Ing. Jiří Maier

This paper presents a novel structure for linear position sensors with external armature. The coils are designed to have a nonoverlapping structure to increase the coils’ design optimization flexibility. The 3D finite element method is utilized for design optimization to extend the linearity range of the position sensor. The excitation and pickup coils are segmented to facilitate and improve the winding process. The number of turns in each pickup coil is optimized using the 3D finite element method to minimize the nonlinearity error and enhance the linearity range of the position sensor. The simulation results are compared with experiments to validate the optimization process of the position sensor.

This paper presents a magnetic design-optimized model of a linear variable differential transformer sensor with short coils and long armatures. The sensor has one excitation coil and two antiserially connected pickup coils located between two parallel armatures’ plates. A developed 3D analytical method and the finite element method are used for magnetic analysis and design optimization of a linear variable differential transformer sensor. The structure of the armatures is optimized to enhance the linearity range of the linear variable differential transformer sensor. The rectangular shape of the armature has been changed to a trapezoidal shape to decrease the nonlinearity error and extend the linearity range. The measured nonlinearity error is as low as 1.0% for the ±90 mm movement range.

Miniaturized fluxgate sensors typically use fewer coil turns due to technological limitations. Therefore, higher excitation frequencies are required to reach sufficient sensitivity. When using common materials, such as Vitrovac 6025F, the minimal thickness of the core is limited to 25 μm, which is the only commercially available thickness of the amorphous tape. The penetration depth of a 1-MHz signal is around 6 μm, which is much less than the thickness of the core. This leads to problems with saturating the core. Reaching deep saturation of the core requires high excitation current, which leads to excessive power consumption. Noise and perming are also increasing at high frequencies. In this letter, we show that the performance of the sensor can be greatly improved when using a 10-μm-thick core. The effect of eddy currents in the core is examined using finite element method simulations, as well as measurements on the actual microfluxgate sensor.

This paper presents enhancing the linearity range of linear variable differential (displacement) transformer (LVDT) sensors by optimizing the excitation and pickup coils. The paper aims to increase the linearity without complicating the sensor structure and measurement systems. The linearity range is essential for the efficient operation of LVDT position sensors. Conventional LVDT position sensors usually have one excitation coil and two differentially connected pickup coils for the stationary part. They have one armature with a ferromagnetic core for the moving part. The axial length of the excitation coil and the number of turns in the pickup coils are optimized for the linearity range enhancement. The two-dimensional (2D) axisymmetric finite element method (FEM) is used for analysis and optimization. The optimizations are performed based on a Ferrite core armature with a cylindrical structure and a fixed axial length and radius. A constraint of a maximum total axial length of the coils is also applied for the design optimization. The experiments are conducted to validate the LVDT’s pickup coils optimization to enhance the linearity range using measurement results. The measured nonlinearity error of 1% is achieved using optimized coils for the LVDT position sensors. The maximum repeatability error is below 0.2% for a prototyped position sensor.

This work introduces an integrated fluxgate sensor fabricated using CMOS chip technology. The sensor uses a “racetrack” shape of the core. The material used for the core is VITROVAC 6025F, and the shape was laser-cut from 25 um thick foil. The coils are solenoids fabricated using metal layers of the chip and bonding wires. Sensing and excitation coils have 60 and 40 turns respectively. TSMC D35 technology was used for fabrication. The size of the core is 8 mm x 1.75 mm. Dimensions of the chip are 8 mm x 2.7 mm (21.6 mm2). The sensor was tested in open-loop operation using a sinewave excitation. Sensitivity increases with frequency up to 1.5 MHz, reaching 5000 V/T. This is a significantly higher value than what can be achieved using a flat pick-up coil (around 10 V/T). Fully saturating the core requires a 110 mA excitation current, leading to 300 mW power dissipation in the coil. The Core loss is 100 mW at 1 MHz excitation. The Noise at 1 Hz may be as low as 2nT/sqrt(Hz) depending on excitation signal parameters. The typical offset is below 1 uT.

We propose a novel flat 2-D inductive position sensor based on stationary coils and moving armature. The geometry was optimized by FEM simulations, the predicted parameters of the final design fit well to the measured values. The position sensitivity of 100 mV/cm for 500 kHz/140 mA excitation achieved with laminated nanocrystalline armature was 5-times higher than with FeSi material. We have also shown by measurements that the influence of the liftoff variations can be effectively suppressed by ratiometric method. The total sensor thickness is only 2.5 mm. The developed sensor is suitable for position alignment in industrial applications.The present design has linear range of ±10 mm for directions up to ±30° from X and Y axes. The minimum linear range of ±5 mm is in the diagonal (45°) direction.