existent technique for shape optimization based on exact reanalysis of methodofmoments models is extended by symmetry operators. Their application is twofold: to prescribe a given symmetry and accelerate the optimization by reducing the number of unknowns, or to penalize unsymmetrical shapes, constraining thus the regularity and simplifying potential manufacturing.
Shape Representation in a Fixed Discretization Grid for Accelerated Topology Optimization
 Autoři: Ing. Vojtěch Neuman, prof. Ing. Miloslav Čapek, Ph.D., doc. Ing. Lukáš Jelínek, Ph.D.,
 Publikace: Proceedings of 16th European Conference on Antennas and Propagation. Piscataway, NJ: IEEE, 2022. ISBN 9788831299046.
 Rok: 2022
 Pracoviště: Katedra elektromagnetického pole

Anotace:
The topology optimization based on iterative changes of discretization is introduced. The optimal solution on coarse discretization is translated and enhanced on dense discretization. The similarity matrix used for solution translation is defined. Two examples of Qfactor minimization are shown to depict improvements in evaluation spee
Thickness Evaluation of Hollow Nonmagnetic Cylinders Utilizing a Motional Eddy Current
 Autoři: Ing. Mehran Mirzaei, Ph.D., prof. Ing. Pavel Ripka, CSc., Grim, V., doc. Ing. Lukáš Jelínek, Ph.D., Ing. Jakub Svatoš, Ph.D.,
 Publikace: Measurement. 2022, 189 113. ISSN 1873412X.
 Rok: 2022
 DOI: 10.1016/j.measurement.2021.110463
 Odkaz: https://doi.org/10.1016/j.measurement.2021.110463
 Pracoviště: Katedra elektromagnetického pole, Katedra měření

Anotace:
This paper presents a way to calculate the shell thickness of nonmagnetic hollow cylinders for nondestructive applications. Aluminum cylinders with a solid structure and with a hollow structure are considered. The motion component of the induced eddy currents in a conductive cylinder is utilized to evaluate the shell thickness of hollow conductive cylinders at various frequencies and at variable speeds. One axisymmetric excitation coil and two axisymmetric pickup coils with antiserial connection are used. An analytical method using an axisymmetric computational model is developed for a parametric analysis of solid and hollow cylinder structures and shell thickness calculations, in which Fourier series are utilized. A 2D axisymmetric finite element method is also performed for a comparison with the results of the analytical method. The measurements at variable speeds and at various frequencies are presented with various hollow aluminum cylinders. The high linearity of the induced voltage versus the speed curve makes it possible to calculate the shell thickness of nonmagnetic hollow cylinders at different speeds.
Transition Matrix in Characteristic Modes Theory
 Autoři: doc. Ing. Lukáš Jelínek, Ph.D., Gustafsson, M., Schab, K., prof. Ing. Miloslav Čapek, Ph.D., Moreno Pérez, E.
 Publikace: Proceedings of IEEE International Symposium on Antennas and Propagation and USNCURSI Radio Science Meeting APS/URSI 2022. NEW YORK: The Institute of Electrical and Electronics Engineers, 2022. p. 291292. ISBN 9781665496582.
 Rok: 2022
 DOI: 10.1109/APS/USNCURSI47032.2022.9887318
 Odkaz: https://doi.org/10.1109/APS/USNCURSI47032.2022.9887318
 Pracoviště: Katedra elektromagnetického pole

Anotace:
This abstract presents the versatility and computational effectiveness of characteristic mode decomposition based on the transition matrix. The described treatment is valid for all lossless and linear material distributions and is independent of the numerical method used to resolve a particular scattering scenario.
Unified Theory of Characteristic Modes  Part I: Fundamentals
 Autoři: Gustafsson, M., doc. Ing. Lukáš Jelínek, Ph.D., Schab, K., prof. Ing. Miloslav Čapek, Ph.D.,
 Publikace: IEEE Transactions on Antennas and Propagation. 2022, 70(12), 1180111813. ISSN 0018926X.
 Rok: 2022
 DOI: 10.1109/TAP.2022.3211338
 Odkaz: https://doi.org/10.1109/TAP.2022.3211338
 Pracoviště: Katedra elektromagnetického pole

Anotace:
A unification of characteristic mode decomposition for all methodofmoment (MoM) formulations of the field integral equations describing freespace scattering is derived. The work is based on an algebraic link between the impedance and transition matrices, the latter of which was used in early definitions of characteristic modes and is uniquely defined for all the scattering scenarios. This also makes it possible to extend the known application domain of characteristic mode decomposition to any other frequencydomain solver capable of generating the transition matrices, such as finite difference or finite element methods. The formulation of characteristic modes using a transition matrix allows for the decomposition of induced currents and scattered fields from arbitrarily shaped objects, providing high numerical dynamics and increased stability, removing the issue of spurious modes, and offering good control of convergence. This first part of a twopart article introduces the entire theory, extensively discusses its properties, and offers its basic numerical validation.
Unified Theory of Characteristic Modes  Part II: Tracking, Losses, and FEM Evaluation
 Autoři: Gustafsson, M., doc. Ing. Lukáš Jelínek, Ph.D., Schab, K., prof. Ing. Miloslav Čapek, Ph.D.,
 Publikace: IEEE Transactions on Antennas and Propagation. 2022, 70(12), 1181411824. ISSN 0018926X.
 Rok: 2022
 DOI: 10.1109/TAP.2022.3209264
 Odkaz: https://doi.org/10.1109/TAP.2022.3209264
 Pracoviště: Katedra elektromagnetického pole

Anotace:
This is the second component of a twopart article dealing with a unification of characteristic mode decomposition. This second part addresses modal tracking, interpolation, and the role of ohmic losses, and presents several numerical examples for surfacebased methodofmoment (MoM) formulations. A new tracking algorithm based on the algebraic properties of the transition matrix is developed, achieving excellent precision and requiring a very low number of frequency samples when compared with procedures previously reported in the literature. The transition matrix is further used to show that characteristic mode decomposition of lossy objects fails to deliver orthogonal farfields and to demonstrate how characteristic modes can be evaluated using the finite element method (FEM).
Upper bounds on focusing efficiency
 Autoři: Schab, K., doc. Ing. Lukáš Jelínek, Ph.D., prof. Ing. Miloslav Čapek, Ph.D., Gustafsson, M.
 Publikace: Optics Express. 2022, 30(25), 4570545723. ISSN 10944087.
 Rok: 2022
 DOI: 10.1364/OE.472558
 Odkaz: https://doi.org/10.1364/OE.472558
 Pracoviště: Katedra elektromagnetického pole

Anotace:
Upper bounds on the focusing efficiency of aperture fields and lens systems are formulated using integral equation representations of Maxwell’s equations and Lagrangian duality. Two forms of focusing efficiency are considered based on lens exit plane fields and optimal polarization currents within lens design regions of prescribed shape and available materials. Bounds are compared against the performance of classical prescriptions of ideal lens aperture fields, hyperbolic lens designs, and lenses produced by inverse design. Results demonstrate that, without regularization, focusing efficiency based solely on lens exit plane fields is unbounded, similar to the problem of unbounded antenna directivity. Additionally, results considering extruded twodimensional dielectric geometries driven by outofplane electric fields for the calculation of bounds and inverse design demonstrate that aperture fields based on timereversal do not necessarily yield optimal lens focusing efficiency, particularly in the case of nearfield (high numerical aperture) focusing.
A Role of Symmetries in Evaluation of Fundamental Bounds
 Autoři: prof. Ing. Miloslav Čapek, Ph.D., doc. Ing. Lukáš Jelínek, Ph.D., Mašek, M.
 Publikace: IEEE Transactions on Antennas and Propagation. 2021, 69(11), 77297742. ISSN 0018926X.
 Rok: 2021
 DOI: 10.1109/TAP.2021.3070103
 Odkaz: https://doi.org/10.1109/TAP.2021.3070103
 Pracoviště: Katedra elektromagnetického pole

Anotace:
A problem of the erroneous duality gap caused by the presence of symmetries is solved in this paper utilizing point group theory. The optimization problems are first divided into two classes based on their predisposition to suffer from this deficiency. Then, the classical problem of Qfactor minimization is shown in an example where the erroneous duality gap is eliminated by combining solutions from orthogonal subspaces. Validity of this treatment is demonstrated in a series of subsequent examples of increasing complexity spanning the wide variety of optimization problems, namely minimum Qfactor, maximum antenna gain, minimum total active reflection coefficient, or maximum radiation efficiency with selfresonant constraint. They involve problems with algebraic and geometric multiplicities of the eigenmodes, and are completed by an example introducing the selective modification of modal currents falling into one of the symmetryconformal subspaces. The entire treatment is accompanied with a discussion of finite numerical precision, and mesh grid imperfections and their influence on the results. Finally, the robust and unified algorithm is proposed and discussed, including advanced topics such as the uniqueness of the optimal solutions, dependence on the number of constraints, or an interpretation of the qualitative difference between the two classes of the optimization problems.
Excitation of Orthogonal Radiation States
 Autoři: Mašek, M., doc. Ing. Lukáš Jelínek, Ph.D., prof. Ing. Miloslav Čapek, Ph.D.,
 Publikace: IEEE Transactions on Antennas and Propagation. 2021, 69(9), 53655376. ISSN 0018926X.
 Rok: 2021
 DOI: 10.1109/TAP.2021.3061161
 Odkaz: https://doi.org/10.1109/TAP.2021.3061161
 Pracoviště: Katedra elektromagnetického pole

Anotace:
A technique of designing antenna excitation realizing orthogonal states is presented. It is shown that a symmetric antenna geometry is required in order to achieve orthogonality with respect to all physical quantities. A maximal number of achievable orthogonal states and a minimal number of ports required to excite them are rigorously determined from the knowledge of an antenna’s symmetries. The number of states and number of ports are summarized for commonly used point groups (a rectangle, a square, etc.). The theory is applied to an example of a rectangular rim where the positions of ports providing the best total active reflection coefficient, an important metric in multiport systems, are determined. The described technique can easily be implemented in existing solvers based on integral equations.
Finding Optimal Total Active Reflection Coefficient and Realized Gain for Multiport Lossy Antennas
 Autoři: prof. Ing. Miloslav Čapek, Ph.D., doc. Ing. Lukáš Jelínek, Ph.D., Mašek, M.
 Publikace: IEEE Transactions on Antennas and Propagation. 2021, 69(5), 24812493. ISSN 0018926X.
 Rok: 2021
 DOI: 10.1109/TAP.2020.3030941
 Odkaz: https://doi.org/10.1109/TAP.2020.3030941
 Pracoviště: Katedra elektromagnetického pole

Anotace:
A numerically effective description of the total active reflection coefficient and realized gain are studied for multiport antennas. Material losses are fully considered. The description is based on operators represented in an entiredomain portmode basis, i.e., on matrices with favorably small dimensions. Optimal performance is investigated and conditions on optimal excitation and matching are derived. The solution to the combinatorial problem of optimal ports’ placement and optimal feeding synthesis is also accomplished. Four examples of various complexity are numerically studied, demonstrating the advantages of the proposed method. The final formulas can easily be implemented in existing electromagnetic simulators using integral equation solver.
Fundamental Bounds for MultiPort Antennas
 Autoři: prof. Ing. Miloslav Čapek, Ph.D., doc. Ing. Lukáš Jelínek, Ph.D., Mašek, M.
 Publikace: 15th European Conference on Antennas and Propagation. Berlin: IEEE, 2021. p. 14. ISSN 21643342. ISBN 9788831299022.
 Rok: 2021
 DOI: 10.23919/EuCAP51087.2021.9411454
 Odkaz: https://doi.org/10.23919/EuCAP51087.2021.9411454
 Pracoviště: Katedra elektromagnetického pole

Anotace:
Currentdensity fundamental bounds are formulated for Nport radiators utilizing a port mode basis. A prescription is given for the transformation of fullwave methodofmoments matrix operators into port matrices. Fundamental bound on the total active reflection coefficient is presented as an example. Significant reduction of size of underlying matrices allows for simultaneous optimization of ports' placement and excitation amplitudes.
Fundamental Bounds on Cloaking Based on Convex Optimization
 Autoři: doc. Ing. Lukáš Jelínek, Ph.D., Gustafsson, M., Schab, K., prof. Ing. Miloslav Čapek, Ph.D.,
 Publikace: Proceedings of the 2021 Fifteenth International Congress on Artificial Materials for Novel Wave Phenomena. Rome: METAMORPHOSE VI AISBL, 2021. p. 13. ISBN 9781728150185.
 Rok: 2021
 DOI: 10.1109/Metamaterials52332.2021.9577149
 Odkaz: https://doi.org/10.1109/Metamaterials52332.2021.9577149
 Pracoviště: Katedra elektromagnetického pole

Anotace:
A convex optimization framework over contrast current density is developed to calculate fundamental bounds on the performance of linear passive cloaks. The formulation uses the method of moments applied to the electric field integral equation while using extincted power as the optimized metric. The presented results show that high cloaking efficiency requires cloaks made of lowloss and highcontrast materials.
Fundamental bounds on the performance of monochromatic passive cloaks
 Autoři: doc. Ing. Lukáš Jelínek, Ph.D., Gustafsson, M., prof. Ing. Miloslav Čapek, Ph.D., Schab, K.
 Publikace: Optics Express. 2021, 29(15), 2406824082. ISSN 10944087.
 Rok: 2021
 DOI: 10.1364/OE.428536
 Odkaz: https://doi.org/10.1364/OE.428536
 Pracoviště: Katedra elektromagnetického pole

Anotace:
Fundamental bounds on the performance of monochromatic scatteringcancellation and fieldzeroing cloaks made of prescribed linear passive materials occupying a predefined design region are formulated by projecting field quantities onto a subsectional basis and applying quadratically constrained quadratic programming. Formulations are numerically tested revealing key physical trends as well as advantages and disadvantages between the two classes of cloaks. Results show that the use of lowloss materials with high dielectric contrast affords the highest potential for effective cloaking.
Maximum Radiation Efficiency of Implanted Antennas Employing a Novel Hybrid Method
 Autoři: doc. Ing. Lukáš Jelínek, Ph.D., Ing. Jakub Liška, prof. Ing. Miloslav Čapek, Ph.D., Losenický, V., Gustafsson, M.
 Publikace: Proceedings of the 2021 IEEE International Symposium on Antennas and Propagation and North American Radio Science Meeting. Piscataway (New Jersey): IEEE, 2021. p. 13391340. ISBN 9781728146706.
 Rok: 2021
 DOI: 10.1109/APS/URSI47566.2021.9704153
 Odkaz: https://doi.org/10.1109/APS/URSI47566.2021.9704153
 Pracoviště: Katedra elektromagnetického pole

Anotace:
A hybrid combining Tmatrix method and electric field integral equation is used to formulate fundamental bounds on radiation efficiency of an implanted antenna. Resulting quadratic optimization problem is solved using a dual formulation. The results present the versatility of the described computational scheme and show the optimal current densities that are the least impaired by dissipation in the tissue.
Topology Optimization of Electrically Small Antennas With Shape Regularity Constraints
 Autoři: prof. Ing. Miloslav Čapek, Ph.D., Ing. Vojtěch Neuman, Ing. Jonáš Tuček, doc. Ing. Lukáš Jelínek, Ph.D., Gustafsson, M.
 Publikace: 15th European Conference on Antennas and Propagation. Berlin: IEEE, 2021. ISSN 21643342. ISBN 9788831299022.
 Rok: 2021
 Pracoviště: Katedra elektromagnetického pole

Anotace:
The existent framework for shape optimization of electrically small antennas is extended by a new set of geometrical operators. They are capable of operating over shapes directly, controlling their regularity, amount of used material, etc. The formulation is compatible with existent physical fitness functions and known fundamental bounds. A simple example of Qfactor minimization is presented.
Unified Approach to Characteristic Modes
 Autoři: prof. Ing. Miloslav Čapek, Ph.D., doc. Ing. Lukáš Jelínek, Ph.D., Losenický, V., Gustafsson, M., Schab, K.
 Publikace: Proceedings of the 2021 IEEE International Symposium on Antennas and Propagation and North American Radio Science Meeting. Piscataway (New Jersey): IEEE, 2021. p. 12. ISBN 9781728146706.
 Rok: 2021
 DOI: 10.1109/APS/URSI47566.2021.9703910
 Odkaz: https://doi.org/10.1109/APS/URSI47566.2021.9703910
 Pracoviště: Katedra elektromagnetického pole

Anotace:
An algebraic link between transition matrix and impedance matrix is utilized in this work to unify characteristic mode decomposition originally proposed by Garbacz with a framework proposed later on by Harrington and Mautz. The resulting formulation is unique to all method of moments formulations, valid for all linear and lossless materials, and has many favorable properties. The unified prescription is applicable to surface equivalence, bodyofrevolution, or volumetric method of moments formulations. The unification paves a way to establish characteristic modes as a standalone technique in timeharmonic domain being independent of method of moment paradigm, i.e., to utilize  for example  finite element method instead.
Design of a Linear Antenna Array: Variable Number of Dimensions Approach
 Autoři: Kadlec, P., prof. Ing. Miloslav Čapek, Ph.D., Rymus, J., Marek, M., Stumpf, M., doc. Ing. Lukáš Jelínek, Ph.D., Mašek, M., Kotalik, P.
 Publikace: 30th International Conference Radioelektronika. Piscataway: IEEE Service Center, 2020. p. 4752. ISBN 9781728164694.
 Rok: 2020
 DOI: 10.1109/RADIOELEKTRONIKA49387.2020.9092422
 Odkaz: https://doi.org/10.1109/RADIOELEKTRONIKA49387.2020.9092422
 Pracoviště: Katedra elektromagnetického pole

Anotace:
A linear antenna array design is usually formulated as a binary optimization task. A global optimization algorithm is then used to turn on/off a fixed number of elements positioned on a uniform grid. This paper introduces a new formulation of the problem: the optimizer searches for distances between individual elements and their total amount at the same time. Such a formulation has to be solved using the optimization with a variable number of dimensions that enables to work with decision space vectors having different lengths. Here, the Particle Swarm Optimization algorithm is used to solve different formulations of the linear antenna array design problem. The “uniform grid” formulation is compared with the “variable number of dimensions” formulation on several optimization tasks encompassing the minimization of selected antenna parameters: the SideLobe Level, the First Null Beam Width and the number of used (active) elements.
Feeding Positions Providing the Lowest TARC of Uncorrelated Channels
 Autoři: Mašek, M., prof. Ing. Miloslav Čapek, Ph.D., doc. Ing. Lukáš Jelínek, Ph.D.,
 Publikace: 2020 14TH EUROPEAN CONFERENCE ON ANTENNAS AND PROPAGATION (EUCAP). IEEE (Institute of Electrical and Electronics Engineers), 2020. ISBN 9788831299008.
 Rok: 2020
 Pracoviště: Katedra elektromagnetického pole

Anotace:
In this paper, point group theory is utilized for the simultaneous blockdiagonalization of all linear operators representing the underlying symmetrical structure. This procedure is utilized for designing orthogonal channels suitable, for example, for MIMO systems. Within these uncorrelated channels, the total active reflection coefficient is further formulated within the method of moments framework and is used to find position of feeders that provide orthogonal channels with maximum radiation.
Fundamental Bounds For Volumetric Structures and Their Feasibility
 Autoři: prof. Ing. Miloslav Čapek, Ph.D., doc. Ing. Lukáš Jelínek, Ph.D., Gustafsson, M., Schab, K.
 Publikace: 2020 14TH EUROPEAN CONFERENCE ON ANTENNAS AND PROPAGATION (EUCAP). IEEE (Institute of Electrical and Electronics Engineers), 2020. ISBN 9788831299008.
 Rok: 2020
 DOI: 10.23919/EuCAP48036.2020.9135082
 Odkaz: https://doi.org/10.23919/EuCAP48036.2020.9135082
 Pracoviště: Katedra elektromagnetického pole

Anotace:
Fundamental bounds on antenna and scattering metrics are presented in this paper utilizing volumetric method of moments. This makes it possible to investigate scenarios not solvable with classical surface method of moments which assumes that good conductors as used. One practical example is the study of plasmonic devices whose operation relies on the interaction between material properties and radiation mechanisms. The implementation of the code is briefly summarized, including some implementation hints which allow for fast evaluation of necessary matrix operators. Two optimization problems are introduced and solved for scattering and antenna problems. Feasibility of the bounds will be investigated with topology optimization and the results will be presented during the conference.
Hybrid MoM/TMatrix Method for Analysis of Interaction Between Objects
 Autoři: Losenický, V., prof. Ing. Miloslav Čapek, Ph.D., doc. Ing. Lukáš Jelínek, Ph.D., Gustafsson, M.
 Publikace: 2020 14TH EUROPEAN CONFERENCE ON ANTENNAS AND PROPAGATION (EUCAP). IEEE (Institute of Electrical and Electronics Engineers), 2020. ISBN 9788831299008.
 Rok: 2020
 Pracoviště: Katedra elektromagnetického pole

Anotace:
A hybrid method for analysis of an interaction between electromagnetic scatterers is introduced. The method connects the method of moments and Tmatrix method and represents a promising candidate capable of solving problems associated with 5G or antennas close to the human body. Two specific cases of the mutual position of the objects are shown. Preliminary results are demonstrated on two examples. The advantages and limitations of the method are discussed.
Modal Tracking Based on Group Theory
 Autoři: Mašek, M., prof. Ing. Miloslav Čapek, Ph.D., doc. Ing. Lukáš Jelínek, Ph.D., Schab, K.
 Publikace: IEEE Transactions on Antennas and Propagation. 2020, 68(2), 927937. ISSN 0018926X.
 Rok: 2020
 DOI: 10.1109/TAP.2019.2943354
 Odkaz: https://doi.org/10.1109/TAP.2019.2943354
 Pracoviště: Katedra elektromagnetického pole

Anotace:
Issues in modal tracking in the presence of crossings and crossing avoidances between eigenvalue traces are solved via the theory of point groups. The von~NeumannWigner theorem is used as a key factor in predictively determining mode behavior over arbitrary frequency ranges. The implementation and capabilities of the proposed procedure are demonstrated using characteristic mode decomposition as a motivating example. The procedure is, nevertheless, general and can be applied to an arbitrarily parametrized eigenvalue problems. A treatment of modal degeneracies is included and several examples are presented to illustrate modal tracking improvements and the immediate consequences of improper modal tracking. An approach leveraging a symmetryadapted basis to accelerate computation is also discussed. A relationship between geometrical and physical symmetries is demonstrated on a practical example.
SubStructure Limits to Optical Phenomena
 Autoři: doc. Ing. Lukáš Jelínek, Ph.D., Gustafsson, M., prof. Ing. Miloslav Čapek, Ph.D., Schab, K.
 Publikace: Proceedings of the 14th International Congress on Artificial Materials for Novel Wave Phenomena, Metamaterials 2020. Rome: METAMORPHOSE VI AISBL, 2020. p. 1402. ISBN 9788894114157.
 Rok: 2020
 DOI: 10.1109/Metamaterials49557.2020.9285045
 Odkaz: https://doi.org/10.1109/Metamaterials49557.2020.9285045
 Pracoviště: Katedra elektromagnetického pole

Anotace:
Fundamental limits on scattering metrics such as absorption, extinction, and Purcell’s factor are formulated by separating a scattering structure into controllable and uncontrollable regions. We present each bound as a special case of a general methodology based on the method of moments and convex optimization.
Tradeoffs in absorption and scattering by nanophotonic structures
 Autoři: Schab, K., Rothschild, A., Nguyen, K., prof. Ing. Miloslav Čapek, Ph.D., doc. Ing. Lukáš Jelínek, Ph.D., Gustafsson, M.
 Publikace: Optics Express. 2020, 28(24), 3658436599. ISSN 10944087.
 Rok: 2020
 DOI: 10.1364/OE.410520
 Odkaz: https://doi.org/10.1364/OE.410520
 Pracoviště: Katedra elektromagnetického pole

Anotace:
Tradeoffs between absorption and scattering cross sections of lossy obstacles confined to an arbitrarily shaped volume are formulated as a multiobjective optimization problem solvable by Lagrangiandual methods. Solutions to this optimization problem yield a Paretooptimal set, the shape of which reveals the feasibility of achieving simultaneously extremal absorption and scattering. Two forms of the tradeoff problems are considered involving both preassigned loss and reactive material parameters. Numerical comparisons between the derived multiobjective bounds and several classes of realized structures are made. Additionally, lowfrequency (electrically small, long wavelength) limits are examined for certain special cases.
Upper bounds on absorption and scattering
 Autoři: Gustafsson, M., Schab, K., doc. Ing. Lukáš Jelínek, Ph.D., prof. Ing. Miloslav Čapek, Ph.D.,
 Publikace: New Journal of Physics. 2020, 22(7), ISSN 13672630.
 Rok: 2020
 DOI: 10.1088/13672630/ab83d3
 Odkaz: https://doi.org/10.1088/13672630/ab83d3
 Pracoviště: Katedra elektromagnetického pole

Anotace:
A general framework for determining fundamental bounds in nanophotonics is introduced in this paper. The theory is based on convex optimization of dual problems constructed from operators generated by electromagnetic integral equations. The optimized variable is a contrast current defined within a prescribed region of a given material constitutive relations. Two power conservation constraints analogous to the optical theorem are utilized to tighten the bounds and to prescribe either losses or material properties. Thanks to the utilization of matrix rank1 updates, modal decompositions, and model order reduction techniques, the optimization procedure is computationally efficient even for complicated scenarios. No dual gaps are observed. The method is wellsuited to accommodate material anisotropy and inhomogeneity. To demonstrate the validity of the method, bounds on scattering, absorption, and extinction cross sections are derived first and evaluated for several canonical regions. The tightness of the bounds is verified by comparison to optimized spherical nanoparticles and shells. The next metric investigated is bidirectional scattering studied closely on a particular example of an electrically thin slab. Finally, the bounds are established for Purcell's factor and local field enhancement where a dimer is used as a practical example.
Approaching QFactor Bounds by Combining TM and TE Modes on a Cylindrical Shell
 Autoři: Losenický, V., prof. Ing. Miloslav Čapek, Ph.D., doc. Ing. Lukáš Jelínek, Ph.D.,
 Publikace: 2019 13TH EUROPEAN CONFERENCE ON ANTENNAS AND PROPAGATION (EUCAP). IEEE (Institute of Electrical and Electronics Engineers), 2019. p. 15. ISSN 21643342. ISBN 9788890701887.
 Rok: 2019
 Pracoviště: Katedra elektromagnetického pole

Anotace:
Surface current densities on cylindrical shells are studied in terms of fundamental bounds on Qfactor. It is shown that the optimal current solution is not feasible by means any of practical realization. A solution with the second lowest Qfactor is found using the resonant composition of modes. This current solution is proved to be attainable as a cylindrical helix. Optimal modal composition is studied with respect to cylinder eccentricity and diameter to length ratio. It is shown that a circular cylinder yields a Qfactor close to fundamental bounds, however, the limiting case of a rectangular plate yields only a Qfactor associated with the TM bound. The physical reasons for this behaviour are explained.
InversionFree Evaluation of Nearest Neighbors in Method of Moments
 Autoři: prof. Ing. Miloslav Čapek, Ph.D., doc. Ing. Lukáš Jelínek, Ph.D., Gustafsson, M.
 Publikace: IEEE Antennas and Wireless Propagation Letters. 2019, 18(11), 23112315. ISSN 15361225.
 Rok: 2019
 DOI: 10.1109/LAWP.2019.2912459
 Odkaz: https://doi.org/10.1109/LAWP.2019.2912459
 Pracoviště: Katedra elektromagnetického pole

Anotace:
A recently introduced technique of topology sensitivity in method of moments is extended by the possibility of adding degreesoffreedom (reconstruct) into underlying structure. The algebraic formulation is inversionfree, suitable for parallelization and scales favorably with the number of unknowns. The reconstruction completes the nearest neighbors procedure for an evaluation of the smallest shape perturbation. The performance of the method is studied with a greedy search over a Hamming graph representing the structure in which initial positions are chosen from a random set. The method is shown to be an effective data mining tool for machine learningrelated applications.
InversionFree Evaluation of Small Geometry Perturbation in Method of Moments
 Autoři: prof. Ing. Miloslav Čapek, Ph.D., doc. Ing. Lukáš Jelínek, Ph.D., Gustafsson, M.
 Publikace: 2019 IEEE International Symposium on Antennas and Propagation and USNCURSI Radio Science Meeting  Proceedings. Piscataway, NJ: IEEE, 2019. p. 10391040. ISBN 9781728106922.
 Rok: 2019
 DOI: 10.1109/APUSNCURSINRSM.2019.8888974
 Odkaz: https://doi.org/10.1109/APUSNCURSINRSM.2019.8888974
 Pracoviště: Katedra elektromagnetického pole

Anotace:
Topology sensitivity is introduced and defined to be utilized within method of moments. It is based on a series of the smallest perturbations of the investigated structure and, thanks to the application of the Woodbury matrix identity, its evaluation is inversionfree, suitable for vectorization and parallelization, and results in a fast and versatile tool for analyzing antenna optimality.
Modal Crossing Treatment Using Group Theory
 Autoři: Mašek, M., prof. Ing. Miloslav Čapek, Ph.D., doc. Ing. Lukáš Jelínek, Ph.D., Schab, K.
 Publikace: 2019 13TH EUROPEAN CONFERENCE ON ANTENNAS AND PROPAGATION (EUCAP). IEEE (Institute of Electrical and Electronics Engineers), 2019. ISSN 21643342. ISBN 9788890701887.
 Rok: 2019
 Pracoviště: Katedra elektromagnetického pole

Anotace:
Detecting modal crossings and crossing avoidances between eigenvalue traces in modal tracking is solved based on group theory. Rules based on the presence of symmetry are applied to predictively determine mode behavior over a frequency range. The procedure can be used for a large class of generalized eigenvalue problems and is demonstrated by an example of characteristic modes. An approach leveraging this procedure to accelerate computation is also discussed.
Optimal Planar Electric Dipole Antennas: Searching for antennas reaching the fundamental bounds on selected metrics
 Autoři: prof. Ing. Miloslav Čapek, Ph.D., doc. Ing. Lukáš Jelínek, Ph.D., Schab, K., Gustafsson, M., Jonsson, B.L.G., Ferrero, F., Ehrenborg, C.
 Publikace: IEEE Antennas and Propagation Magazine. 2019, 61(4), 1929. ISSN 10459243.
 Rok: 2019
 DOI: 10.1109/MAP.2019.2920088
 Odkaz: https://doi.org/10.1109/MAP.2019.2920088
 Pracoviště: Katedra elektromagnetického pole

Anotace:
Considerable time is often spent optimizing antennas to meet specific design metrics. Rarely, however, are the resulting antenna designs compared to rigorous physical bounds on those metrics. Here we study the performance of optimized planar meander line antennas with respect to such bounds. Results show that these simple structures meet the lower bound on radiation Qfactor (maximizing single resonance fractional bandwidth), but are far from reaching the associated physical bounds on efficiency. The relative performance of other canonical antenna designs is compared in similar ways, and the quantitative results are connected to intuitions from small antenna design, physical bounds, and matching network design.
Resonance Tuning Cost in Radiation Efficiency of Electrically Small Antennas
 Autoři: doc. Ing. Lukáš Jelínek, Ph.D., prof. Ing. Miloslav Čapek, Ph.D., Schab, K.
 Publikace: 2019 IEEE International Symposium on Antennas and Propagation and USNCURSI Radio Science Meeting  Proceedings. Piscataway, NJ: IEEE, 2019. p. 21652166. ISBN 9781728106922.
 Rok: 2019
 DOI: 10.1109/APUSNCURSINRSM.2019.8888674
 Odkaz: https://doi.org/10.1109/APUSNCURSINRSM.2019.8888674
 Pracoviště: Katedra elektromagnetického pole

Anotace:
Numerical tools are used to predict the upperbounds on radiation efficiency with and without a constraint on selfresonance. It is demonstrated that the assumption of lossless external tuning produces unrealistic results. The main result of this contribution is that, when realistic (e.g., finite conductivity) materials are used, the cost of resonance tuning in the radiation efficiency of small antenna systems is high and is manifested by a dissipation factor which scales as a fourth power of electrical size.
Shape Synthesis Based on Topology Sensitivity
 Autoři: prof. Ing. Miloslav Čapek, Ph.D., doc. Ing. Lukáš Jelínek, Ph.D., Gustafsson, M.
 Publikace: IEEE Transactions on Antennas and Propagation. 2019, 67(6), 38893901. ISSN 0018926X.
 Rok: 2019
 DOI: 10.1109/TAP.2019.2902749
 Odkaz: https://doi.org/10.1109/TAP.2019.2902749
 Pracoviště: Katedra elektromagnetického pole

Anotace:
A method evaluating the sensitivity of a given parameter to topological changes is proposed within the method of moments paradigm. The basis functions are used as degrees of freedom which, when compared to the classical pixeling technique, provide important advantages, one of them being impedance matrix inversion free evaluation of the sensitivity. The devised procedure utilizes port modes and their superposition which, together with only a single evaluation of all matrix operators, leads to a computationally effective procedure. The proposed method is approximately one hundred times faster than contemporary approaches, which allows the investigation of the sensitivity and the modification of shapes in realtime. The method is compared with known approaches and its validity and effectiveness is verified using a series of examples. The procedure can be implemented in uptodate EM simulators in a straightforward manner. It is shown that the iterative repetition of the topology sensitivity evaluation can be used for gradientbased topology synthesis. This technique can also be employed as a local step in global optimizers.
Topology Sensitivity in Method of Moments
 Autoři: prof. Ing. Miloslav Čapek, Ph.D., doc. Ing. Lukáš Jelínek, Ph.D., Gustafsson, M., Losenický, V.
 Publikace: 2019 13TH EUROPEAN CONFERENCE ON ANTENNAS AND PROPAGATION (EUCAP). IEEE (Institute of Electrical and Electronics Engineers), 2019. p. 13. ISSN 21643342. ISBN 9788890701887.
 Rok: 2019
 Pracoviště: Katedra elektromagnetického pole

Anotace:
Topology sensitivity is derived for the method of moments. It is a powerful technique for studying possible shape modifications of an antenna, showing how sensitive a structure is with respect to a given parameter when the smallest possible shape perturbation is performed. The method utilizes port modes and Woodbury identity. This makes it possible to evaluate sensitivity without the necessity of inverting the impedance matrix. No modification of the existent method of moments kernel is needed. Several examples are presented with discussion of different shapes and antenna parameters. The method can be extended so it consecutively removes degrees of freedom while performing shape optimization.
Utilization of Symmetries in Method of Moments
 Autoři: Mašek, M., prof. Ing. Miloslav Čapek, Ph.D., doc. Ing. Lukáš Jelínek, Ph.D., Schab, K.
 Publikace: 2019 IEEE International Symposium on Antennas and Propagation and USNCURSI Radio Science Meeting  Proceedings. Piscataway, NJ: IEEE, 2019. p. 21912192. ISBN 9781728106922.
 Rok: 2019
 DOI: 10.1109/APUSNCURSINRSM.2019.8888654
 Odkaz: https://doi.org/10.1109/APUSNCURSINRSM.2019.8888654
 Pracoviště: Katedra elektromagnetického pole

Anotace:
The utilization of symmetries on operators within method of moments is presented. Three examples are presented and commented upon  (i) the separation of the problem into a set of smaller subproblems solved independently making significant reduction in computational time, (ii) effective modal tracking where a decision on modal crossing is made in a deterministic manner, and (iii) a design of feeding schemes to obtain orthogonal channels to be used in MIMO systems.
Accurate and Efficient Evaluation of Characteristic Modes
 Autoři: Tayli, D., prof. Ing. Miloslav Čapek, Ph.D., Akrou, L., Losenický, V., doc. Ing. Lukáš Jelínek, Ph.D., Gustafsson, M.
 Publikace: IEEE Transactions on Antennas and Propagation. 2018, 66(12), 70667075. ISSN 0018926X.
 Rok: 2018
 DOI: 10.1109/TAP.2018.2869642
 Odkaz: https://doi.org/10.1109/TAP.2018.2869642
 Pracoviště: Katedra elektromagnetického pole

Anotace:
A new method to improve the accuracy and efficiency of characteristic mode (CM) decomposition for perfectly conducting bodies is presented. The method uses the expansion of the Green dyadic in spherical vector waves. This expansion is utilized in the method of moments (MoM) solution of the electric field integral equation (EFIE) to factorize the real part of the impedance matrix. The factorization is then employed in the computation of CMs, which improves the accuracy as well as the computational speed. An additional benefit is a rapid computation of far fields. The method can easily be integrated into existing MoM solvers. Several structures are investigated illustrating the improved accuracy and performance of the new method.
Accurate Evaluation of Characteristic Modes
 Autoři: prof. Ing. Miloslav Čapek, Ph.D., Tayli, D., Akrou, L., Losenický, V., doc. Ing. Lukáš Jelínek, Ph.D., Gustafsson, M.
 Publikace: 2018 12th European Conference on Antennas and Propagation. Bruxelles: The European Association on Antennas and Propagation, 2018. p. 13. ISSN 05379989. ISBN 9781785618154.
 Rok: 2018
 Pracoviště: Katedra elektromagnetického pole

Anotace:
The wellknown issue of illconditioned characteristic modes decomposition is challenged in this contribution. Spherical waves are utilized to decompose the resistance operator as a product of two identical matrices. The modal decomposition can be reformulated using this projection matrix to double the numerical precision and, consequently, the number of properly found modes. It has notable properties related to the numerical convergence or a priori estimation of the number of attainable modes.
Dissipation Factors of Spherical Current Modes on Multiple Spherical Layers
 Autoři: Losenický, V., doc. Ing. Lukáš Jelínek, Ph.D., prof. Ing. Miloslav Čapek, Ph.D., Gustafsson, M.
 Publikace: IEEE Transactions on Antennas and Propagation. 2018, 66(9), 49484952. ISSN 0018926X.
 Rok: 2018
 DOI: 10.1109/TAP.2018.2841408
 Odkaz: https://doi.org/10.1109/TAP.2018.2841408
 Pracoviště: Katedra elektromagnetického pole

Anotace:
Radiation efficiencies of modal current densities distributed on a spherical shell are evaluated in terms of dissipation factor. The presented approach is rigorous, yet simple and straightforward, leading to closedform expressions. The same approach is utilized for a twolayered shell and the results are compared with other models existing in the literature. Discrepancies in this comparison are reported and reasons are analyzed. Finally, it is demonstrated that radiation efficiency potentially benefits from the use of internal volume which contrasts with the case of the radiation Qfactor.
Energy Stored by Radiating Systems
 Autoři: Schab, K., doc. Ing. Lukáš Jelínek, Ph.D., prof. Ing. Miloslav Čapek, Ph.D., Ehrenborg, C., Tayli, D., Vandenbosch, G.A.E., Gustafsson, M.
 Publikace: IEEE Access. 2018, 6 1055310568. ISSN 21693536.
 Rok: 2018
 DOI: 10.1109/ACCESS.2018.2807922
 Odkaz: https://doi.org/10.1109/ACCESS.2018.2807922
 Pracoviště: Katedra elektromagnetického pole

Anotace:
Though commonly used to calculate Qfactor and fractional bandwidth, the energy stored by radiating systems (antennas) is a subtle and challenging concept that has perplexed researchers for over half a century. Here, the obstacles in defining and calculating stored energy in general electromagnetic systems are presented from first principles as well as using demonstrative examples from electrostatics, circuits, and radiating systems. Along the way, the concept of unobservable energy is introduced to formalize such challenges. Existing methods of defining stored energy in radiating systems are then reviewed in a framework based on technical commonalities rather than chronological order. Equivalences between some methods under common assumptions are highlighted, along with the strengths, weaknesses, and unique applications of certain techniques. Numerical examples are provided to compare the relative margin between methods on several radiating structures.
Modal Tracking Based on Group Theory
 Autoři: Mašek, M., prof. Ing. Miloslav Čapek, Ph.D., doc. Ing. Lukáš Jelínek, Ph.D.,
 Publikace: 2018 12th European Conference on Antennas and Propagation. Bruxelles: The European Association on Antennas and Propagation, 2018. ISSN 05379989. ISBN 9781785618154.
 Rok: 2018
 Pracoviště: Katedra elektromagnetického pole

Anotace:
The tracking of characteristic modes is solved based on group theory. Recent findings on symmetry aspects and the occurrence of crossing avoidance mechanism are applied and related to particular boundary conditions. A novel approach leads to the acceleration of the calculation and precise tracking of eigenmodes. The current understanding of tracking issues is broadened and the necessity of tracking is reviewed based on physical insight into the problem. The procedure can be used for a large class of generalized eigenvalue problems and is validated by an example of an antenna array made of identical radiating elements.
Optimal Currents and Optimal Antennas
 Autoři: prof. Ing. Miloslav Čapek, Ph.D., doc. Ing. Lukáš Jelínek, Ph.D.,
 Publikace: 2018 12th European Conference on Antennas and Propagation. Bruxelles: The European Association on Antennas and Propagation, 2018. p. 14. ISSN 05379989. ISBN 9781785618154.
 Rok: 2018
 Pracoviště: Katedra elektromagnetického pole

Anotace:
This contribution studies the realizability of already known fundamental bounds on small radiating structures using a single discrete feeder and the geometry optimization of a radiator’s shape. Shape optimization is performed by using pixelization technique powered by heuristic optimization. The feeding optimization is carried out directly. The model of an antenna is parametrized by a map between pixels of varying shape and RaoWiltonGlisson (RWG) basis functions. Robust postprocessing suppresses the occurrence of single pixels and unwanted artifacts. Some known or recently theorized statements are verified and the complexity of the optimization problem is investigated.
Radiation Efficiency Cost of Resonance Tuning
 Autoři: doc. Ing. Lukáš Jelínek, Ph.D., Schab, K., prof. Ing. Miloslav Čapek, Ph.D.,
 Publikace: IEEE Transactions on Antennas and Propagation. 2018, 66(12), 67166723. ISSN 0018926X.
 Rok: 2018
 DOI: 10.1109/TAP.2018.2870492
 Odkaz: https://doi.org/10.1109/TAP.2018.2870492
 Pracoviště: Katedra elektromagnetického pole

Anotace:
Existing optimization methods are used to calculate the upperbounds on radiation efficiency with and without the constraint on selfresonance. These bounds are used for the design and assessment of small electricdipoletype antennas. We demonstrate that the assumption of lossless, lumped, external tuning skews the true nature of radiation efficiency bounds when practical material characteristics are used in the tuning network. A major result is that, when realistic (e.g., finite conductivity) materials are used, small antenna systems exhibit dissipation factors which scale as (ka)–4, rather than (ka)–2 as previously predicted under the assumption of lossless external tuning.
Evaluation of polarisability tensors of arbitrarily shaped highly conducting bodies
 Autoři: doc. Ing. Lukáš Jelínek, Ph.D., Krátký, O., prof. Ing. Miloslav Čapek, Ph.D.,
 Publikace: IET Microwaves, Antennas & Propagation. 2017, 11(6), 852858. ISSN 17518725.
 Rok: 2017
 DOI: 10.1049/ietmap.2016.0793
 Odkaz: https://doi.org/10.1049/ietmap.2016.0793
 Pracoviště: Katedra elektromagnetického pole

Anotace:
A fullwave numerical scheme of polarizability (polarisability) tensors evaluation is presented. The method accepts highly conducting bodies of arbitrary shape and explicitly accounts for the radiation as well as ohmic losses. The method is verified on canonical bodies with known polarizability tensors, such as a sphere and a cube, as well as on realistic scatterers. The theoretical developments are followed by a freely available code whose sole user input is the triangular mesh covering the surface of the body under consideration.
Minimum energy storage in dissipative electromagnetic systems
 Autoři: doc. Ing. Lukáš Jelínek, Ph.D., Schab, K., prof. Ing. Miloslav Čapek, Ph.D.,
 Publikace: Proceedings of International Symposium on Antennas and Propagation & USNC/URSI National Radio Science Meeting. Piscataway, NJ: IEEE, 2017. p. 4142. ISSN 19471491. ISBN 9781538632840.
 Rok: 2017
 DOI: 10.1109/APUSNCURSINRSM.2017.8072063
 Odkaz: https://doi.org/10.1109/APUSNCURSINRSM.2017.8072063
 Pracoviště: Katedra elektromagnetického pole

Anotace:
This contribution discusses the concept of recoverable energy of a general electromagnetic system and practical way of its evaluation. The paper also shows how the concept is linked to fractional bandwidth, and, more significantly, how it is related to minimum energy storage and a minimumphaseshift of Darlington's synthesis.
Numerical benchmark based on characteristic modes of a spherical shell
 Autoři: prof. Ing. Miloslav Čapek, Ph.D., Losenický, V., doc. Ing. Lukáš Jelínek, Ph.D., Gustafsson, M., Tayli, D.
 Publikace: Proceedings of International Symposium on Antennas and Propagation & USNC/URSI National Radio Science Meeting. Piscataway, NJ: IEEE, 2017. p. 965966. ISSN 19471491. ISBN 9781538632840.
 Rok: 2017
 DOI: 10.1109/APUSNCURSINRSM.2017.8072525
 Odkaz: https://doi.org/10.1109/APUSNCURSINRSM.2017.8072525
 Pracoviště: Katedra elektromagnetického pole

Anotace:
Characteristic modes of a spherical shell are found analytically and compared with numerical solutions acquired from both inhouse and commercial packages. These studies led to a proposal of several independent benchmarks, all with analytically known results. Dependence on mesh size, electrical size and other parameters can easily be incorporated. It is observed that all contemporary implementations have limitations.
Optimal Currents on Arbitrarily Shaped Surfaces
 Autoři: doc. Ing. Lukáš Jelínek, Ph.D., prof. Ing. Miloslav Čapek, Ph.D.,
 Publikace: IEEE Transactions on Antennas and Propagation. 2017, 65(1), 329341. ISSN 0018926X.
 Rok: 2017
 DOI: 10.1109/TAP.2016.2624735
 Odkaz: https://doi.org/10.1109/TAP.2016.2624735
 Pracoviště: Katedra elektromagnetického pole

Anotace:
An optimization problem has been formulated to find a resonant current extremizing various antenna parameters. The method is presented on, but not limited to, particular cases of gain G, quality factor Q, gain to quality factor ratio G/Q, and radiation efficiency $\eta$ of canonical shapes with conduction losses explicitly included. The RaoWiltonGlisson basis representation is used to simplify the underlying algebra while still allowing surface current regions of arbitrary shape to be treated. By switching to another basis generated by a specific eigenvalue problem, it is finally shown that the optimal current can, in principle, be found as a combination of a few eigenmodes. The presented method constitutes a general framework in which the antenna parameters, expressed as bilinear forms, can automatically be extremized.
Polarizability tensors of highly conductive bodies
 Autoři: doc. Ing. Lukáš Jelínek, Ph.D., prof. Ing. Miloslav Čapek, Ph.D., Krátký, O.
 Publikace: Proceedings of International Symposium on Antennas and Propagation & USNC/URSI National Radio Science Meeting. Piscataway, NJ: IEEE, 2017. p. 19651966. ISSN 19471491. ISBN 9781538632840.
 Rok: 2017
 DOI: 10.1109/APUSNCURSINRSM.2017.8073025
 Odkaz: https://doi.org/10.1109/APUSNCURSINRSM.2017.8073025
 Pracoviště: Katedra elektromagnetického pole

Anotace:
A freely available code, whose sole user input is the triangular mesh covering the surface of the body under consideration and which provides fullwave extraction of polarizability tensors, is presented. The code accepts highly conductive bodies of arbitrary shape and is verified on canonical bodies with known polarizability tensors.
Validating the Characteristic Modes Solvers
 Autoři: prof. Ing. Miloslav Čapek, Ph.D., Losenický, V., doc. Ing. Lukáš Jelínek, Ph.D., Gustafsson, M.
 Publikace: IEEE Transactions on Antennas and Propagation. 2017, 65(8), 41344145. ISSN 0018926X.
 Rok: 2017
 DOI: 10.1109/TAP.2017.2708094
 Odkaz: https://doi.org/10.1109/TAP.2017.2708094
 Pracoviště: Katedra elektromagnetického pole

Anotace:
Characteristic modes of a spherical shell are found analytically as spherical harmonics normalized to radiate unitary power and to fulfill specific boundary conditions. The presented closedform formulas lead to a proposal of precise synthetic benchmarks which can be utilized to validate the method of moments matrix or performance of characteristic mode decomposition. Dependence on the mesh size, electrical size and other parameters can systematically be studied, including the performance of various mode tracking algorithms. A noticeable advantage is the independence on feeding models. Both theoretical and numerical aspects of characteristic mode decomposition are discussed and illustrated by examples. The performance of stateoftheart commercial simulators and academic packages having been investigated, we can conclude that all contemporary implementations are capable of identifying the first dominant modes while having severe difficulties with higherorder modes. Surprisingly poor performance of the tracking routines is observed notwithstanding the recent ambitious development.
Comments on "On Stored Energies and Radiation Q"
 Autoři: prof. Ing. Miloslav Čapek, Ph.D., doc. Ing. Lukáš Jelínek, Ph.D.,
 Publikace: IEEE Transactions on Antennas and Propagation. 2016, 64(10), 45754576. ISSN 0018926X.
 Rok: 2016
 DOI: 10.1109/TAP.2015.2473678
 Odkaz: https://doi.org/10.1109/TAP.2015.2473678
 Pracoviště: Katedra elektromagnetického pole

Anotace:
The commented paper [1] claims to provide a new expression for an energy stored around a general radiator. The major purpose of this comment is to show that the claim is unjustified. Alongside with this issue, it is pointed out that some of the core formulas of [1] are not completely correct, and that their correct form has in fact been derived elsewhere, though for the purpose of evaluating the quality factor QZ and not the stored energies.
Optimal composition of characteristic modes for minimal quality factor Q
 Autoři: prof. Ing. Miloslav Čapek, Ph.D., doc. Ing. Lukáš Jelínek, Ph.D.,
 Publikace: 2016 IEEE Antennas and Propagation Society International Symposium  Proceedings. Piscataway, NJ: IEEE, 2016. p. 12. ISBN 9781509028863.
 Rok: 2016
 DOI: 10.1109/APS.2016.7695709
 Odkaz: https://doi.org/10.1109/APS.2016.7695709
 Pracoviště: Katedra elektromagnetického pole

Anotace:
This work describes an efficient and powerful technique to obtain optimal currents with respect to the lower bounds of quality factor Q for an arbitrarily shaped electrically small antenna made of perfect conductor. The resulting optimal currents are expressed in terms of characteristic mode basis with the minimum always being obtained by either one mode tuned to the resonance, or, by properly combining two modes. The calculation of the stored electromagnetic energy is based on matrix representation of the integrodifferential expressions derived by Vandenbosch, an approach which simplifies the entire development resulting in an uncomplicated numerical evaluation.
Optimal Composition of Modal Currents For Minimal Quality Factor Q
 Autoři: prof. Ing. Miloslav Čapek, Ph.D., doc. Ing. Lukáš Jelínek, Ph.D.,
 Publikace: IEEE Transactions on Antennas and Propagation. 2016, 64(12), 52305242. ISSN 0018926X.
 Rok: 2016
 DOI: 10.1109/TAP.2016.2617779
 Odkaz: https://doi.org/10.1109/TAP.2016.2617779
 Pracoviště: Katedra elektromagnetického pole

Anotace:
This work describes a powerful, yet simple, procedure how to acquire a current approaching the lower bound of quality factor Q. This optimal current can be determined for an arbitrarily shaped electrically small radiator made of a perfect conductor. Quality factor Q is evaluated by Vandenbosch’s relations yielding stored electromagnetic energy as a function of the source current density. All calculations are based on a matrix representation of the integrodifferential operators. This approach simplifies the entire development and results in a straightforward numerical evaluation. The optimal current is represented in a basis of modal currents suitable for solving the optimization problem so that the minimum is approached by either one mode tuned to the resonance, or, by two properly combined modes. An overview of which modes should be selected and how they should be combined is provided and results concerning rectangular plate, spherical shell, capped dipole antenna and fractal shapes of varying geometrical complexity are presented. The reduction of quality factor Q and the G/Q ratio are studied and, thanks to the modal decomposition, the physical interpretation of the results is discussed in conjunction with the limitations of the proposed procedure.
Optimal currents in the characteristic modes basis
 Autoři: doc. Ing. Lukáš Jelínek, Ph.D., prof. Ing. Miloslav Čapek, Ph.D.,
 Publikace: 2016 IEEE Antennas and Propagation Society International Symposium  Proceedings. Piscataway, NJ: IEEE, 2016. pp. 421422. ISBN 9781509028863.
 Rok: 2016
 DOI: 10.1109/APS.2016.7695919
 Odkaz: https://doi.org/10.1109/APS.2016.7695919
 Pracoviště: Katedra elektromagnetického pole

Anotace:
An optimization scheme yielding a current density in a given spatial region exhibiting the lowest tuned radiation quality factor is presented. Rather than assuming an external tuning by a lumped element, the current density is constrained to be selfresonant. The solution is presented as a weighted sum of characteristic modes and some important remarks are given with respect to their Qoptimality.
Stored Electromagnetic Energy and Quality Factor of Radiating Structures
 Autoři: prof. Ing. Miloslav Čapek, Ph.D., doc. Ing. Lukáš Jelínek, Ph.D., Vandenbosch, G. A. E.
 Publikace: Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences. 2016, 472 ISSN 13645021.
 Rok: 2016
 DOI: 10.1098/rspa.2015.0870
 Odkaz: https://doi.org/10.1098/rspa.2015.0870
 Pracoviště: Katedra elektromagnetického pole

Anotace:
This paper deals with the old yet unsolved problem of defining and evaluating the stored electromagnetic energy  a quantity essential for calculating the quality factor, which reflects the intrinsic bandwidth of the considered electromagnetic system. A novel paradigm is proposed to determine the stored energy in the time domain leading to the method, which exhibits positive semidefiniteness and coordinate independence, i.e. two key properties actually not met by the contemporary approaches. The proposed technique is compared with an uptodate frequency domain method that is extensively used in practice. Both concepts are discussed and compared on the basis of examples of varying complexity.
A Novel Scheme for Stored Energy Evaluation
 Autoři: prof. Ing. Miloslav Čapek, Ph.D., doc. Ing. Lukáš Jelínek, Ph.D., Vandenbosch, G.A.E., doc. Ing. Pavel Hazdra, Ph.D.,
 Publikace: Proceedings of the 9th European Conference on Antennas and Propagation (EUCAP 2015). Piscataway: IEEE, 2015. ISBN 9788890701856.
 Rok: 2015
 Pracoviště: Katedra elektromagnetického pole

Anotace:
The old and still unsolved problem of defining and evaluating stored electromagnetic energy is treated in this contribution. A novel timedomain scheme is proposed for evaluating the stored electromagnetic energy for nonstationary fields. In order to obtain the stored energy of the total electromagnetic energy, the wellknown definition of radiated energy is utilized, and the subtraction is performed in the time domain during a transient state of the system under study.
A System of Split Ring Resonators with Randomly Dispersed Resonance Frequencies
 Autoři: prof. Ing. Jan Macháč, DrSc., doc. Ing. Lukáš Jelínek, Ph.D.,
 Publikace: Proceedings of Asia Pacific Microwave Conference 2015. Nanjing: Southeast University, 2015. ISBN 9781479987658.
 Rok: 2015
 Pracoviště: Katedra elektromagnetického pole

Anotace:
This paper reports on a 3D system of broad side coupled split ring resonators with randomly dispersed resonance frequencies. This dispersion is caused by the varied geometric and material parameters of the resonators. The resonance frequency band of the effective permeability of the metamaterial is significantly widened, the value of the real part of the permeability is reduced, or the band of negative permeability even disappears. The paper comments on the design of a lens aimed at improving the imaging properties of the MRI system. The proposed homogenization method is verified by measuring the scattering parameters of the metamaterial in a rectangular waveguide.
An Analytical Evaluation of The Quality Factor Qz for Dominant Spherical Modes
 Autoři: doc. Ing. Lukáš Jelínek, Ph.D., prof. Ing. Miloslav Čapek, Ph.D., doc. Ing. Pavel Hazdra, Ph.D., Eichler, J.
 Publikace: IET Microwaves, Antennas & Propagation. 2015, 9(10), 10961103. ISSN 17518725.
 Rok: 2015
 DOI: 10.1049/ietmap.2014.0302
 Odkaz: https://doi.org/10.1049/ietmap.2014.0302
 Pracoviště: Katedra elektromagnetického pole

Anotace:
This paper describes an analytical evaluation of the quality factor Qz in a separable system in which the vector potential is known. The proposed method uses a potential definition of active and reactive power, implicitly avoiding infinite entire space integration and extraction of radiation energy. As a result, all the used quantities are finite, and the calculated Qz is always nonnegative function of frequency. The theory is presented on the canonical example of the currents flowing on a spherical shell. The Qz for the dominant spherical TM and TE mode and their linear combination are found in closed forms, including both internal and external energies. The proposed analytical method and its results are compared to previously published limits of the quality factor Q.
An electronlight wave analogy for Cartesian and spherical systems
 Autoři: Hrebíková, I., doc. Ing. Lukáš Jelínek, Ph.D.,
 Publikace: DoKDoK 2015 Proceedings. Jena: Friedrich Schiller University, 2015. p. 9091.
 Rok: 2015
 Pracoviště: Katedra elektromagnetického pole

Anotace:
The analogy between ballistic electrons and electromagnetic waves for heterostructures exhibiting planar and spherical symmetry is presented. Theory exposing similar behavior of the electromagnetic field and quantum mechanical waves is presented, together with subsequent possible applications.
Bound States Within the Continuum  A MetamaterialSemiconductor Analogy
 Autoři: Hrebíková, I., doc. Ing. Lukáš Jelínek, Ph.D., Silveirinha, M. G.
 Publikace: 9th International Congress on Advanced Electromagnetic Materials in Microwaves and Optics Proceedings. LouvainlaNeuve: UCL, Laboratoire d´Hyperfréquences, 2015. pp. 112114. ISBN 9788894114102.
 Rok: 2015
 DOI: 10.1109/MetaMaterials.2015.7342540
 Odkaz: https://doi.org/10.1109/MetaMaterials.2015.7342540
 Pracoviště: Katedra elektromagnetického pole

Anotace:
The existence of bound states within the continuum has been known since the early years of quantum mechanics. However a realistic quantum system supporting such bound states has not yet been designed. Here we present a core–shell semiconductor heterostructure composed of Hg(1x)Cd(x)Te compounds, which is able to support the bound states within the continuum using zerovalued effective mass within the outer shell. The working principle is analogous to that of the recently proposed open coreshell plasmonic resonators for light waves.
Embedded Energy State in an Open Semiconductor Heterostructure
 Autoři: Hrebíková, I., doc. Ing. Lukáš Jelínek, Ph.D., Silveirinha, M. G.
 Publikace: Physical Review B. 2015, 92(15), 155303155311. ISSN 10980121.
 Rok: 2015
 DOI: 10.1103/PhysRevB.92.155303
 Odkaz: https://doi.org/10.1103/PhysRevB.92.155303
 Pracoviště: Katedra elektromagnetického pole

Anotace:
In this paper, we show that HgCdTe heterostructures may supporttextcolor{red}{, within the envelope function approximation,} bound electronic states embedded in the continuum, such that the discrete energy spectrum overlaps the continuous spectrum. Although the proposed heterostructures are generally penetrable by an incoming electron wave, it is shown that they may support spatially localized trapped stationary states with an infinite lifetime. We discuss the possibility of a free electron being captured by the proposed open resonator, and present a detailed study of the trapping lifetime in the case of a detuned resonator.
Metamaterial Made of BCSRRs with Randomly Dispersed Resonance Frequencies
 Autoři: prof. Ing. Jan Macháč, DrSc., doc. Ing. Lukáš Jelínek, Ph.D.,
 Publikace: 2015 IEEE MTTS International Microwave Symposium  Conference Proceedings. Piscataway: IEEE Microwave Theory and Techniques Society, US, 2015. ISBN 9781479982752.
 Rok: 2015
 DOI: 10.1109/MWSYM.2015.7166793
 Odkaz: https://doi.org/10.1109/MWSYM.2015.7166793
 Pracoviště: Katedra elektromagnetického pole

Anotace:
This paper reports on an investigation of a metamaterial designed as a 3D system of broad side coupled split ring resonators. Imperfections in the fabrication process cause dispersion of the geometrical and material parameters of the resonators, and thus dispersion of their resonance frequencies. Homogenization of a 3D cubic lattice of these imperfect resonators reveals that the resulting resonance frequency band of the effective permeability is significantly widened, but at the cost of reducing its magnitude or even completely disappearing the negative values of its real part. An experiment performed in the rectangular waveguide verifies the theoretical predictions.
New aspects of artificial diamagnetics
 Autoři: Lapine, M., doc. Ing. Lukáš Jelínek, Ph.D.,
 Publikace: Advanced Electromagnetic Materials in Microwaves and Optics (METAMATERIALS), 2015 9th International Congress on. Rome: METAMORPHOSE VI AISBL, 2015. pp. 172174. ISSN 10459243. ISBN 9781479978366.
 Rok: 2015
 DOI: 10.1109/MetaMaterials.2015.7342562
 Odkaz: https://doi.org/10.1109/MetaMaterials.2015.7342562
 Pracoviště: Katedra elektromagnetického pole

Anotace:
Artificial diamagnetic metamaterials are known to produce impressively low permeability values in a broad frequency range. As an observable feature however, the same is true for good conductors. We analyse performance of artificial diamagnetics with regards to applications such as levitation, in comparison to bulk metals, and show that as long as the fields in the exterior of the body are concerned, nonstructured metals outperform metamaterial structure. Furthermore, we calculate the response of practical samples of artificial diamagnetics, taking their discrete structure and finite size into account, and find that predictions of effective medium theory are much better applicable to nonresonant structures than to resonant ones.
On the Functional Relation Between Quality Factor and Fractional Bandwidth
 Autoři: prof. Ing. Miloslav Čapek, Ph.D., doc. Ing. Lukáš Jelínek, Ph.D., doc. Ing. Pavel Hazdra, Ph.D.,
 Publikace: IEEE Transactions on Antennas and Propagation. 2015, 63(6), 27872790. ISSN 0018926X.
 Rok: 2015
 DOI: 10.1109/TAP.2015.2414472
 Odkaz: https://doi.org/10.1109/TAP.2015.2414472
 Pracoviště: Katedra elektromagnetického pole

Anotace:
The functional relation between the fractional bandwidth and the quality factor of a radiating system is investigated in this note. Several widely used definitions of the quality factor are compared on two examples of RLC circuits that serve as a simplified model of a single resonant antenna tuned to its resonance. It is demonstrated that for a firstorder system, only the quality factor based on differentiation of the input impedance has unique proportionality to the fractional bandwidth, whereas e.g. the classical definition of the quality factor, i. e. the ratio of the stored energy to the lost energy per one cycle, is not uniquely proportional to the fractional bandwidth. In addition, it is shown that for higherorder systems the quality factor based on differentiation of the input impedance ceases to be uniquely related to the fractional bandwidth.
On the Properties of Stored Electromagnetic Energy
 Autoři: prof. Ing. Miloslav Čapek, Ph.D., doc. Ing. Lukáš Jelínek, Ph.D.,
 Publikace: Proceedings of PIERS 2015 in Prague. Cambridge: Electromagnetics Academy, 2015. ISSN 15599450. ISBN 9781934142301.
 Rok: 2015
 Pracoviště: Katedra elektromagnetického pole

Anotace:
In our talk, we will review all the available concepts that have attempted to determine stored energy. It will be pointed out that all these concepts fail in at least one of the "must have" properties mentioned above. Finally, it will be concluded that no fully consistent denition of stored electromagnetic energy is yet known. This of course raises the question whether the very idea of stored (and radiated) energy is wellposed.
On the Stored and Radiated Energy Density
 Autoři: doc. Ing. Lukáš Jelínek, Ph.D., prof. Ing. Miloslav Čapek, Ph.D.,
 Publikace: Proceedings of the 9th European Conference on Antennas and Propagation (EUCAP 2015). Piscataway: IEEE, 2015. ISBN 9788890701856.
 Rok: 2015
 Pracoviště: Katedra elektromagnetického pole

Anotace:
This contribution reviews and discusses several concepts of stored and radiated energy density of an electromagnetic field. The contribution exposes the most important differences between the up to date definitions and discusses consequences in terms of the energy density of the dominant spherical TE mode.
The Quality Factor QZ of the Combined TE10 / TM10 Spherical Mode
 Autoři: doc. Ing. Lukáš Jelínek, Ph.D., prof. Ing. Miloslav Čapek, Ph.D.,
 Publikace: Proceedings of the 2015 IEEE International Symposium on Antennas and Propagation and North Americal Radio Science Meeting. Piscataway: IEEE, 2015. pp. 10641065. ISBN 9781479978151.
 Rok: 2015
 DOI: 10.1109/APS.2015.7304920
 Odkaz: https://doi.org/10.1109/APS.2015.7304920
 Pracoviště: Katedra elektromagnetického pole

Anotace:
This contribution describes an evaluation of the quality factor QZ of the combined TE10 / TM10 mode, including the internal and the external region of the bounding sphere. The proposed method uses a potential definition of complex power, implicitly avoiding infinite entire space integration. It is shown that QZ of the combined mode is not (unlike classical Q) limited to one half of the value for the pure TM10 mode. It is shown that the QZ factor does not have a strict lower bound other than zero.
The Relation Between Fractional Bandwidth and Q Factor
 Autoři: prof. Ing. Miloslav Čapek, Ph.D., doc. Ing. Lukáš Jelínek, Ph.D.,
 Publikace: Proceedings of the 2015 IEEE International Symposium on Antennas and Propagation and North Americal Radio Science Meeting. Piscataway: IEEE, 2015. pp. 858859. ISBN 9781479978151.
 Rok: 2015
 DOI: 10.1109/APS.2015.7304816
 Odkaz: https://doi.org/10.1109/APS.2015.7304816
 Pracoviště: Katedra elektromagnetického pole

Anotace:
The functional relation between the fractional bandwidth and the quality factor of a radiating system is studied from simple firstorderlike RLClike systems to higherorder radiating systems. It is demonstrated that, considering a firstorder system, only the quality factor based on differentiation of the input impedance has unique proportionality to the fractional bandwidth. In the general case of higherorder systems, it is however shown that this property is lost.
Time Domain Scheme for Stored Energy Evaluation
 Autoři: prof. Ing. Miloslav Čapek, Ph.D., doc. Ing. Lukáš Jelínek, Ph.D., Vandenbosch, G.S.E., doc. Ing. Pavel Hazdra, Ph.D.,
 Publikace: Proceedings of the 2015 IEEE International Symposium on Antennas and Propagation and North Americal Radio Science Meeting. Piscataway: IEEE, 2015. pp. 17061707. ISBN 9781479978151.
 Rok: 2015
 DOI: 10.1109/APS.2015.7305242
 Odkaz: https://doi.org/10.1109/APS.2015.7305242
 Pracoviště: Katedra elektromagnetického pole

Anotace:
A novel method for evaluation of the stored energy contained in a nonstationary electromagnetic field is presented in this paper. The method utilizes the classical definition of the radiated energy, which subtraction from the total electromagnetic energy is carried out in time domain during a transient state of the system under study.
A Perfect Lens for Ballistic Eectrons: An ElectronLight Wave Analogy
 Autoři: Hrebíková, I., doc. Ing. Lukáš Jelínek, Ph.D., doc. RNDr. Jan Voves, CSc., Baena, J.D.
 Publikace: Photonics and Nanostructures  Fundamentals and Applications. 2014, 12(1), 915. ISSN 15694410.
 Rok: 2014
 DOI: 10.1016/j.photonics.2013.08.005
 Odkaz: https://doi.org/10.1016/j.photonics.2013.08.005
 Pracoviště: Katedra elektromagnetického pole, Katedra mikroelektroniky

Anotace:
The analogy between electromagnetic waves and ballistic electrons within the Kane's model is developed and subsequently applied to a theoretical description of a quantum version of a metamaterial planar lens. Restrictions imposed on the perfect lens and the poor man's lens by available semiconductor band structures are discussed. A realistic implementation is proposed for the quantum poor man's lens, which uses specific properties of the HgTe compound. The properties of the lens are presented on the basis of a calculated transmission of oblique electrons through the lens structure.
A Polarizability Measurement Method for Electrically Small Particles
 Autoři: doc. Ing. Lukáš Jelínek, Ph.D., prof. Ing. Jan Macháč, DrSc.,
 Publikace: IEEE Antennas and Wireless Propagation Letters. 2014, 13(1), 10511053. ISSN 15361225.
 Rok: 2014
 DOI: 10.1109/LAWP.2014.2327152
 Odkaz: https://doi.org/10.1109/LAWP.2014.2327152
 Pracoviště: Katedra elektromagnetického pole

Anotace:
A simple and precise free space polarizability measurement method for electrically small particles is presented. The method is based on measuring the scattering parameters of a waveguide loaded by a particle, and on knowledge of the dipolar polarizabilities of two calibration standards. The method is verified on a metallic disk and a resonant conducting ring terminated by a capacitor.
Applicability of nonresonant artificial diamagnetics
 Autoři: doc. Ing. Lukáš Jelínek, Ph.D., Lapine, M., McPhedran, R. C.
 Publikace: Physical Review B. 2014, 90 ISSN 10980121.
 Rok: 2014
 DOI: 10.1103/PhysRevB.90.104413
 Odkaz: https://doi.org/10.1103/PhysRevB.90.104413
 Pracoviště: Katedra elektromagnetického pole

Anotace:
Artificial diamagnetics are prominent for achieving extraordinarily strong diamagnetism in a wide frequency range. However, as far as the magnetic fields outside the artificial medium are concerned, bulk conductors show a very similar pattern. The question arises whether the complicated internal structure of artificial diamagnetics can, to this end, be replaced by a simpler object.We show that for an electrically small body, internal structuring is likely to make the effective diamagnetic response weaker than that of a simple conducting object.
Lower bounds of the quality factor QZ
 Autoři: doc. Ing. Lukáš Jelínek, Ph.D., prof. Ing. Miloslav Čapek, Ph.D., doc. Ing. Pavel Hazdra, Ph.D., Eichler, J.
 Publikace: Proceedings of the 2014 IEEE International Symposium on Antennas and Propagation and North Americal Radio Science Meeting. Piscataway: IEEE, 2014. pp. 5354. ISSN 15223965. ISBN 9781479935383.
 Rok: 2014
 DOI: 10.1109/APS.2014.6904358
 Odkaz: https://doi.org/10.1109/APS.2014.6904358
 Pracoviště: Katedra elektromagnetického pole

Anotace:
This paper describes an analytical evaluation of the measurable quality factor QZ of a system in which the vector potential is known. The method is presented on a canonical example of the currents flowing on a spherical shell, which leads to the analytical prescription for the lower bound of QZ.
The Measurable Q Factor and Observable Energies of Radiating Structures
 Autoři: prof. Ing. Miloslav Čapek, Ph.D., doc. Ing. Lukáš Jelínek, Ph.D., doc. Ing. Pavel Hazdra, Ph.D., Eichler, J.
 Publikace: IEEE Transactions on Antennas and Propagation. 2014, 62(1), 311318. ISSN 0018926X.
 Rok: 2014
 DOI: 10.1109/TAP.2013.2287519
 Odkaz: https://doi.org/10.1109/TAP.2013.2287519
 Pracoviště: Katedra elektromagnetického pole

Anotace:
New expressions are derived to calculate the Q factor of a radiating device. The resulting relations link Q based on the frequency change of the input impedance at the input port (QX, QZ) with expressions based solely on the current distribution on an radiating device. The question of which energies of a radiating system are observable is reviewed, and then the proposed Q factor as defined in this paper is physical. The derivation is based on potential theory rather than fields. This approach hence automatically eliminates all divergent integrals associated with electromagnetic energies in infinite space. The new formulas allow us to study the radiation Q factor for antennas without feeding (through e.g. Characteristic Modes) as well as fed by an arbitrary number of ports. The new technique can easily be implemented in any numerical software dealing with current densities. To present the merits of proposed technique, three canonical antennas are studied. Numerical examples show excellent agreement between the measurable QZ derived from input impedance and the new expressions.
The source definition of the quality factor QZ, 2014 IEEE International Symposium on Antennas and Propagation
 Autoři: prof. Ing. Miloslav Čapek, Ph.D., doc. Ing. Lukáš Jelínek, Ph.D., doc. Ing. Pavel Hazdra, Ph.D., Eichler, J.
 Publikace: Proceedings of the 2014 IEEE International Symposium on Antennas and Propagation and North Americal Radio Science Meeting. Piscataway: IEEE, 2014. pp. 5152. ISSN 15223965. ISBN 9781479935383.
 Rok: 2014
 DOI: 10.1109/APS.2014.6904357
 Odkaz: https://doi.org/10.1109/APS.2014.6904357
 Pracoviště: Katedra elektromagnetického pole

Anotace:
New expressions for calculating of the quality factor QZ are presented. The resulting relations link QZ, based on the frequency change of the input impedance at the input port, with expressions based solely on the current distribution on a radiator. The derivation is based on electromagnetic potentials, automatically eliminating all divergent integrals associated with electromagnetic energies in infinite space.
A Building Element of an Active Negative Permeability Metamaterial
 Autoři: prof. Ing. Jan Macháč, DrSc., doc. Ing. Lukáš Jelínek, Ph.D.,
 Publikace: Proceedings of 13th Conference on Microwave Techniques COMITE 2013. Pardubice: Univerzita Pardubice, 2013. pp. 198199. ISBN 9781467355131.
 Rok: 2013
 Pracoviště: Katedra elektromagnetického pole

Anotace:
This paper presents an active particle designed as a building block of an active volumetric metamaterial showing negative magnetic polarizability. The particle is composed of a conducting ring loaded by an impedance with a negative real part. This impedance is produced by a oneport transistor circuit. Measurements of the fabricated element verified its working principle in the RF range.
A Perfect Lens for Ballistic Electrons
 Autoři: Hrebíková, I., doc. Ing. Lukáš Jelínek, Ph.D., doc. RNDr. Jan Voves, CSc., Baena, J. D.
 Publikace: Proceedings of Metamaterials´ 2013: The 7th International Congress on Advanced Electromagnetic Materials in Microwaves and Optics. LouvainlaNeuve: UCL, Laboratoire d´Hyperfréquences, 2013. ISBN 9789526761152.
 Rok: 2013
 Pracoviště: Katedra elektromagnetického pole, Katedra mikroelektroniky

Anotace:
The analogy between plane electromagnetic waves and electron waves is presented and subsequently applied to the description of a quantum perfect lens. The natural constraints resulting from available semiconductor compounds are discussed. The final lens design relies on the inverted bandstructure of the HgTe compound, and uses a voltage gate to created the lens structure.
CoupledWave SurfaceImpedance Analysis of Extraordinary Transmission Through Single and Stacked Metallic Screens
 Autoři: Delgado, V., Marques, R., doc. Ing. Lukáš Jelínek, Ph.D.,
 Publikace: IEEE Transactions on Antennas and Propagation. 2013, 61(3), 13421351. ISSN 0018926X.
 Rok: 2013
 DOI: 10.1109/TAP.2012.2227657
 Odkaz: https://doi.org/10.1109/TAP.2012.2227657
 Pracoviště: Katedra elektromagnetického pole

Anotace:
In this paper, we present an efficient coupledwave surfaceimpedance method for the analysis of extraordinary optical transmission (EOT) through single and stacked realistic metallic screens under normal and oblique incidence, including possible dielectric interlayers. The proposed theory is valid for the complete frequency range where EOT has been reported, including microwaves and optics. Electromagnetic simulations validate the results of the model, which enable fast and accurate characterization of the analyzed structures.
Loss compensation in RF metamaterials by single transistor circuits
 Autoři: doc. Ing. Lukáš Jelínek, Ph.D., prof. Ing. Jan Macháč, DrSc.,
 Publikace: Proceedings of the 7th International Congress on Advanced Electromagnetic Materials in Microwaves and Optics (METAMATERIALS). Piscataway: IEEE, 2013. pp. 217219. ISBN 9781479912322.
 Rok: 2013
 DOI: 10.1109/MetaMaterials.2013.6809005
 Odkaz: https://doi.org/10.1109/MetaMaterials.2013.6809005
 Pracoviště: Katedra elektromagnetického pole

Anotace:
This paper shows that reduction of losses, or even addition of gain, in RF metamaterials can be achieved by a single transistor circuit that exploits its conditional stability. The presented solution offers not only extreme simplicity, but also absolute control over stability and achieved gain values.
New results on extraordinary optical transmission and Fishnet Metamaterials
 Autoři: Delgado, V., Marques, R., doc. Ing. Lukáš Jelínek, Ph.D.,
 Publikace: Proceedings of the 7th International Congress on Advanced Electromagnetic Materials in Microwaves and Optics (METAMATERIALS). Piscataway: IEEE, 2013. p. 5557. ISBN 9781479912322.
 Rok: 2013
 DOI: 10.1109/MetaMaterials.2013.6808951
 Odkaz: https://doi.org/10.1109/MetaMaterials.2013.6808951
 Pracoviště: Katedra elektromagnetického pole

Anotace:
A generalized transverse waveguide analysis for Extraordinary Transmission (ET) and Fishnet Metamaterials (FMs) in realistic metallic screens has recently been published by the authors [1]. The model is valid for lossy metallic screens thanks to the Surface Impedance (SI) approximation (e.g. [2]). A standard scattering matrixes formalism makes the model applicable to stacked screens with possible dielectric boards. A number of reported phenomena [3, 4] related to screens with a periodic array of slits or holes are reproduced efficiently with the presented analysis.
Precise Measurement Using CoaxialtoMicrostrip Transition Through Radiation Suppression
 Autoři: Morávek, O., prof. Ing. Karel Hoffmann, CSc., doc. Ing. Milan Polívka, Ph.D., doc. Ing. Lukáš Jelínek, Ph.D.,
 Publikace: IEEE Transactions on Microwave Theory and Techniques. 2013, 61(8), 29562965. ISSN 00189480.
 Rok: 2013
 DOI: 10.1109/TMTT.2013.2272380
 Odkaz: https://doi.org/10.1109/TMTT.2013.2272380
 Pracoviště: Katedra elektromagnetického pole

Anotace:
This paper presents a study about the radiation problem of coaxialtomicrostrip launchers and suggests their improvement with a novel design. The proposed solution is based on a coaxialtomicrostrip transition enclosed in a parallelplate transmission line that has its cutoff frequency above the working frequency band of interest. Any radiated field is quickly attenuated because it is propagating inside a subcritical parallelplate transmission line. The proposed method is extensively analyzed in the CST Microwave Studio and simulation results are verified on fabricated testfixture by multiple measurements. The proposed solution improves the accuracy and reduces the uncertainty during measurements on microstrip.
Surface mesoscopic effects in finite metamaterials
 Autoři: Lapine, M., doc. Ing. Lukáš Jelínek, Ph.D., Marques, R.
 Publikace: Optics Express. 2012, 20(16), 1829718302. ISSN 10944087.
 Rok: 2012
 DOI: 10.1364/OE.20.018297
 Odkaz: https://doi.org/10.1364/OE.20.018297
 Pracoviště: Katedra elektromagnetického pole

Anotace:
While the effective medium treatment of unbounded metamaterials appears to be well established and firmly proven, related phenomena in finite structures have not received sufficient attention. We report on mesoscopic effects associated with the boundaries of finite discrete metamaterial samples, which can invalidate an effective medium description. We show how to avoid such effects by proper choice of boundary configuration. As all metamaterial implementations are naturally finite, we are confident that our findings are crucial for future metamaterial research.
An FETBased Unit Cell for an Active Magnetic Metamaterial
 Autoři: doc. Ing. Lukáš Jelínek, Ph.D., prof. Ing. Jan Macháč, DrSc.,
 Publikace: IEEE Antennas and Wireless Propagation Letters. 2011, 10 927930. ISSN 15361225.
 Rok: 2011
 DOI: 10.1109/LAWP.2011.2167311
 Odkaz: https://doi.org/10.1109/LAWP.2011.2167311
 Pracoviště: Katedra elektromagnetického pole

Anotace:
A particle that can be used to create an active magnetic metamaterial has been designed using an FET transistor loaded in its gate by a conducting ring and in its source by a parallel resonance circuit. The design procedure is discussed, and the working principle is experimentally demonstrated in the RF range.
Bulk Metamaterials Made of Resonant Rings
 Autoři: Marques, R., doc. Ing. Lukáš Jelínek, Ph.D., Freire, J.R., Baena, J.D., Lapine, M.
 Publikace: Proceedings of the IEEE. 2011, 99(10), 16601668. ISSN 00189219.
 Rok: 2011
 DOI: 10.1109/JPROC.2011.2141970
 Odkaz: https://doi.org/10.1109/JPROC.2011.2141970
 Pracoviště: Katedra elektromagnetického pole

Anotace:
In this brief review, we present the fundamentals of bulk resonant ring metamaterial (RRM) theory. Metamaterials made of resonant rings are discussed, and some basic design rules are provided. Homogenization (including spatial dispersion) of 3D resonant ring latices is reviewed, with emphasis in isotropic designs. Edge effects in finite size metamaterial samples are discussed. Finally, possible applications and future trends are briefly reviewed.
Extraordinary transmission through dielectric screens with 1D subwavelength metallic inclusions
 Autoři: Delgado, V., Marques, R., doc. Ing. Lukáš Jelínek, Ph.D.,
 Publikace: Optics Express. 2011, 19(14), 1361213617. ISSN 10944087.
 Rok: 2011
 DOI: 10.1364/OE.19.013612
 Odkaz: https://doi.org/10.1364/OE.19.013612
 Pracoviště: Katedra elektromagnetického pole

Anotace:
Extraordinary optical transmission (EOT) through dielectric screens periodically loaded with subwavelength 1D discontinuities, such as apertures or metallic insets is analyzed. The results of the analysis and computational electromagnetic simulations show that the transmission is higher for for metallic inclusions than for empty slits. This effect confirms that EOT is a quite general property of weakly transparent periodic diffraction screens and opens the door to optically induced EOT in photoconductive semiconductor screens.
Free Space Polarizability Measurement Method
 Autoři: doc. Ing. Lukáš Jelínek, Ph.D., prof. Ing. Jan Macháč, DrSc.,
 Publikace: Proceedings of Metamaterials´ 2011: The Fifth International Congress on Advanced Electromagnetic Materials in Microwaves and Optics. LouvainlaNeuve: UCL, Laboratoire d´Hyperfréquences, 2011. pp. 967969. ISBN 9789526761107.
 Rok: 2011
 Pracoviště: Katedra elektromagnetického pole

Anotace:
A simple and precise method for free space polarizability measurement of electrically small particles is presented. The method is based on a measurement of the scattering parameters of a waveguide loaded by a particle, and on knowledge of the dipolar polarizabilities of two calibration standards.
Further support for the alignment of cattle along magnetic field lines: reply to Hert et al. response
 Autoři: Heřt, J., doc. Ing. Lukáš Jelínek, Ph.D., Pekárek, L., Pavlíček, A.
 Publikace: Journal of Comparative Physiology A. 2011, 197(12), 11351136. ISSN 03407594.
 Rok: 2011
 DOI: 10.1007/s0035901106888
 Odkaz: https://doi.org/10.1007/s0035901106888
 Pracoviště: Katedra elektromagnetického pole

Anotace:
We have carefully read the text of the comments of Begall et al. (2011) on our publication (Hert et al. 2011), and meticulously considered the objections concerning our paper as well as the results of the reevaluation, reassessment and reinterpretation of our data. In the following, we present our response.
Metamaterialinspired Perfect Tunnelling in Semiconductor Heterostructures
 Autoři: doc. Ing. Lukáš Jelínek, Ph.D., Baena, J.D., doc. RNDr. Jan Voves, CSc., Marques, R.
 Publikace: New Journal of Physics. 2011, 13 ISSN 13672630.
 Rok: 2011
 DOI: 10.1088/13672630/13/8/083011
 Odkaz: https://doi.org/10.1088/13672630/13/8/083011
 Pracoviště: Katedra elektromagnetického pole, Katedra mikroelektroniky

Anotace:
In this paper, we use a formal analogy of the electromagnetic wave equation and the Schrödinger equation in order to study the phenomenon of perfect tunnelling (tunnelling with unitary transmittance) in a onedimensional semiconductor heterostructure. Using the Kane model of a semiconductor, we show that this phenomenon can indeed exist, resembling all the interesting features of the corresponding phenomenon in classical electromagnetism in which metamaterials (substances with negative material parameters) are involved. We believe that these results can pave the way toward interesting applications in which metamaterial ideas are transferred into the semiconductor domain.
No Alignment of Cattle Along Geomagnetic Field Lines Found
 Autoři: Hert, J., doc. Ing. Lukáš Jelínek, Ph.D., Pekárek, L., Pavlíček, A.
 Publikace: Journal of Comparative Physiology A. 2011, 197(6), 677682. ISSN 03407594.
 Rok: 2011
 DOI: 10.1007/s0035901106287
 Odkaz: https://doi.org/10.1007/s0035901106287
 Pracoviště: Katedra elektromagnetického pole

Anotace:
This paper presents a study of the body orientation of domestic cattle on free pastures in everal European states, based on the satellite photographs. In sum, 232 herds with 3,412 individuals were evaluated. Two independent groups participated in our study and came to the same conclusion that in contradiction to the recent findings of other researchers, no alignment of the animals and of their herds along geomagnetic field lines could be found. Several possible reasons for this discrepancy should be taken into consideration: poor quality of satellite photographs, difficulties in determining body axis, selection of herds or animals within herds, lack of blinding in the evaluation, possible subconscious bias, and, most importantly, high sensitivity of the calculated main directions of the Rayleigh vectors to some kind of bias or to some overlooked or ignored confounder. This factor could easily have led to an unsubstantiated positive conclusion about the existence of magnetoreception.
Perfect Tunneling in Semiconductor Heterostructures
 Autoři: doc. Ing. Lukáš Jelínek, Ph.D., Baena, J.D., doc. RNDr. Jan Voves, CSc., Marques, R.
 Publikace: Proceedings of Metamaterials´ 2011: The Fifth International Congress on Advanced Electromagnetic Materials in Microwaves and Optics. LouvainlaNeuve: UCL, Laboratoire d´Hyperfréquences, 2011. pp. 10211023. ISBN 9789526761107.
 Rok: 2011
 Pracoviště: Katedra elektromagnetického pole, Katedra mikroelektroniky

Anotace:
We study the phenomenon of perfect tunneling (tunneling with unitary transmittance) in a 1D semiconductor heterostructure using a formal analogy of the electromagnetic wave equation and the Schrodinger equation. The Kane model of a semiconductor is used and it is shown that this phenomenon can indeed exist, resembling all the interesting features of the corresponding phenomenon in classical electromagnetism in which metamaterials are involved.
A Resonant Particle for a Volumetric DNG Metamaterial
 Autoři: Bláha, M., doc. Ing. Lukáš Jelínek, Ph.D., prof. Ing. Jan Macháč, DrSc.,
 Publikace: European Microwave Week 2010 "Connecting the World" Conference Proceedings. London: Horizon House Publications, 2010. pp. 14131416. ISBN 9782874870194.
 Rok: 2010
 Pracoviště: Katedra elektromagnetického pole

Anotace:
This paper studies a combination of electric and magnetic particles in order to obtain simultaneously negative electric and magnetic polarisability under irradiation by an electromagnetic wave. The magnetic particle is represented by a split ring resonator, and electric particle is represented by an electric dipole terminated by an inductor. They are combined together in a way that obtains a resonant element with inversion symmetry. The internal coupling between these resonators located in a waveguide is subjected to a special study. The response of this particle is strongly anisotropic, but an isotropic response can be achieved by a proper spatial arrangement.
Analytical Theory of Extraordinary Optical Transmission Through Realistic Metallic Screens
 Autoři: Delgado, V., Marques, R., doc. Ing. Lukáš Jelínek, Ph.D.,
 Publikace: Optics Express. 2010, 18(7), 65066515. ISSN 10944087.
 Rok: 2010
 DOI: 10.1364/OE.18.006506
 Odkaz: https://doi.org/10.1364/OE.18.006506
 Pracoviště: Katedra elektromagnetického pole

Anotace:
An analytical theory of extraordinary optical transmission (EOT) through realistic metallic screens perforated by a periodic array of subwavelength holes is presented. The theory is based on our previous work on EOT through perfect conducting screens and on the surface impedance concept. The proposed theory is valid for the complete frequency range where EOT has been reported, including microwaves and optics. A reasonably good agreement with electromagnetic simulations is shown in all this frequency range. We feel that the proposed theory may help to clarify the physics underlying EOT and serve as a first step to more accurate analysis.
Artificial Magnetism and Lefthanded Media from Dielectric Rings and Rods
 Autoři: doc. Ing. Lukáš Jelínek, Ph.D., Marqués, R.
 Publikace: Journal of Physics: Condensed Matter. 2010, 22(1), 16. ISSN 09538984.
 Rok: 2010
 DOI: 10.1088/09538984/22/2/025902
 Odkaz: https://doi.org/10.1088/09538984/22/2/025902
 Pracoviště: Katedra elektromagnetického pole

Anotace:
It is shown that artificial magnetism with relatively large frequency bandwidth can be obtained from periodic arrangements of dielectric rings. Combined with dielectric rods, dielectric rings can provide 3D isotropic lefthanded metamaterials which are an advantageous alternative to metallic split ring resonators (SRRs) and/or metallic wires when undetectability by low frequency external magnetic fields is desired. Furthermore it is shown that, unlike conventional SRRs, dielectric rings can also be combined with natural plasmalike media to obtain a lefthanded metamaterial.
Edge Effects in Finite Size Resonant Ring Metamaterials
 Autoři: Marqués, R., Lapine, M., doc. Ing. Lukáš Jelínek, Ph.D.,
 Publikace: Metamaterials 2010. Karlsruhe: Universität Karlsruhe, 2010. pp. 330332. ISBN 9789529277346.
 Rok: 2010
 Pracoviště: Katedra elektromagnetického pole

Anotace:
It is reported how finite size resonant ring metamaterials may present strong deviations from the expected behavior in the negative magnetic permeability region, even for moderate losses. This effect seems to be related with the excitation of magnetoinductive quasistatic resonances which are closely related to the "unphysical" resonances that may appear near sharp wedges in negative magnetic permeability continuous media.
Exact Modelling Method for Discrete Finite Metamaterial Lens
 Autoři: Lapine, M., doc. Ing. Lukáš Jelínek, Ph.D., Marques, M., Freire, M.J.
 Publikace: IET Microwaves, Antennas & Propagation. 2010, 4(8), 11321139. ISSN 17518725.
 Rok: 2010
 DOI: 10.1049/ietmap.2009.0598
 Odkaz: https://doi.org/10.1049/ietmap.2009.0598
 Pracoviště: Katedra elektromagnetického pole

Anotace:
The authors analyse the properties of metamaterial lens composed of capacitively loaded ring resonators, with the help of an efficient rigorous model suitable for calculating the properties of finite metamaterial samples. This approach takes into account the discrete structure and finite extent of realistic metamaterials. The authors show that the discrete model reveals the effects, which can be missed by a continuous model based on effective parameters and that the results are in close agreement with the experimental data.
Fishnet Metamaterials  Rules for Refraction and Limits of Homogenization
 Autoři: doc. Ing. Lukáš Jelínek, Ph.D., Marques, L., prof. Ing. Jan Macháč, DrSc.,
 Publikace: Optics Express. 2010, 18(17), 1794017949. ISSN 10944087.
 Rok: 2010
 DOI: 10.1364/OE.18.017940
 Odkaz: https://doi.org/10.1364/OE.18.017940
 Pracoviště: Katedra elektromagnetického pole

Anotace:
The perfectly conducting stacked fishnet metamaterial is studied in this paper. The analysis is based on a combination of the mode matching method together with the generalized eigenvalue problem, and takes into account wave propagation along all three Cartesian axes. The analysis has been developed for a fishnet of square lateral periodicity and for two particular polarizations, namely TE and TM, corresponding to the two most common excitations. The 1D and 2D dispersion characteristics are calculated for both polarizations, showing that the TM waves undergo negative refraction in a narrow frequency band just below Wood's anomaly, whereas TE polarized waves exhibit ordinary positive refraction. Finally, possible homogenization of the fishnet metamaterial is considered, showing that only for small angles of incidence and in the immediate vicinity of Wood's anomaly can the fishnet be seen as homogenizable uniaxial medium.
Homogenization of Fishnet Metamaterials: Possibilities and Restrictions
 Autoři: doc. Ing. Lukáš Jelínek, Ph.D., Marques, R., prof. Ing. Jan Macháč, DrSc.,
 Publikace: Metamaterials 2010. Karlsruhe: Universität Karlsruhe, 2010. pp. 3335. ISBN 9789529277346.
 Rok: 2010
 Pracoviště: Katedra elektromagnetického pole

Anotace:
The possibilities and restrictions of homogenization in fishnet metamaterials are studied. By means of 1D and 2D dispersion diagrams obtained by combination of modematching with generalized eigenvalue problem it is shown that in narrow frequency region just below Wood's anomaly the approximation of fishnet by uniaxial medium is allowed. It is also shown that this is the frequency band of possible negative refraction.
Realistic Metamaterial Lenses: Limitations Imposed by Discrete Structure
 Autoři: Lapine, M., doc. Ing. Lukáš Jelínek, Ph.D., Freire, M.J., Marqués, R.
 Publikace: Physical Review B. 2010, 82(16), 18. ISSN 10980121.
 Rok: 2010
 DOI: 10.1103/PhysRevB.82.165124
 Odkaz: https://doi.org/10.1103/PhysRevB.82.165124
 Pracoviště: Katedra elektromagnetického pole

Anotace:
We study the peculiarities of a metamaterial "superlens," caused by its discrete structure and finite size. We show that precise modeling of the lens provides remarkable distinctions from continuous medium approximation. In particular, we address the problem of highest resolution that can be achieved with a realistic electrically thin metamaterial lens. We conclude that discrete structure imposes essential limitations on the resolution and that the resolution cannot be improved by decreasing dissipation in the system. Further implications related to effective medium description of discrete structures are discussed.
Accurate modeling of split ring metamaterial lenses for magnetic resonance imaging applications
 Autoři: doc. Ing. Lukáš Jelínek, Ph.D., Marques, R., Freire, M.
 Publikace: Journal of Applied Physics. 2009, 105(2), ISSN 00218979.
 Rok: 2009
 DOI: 10.1063/1.3067788
 Odkaz: https://doi.org/10.1063/1.3067788
 Pracoviště: Katedra elektromagnetického pole

Anotace:
The usefulness of thin split ring metamaterial slabs for imaging applications, including magnetic resonance imaging applications, has attracted some attention in the past years. However, the small number of unit cells across these thin slabs prevents the direct application of continuous medium models for its characterization. The main aim of this contribution is to provide a rigorous model for these structures, also clarifying the usefulness of continuous medium approach for their characterization. The proposed model is a generalization of the classical Lorentz procedure to two dimensions and is able to deal with electrically thin slabs made of small resonant closed current loops. The obtained results are validated by fullwave electromagnetic simulations and compared with the continuous model approximation of the slab.
Analytical theory of extraordinary transmission through metallic diffraction screens perforated by small holes
 Autoři: Marques, R., Mesa, F., doc. Ing. Lukáš Jelínek, Ph.D., Medina, F.
 Publikace: Optics Express. 2009, 17(7), 55715579. ISSN 10944087.
 Rok: 2009
 DOI: 10.1364/OE.17.005571
 Odkaz: https://doi.org/10.1364/OE.17.005571
 Pracoviště: Katedra elektromagnetického pole

Anotace:
In this letter, the problem of extraordinary (ET) transmission of electromagnetic waves through opaque screens perforated with subwavelength holes is addressed from an analytical point of view. Our purpose was to find a closedform expression for the transmission coefficient in a simple case in order to explore and clarify, as much as possible, the physical background of the phenomenon. The solution of this canonical example, apart from matching quite well with numerical simulations given by commercial solvers, has provided new insight in extraordinary transmission as well as Wood's anomaly. Thus, our analysis has revealed that one of the key factors behind ET is the continuous increase of excess electric energy around the holes as the frequency approaches the onset of some of the higherorder modes associated with the periodicity of the screen. The same analysis also helps to clarify the role of surface modes or spoof plasmons in the onset of ET.
Analytical Theory of Wave Propagation through Stacked Fishnet Metamaterials
 Autoři: Marqués, R., doc. Ing. Lukáš Jelínek, Ph.D., Mesa, F., Medina, F.
 Publikace: Optics Express. 2009, 17(14), 1158211593. ISSN 10944087.
 Rok: 2009
 DOI: 10.1364/OE.17.011582
 Odkaz: https://doi.org/10.1364/OE.17.011582
 Pracoviště: Katedra elektromagnetického pole

Anotace:
This work analyzes the electromagnetic wave propagation through periodically stacked fishnets from zero frequency to the first Wood's anomaly. It is shown that, apart from FabryPerot resonances, these structures support two transmission bands that can be backward under the appropriate conditions. The first band starts at Wood's anomaly and is closely related to the wellknown phenomena of extraordinary transmission through a single fishnet. The second band is related to the resonances of the fishnet holes. In both cases, the inplane periodicity of the fishnet cannot be made electrically small, which prevents any attempt of homogenization of the structure along the fishnet planes. However, along the normal direction, even with very small periodicity transmission is still possible. An homogenization procedure can then be applied along this direction, thus making that the structure can behave as a backwardwave transmission line for such transmission bands.
Characterization of miniaturized metamaterial resonators coupled to planar transmission lines through parameter extraction
 Autoři: Aznar, F., Gil, M., Bonache, J., doc. Ing. Lukáš Jelínek, Ph.D., Baena, J., Marques, R., Martin, F.
 Publikace: Journal of Applied Physics. 2008, 104(11), ISSN 00218979.
 Rok: 2008
 DOI: 10.1063/1.3021109
 Odkaz: https://doi.org/10.1063/1.3021109
 Pracoviště: Katedra elektromagnetického pole

Anotace:
In this paper, a method for obtaining the electrical characteristics of metamaterial resonators coupled to planar transmission lines is proposed. This parameter extraction technique is based on the comparison between the measured (or full wave electromagnetic simulated) transmission and reflection characteristics of a host line loaded with such resonators and those obtained from its lumped element equivalent circuit model (previously reported by some of the authors). The resonant particles considered in this study are split ring resonators, spiral resonators, and other electrically small resonant particles based on two metal levels. The interest in this technique lies in the lack of analytical models providing the electrical parameters of several of the considered ultrasmall resonator topologies (due to their complexity). From the extracted parameters, it is concluded that the circuit models predict very accurately the frequency responses of the considered structures for the different resonators under study. There is an increasing interest in the synthesis of metamaterial transmission lines with extremely small unit cell size. In order to achieve dimensions close to (or even below) lambda(g)/100, it is imperative to use complex resonator topologies that combine broadside coupling and extremely elongated metallic strips (etched in different metal levels connected through vias). This justifies the proposed technique. Thus, this work is useful in aiding the synthesis of microwave components based on resonant type metamaterial transmission lines.
Experimental demonstration of a mu=1 metamaterial lens for magnetic resonance imaging
 Autoři: Freire, M., Marques, R., doc. Ing. Lukáš Jelínek, Ph.D.,
 Publikace: Applied Physics Letters. 2008, 93(23), ISSN 00036951.
 Rok: 2008
 DOI: 10.1063/1.3043725
 Odkaz: https://doi.org/10.1063/1.3043725
 Pracoviště: Katedra elektromagnetického pole

Anotace:
In this work a mu=1 metamaterial (MM) lens for magnetic resonance imaging (MRI) is demonstrated. MRI uses surface coils to detect the radio frequency (rf) energy absorbed and emitted by the nuclear spins in the imaged object. The proposed MM lens manipulates the rf field detected by these surface coils so that the coil sensitivity and spatial localization are substantially improved. Beyond this specific application, we feel that the reported results are the experimental confirmation of a new concept for the manipulation of rf field in MRI, which paves the way to many other interesting applications.
Periodic arrangements of chiral scatterers providing negative refractive index biisotropic media
 Autoři: doc. Ing. Lukáš Jelínek, Ph.D., Marques, R., Mesa, F., Baena, J.
 Publikace: Physical Review B. 2008, 77(20), ISSN 10980121.
 Rok: 2008
 DOI: 10.1103/PhysRevB.77.205110
 Odkaz: https://doi.org/10.1103/PhysRevB.77.205110
 Pracoviště: Katedra elektromagnetického pole

Anotace:
The main goal of this contribution is to show that periodic arrangements of chiral scatterers can be the basis for the development of three dimensional and isotropic negative refractive index artificial media. Three dimensionality and isotropy are key issues in this context since only three dimensional structures can be properly viewed as a "medium," and only in isotropic media the refractive index is unambiguously defined. The proposed arrangements are cubic lattices of chiral split ring resonators conveniently designed to yield an isotropic behavior. The reported structures are shown to provide a significant frequency band of negative refraction with good matching to free space.
Unified homogenization theory for magnetoinductive and electromagnetic waves in splitring metamaterials
 Autoři: Baena, J., doc. Ing. Lukáš Jelínek, Ph.D., Marques, R., Silveirinha, M.
 Publikace: Physical Review A. 2008, 78(1), ISSN 10502947.
 Rok: 2008
 DOI: 10.1103/PhysRevA.78.013842
 Odkaz: https://doi.org/10.1103/PhysRevA.78.013842
 Pracoviště: Katedra elektromagnetického pole

Anotace:
A unified homogenization procedure for splitring metamaterials taking into account time and spatial dispersion is introduced. It is shown that electromagnetic and magnetoinductive waves propagating in the metamaterial are obtained from this analysis. Therefore, the proposed time and spatially dispersive permeability accounts for the characterization of the complete spectrum of waves of the metamaterial. Finally, it is shown that the proposed theory is in good quantitative and qualitative agreement with full wave simulations.
A Magnetic Metamaterial Composed of Randomly Oriented SRRs
 Autoři: doc. Ing. Lukáš Jelínek, Ph.D., prof. Ing. Jan Macháč, DrSc., Zehentner, J.
 Publikace: PIERS 2007 Progress In Electromagnetics Research Symposium  Proceedings  CN. Cambridge, MA: The Electromagnetics Academy, 2007. pp. 474477. ISSN 15599450.
 Rok: 2007
 Pracoviště: Katedra elektromagnetického pole

Anotace:
The concept, manufacture and testing of a volumetric isotropic magnetic metamaterial composed of randomly distributed broadside coupled split ring resonators is presented in this paper. An estimate of the isotropy based on the measured transmissions is made in terms of the arithmetic mean value and the standard deviation of the sample. We offer conclusions and recommendations for the development of a genuine bulk isotropic medium of various densities and distributions of the particles, based on the 64 measured frequency responses of each sample.
Characterization of Resonant Modes in a Cube of SRR´s
 Autoři: Baena, J.D., doc. Ing. Lukáš Jelínek, Ph.D., Marqués, R., Zehentner, J.
 Publikace: PIERS 2007 Progress In Electromagnetics Research Symposium  Proceedings  CN. Cambridge, MA: The Electromagnetics Academy, 2007. pp. 469. ISSN 15599450.
 Rok: 2007
 Pracoviště: Katedra elektromagnetického pole

Anotace:
A general quasistatic circuit model of the cubical unit cell consisting of six particles deposited on the walls of a cube is presented in this paper. The matrix description of the equivalent circuit of the cube, incorporating the self and mutual impedances, is applied to determining of that unit cell response. It is shown that the resonance splitting due to the EM coupling between faces of the cube does not take place and all unit cells of this kind possess only one magnetic resonance as does the original SRR. The theoretical prediction of that unit cell behavior has been experimentally demonstrated.
Isotropic frequency selective surfaces made of cubic resonators
 Autoři: Baena, J., doc. Ing. Lukáš Jelínek, Ph.D., Marques, R., Mock, J., Gollub, J., Smith, D.
 Publikace: Applied Physics Letters. 2007, 91(19), ISSN 00036951.
 Rok: 2007
 DOI: 10.1063/1.2806915
 Odkaz: https://doi.org/10.1063/1.2806915
 Pracoviště: Katedra elektromagnetického pole

Anotace:
Isotropic frequency selective surface (FSS) made of cubic arrangements of split ring resonators (SRRs) is proposed and analyzed. For this purpose, a suitable isotropic modification of the SRR was used in the design of a cubic unit element invariant under the tetrahedral point symmetry group. It was experimentally demonstrated that the transmission through such a FSS is angle and polarization independent. For comparison, another FSS, whose unit elements do not satisfy necessary symmetries, was measured, showing clearly anisotropic behavior. We feel then that symmetries play an important role. Potential device applications are envisioned for antenna technology at microwave and terahertz frequencies.
Metamaterials  A Challenge for Contemporary Advanced Technology
 Autoři: doc. Ing. Lukáš Jelínek, Ph.D., prof. Ing. Jan Macháč, DrSc., Zehentner, J.
 Publikace: Proceedings of 17th International Conference Radioelektronika 2007. Brno: FEKT VUT v Brně, 2007. p. 251262. ISBN 9781424408214.
 Rok: 2007
 Pracoviště: Katedra elektromagnetického pole

Anotace:
Metamaterials are artificial composite media exhibiting electromagnetic responses that natural materials do not provide. They enable their permittivity and permeability to be cast down to negative values. Metamaterials are known in two forms: volumetric medium and planar version. The first form is characterized by field theory, while the second form utilizes transmission line theory. There is a brief report on the authors' innovative findings. It concerns the utilization of split ring resonators in isotropic negative permeability metamaterials, an isotropic negative permittivity medium, CPW supporting a lefthanded wave, and wire media exhibiting negative permittivity. Finally, prospects for further developments in this interesting field are presented.
Negative refraction from balanced quasiplanar chiral inclusions
 Autoři: Marques, R., doc. Ing. Lukáš Jelínek, Ph.D., Mesa, F.
 Publikace: Microwave and Optical Technology Letters. 2007, 49(10), 26062609. ISSN 08952477.
 Rok: 2007
 DOI: 10.1002/mop.22736
 Odkaz: https://doi.org/10.1002/mop.22736
 Pracoviště: Katedra elektromagnetického pole

Anotace:
This work proposes a quasiplanar chiral resonator suitable for the design of negative refraction index metamaterials. It is presented as an analytical model to determine the metamaterial polarizabilities, which is also the basis of a further study of the viability of negative refraction in chiral and racemic arrangements of inclusions made up with the proposed quasiplanar chiral resonator. The present analysis is expected to pave the way for the design and building feasible negative refractive index metamaterials whose inclusions can be manufactured by means of standard photoetching techniques.
Quasiisotropic Frequency Selective Surface
 Autoři: Baena, J.D., Mock, J., doc. Ing. Lukáš Jelínek, Ph.D., Smith, D.R., Marqués, R., Gollub, J.
 Publikace: PIERS 2007 Progress In Electromagnetics Research Symposium  Proceedings  CN. Cambridge, MA: The Electromagnetics Academy, 2007. pp. 478. ISSN 15599450.
 Rok: 2007
 Pracoviště: Katedra elektromagnetického pole

Anotace:
The cubic cell, satisfying the inversion symmetry removing the magnetoelectric coupling, was proposed and is presented in this paper. The quasiisotropic frequency selective surface was designed, manufactured and measured under different angle and polarization of the incident wave between horn antennas. A weak dependence of the transmission on the incident angle and polarization of the illumination has been observed. A simple model based on surface impedance deduced from the polarizability of a single unit cell is given in the presentation.
Towards a systematic design of isotropic bulk magnetic metamaterials using the cubic point groups of symmetry
 Autoři: Baena, J., doc. Ing. Lukáš Jelínek, Ph.D., Marques, R.
 Publikace: Physical Review B. 2007, 76(24), ISSN 10980121.
 Rok: 2007
 DOI: 10.1103/PhysRevB.76.245115
 Odkaz: https://doi.org/10.1103/PhysRevB.76.245115
 Pracoviště: Katedra elektromagnetického pole

Anotace:
In this paper, a systematic approach to the design of bulk isotropic magnetic metamaterials is presented. The roles of the symmetries of both the constitutive element and the lattice are analyzed. For this purpose, it is assumed that the metamaterial is composed of cubic split ring resonators (SRRs) arranged in a cubic lattice. The minimum symmetries needed to ensure an isotropic behavior are analyzed, and some particular configurations are proposed. Besides, an equivalent circuit model is proposed for the considered cubic SRRs. Experiments are carried out in order to validate the proposed theory. We hope that this analysis will pave the way to the design of bulk metamaterials with strong isotropic magnetic response, including negative permeability and lefthanded metamaterials.
3D Magnetic Resonators for Isotropic Metamaterial Design
 Autoři: doc. Ing. Lukáš Jelínek, Ph.D., Baena, J.D., Marques, R., Zehentner, J.
 Publikace: Radioelektronika 2006  Conference Proceedings. Bratislava: Slovak University of Technology, 2006. pp. 264266. ISBN 8022723886.
 Rok: 2006
 Pracoviště: Katedra elektromagnetického pole

Anotace:
The paper presents 3Disotropic magnetic resonators, made of 6 planar resonator placed on the faces of a cube so that the whole particle satisfies necessary spatial symmetries to reduce all second order (pseudo)tensors to (pseudo)scalars. The isotropy is experimentally confirmed by measuring the transmission coefficent through a waveguide loaded with such 3D particle in several orientations.
Computer Controlled Measurement of Electromagnetic Fields
 Autoři: Holubec, B., doc. Ing. Lukáš Jelínek, Ph.D., prof. Ing. Jan Macháč, DrSc., Zehentner, J.
 Publikace: Radioelektronika 2006  Conference Proceedings. Bratislava: Slovak University of Technology, 2006. pp. 284287. ISBN 8022723886.
 Rok: 2006
 Pracoviště: Katedra elektromagnetického pole

Anotace:
This paper presents a system for measuring high frequency electromagnetic fields fully controlled by a computer. A measuring probe is driven in one direction by a step motor, and in two other directions it is set manually. The paper collects some experimental data on field distributions taken along a transmission line and a leaky wave antenna.
Direct Polarisability Extraction Method
 Autoři: doc. Ing. Lukáš Jelínek, Ph.D., Baena, J.D., Marques, R., Zehentner, J.
 Publikace: Proceedings of the 36th European Microwave Conference. Piscataway: IEEE, 2006. ISBN 2960055160.
 Rok: 2006
 DOI: 10.1109/EUMC.2006.281087
 Odkaz: https://doi.org/10.1109/EUMC.2006.281087
 Pracoviště: Katedra elektromagnetického pole

Anotace:
The method of finding the polarisability of a particle under test is described in the paper. To this point the particle is placed inside the waveguide and its polarisability is calculated either from known field at the input and the output port or from scattering parameters. The method is verified by electromagnetic simulation in the case of particle with known polarisability.
Electrically Small Isotropic ThreeDimensional Magnetic Resonators for Metamaterial Design
 Autoři: Baena, J.D., doc. Ing. Lukáš Jelínek, Ph.D., Marqués, R., Zehentner, J.
 Publikace: Applied Physics Letters. 2006, 88(134108), 13410811341083. ISSN 00036951.
 Rok: 2006
 DOI: 10.1063/1.2190442
 Odkaz: https://doi.org/10.1063/1.2190442
 Pracoviště: Katedra elektromagnetického pole

Anotace:
The problem of the design of artificial magnetic resonators for isotropic metamaterials is addressed. The internal symmetries that ensure an isotropic behavior of such resonators are analyzed and some specific designs based on the proper arrangement of modified split ring resonators are proposed. These proposals are validated by electromagnetic simulations and experiments. The reported results are likely to have applications in the design of devices such as negative refractive index materials, superlenses, and metasurfaces with isotropic response
On the Design of Isotropic Magnetic Metamaterials
 Autoři: doc. Ing. Lukáš Jelínek, Ph.D., Zehentner, J., Baena, J.D., Marques, R.
 Publikace: The 13th IEEE Mediterranean Electrotechnical Conference  MELECON 2006  Electronic Proceedings. Piscataway: IEEE, 2006. pp. 250253. ISBN 1424400880.
 Rok: 2006
 Pracoviště: Katedra elektromagnetického pole

Anotace:
In this paper new 3Disotropic magnetic resonators are proposed. These new particles possess spatial symmetries under whose all second order (pseudo)tensors are reduced to (pseudo)scalars. If then the contribution of higher order tensors is neglected, the particles are isotropic. To confirm that proposed particles still generate magnetic response, a quasistatic model, showing the qualitative behavior of the reported resonators, is proposed. Finally, the isotropy is experimentally checked by measuring the transmission coefficient through a waveguide loaded with such 3D particle in several orientations and results are compared with some previous proposals lacking these symmetries.
Analysis of 2D and 3DIsotropic Split Ring Resonators
 Autoři: Baena, J.D., doc. Ing. Lukáš Jelínek, Ph.D., Marqués, R., Zehentner, J.
 Publikace: ICECom 2005  Conference Proceedings 18th International Conference on Applied Electromagneics and Communications. Dubrovnik: IEEE Croatia Section, 2005. pp. 325328. ISBN 9536037440.
 Rok: 2005
 Pracoviště: Katedra elektromagnetického pole

Anotace:
Previously proposed 2D isotropic split ring resonators are analyzed. Furthermore, a new isotropic 3D particle is proposed and analyzed. To this end a quasistatic LC circuit model, that provides the frequency of resonance, is developed. Theoretical computations of resonant frequency are in good agreement with the values obtained with a commercial electromagnetic solver. Finally the complete isotropy of the proposed 3D particle is demonstrated by its symmetries and is confirmed by numerical simulations.
Nearperfect Tunneling and Amplification of Evanescent Electromagnetic Waves in a Waveguide
 Autoři: Baena, J.D., doc. Ing. Lukáš Jelínek, Ph.D., Marqués, R., Medina, F.
 Publikace: Physical Review B. 2005, 72(7), 07511610751168. ISSN 10980121.
 Rok: 2005
 DOI: 10.1103/PhysRevB.72.075116
 Odkaz: https://doi.org/10.1103/PhysRevB.72.075116
 Pracoviště: Katedra elektromagnetického pole

Anotace:
Amplification of evanescent electromagnetic waves by a metamaterial slab is still a controversial issue. Metallic waveguides operating in cutoff provide a unique physical environment to produce and study these waves because isolated evanescent modes can be excited in such environment. In this paper, the tunneling of electromagnetic waves through a rectangular waveguide partially filled by a metamaterial is analyzed. Enhanced tunneling due to the amplification of evanescent waves in the metamaterial filled waveguide section is demonstrated. Since evanescent modes in rectangular waveguides are the superposition of two plane waves, the aforementioned results also show the amplification and tunneling of evanescent plane waves by a metamaterial slab in free space.
On the Resonances and Polarizabilities of Split Ring Resonators
 Autoři: Baena, J.D., Marqués, R., doc. Ing. Lukáš Jelínek, Ph.D., GarcíaGarcía, J., Martín, F.
 Publikace: Journal of Applied Physics. 2005, 98(033103), 19. ISSN 00218979.
 Rok: 2005
 DOI: 10.1063/1.2006224
 Odkaz: https://doi.org/10.1063/1.2006224
 Pracoviště: Katedra elektromagnetického pole

Anotace:
In this paper, the behavior at resonance of split ring resonators SRRs and other related topologies, such as the nonbianisotropic SRR and the broadsidecoupled SRR, are studied. It is shown that these structures exhibit a fundamental resonant mode the quasistatic resonance and other higherorder modes which are related to dynamic processes. The excitation of these modes by means of a properly polarized time varying magnetic and/or electric fields is discussed on the basis of resonator symmetries. To verify the electromagnetic properties of these resonators, simulations based on resonance excitation by nonuniform and uniform external fields have been performed. Inspection of the currents at resonances, inferred from particle symmetries and fullwave electromagnetic simulations, allows us to predict the firstorder dipolar moments induced at the different resonators and to develop a classification of the resonances based on this concept.
Perfect Tunneling and Amplification of Evanescent EM Waves in a Waveguide
 Autoři: doc. Ing. Lukáš Jelínek, Ph.D., Baena, J.D.
 Publikace: 9th International Student Conference on Electrical Engineering. Praha: České vysoké učení technické v Praze, Fakulta elektrotechnická, 2005. pp. C1.
 Rok: 2005
 Pracoviště: Katedra elektromagnetického pole

Anotace:
Metallic waveguides operating in cutoff provide a unique physical environment for producing and studying evanescent waves: isolated evanescent modes can be excited in such environment. Tunneling of electromagnetic waves through the incutoff rectangular waveguide, filled by a metamaterial, shall be analyzed in this paper and at the same time, enhanced nearperfect tunneling caused by the amplification of evanescent waves in the metamaterial shall be demonstrated.
Perfect Tunneling and Amplification of Evanescent EM Waves in a Waveguide
 Autoři: Baena, J.D., doc. Ing. Lukáš Jelínek, Ph.D., Marques, R., Medina, F.
 Publikace: Odborné semináře  Sborník za rok 2004/2005. Praha: Československá sekce IEEE, 2005. pp. 2226. ISBN 8086582175.
 Rok: 2005
 Pracoviště: Katedra elektromagnetického pole

Anotace:
Metallic waveguides operating in cutoff provide a unique physical environment for producing and studying evanescent waves: isolated evanescent modes can be excited in such environment. Tunneling of electromagneic waves through the incutoff rectangular waveguide, filled by a metamaterial, shall be analyzed in this paper and at the same time, enhanced nearperfect tunneling caused by the amplification of evanescent waves in the metamaterial shall be demonstrated.
Reducing Losses and Dispersion Effects in Multilayer Metamaterial Tunnelling Devices
 Autoři: Baena, J.D., doc. Ing. Lukáš Jelínek, Ph.D., Marqués, R.
 Publikace: New Journal of Physics. 2005, 166(7/2005), 113. ISSN 13672630.
 Rok: 2005
 DOI: 10.1088/13672630/7/1/166
 Odkaz: https://doi.org/10.1088/13672630/7/1/166
 Pracoviště: Katedra elektromagnetického pole

Anotace:
This paper focuses on reduction of losses and dispersion effects on tunnelling through waveguides filled with metamaterial. It will be shown that these unwanted effects could be reduced by dividing the metamaterial into several regions separated by air slabs. In the first part, these effects will be studied for isotropic lefthanded media (LHM). Later this will be substituted by an anisotropic magnetic medium which will lead to a practical realization with broadside coupled split ring resonators (BCSRRs). Finally, it is shown that quasiperfect tunnelling is possible, even in the presence of unavoidable losses and dispersion in the metamaterial.