We aim at determining the value of minimal magnetic induction for magnetic orientation of fibres in cementitious composite in a given mixture and establish the effect of the magnetic field shape on the final mechanical properties. The magnetic orientation is a suitable method to ensure the required direction of steel ferromagnetic fibres in the composite. The strength of the magnetic field (magnetic induction) and rheology of the fresh mixture play a crucial role in the magnetic orientation. A special device generating alternating and direct magnetic fields with different magnetic inductions was built to determine the minimal magnetic induction for the given mixture. Moreover, the effects of using alternating magnetic field are explored. The used magnetic inductions are 60 mT, 80 mT, 100 mT and 120 mT. The nondestructive inductive measuring method is applied to confirm the orientation of fibres in the hardened composite. The effect of the shape of the magnetic field and magnetic induction on flexural strength is presented. Moreover, the effects of using the alternating or direct magnetic field on the microstructure are explored using a scanning electron microscope.
Applicability of magnetic field for directed orientation of steel fibres in high-performing cementitious composites
This paper explores the practical possibility of using a magnetic field to orient steel fibres in a fresh concrete matrix. This process leads to preferential orientation, which increases the desired mechanical properties of the hardened material. In general, this paper focuses on the technical aspects of the orientation process and identifies key areas, such as the strength and shape of the magnetic field, velocity of the sample’s passage through the magnetic field and viscosity of the materials. A proto-type orienting apparatus was constructed with different permanent magnet systems to evaluate their performance. An ultrasound gel and a cementitious matrix were used as a medium for the fibres. Numerical simulations were created to further understand the effects of the magnetic field’s strength and shape. The final orientation of the fibres in hardened concrete was evaluated using Q factor measurements, X-ray scans and bending tests. A sufficiently strong magnetic field can be used to orient fibres in fresh concrete.
Concrete lintels reinforced with steel fibres oriented by a magnetic field
This paper explores the possibility of applying the technique of magnetic orientation of steel fibres for manufacturing a concrete structural element of realistic dimensions, compared to small laboratory specimens. This technique could be a part of an answer to the current need for faster and automated production in the prefabrication industry. The examined specimens have dimensions of commonly used lintels in construction, 80 mm × 100 mm × 980 mm. The properties of specimens with magnetically oriented fibres are compared with same size specimens prefabricated conventionally. The orientation of fibres has been confirmed by Q-factor non-destructive testing method using a measuring coil. All specimens were tested with a four-point bending test. The specimens with oriented fibres show a significantly higher flexural strength, by 150 %, than specimens produced conventionally with the same volume of fibres.
Flexural strength of fibre reinforced concrete in relation to the angle of magnetically orientated fibres
This paper focuses on high-performance fibre-reinforced concrete and its flexural strength
concerning fibre orientation. The orientation is provided by a fully controlled special device. This device can
align the fibres in fresh concrete using a magnetic field. The specimens are inserted into the device at different
angles to ensure different fibre orientations concerning the longer side of the sample, which corresponds to
the direction of the main tensile stresses. Specifically, angles of 0 °, 30 °, 60 ° and 90 ° are tested and compared
with each other and with reference specimens that are not exposed to a magnetic field. All samples are
measured by a non-destructive method. This method was developed in our previous research and is based on
measuring the quality factor Q of a measuring coil using an impedance meter. The samples are inserted into
a measuring coil connected to an impedance meter. Flexural strength is obtained from the results of a threepoint bending test. All samples are tested until complete failure.
Magnetic properties of steel fibres commonly used in concrete
The paper deals with measuring of magnetic properties of selected steel fibres commonly used in concrete. The results in relation to the possibility to orient fibres by magnetic field in fresh concrete are explained. The principle of the measurement setup used to obtain the magnetic parameters of the fibres is presented. The measurement setup is chosen to test fibres as they are with only the necessary mechanical shortening for fibres with shaped ends. Furthermore, the results for ten types of commonly used steel fibres from different manufacturers are presented and compared. For overview and control, the measurements on the fibres are supplemented by testing of known materials used in magnetic circuits.
Mechanical properties of high-performance concrete with steel fibres oriented by an electromagnetic field
In order to achieve better efficiency of dispersed fibre reinforcement in cementitious composites, manufacturers need to be able to directly control the fibre orientation. The magnetic orientation of fibres is an effective way to align fibres in the desired direction of the main tensile stresses and significantly improve the load-bearing capacity of the composite material. In this study, cementitious composites with different percentages of fibre reinforcement were subjected to the magnetic fibre-orienting process and their resulting mechanical parameters were examined. Also, a non-destructive method was used to evaluate the fibre orientation and volume. The flexural strengths and the capacity to dissipate mechanical energy were improved considerably compared to the reference non-oriented specimens. The non-destructive method was also reasonably accurate to predict these results.
Quality factor as a tool to measure concentration and orientation of ferromagnetic fibres in sample
Fibre-reinforced concrete is a modern composite material. Steel fibres are often used as scattered reinforcement in cement composites. We can achieve anisotropic final products by orienting the fibres, i.e. higher strength in the required direction. One of the ways, how to control the orientation of ferromagnetic fibre in composites, is a non-destructive method based on mutual induction. The advantage of non-destructive testing is, among other things, the possibility of application to fresh cement mixtures. This paper presents a fast and effective non-destructive measuring method of fibres orientation degree and fibre volume in cementitious composites. Furthermore, the measurement of fibres oriented at different angles and different fibre volumes is shown.
Simulations of the behaviour of steel ferromagnetic fibres commonly used in concrete in a magnetic field
The efficiency of fibre reinforcement in concrete can be drastically increased by orienting the fibres using a magnetic field. However, the parameters of such a field are not immediately apparent, as they depend on the specific fibre reaction to the magnetic field. In this paper, numerical simulations are conducted to study the mechanical torque acting on fibres placed in a magnetic field. The simulations are verified with an experimental setup as well as theoretical relationships. Ten different fibre types, both straight and hook-ended, are examined. The developed model can be successfully used to study the behaviour of fibres in a magnetic field. The fibre size plays the most important role together with the magnetic saturation of the fibre material. Multiple fibres show significant interactions.
Summary of findings on magnetic orientation of fibers in cement composites
This article summarizes the findings in newly developed technology – Magnetic Orientation of Fibers (MOF). New incoming technology MOF can easily and effectively reinforce concrete elements in a specific direction with ferromagnetic fibers using a magnetic field. Using this technology, it is possible to provide the required orientation of steel ferromagnetic fibers in a fresh mixture of High-Performance Fiber Reinforced Cementitious Composite (HPFRC) with the help of a magnetic field. This article aims to inform about the existing research that deals with this technology. It summarizes the experiments performed, the development of magnetic field generation devices and fiber alignment measurement equipment.
Electromagnetic Properties of Steel Fibres for Use in Cementitious Composites, Fibre Detection and Non-Destructive Testing
This paper deals with the description, measurement, and use of electromagnetic properties of ferromagnetic fibres used as dispersed fibre reinforcement in composite mixtures. Firstly, the fibres’ magnetic properties are shown, and a method of measuring the hysteresis loop of fibres is proposed. The results from the measurements are presented and a discussion of the influence of measured parameters on the fibres’ orientation in a magnetic field is performed. Furthermore, methods of non-destructive estimation, of their amount and orientation in the composite specimens, are discussed. The main experimental goal of this paper is to show the relationship between this non-destructive method’s results and the destructive flexural strength measurements. The method is sensitive enough to provide information related to fibre reinforcement.
Wafer resistivity is one of the most important parameters in production of Power Semiconductor Devices (PSD). This parameter is mainly responsible for achieving required breakdown voltage and other electric parameters. Proposal article describes principles and details of newly designed resonant method and new equipment according patent  and compares it with commonly known 4point method. This new method is based on resonant measurement of capacity and following calculation. New method exhibits comparable accuracy with 4point method and brings additional advantages.
Directed orientation of steel fibres in ultra-high-performance cementitious composite using the magnetic field
WIT Transactions on the Built Environment. Wessex: WIT PRESS, 2020. p. 39-49. High Performance and Optimum Design of Structures and Materials IV. vol. 196. ISSN 1746-4498. ISBN 978-1-78466-389-6.
Ultra-high-performance fibre-reinforced cementitious composites are one of the key industries in the field of concrete technology. Thanks to their exceptional mechanical properties and significantly improved ductility, they are widely used for various special applications such as defensive and protective structures. In composite materials, it is desirable to place the reinforcement where it is needed and in the direction, it is needed. In fibre-reinforced cementitious composites, this orientation is possible through a magnetic field. In the framework of this study, a prototype device for controlled fibre orientation in a cementitious composite was developed. Mixtures of both cementitious composite and ultrasound gel having similar rheological properties to the cementitious matrix were tested. It has been observed that is possible to control the orientation of the steel fibres and direct the fibres in the desired direction by employing an electromagnetic field.
Optimization of a photovoltaic LiFePO4 battery charger
The paper describes the analysis and construction of an autonomous photovoltaic system for charging a LiFePO4 battery. The system is optimized for available components and their pricing to achieve a minimum battery charging time. The efficiency of the power transmission from the photovoltaic generator to the terminals of the charging battery, when they are directly inter-connected, is compared to the efficiency of conventional chargers with a DC/DC converter controlled by the “Maximum Power Point Tracking” algorithm.
Radiofrequency and Microwave Dielectric Properties of Plasma Sprayed and Annealed Thick Layers of Titanium Dioxide
Titanium dioxide (TiO2) was plasma sprayed
using a high feed-rate spray system with hybrid water–
argon stabilization torch (WSP-H). TiO2 powder agglom-
erated from nanometric particles was used as the feedstock.
The produced coating had thickness over 4 mm, to be
comparable with bulk ceramic bodies. The deposit was
removed from the substrate and annealed in air to reoxidize
the oxygen deﬁcient as-sprayed titania and to obtain
material with a proper dielectric behavior. Besides the
microstructure studies, radiofrequency dielectric spec-
troscopy and microwave dielectric spectroscopy were in
the focus of investigation. The approach to annealing of an
extremely thick coating is studied: The signiﬁcance of
annealing of a large-area thick coating is discussed, as the
role of grain interior and grain boundaries in the charge
transport is inﬂuenced. Relative permittivity 94 and the
Q*f product 12,800 GHz were reached at frequency
4 GHz, whereas the frequency response under 1 MHz was
mapped continuously and the values (i.e., low and
stable loss tangent) conﬁrmed that a sprayed and air-an-
nealed TiO2 is able to approach or also overperform
dielectric parameters typical for TiO2 sintered bulk.
Study of Friction Force in Electrodynamic Rail Accelerator: Experiment and Interpretation Using FEM Modelling
The paper presents experimental data and a model of an electromagnetic rail accelerator. The model includes an equivalent circuit, magnetic field in the system and movement of the projectile (that is solved separately) which is computed numerically. The main results are compared with our experimental data and friction force during acceleration is evaluated.
Effective control and battery charging system of an island PV power plant
The paper presents a new concept of an autonomous PV power plant regulatory system with LiFePO4 batteries, which was functionally verified. The hardware system is significantly simpler and more operationally reliable. It also shows higher efficiency and lower acquisition costs than conventional commercial systems. The proposed control system was optimized for charging a multicell battery by PV electric energy. The system automatically maximizes the power supplied by the photovoltaic source and minimizes the power loss caused by balancing the individual cell charging processes. The problem of charge balancing is solved without the balancers. Battery cells are recharged from the separate converters supplying the PV power. The converters are controlled to observe a LiFePO4 battery charging mode while controlling the photovoltaic generator (PVG) load resistance based on an MPP monitoring. PVG power is not supplied to the charged cells, which are in this way protecte from overcharging. The entire PVG power is fed to the cells to be charged. The transmission from the converters is controlled in order not to exceed the voltage and current limits at the terminals and to minimize the actual voltage deviation from the control voltage at the PVG output. The control voltage is generated as an MPP voltage approximation according to the load characteristics and the actual PVG operating conditions.
Model degradace kondenzátorů s metalizovanou elektrodou
The article describes the analysis of a possible influence of a measuring circuit on the results of the OCVD method. The influence of further junction parameters on effective carrier lifetime measurements is evaluated, which has not been currently monitored by the OCVD method. Then the influence of the exciting current generator, exciting current waveform and parasitic properties of the generator is searched. A especial emphasis is given on the impedance matching between an analysed PN junction and an evaluating part of a measuring circuit. A simulation algorithm expressing the processes both in the tested junction and measurement circuit was found. The measuring system was implemented in several variants and typical measurements were carried out. For experimentally determined parameters, the simulations, whose results showed a good compliance with the results of the experiments, were performed.
A lithium-iron-phosphate (LiFePO4) battery is nowadays considered one of the best
types of batteries. The paper deals with the evaluation of the drop in their capacity during operation. Based on the physical analysis of charging and discharging processes, a mathematical model of the battery capacity has been developed during its lifetime. The decrease in capacity during battery operation is evaluated according to the loss of active material, which gradually diminishes due to a number of different processes. The analysis of the loss of the active material is carried out, in particular, according to the depth of discharge, battery temperature, charging and discharging time, including the time when the battery is out of service. The tests were
performed on the Winston Battery, Calb, Thunder Sky and Sinopoly batteries by cyclic discharging and charging at the 50%, 90% or 100% depth of discharge. Their real parameters were determined, compared to the model parameters and the parameters specified by the manufacturers and suppliers. Two automated systems were used for testing. During the test, in the tested battery with several cells, charging and discharging by a constant current were carried out automatically. Operating parameters of the tested battery were continuously scanned, recorded and evaluated by the control computer. The capacity curves during the battery operation,
determined by the type of models, were compared with the results of long-term real battery tests.
The depth of soil freezing, i.e., the depth at which water is frozen, is a significant factor
in meteorology, as it affects many processes in agriculture, building, etc. Soil frost penetration is an important factor for overwintering organisms, but also for physical and chemical processes in soil, particularly for its mechanical properties. The depth of freezing is normally determined directly, i.e. mechanically, using a special soil freezing meter, i.e., frost-depth indicator, according to the process of water freezing in the probe. Another method lies in determining the soil temperature by the interpolation of the curves from the graph, as measured by soil thermometers according to the change in the resistivity of soil or water, when frozen. The
principle of the frost-depth indicator function is to evaluate the temperature dependence of water permittivity, which decreases, when water is frozen, from r ~ 87 at 1 r ~ 3.2 at -1 typical for ice. The water permittivity is evaluated by a measuring capacitor, which is adapted into the shape of the frost depth indicator probe, whose dielectric is deionized water. During freezing, the capacity is reduced in this area. The capacity of the partially frozen probe is directly proportional to the length of its non-frozen section. The measuring capacitor is a part of the resonant circuit of the oscillator. The frequency of the oscillator varies with the capacity of the probe and is further evaluated. The achievable measurement accuracy is approximately 2% for the probe of a 1m length and in direct evaluation by an autonomous counter. For the computer evaluation, with the possibility to compensate the probe non-linearity, the measurement accuracy is approximately 0.5%.
Optimized balancers, whose construction is described in th
e paper, work on a principle of a linear feedback controller. They can work with a maximum charging current up to 20 A, they have very low dynamic resistance of about 1 mW, and are absolutely stable. Their properties are further compared both with previously used circuits and commercial circuits.
Target position determining in aeronautical issues
This article discusses the possibilities of the location of aircraft via active and passive radiolocation systems. The next part is dedicated to location recording of the aircraft, which uses the general type of Radiolocation Warning Receiver by triangulation method and PG method. Then we examine the analysis of the measured data with the purpose of determination of the location of source radiotechnical signal, using the general calculation algorithm and map image. Finally, we check the relevance of the results via graphical analysis, which was based on line of sight and special software computing.
Automated measuring station for accumulator testing
The paper describes the design and implementation of the system allowing the testing of the lithium-iron-phosphate (LiFePO4) cell parameters during long-term loading. Manufacturers and retailers, in particular, accentuate their beneficial properties the possibility of charging and discharging by high currents, minimum influence of the discharge time on capacity, long durability. At the same time, their operational conditions are a lot more strictly defined than those for other types of accumulators.
This article describes both the design and construction of the switch that enables switching with a high di/dt rate and a special type of a shunt for measuring current. A designed circuit is based on a parallel connection of high power MOSFET transistors with independent drivers. Negative influence of parasitic inductions of transistor leads was analyzed. Film capacitor testing is based on applying a very fast discharging process. Current and voltage waveforms arising during the measurement are used to create an equivalent circuit of the capacitor.
Optimization of a solar power station with LiFePO4 accumulators
The paper describes the design and construction of an isolated solar power station supplying energy at weekends to a remote location. The system comprises two parts: A photovoltaic system generating electric energy in sunlight, and an accumulator accumulating energy to be permanently available and to be able to supply a peak power of several kW. The design of the system optimized with respect to maximum reliability, ease of operation and minimum purchase costs. The control circuits were therefore constructed by means of simple analog circuits
Capacitive methodes for testing of power semiconductor devices
Electrical capacity of power semiconductor devices is quite an important parameter that can be utilized not only for testing a component itself, but it can also be applied practically; e.g. in series-connected high voltage devices. This paper first analyzes the theoretical voltage distribution on the bases of the polarized p-n junction, as well as the size of capacity. The measurement of the voltage capacity dependence using the resonance principle is illustrated on the samples of 4kV and 6kV thyristors. The correspondence between theoretical estimate of the capacity, measured voltage capacity dependence based on the resonance principle and experimentally determined by injected charge proves the correctness of the applied procedures and assumptions.
The paper describes a design of a simple small solar photovoltaic energy system that has been realized for electric power supply of objects situated on a (far-away) remote site out of reach of the power line system. Output of this power system is designed in order to supply a week-end operation of a shooting range for a hunting association and an amateur transmitting station. This system delivers approximately 5 kWh during Saturday and Sunday, in months with minimum sunshine (since November to February) and up to 10 kWh in months with higher level of sunshine. The construction of the system is optimised regarding maximal reliability, service unpretentiousness and minimal purchase costs.
MEASUREMENT OF TIME BASE CHARACTERISTICS OF HIGH RESOLUTION DIGITIZERS
2015 12th International Conference on Telecommutications in Modern Satellite, Cable and Broadcasting Services. Niš: Faculty Electrical Engineering of Niš, 2015. pp. 323-326. ISBN 978-1-4673-7516-0.
2015 12th International Conference on Telecommutications in Modern Satellite, Cable and Broadcasting Services. Niš: Faculty Electrical Engineering of Niš, 2015. pp. 327-330. ISBN 978-1-4673-7516-0.
The article deals with investigation physical and electrical parameters of power semiconductor devices. The samples of the diodes with reverse voltage exceeding 6 kV were used for the measurement of p-n junction capacity. Capacity of p-n junction has been evaluated according current pulse during a fast transient waveform of reverse voltage. Another way is presented as the evaluation of voltage dependence of dynamic capacity of reverse biased diode. These non-destructive measurements enabled to evaluate the following parameters: (i) the resistivity of initial bulk silicon used for the processing of wafers, (ii) so called critical intensity of an electric field, which can be used as a quality marker of final (capsulated) devices and is inherently connected with the quality of the used input silicon material; this critical intensity is also a quality indicator of high temperature diffusion processes.
Equipment for the automatic testing of power capacitors
This contribution investigates transient degradation of reverse characteristics of diodes by means of a noise
measurement. This effect appears immediately after external heating or after a long time on-state polarisation of diodes
(without a significant temperature growth of the device in this case). Simultaneously with the reverse characteristics
degradation, the noise power measured under a low voltage DC reverse bias is influenced. The first possible cause of these
effects is connected with so called slow surface states (SSS). The SSS are caused by the presence of material process induced
defects in the region of a p-n junction surface termination. SSS have fundamental impact on the reverse properties of diodes
and their low frequency noise behaviour. The second cause is connected with so called volume structural defects (VSD).
Their origin can be genetic (e.g. the presence of imperfection inside a silicon crystal) or they can be induced during
technological processing. These defects are not repairable and under the reverse bias they will form so called hot spots that
is, places with a local high current density. Rapid and operative measurements of the noise power can reveal latent
instabilities of reverse characteristics invisible during a standard inspection process during the production.
Current Loading of Adhesive Joints Aged in Environment with High Humidity
Electrically conductive adhesive with epoxy matrix and silver filler was used for forming of adhesive joints. The joints were at first aged at the humidity near 100 % for 300 hours. The joints were then loaded with the rectangular current pulses with the amplitude 10 A, 20 A and 50 A. The width of the pulses was 5 microseconds, the frequency 50 Hz. It was found that the pulses changed the joints resistance.
Frequency Compensated High Power Matrix Resistor Network
2013 11th International Conference on Telecommunications in Modern Satellite, Cable and Broadcasting Services. Beograd: IEEE - Jugoslovenskog IEEE, 2013. pp. 497-500. 1.. ISBN 978-1-4799-0899-8.
The special construction of power load consisting of many pieces of thick film flanged resistors, which are in serial parallel connected so that load had different impedance than individual resistors, or it can be loaded with a greater power than a single part.
2013 11th International Conference on Telecommunications in Modern Satellite, Cable and Broadcasting Services. Beograd: IEEE - Jugoslovenskog IEEE, 2013. pp. 493-496. 1.. ISBN 978-1-4799-0899-8.
This article deals with design and realization of control system for foodstuffs air-conditioned storing. System was developed with regard to minimal demand on energy consumption. It controls the operation of ventilators ensuring the exchange of air with the outside environment according to temperature of outside environment and temperature inside of stock room.
Influence of Intermetallic Compounds on RF Resistance of Joints Soldered with Lead Free Alloys
During soldering process intermetallic compounds as a reaction between solder and substrate are created. Physical properties of those compounds are different to properties of solder and substrate. The influence of intermetallic compounds (IMC) on radio frequency resistance of soldered joint has been identified. Tested solders were lead free Sn-1Cu, Sn-4Ag and Sn-3.8Ag-0.7Cu and lead containing Sn-37Pb (all in weight percent). Samples were annealed up to 3000 hours at 150 °C to accelerated growing of IMC. Radio frequency measuring method has been developed and is described. Influence of IMC on resistance of joint is growing with growing frequency because IMC with slightly different resistivity to base solder is creating barrier to current. Resistance of joints has been measured up to 3 GHz.
Influence of surface states on reverse and noise properties of silicon
This contribution investigates transient degradation of reverse characteristics of diodes. This effect appears immediately after external heating or after a long time on-state polarization of diodes (without significant temperature growth of the device in this case). Simultaneously with the reverse characteristics degradation, the noise power (measured under low voltage reverse bias) is influenced.
Common factor (which acts on both reverse and noise properties of diodes) is connected with so called surface states. The slow surface states (SSS) are caused by presence of material process induced defects in the region of p-n junction surface termination. SSS have fundamental impact on reverse properties of diodes and their low frequency noise behavior.
The kinetics of processes evoked by temperature heating of diodes is described in former study. Presented article extends interest also on changes induced by on-state polarization of diodes.
Inherent connection between SSS on semiconductor-dielectric interface and reverse behavior of diodes has a fundamental importance for a good prognosis of function and reliability. Rapid and operative measurements of noise power can reveal latent instabilities of reverse characteristics (invisible during standard inspection process) in production.
Investigation of Flicker Noise in Silicon Diodes under Reverse Bias
This article analyses some connections between the reverse properties of silicon power diodes and their flicker noise under reverse bias conditions. It is shown that the presence of defects in the silicon surface near the pn-junction termination has a significant influence on both the reverse VA characteristics (RVAC) and the low-frequency power noise of diodes under reverse bias conditions. However, the inherent relationship between both effects becomes apparent only under special conditions and by the use of sophisticated measurements.
The article presents a simple physical model, describing the behaviour and effect of surface structural defects on the silicon surfaces in connection with the reverse and noise properties of the tested diodes. The model identifies and consequently performs the mutual relationships with respect to the physical nature of the investigated defects.
The most important practical contribution of this article is to identify a simple way to reveal latent defects of chip reverse properties undetected by the standard in-process inspection, and to rectify these defects by a simple operation process (e.g. chemical etching). This information has great importance for reasonable prognosis of devices' reliability and lifetime, especially before encapsulation and introduction on the market.
Střední hodnota okamžitého výkonu pro řízení aktivních filtrů
Příspěvek se zabývá problematikou výpočtu střední hodnoty okamžitého výkonu v řídicích programech aktivních harmonických kondicionérů (aktivních filtrů). Obvyklé metody založené na číslicových filtrech s nekonečnou impulsní odezvou (IIR), nemusí být v určitých aplikacích optimální. Důvodem může být například jejich velká výpočetní nebo paměťová náročnost. Příspěvek popisuje případy, kdy navíc mohou být tyto číslicové filtry nestabilní a zapříčinit tak chybnou funkci řídícího programu. Jako jejich zajímavá náhrada je zde prezentována CIC struktura decimačního filtru.
Abstract - All electronic equipment where large S/N ratio is requested for the signal processing is very sensitive on disturbances coming from power supplies. This is especially true for high accuracy measurement equipment. Then simple solution is to feed such equipment from accumulators or batteries; nevertheless, this brings problems with their servicing. This contribution presents the results of study of noise disturbance of laboratory power supply on high pure sine-wave signal source and describes a design of realized special power supply with minimum noise.
Bio-impedance Signal Processing using Adaptive Digital Filter
Flicker noise is one of the most important quality indicators of electronic devices. Quality of passive elements is often evaluated according noise level, which is deeply affected by material ageing. Noise measurement can be used for lifetime prediction and probability of failures. Concerning semiconductor devices flicker noise is a criterion of used production technology. Influence of ageing is (contrary of passive devices) not so expressive. However, noise measurement allows to reveal latent defects of diode reverse properties that are unidentified by means of standard in-process inspection. Unlike other standard methods noise measurement requires perfect matching of analyzing circuit and investigated device. Used equipment and method deeply affect results of measurement.
The paper deals with solder film measurement using high frequency resonator. Measurement of surface resistance of a conductor that consists of a layer of solder that is applied to the conductive material was done on high frequency, in the range of 500-5000 MHz.
Special Harmonic Signal Generators for ADC Testing
This paper described the parameters of harmonic signal are analysed in contribution, which is needed for inverters testing and further a construction of a special generator with high spectral purity is described.
Using of buck-converter to provide quality of the electricity
This project deals with the solution of AC/ AC converter based on buck-converter circuit. The circuit has interesting features in AC circuits, which were hardly described before. First of all it doesn't need a rectifier for its run. The conversion is made direct from AC circuit to AC circuit. The distortion of input current can be removed by simple passive filters without need any complicated PFC. The output voltage can be also easy sinusoidal if it is wanted. The control of the converter is also very easy, because the switches work with static duty-cycle.
Behavior of the converter is very similar to regulated transformer. That can be utilize to construct an active compensator cos(φ). Unfortunately there are some catches in construction of the converter. This article tries to describe all of the main features and problems of the AC buck-converter.
An evaluation of the influence of a magnetic field on a human subject with the use of bio-impedance
The contribution presents the measurement of thin films exploiting the change of complex coil impedance. A special algoritm, ensuring the explicit evaluation of the measuring, is used for determining the layer thickness or sheet resistance.
This contribution presents the results of study of noise disturbance of laboratory power supply on high pure sine-wave signal source and describes a design of special power supply with minimum noise, which was realized
Evaluation of the Influence of the Magnetic Field on a Living Tissue
4th IMECO International Symposium on Measurement, Analysis and Modelling of Human Functions - ISHF 10. Praha: České vysoké učení technické v Praze, Fakulta strojní, 2010. pp. 152-156. ISBN 978-1-61738-984-9.
The paper provides a practicable methodology for direct quantitative observation of the influence of a magnetic field on live tissue by means evaluation of vasodilatation effects using infrared thermography, bio-impedance measurement and plethysmography.
Investigation of Flicker Noise in Silicon Diodes under Reverse Bias
This article analyses some connections between reverse properties of silicon power diodes and their flicker noise under reverse bias. Common (connecting) aspect of these different angles of view is technological production process.
The article presents a simple physical model describing a behavior and effect of surface structural defects in connection with a reverse and noise properties of tested diodes. Model defines and consequently performs mutual relations with respect to physical nature of the investigated defects. An interesting output of the model is the possibility to identify energy level and density of investigated defects.
Non-linearity diagnostics for Conductive Adhesives
The contribution present measuring equipment for non-linearity diagnostics of conductive adhesives. The equipment measures non-linearity of 3 orders. The measured level of non-linearity is - 180 dB with respect to the actuating signal.
A method of non-linearity evaluation for low resistances by the use of determination of the level of intermodulation signals is described. The equipment can measure small resistances powered with current 2 A and an inherent signal to carriers ratio of 180 dB.
PHOTOVOLTAIC POWER SUPPLY FOR A DISTANT STANDPOINT
Contribution describes a small autonomic source of electrical power, which is used for continual power supply of a small radio relay terminal station. The station is placed on a hilltop in a distance about 1,5 km from the village. This source is realized as photovoltaic system, which consists of silicon solar cells, accumulators and control circuits. The parameters of the arrangement during one year of the operation are presented in conclusion of our paper.
Profesní vzdělávání v oblasti elektromagnetické kompatibility
Kniha se zabývá širším pohledem na oblast EMC, který kromě "klasických" kapitol zahrnuje i legislativní a ekonomické aspekty, postupy při návrhu, realizaci a uvádění zařízení do provozu. Dále se autoři podrobně věnovali novému termínu "pevné instalace", který je zanesen v nových normách Evropské unie pro oblast EMC. Důraz na popis aktuálního legislativního stavu a dalších aspektů EMC činí tuto publikaci jedinou svého druhu u nás.
Signal Generator with Minimal Distortion for ADC Testing
The contribution presents signal generator with minimal distortion. The frequency stability of the generator is in order of 10-6/day, the output power 1W, the value of SINAD is close to 120 dB and the total harmonic distortion under - 170 dB by using of linear narrow-band filter.
The contribution presents the analysis of parameters of testing generators und the construction of special generators with a high signal purity. The total harmonic distortion of the generators is under -170 dB, the value of SINAD is close to 120 dB, the output power is 1W.
Thermal evaluation of the quality of electrically conductive adhesive joints
The paper deals with electrically conductive adhesives and inovative quality estimation method based on thermal field evaluation. The resistance of joint heated by passing current can be roughly estimated by the used of temperature field picture.
Analysis of the Signal Network Non-Linearity in a Metrological Laboratory
The special testing signal generators designed for a series of frequencies in the frequency band 0.5 to 20 MHz. The frequency stability of the generators is in the order of 10-6/day, the output power is 1 W, the value of SINAD is under - 130 dB.
The influence of a magnetic field on human is monitored by a special system which enables quantitative monitoring and evaluation of the influence of a pulse magnetic field on a live organism by using of bio-impedance evaluation of vasodilatation effects.
Vlastnosti vysokonapěťových kabelů a motorů při přenosu impulzů
Příspěvek presentuje výsledky vysokofrekvenčních měření na nízkonapěťovém a vysokonapěťovém kabelu a motoru. Jsou ukázány Bodeův diagram a Nyquistův diagram a jsou stanoveny skutečné parametry měřených kabelů a motorů. Je také provedeno porovnání naměřených parametrů s parametry v katalozích.
The article describes a development of system that automatically stabilizes operating point of the MOSFETs used in Radio Frequency Power Amplifier (RFPA) with output power approx 500 W. This device uses a micro controller based system for measurement of power MOSFETs temperature and generating output bias voltage.
Reliability of Reverse Properties of Power Semiconductor Devices: Influence of Surface Dielectric Layer and its Experimental Verification
In the paper are evaluated properties of the concrete power supplies used in laboratory - AC power network, testing AC power supply, UPC power supply, DC/AC inverter and special sources with minimal distribution - inverter with harmonic output voltage and motor - generator power supply.
Statictical Analysis of the Serial Connected Diode Chain Under Reverse Bias Devices
This articla deals with the reverse voltage distribution along a chain of large number serial connected power silicon diodes. Reverse properties of an individual diode can be affected by random influences of its production process.
Příspěvek se zabývá praktickými otázkami laboratorních výkonových zdrojů sinusového napětí síťového (nebo jemu blízkého) kmitočtu, které přitom samy nejsou zdrojem rušivých signálů znehodnocujících vlastní měření. Především se jedná o měření v oblasti harmonických síťového kmitočtu a dále o měření rušivých signálů šířených po vedení (tedy zejména v oblasti 150 kHz - 30 MHz) a dalších citlivých a přesných měření. Článek popisuje možné způsoby realizace takových zdrojů, které doplňuje řadou praktických měření vlastností takových zdrojů. V neposlední řadě je zmíněna vhodná filtrace signálů.
Zdroje sinusových signálů pro testování rychlých analogově-číslicových převodníků s vysokým rozlišením
It is necessary to keep at the disposition test signals with a high spectral purity for series measuring e.g. in the area of metrology or electronics. Commercial signal generators do not satisfy higher requirements in this area. Our contribution describes chances of the improvement of their quality while using of suitable filters. There is described the construction of a special generator with a high spectral purity of a signal.
Impedance of Adhesive Joints over Frequency Range 0.3 to 3 GHz
A magnetic field effect on a human being has been monitored at the exposure of a part body by a strong pulse magnetic field. A pulse magnetic field, generated by a pseudo-random current, has been used for experimental exposures. A couple of Helmholz coils have been chosen as an applicator. The high-level of the flux density of used magnetic field was c. 60 mT. The influence of the magnetic field has been monitored by evaluations of the bio-impedance changes and by the blood pressure. The bio-impedance has been measured by use of RF signal with the frequency 75 kHz by four-point method on the forearm. The bio-impedance change is a measure of a vasodilatation effect during the cardiac cycle and affection of those effects by a magnetic field too. The blood pressure has been measured in brachial artery by using common semi-automatic cuff pressure gauge
The functions of measuring instruments and measured equipments are always affected by technical parameters of the electrical energy, which supplies apparatus and arrangements. Disturbing signals, which are spread by power line along the supply system or by the form of radiated electromagnetic waves, get through measuring circuits. The relevance of all effects grows up with the increasing of the accuracy and sensitivity of taken measurements. In this paper there are analysed parameters of typical sources that are used for power supply of measuring instruments in laboratory. There is described the construction of a special source with minimal distortion too.
Technological Aspects of Noise-suppressing Filter Design
The noise suppression is up to date problem of power electronic devices like power sources, power converters etc. Paper deals with suppression of conducted disturbances. Main topic is the filter design and it's assembling from real devices with theirs real characteristics. Filter topology and device wiring are very important too. Paper calls attention to selected questions and proposes their solution.
Nonlinearity of a nominally linear components is a significant parameter which informs about the difference of and investigated component from ideal one.Equipment is based on evaluation of intermodulation distortion.Experiment is focus on measurement of conductive adhesive joints.
Equipment for Noise Monitoring of Power Supply Units
Electrically conductive adhesives have in comparison with solders, significantily higher in-homogeneity of the structure and therefore electrical as well as mechanical properties of adhesive joints differ in comparison with that soldered ones. The joint impedances in the frequency range of 300 MHz to 3.4 GHz have been investigated.
Frequency Filters With High Linearity Design and Used Devices
This paper deskribes a system, which enebles quantitative monitoring and evaluation of the influence of a pulse magnetic field on a live organism by using of bioimpedance measurement. There are present results of performed experiments.
Nonlinearity Correction of a Pressure Sensor on the Basis of a Conductive Elastomer
The paper deals with OCVD Carrier Lifetime in P+NN+ diode structures with axial carrier lifetime gradient. Theoretically and experimentally is evaluated influence of carrier lifetime gradient on voltage courses during OCVD measurement and on the resulting carrier lifetime.
Reliability of Reverse Properties of Power Semiconductor Devices
The paper deals with methods of a sine-wave signal generation for dynamic testing high-speed (1 MSa/s) to 100 MSa/s) ADCs with high resolution (14 to 20 bits). The techniques of noise and distortion measurement of spectrally-pure sine-wave signals are also discussed.
A Simple Technique for Measuring Signal Source Noise
Proceedings of the 14th International Symposium on New Technologies in Measurement and Instrumentation. Gdynia/Jurata: Gdynia Maritime University, Faculty of Marine Electrical Engineering, 2005. pp. 57-60. ISBN 83-89786-37-0.
Proceedings of the 14th International Symposium on New Technologies in Measurement and Instrumentation. Gdynia/Jurata: Gdynia Maritime University, Faculty of Marine Electrical Engineering, 2005. pp. 101-104. ISBN 83-89786-37-0.
The close-to-carrier noise measurement can be provided by a specially designed notch filter to suppress the dynamic range of sine-wave signal produced by high-quality signal generators. Filter design and experimental measurements at several commercial generators are presented in the paper.
Sine-Wave Signal Distortion Measurement at Higher Frequencies
Noise and distortion measurement of sine-wave signal can be provided by a specially designed notch filter to suppress the dynamic range of sine-wave signal produced by high-quality signal generators. Filter design and experimental measurements at several commercial generators are presented in the paper.
Conditions of Temperature and Time Instability Occurrance of Reverse-Biased Semiconductor Power Devices
The paper describes the design and construction of the source of the testing signal with a high spectrl purity for the dynamic testing of the new high speed ADCs with more than 14-bits resolution. The system is based on a common sine-wave signal generator and the precise narrow-band band pass passive filter, and it performs a sine-wave signal with spectral purity higher than 130 dBc. It can be used for the dynamic testing of the ADCs up to 20-bits resolution.
Influence of a Magnetic Field on the Impedance of Living Tissue
Degradation of adhesive bonds powered by rectangular very short current pulses of the width of 1 microsec. and frequency of 1 kHz of high amplitude has been examined. The amplitudes of the pulses have been 5 and 10 A.
Příspěvek popisuje klimatizační zařízaní skladu potravin.Zařízení umožňuje dodržování optimálního teplotního režimu pro dlouhodobé uskladnění potravin během podzimu,zimy a jara.Teplotní režim je regulován s využitím značné teplotní kapacity skladovaného materiálu a kolísání venkovní teploty vhodným řízením nuceného větrání skladu. Řídící systém sleduje teploty uvnitř skladovacích prostor a venkovní teploty a řídí větrání tak,aby byl dodržen zvolený teplotní režim.
The problems of RF conducted emissions measurement
This article describes and analzses the fast transient processes that can occur during a local non-destructive breakdown in a circuit consisting of a serial connection of reverse biased high-voltage silicon diodes. Measurements of the reverse current-voltage characteristics of the individual diodes showed that a breakdown had occured. However, this phenomenon is very difficult to study when there are many diodes connected in series in a stack. A physicalmodel was therefore created to show the individual local breakdown in this case. The validity of the model was verified by means of circuit simulation of the process under investigation. The statistical significance of the process was considered with respect to the reliability and lifetime of a high-voltage diode stack.
Transient Effects on High Voltage Diode Stack under Reverse Bias
The existance of the non-destructive breakdown was observed at some measurements of reverse current-voltage characteristics of individual diodes. However, the study of this phenomenon is very difficult for many in series connected diodes in stack.
Transient Effects on High Voltage Diode Stack under Reverse Bias
New Measurement and Calibration Methods of Electrical Quantities and Instruments. Budapest: IMEKO TC4 Technical Committee on Measurement of Electrical Quantities, 1996, pp. 88-91. ISBN 963-420-491-0.