This article presents a compact wireless readout circuit capable of simultaneous and independent measurement of inductance and resistance in a series-RLC configuration. The sensing elements, a resistor and an inductor, are connected in series with a known capacitor in the secondary circuit, while the measurements are wirelessly obtained from the primary (readout) coil by analyzing the reflected impedance. The key advantage of the proposed method is its insensitivity to variations in the magnetic coupling coefficient (k) over a wide range, making it robust to misalignment and distance changes between the coils over a wide range of k. Unlike conventional methods, the proposed system enables simultaneous and independent measurement of both inductance and resistance, with a minimum error propagation and thereby enhancing overall measurement accuracy. The proposed method was first validated through numerical simulations and subsequently tested experimentally using different values of standard resistors (10-100 Omega ) and variable inductors (110-180 mu H). A laboratory-scale experimental setup was then implemented, with an inductive displacement sensor and an NTC thermistor connected on the sensing side. The experimental results demonstrate that the worst case error remains within 2.5% for displacement (inductance) measurements and 3% for temperature (resistive) measurements over a range of 0-30 mm and 28 degrees C-73 degrees C.

This paper presents the design optimization of flat-type LVDT position sensors to extend the linearity range. Rectangular-shaped excitation and pickup coils with a discrete and segmented structure, along with a block-shaped Ferrite for the armature, are used. The excitation and pickup coils are optimized for the linearity range extension of LVDT position sensors. The 3D finite element method is utilized for the performance analysis and design optimization of LVDT position sensors. The measured nonlinearity error can be achieved below 1% for an armature movement range of ±55 mm. The movement range with low nonlinearity error below 1% can be further increased using a shorter axial length for the armature. A novel double-sensor structure is also investigated with a 9% higher linearity range without increasing the axial length. The linearity range-to-total axial length of coils ratio is about 73%, with a nonlinearity error of 1%. The measured nonlinearity error can also be further decreased to 0.5% for a ±50 mm movement range.

This paper presents two eddy current sensors for rotating speed measurements. The sensors have one excitation coil and two antiserially connected saddle-shaped pickup coils. The small excitation coil is between two anitserially connected pickup coils in the first sensor. Two anitserially connected pickup coils are inside the second sensor's large excitation coil. The performance of eddy current speed sensors is evaluated and compared. The sensitivity of the speed sensors and susceptibility to the shaft material are calculated. A 2D analytical method and a 3D finite element method are used to model and analyze two eddy current speed sensors. The speed measurements are performed for a +/- 3000 rpm speed range at 500 Hz and 1000 Hz excitation frequencies. Two iron shafts with different material properties are selected for the measurements and analysis. An aluminum shell mounted on the solid iron shaft is used to increase sensitivity and decrease susceptibility to the shaft material. The optimization of eddy current speed sensors is presented to reduce the sensors' dimensions and evaluate the sensitivity and susceptibility to the shaft material. Despite its lower sensitivity, the first sensor has a lower susceptibility, between 1% and 2%, to the shaft material properties.

We introduce a novel design for a flat 2-D differential transformer position sensor. The new geometry results in improved linearity and a larger measurement range in arbitrary directions, making the device a true 2-D position sensor rather than merely an alignment indicator. By employing nanocrystalline material for the armature, the operation frequency can be increased up to 500 kHz, achieving a sensitivity of 200 mV/cm. The nonlinearity error remains below 3% in the +-15 mm range for any position.

This article presents a thin, planar inductive angle sensor designed for accurate and robust noncontact angular position measurement in harsh environments. The proposed sensor employs a single-planar excitation coil and four planar pickup coils fabricated using standard printed circuit board (PCB) technology, together with a high-permeability nanocrystalline core. Unlike conventional inductive angle sensors based on sine-cosine outputs, the proposed configuration directly provides a linear output, thereby eliminating the need for trigonometric computation and significantly simplifying both the analog front-end and signal-processing requirements. A key advantage of the proposed sensing scheme is its inherent insensitivity to axial misalignment (lift-off) between the rotating core and the stationary coils, a condition that commonly occurs in practical automotive and industrial installations. A detailed finite-element simulation study is carried out to explain the operating principle and to analyze the influence of lift-off on the sensor response. Based on this analysis, a normalized ratiobased signal processing approach is employed to suppress lift-off-induced gain variations. A laboratory prototype is fabricated and experimentally evaluated to validate the proposed concept. Experimental results demonstrate excellent linearity with a worst case angular error below 0.8% and a resolution of 0.06 degrees. Even under intentional axial misalignment, the angular error remains minimal, confirming the robustness of the proposed approach. Owing to its extremely thin structure, simple planar realization, and immunity to contaminants such as dust, oil, and water, the sensor is well suited for compact automotive, industrial, and robotic applications.

This paper presents a novel two-dimensional (2D) misalignment sensor based on a combination of variable reluctance and tunnel magnetoresistance (TMR) sensing principles. The system consists of a planar circular excitation coil and four TMR sensors arranged symmetrically above it. A high-permeability core, mechanically coupled to the object being monitored, changes the magnetic flux distribution around the coil when misaligned. These variations are detected by the TMR sensors, which are sensitive to the z-component $(B_{z})$ of the magnetic field. The TMR sensor outputs are then processed to determine the misalignment along both the X and Y axes. A prototype was fabricated in the laboratory using standard PCB technology. A key advantage of the proposed design is its ability to provide dual-axis alignment feedback using a single moving element, thereby reducing complexity and the need for multiple linear displacement sensors. Additionally, the system operates in a non-contact manner and is inherently resistant to contaminants such as dust, oil, and moisture, making it suitable for use in harsh industrial environments. Potential applications include robotics, manufacturing automation, and precision alignment systems.

This article presents a wireless readout circuit designed to measure the resistance of a resistive sensor connected in a series RLC configuration. In this setup, the sensor is placed in the secondary circuit, where its resistance varies with respect to the measurand. The proposed readout technique involves measuring the reflected impedance from the primary side, and the sensor resistance is calculated using the real and imaginary components of the reflected impedance. The key advantage of this method is that the resistance measurement is independent of the coupling coefficient (k) between the primary and the secondary, over a considerable range of k, except in the cases of very weak coupling (low values of k). The design was validated using analytical equations, simulation studies, and later confirmed through experimental studies on the readout prototype built in the laboratory. Initially, the system was tested using commercially available standard resistors, followed by tests with a thermistor under varying temperature conditions. The results demonstrate excellent performance, with the output showing high linearity and a worst case error of less than 1.4%. The key challenges in implementing the proposed readout circuit, along with the various sources of errors, have been identified, analyzed, and presented in this article.

This article presents a magnetic design-optimized model of a linear variable differential transformer (LVDT) 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 3-D analytical method and the finite element method (FEM) are used for magnetic analysis and design optimization of an LVDT sensor. The structure of the armatures is optimized to enhance the linearity range of the LVDT 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.

This article presents the modeling and analysis of eddy current speed sensors for linear speed measurement of rectangular nonmagnetic bars. A novel 3-D computational method is developed to model eddy current speed sensors using combined finite difference and space harmonic methods. The modeling and analysis of the sensors are performed at constant and variable speeds. Detailed measurements of the eddy current speed sensors at two frequencies are performed. Two bars with a square-shaped cross section and one bar with a rectangular cross section are chosen for the measurements and modeling, and their materials are brass and aluminum. A comparison of the measurements and calculations shows adequate precision of the 3-D computational model. This article aims to present an efficient computational tool for 3-D analysis of eddy current speed sensors with rectangular configurations.

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 mu m, which is the only commercially available thickness of the amorphous tape. The penetration depth of a 1-MHz signal is around 6 mu m, 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-mu m-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 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 article presents enhancing the linearity range of linear variable differential (displacement) transformer (LVDT) sensors by optimizing the excitation and pickup coils. This article 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 2-D 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.

Measurement of small temporal and space variations of the magnetic field is required for many applications such as geophysics, space research, defense, industry, or security systems. In this article, the focus is mainly on the vectorial sensors used in the unshielded environment. We proved that not only low noise but also other parameters such as linearity and temperature stability are critical. Hightemperature SQUID gradiometers are finding applications in the airborne scanning system as the magnetic field variations to be detected are small and the instrument's cost is not prohibitive. Despite advances in atomic magnetometers and small tunneling magnetoresistors (TMRs), fluxgate sensors are usually the best solution for many applications. That is the reason why our research is focused on the development of fluxgate magnetometer. In this article, many different applications of these sensors, involving, for example, mapping of the magnetic field using drone, visualization of the magnetic field around the small drone, and spectrogram images created for the diagnostics of a ventilation system, are presented. Based on the knowledge obtained during the research and application of magnetic sensors, the magnetometer application as a part of the developed security system is presented.

An improvement in data processing utilizing gradient information rather than only homogenous field values and calibration of the response of each individual sensor in the AMR sensor array yields significant improvement in positioning accuracy (from about +/-3 to +/-0.6 mm) of a piston-like apparatus with ferromagnetic piston rod. The approach uses low-frequency ac excitation from an external coil allowing sensing through a 2 mm thick aluminum wall.

A detailed analysis of the crosstalk in an uncompensated gapped-core current transducer is presented in this paper. A cut-core current transducer with a magnetic field sensor in the airgap is widely used to measure current in industry and in laboratories. Crosstalk is the effect of a nearby current-carrying conductor on the reading of this type of sensor. We present a study of the dependence of the crosstalk on the position of the external conductor, the core material, and the core geometry, including the number of airgaps. A 3D Finite Element Method (FEM) based model is used to analyze the crosstalk, and the results are compared with measurements. Using a low-permeability ferrite core with two 2 mm airgaps and a single Hall sensor results in a maximum crosstalk error of 18 %. This error can be reduced to 1 % either by using a differential Hall sensor pair, or surprisingly by using a single 4 mm airgap. This error can be further reduced to 0.15 % by using an FeSi core with larger permeability. However, this type of sensor is very sensitive to the position of the Hall sensor in the center of the airgap. Displacement or an angular mismatch can increase the error to 1.5 %, as demonstrated on a commercial sensor.

A yokeless busbar current transducer with frequency-invariant points is presented for the first time in this article. Existing rectangular busbar current transducers suffer from the frequency dependency issue due to the eddy currents in the massive busbar. The proposed transducer has a novel C-shaped structure for the sensing area of the busbar. It is observed for the first time that this structure provides sets of frequency-invariant points on both sides of the C- shaped busbar. In the proposed scheme, two integrated fluxgate sensors in differential form are used to measure the magnetic flux densities at those invariant points. A finite-element method (FEM)-based three-dimensional analysis performed using the Ansys Maxwell eddy current solver provided the exact locations of the frequency-invariant points. A prototype was made, and functionality tests of the C-shape busbar transducer have been carried out in the laboratory using DRV-425 integrated fluxgate sensors from Texas Instruments. In the experiment, fluxgate sensors placed at frequency-invariant points measured the flux densities at multiple frequencies varying from 50 to 4000 Hz. The results obtained from the tests showed that the error due to frequency dependency has been reduced from 14% to −0.85% using the proposed C-shape busbar.

This paper presents a fault current limiter for electrical power system protection. It uses a novel configuration of an electromechanical actuator based on variable reluctance operation. Electromagnetic analysis of the actuator is performed using the finite element method under steady state and transient conditions to evaluate short circuit current limitation. A single-phase model is used for the performance assessment of the fault current limitation.

This paper presents an axial flux eddy current sensor with a compact and simple structure for measuring the rotating speed of iron shafts. The sensor structure is optimized for high sensitivity with a novel configuration of the coils positioned perpendicularly to each other. The sensor comprises two D-shaped excitation coils and two D-shaped pick-up coils in a double-layer structure. A disc-shaped magnetic shield or core shields the coils. Two iron shafts with different material properties are considered. A new cup-shaped configuration of nonmagnetic copper and aluminum caps mounted on iron shafts improves sensitivity and suppresses susceptibility to shaft material properties and airgap variation. 2D and 3D finite element methods are utilized for the performance analysis of the sensor. The measurements are performed at speeds up to +/- 3000 rpm and different excitation frequencies from 400 Hz to 4 kHz. The eddy current speed sensor has excellent linearity characteristics with a nonlinearity error of 0.15%. The geometry of the coils is further optimized and improved for maximum sensitivity and compactness. The fault-tolerant capability of the sensor is also evaluated.