Search Results (850)

Accurate calculation of mutual inductance (MI) between solenoid coils is essential for system design, but complex geometries and spatial arrangements make it challenging. This paper presents a modified analytical method for calculating the MI between two circular-wound air-core solenoid coils arbitrarily oriented in three-dimensional (3D) space. The analytical model used to calculate the MI between two solenoid coils is based on the use of magnetic vector potential (MVP). The helical structure of the solenoid coils is represented by successive coaxial circular filaments arranged along their central axes. Each filament is represented by an equivalent regular polygon with a sufficient number of sides. The proposed approach allows the MI between two solenoid coils to be calculated using a single analytical formula, without imposing restrictions on the relative positions of the coils, while taking lateral and angular misalignments into account. The modified analytical model is validated for accuracy and applicability by comparing its results with experimental measurements and FEM-based simulation results for coil systems with different diameters, turn numbers, and turn pitches. The MI results for various angular and lateral misalignments are in good agreement with experimental measurements and FEM results. The MI calculation model proposed in this work provides a fast and reliable tool for analyzing the electromagnetic behavior of coupled coil systems, designing inductive power transfer systems, and assessing electromagnetic compatibility. Full article

This paper presents an open-source miniaturised readout device designed for the wireless interrogation of passive LC sensors and wireless power transmission. The system is based on a Sparkfun RedBoard Artemis microcontroller with a custom-printed circuit board as an extension, providing a compact, low-cost alternative to expensive laboratory-grade equipment. The reader coil is excited by a signal that can be tuned digitally in both frequency and amplitude. The resonance frequency of a wirelessly coupled LC tank is detected by monitoring the voltage minimum of a rectified signal envelope, which corresponds to the impedance change of the reader inductance at resonance. Experimental validation demonstrates that the device accurately tracks resonance frequency shifts resulting from variations of the LC tank’s capacitance, performing comparably to laboratory-grade impedance analysers. Testing the influence of axial separation between the two coils up to 25 $\mathrm{m}$$\mathrm{m}$ showed stable and identifiable voltage dips. The programmable excitation signal peak-to-peak voltage ranges from $0.81$ V to $5.35$ V. The device enables fully stand-alone operation with a display and navigation switch, making it suitable for untethered LC wireless sensing and actuation applications. Full article

Wireless power transfer (WPT) is increasingly used in smart manufacturing, unmanned platforms, and contactless power-supply applications. However, weak coupling, load-dependent impedance drift, and spatial misalignment can shift the resonant condition, leading to unstable output voltage and reduced transfer efficiency. This paper proposes a constant-voltage WPT method that combines a non-uniform winding coupler, parasitic coils, and dynamic capacitor compensation. A composite magnetic coupler with dense outer windings, loose inner windings, and parasitic coils is first developed, and a region-based electromagnetic model is established to characterise self-inductance, mutual inductance, and coupling coefficients. An improved LCC-S compensation network with a dynamic capacitor compensation matrix is then derived to keep the system close to resonant operation at the nominal 85 kHz operating point under load variation and coil-displacement-induced coupling changes. A zero-voltage-switching-angle tracking method with mutual-inductance correction is further introduced to compensate for phase deviation and maintain soft-switching operation through limited switching-frequency adjustment. Experimental validation demonstrates that the system maintains a stable constant-voltage output across a load range of 20–50 Ω and under 5 cm lateral and longitudinal offsets. The measured efficiency remains above 89% and reaches 93.7% under the optimal coupling and load-matching condition. Full article

Series–series (S–S) compensated wireless power-transfer (WPT) systems are increasingly deployed where connector-free and reliable energy delivery is required, but practical monitoring becomes ambiguous when receiver-resonance drift and magnetic-coupling variation produce similar transmitter-side impedance changes. This paper addresses that ambiguity by separating the two effects without receiver-side sensing. During a low-power diagnostic interval, the receiver terminal is briefly placed in open and short states, and only the fundamental phasors of the inverter output voltage and primary current are processed together with the known compensation capacitances. After the open-state measurement identifies the primary self-impedance, the short-state residual is mapped to an affine D–${\omega }^2$ line; its zero crossing gives the receiver resonant frequency and secondary self-inductance, while its slope gives the mutual inductance and coupling coefficient. The routine is implementable as a start-up or periodic diagnostic function in WPT hardware that already measures the primary voltage and current and can impose the required receiver terminal states; it requires no receiver-side measurement, auxiliary sensing coil, short-loop resistance measurement, or iterative zero-phase search. In simulation, the coupling-coefficient error remained below $0.014\%$ under receiver-inductance tolerance and mutual-inductance variation. In a prototype, the short-state data followed the predicted linear relation with $R^2=0.9979$, and the extracted coupling coefficient agreed with the reference within about $5\%$. The identified receiver resonance was also used to guide operating-frequency adjustment in a practical power-transfer test. Full article

This paper investigates the accuracy of conventional inductive current transformers (iCTs) and Rogowski coils (RCs) in measuring distorted currents, evaluating compliance with the WB0 (up to the 13th harmonic) and WB1 (up to the 60th harmonic) accuracy classes according to the IEC 61869-1 standard. A custom reference iCT, calibrated via the ampere-turns method to achieve a superior baseline accuracy (0.02%), served as the primary benchmark. A zero-flux electronic transducer was utilized strictly to verify this reference. Despite inherent core nonlinearity, tested conventional iCTs with reduced to minimum secondary burdens successfully met the class 0.5-WB1 requirements. In the case of tested Rogowski coils, the study reveals that their wideband performance depends on physical design of the particular type. High-sensitivity coils suffer from increased parasitic capacitance and self-inductance, causing significant additional phase shift at higher frequencies, whereas low-sensitivity, small-diameter coils offer superior linearity. Overall, the tested RCs generally ensured compliance with the 0.5-WB1 class across the evaluated frequency range, with certain units successfully achieving the more restrictive 0.2-WB1 class. Ultimately, conventional iCTs remain a highly reliable solution for metering purposes in low-voltage networks, while properly selected Rogowski coils provide a valuable alternative for power quality analysis and harmonic distortion measurements. Full article

Archaeomagnetic studies provide crucial information on the spatial and temporal evolution of the geomagnetic field as recorded in rocks and archeological artifacts, offering insights into both Earth’s magnetic evolution and past geological and human activities. Measurements of the direction, intensity, and relative variations in the Earth’s Magnetic Field (EMF) are performed using sensitive magnetometers. Among these, induction magnetometers exploit Faraday’s law of electromagnetic induction to measure magnetic fields with high precision. In this work, we present a comparison between two different configurations of Helmholtz-based induction magnetometers carried out through the analysis of the magnetic field distribution obtained through analytical simulations. The study examines both the uniformity and intensity of the magnetic fields produced by each configuration, highlighting the influence of coil geometry on field homogeneity and sensitivity. The results reveal differences between the two configurations, providing important insights for optimizing magnetometer design, improving measurement accuracy, and facilitating analytical procedures in archaeomagnetic research. Full article

Wireless power transfer (WPT) systems for electric vehicles require reliable foreign object detection (FOD) mechanisms both during and prior to power transfer to ensure operational safety and efficiency. The primary purpose of this study was to develop a foreign object detection system to ensure that no objects are present in the area of magnetic coupling (between primary and secondary coils) prior to initiating power transfer. Conventional FOD techniques based on impedance, visual light, or thermal monitoring provide limited spatial information and are sensitive to coil misalignment. This paper proposes a machine learning-based FOD approach using a planar Magnetic Inductance Tomography (MIT) sensor array that enables spatial electromagnetic sensing for early detection and localisation of conductive foreign objects. A dataset comprising 17,800 measurement frames was collected using a custom STM32-based data acquisition system in the absence of (prior to) power transfer. Likewise, a dataset comprising 300 sets of measurement frames was collected during power transfer, in which each frame contains 120 electromagnetic sensor readings. This capture methodology coincides with the detection requirements of live WPT systems. Four classification models, including Random Forest, Support Vector Machine, XGBoost, and Multi-Layer Perceptron, were evaluated. To enhance robustness against sensor drift and environmental variations, feature-engineering techniques incorporating statistical, temporal, frequency-domain, and derivative-based features were developed. Experimental results demonstrate high detection accuracy under both controlled and real-world conditions. The proposed approach demonstrates the feasibility of integrating machine learning-based MIT sensing into wireless EV charging infrastructure for reliable foreign object detection. Full article

To improve temperature uniformity and reduce thermal stress-induced cracking during laser directed energy deposition (laser DED) repair of TiAl blades, this study proposes a refined induction heating coil design based on coupled electromagnetic-thermal finite element simulation. A temperature-dependent model of the induction heating process for a cast 45XD TiAl blade was established and used to compare circular and elliptical coil cross-sectional shapes. The elliptical coil reduced the magnetic field concentration at the leading and trailing edges and decreased the maximum temperature difference across the blade cross-section to below 100 K, thereby improving transverse temperature uniformity. To further improve the temperature distribution along the blade length, a variable-pitch solenoid coil with sparse turns in the middle and dense turns near both ends was designed. This arrangement improved the balance between local heat generation and heat dissipation and reduced the temperature variation within the central 10 cm region of the blade to about 10 K. Experimental validation showed engineering-level agreement with the simulation results, and the blade body was stably maintained at 1020–1030 K, satisfying the preheating requirement for laser DED repair of TiAl blades within the tested design set. Full article

This article presents a comprehensive analytical, numerical, and experimental study of the amplification and detection of weak signals in magnetically coupled electromagnetic systems, using an architecture consisting of three magnetically coupled coils. A rigorous mathematical model of the system is developed, which includes the formulation of the mutual inductance matrix and a state-space representation that captures the dynamic interaction between the coils. It is important to note that the electromagnetic subsystem is linear and that the stochastic resonance effect is achieved by incorporating an external nonlinear bistable element. In this configuration, a weak periodic signal below a threshold is applied to the primary coil, while a controlled source of Gaussian white noise is injected into a secondary coil. A third coil functions as a sensing element, capturing the superimposed magnetic response resulting from coupling effects. The voltage induced in the sensor coil is subsequently processed by a bistable nonlinear element implemented via a Schmitt trigger, which provides the nonlinearity and bistability necessary to enable stochastic resonance and the detection of the weak periodic signal. The conditions of the SR are analyzed in terms of noise intensity, coupling coefficients, and system parameters, highlighting the existence of an optimal noise level that maximizes the signal-to-noise ratio (SNR) at the output. A detailed simulation framework has been developed in MATLAB/Simulink, enabling a systematic exploration of the parameter space and the validation of theoretical predictions. The simulation results are further supported by experimental measurements obtained from a physical prototype, which show agreement with the proposed model. The main contribution of this work lies in demonstrating that magnetically coupled electromagnetic structures can effectively interact with nonlinear bistable elements to exploit stochastic resonance in the detection of weak signals, even when the electromagnetic domain itself remains linear. The results demonstrate that magnetic coupling is an effective mechanism for mediating constructive interactions between noise and weak signals, thereby improving the detection of the latter. These results extend the applicability of stochastic resonance to hybrid electromagnetic systems and demonstrate its relevance in practical applications. Potential applications include ultra-sensitive magnetic detection, low-power signal detection, magnetic transducers, and robust signal recovery in noisy electromagnetic environments, particularly in contexts where conventional linear amplification fails. Full article

Wireless power transfer (WPT), characterized by its excellent insulation properties and ease of maintenance, has recently emerged as a promising solution to the power supply challenges faced by online monitoring equipment on high-voltage transmission towers in complex environments. Existing research primarily relies on regular, closely wound solenoids to power these monitoring devices; however, this approach often makes it difficult to optimize the magnetic field distribution to maximize mutual inductance, thereby limiting transmission efficiency and power and hindering lightweight design. To address these issues, this paper proposes an optimized design scheme for variable-pitch (non-uniform) domino WPT coils based on insulator string structures. First, a parameter calculation model utilizing segmented current analysis is constructed to accurately determine the inductance of non-uniform solenoids, with simulations confirming an error rate below 5%. Subsequently, by integrating domino multi-coil theory into an elitist non-dominated sorting genetic algorithm (NSGA-II), dual-objective optimization is performed. Targeting maximum transmission efficiency and output power under spatial and insulation constraints, a set of Pareto optimal solutions is derived. Ultimately, a 113.7 W insulator domino coil WPT system prototype is constructed to validate the design’s stability. The proposed system achieves a maximum efficiency of 85.73%, with a single-stage load delivering up to 97.48 W. Full article

This paper presents the design and validation of a compact high-performance electromagnetic contactor for high-current direct current (DC) applications in harsh environments, with particular focus on cold cranking of heavy-duty vehicles. Cold cranking imposes stringent requirements due to elevated current demand, reduced battery capability, and tight actuation timing constraints. To address these challenges, a systematic design methodology is used, combining analytical magnetic circuit modelling, finite element analysis (FEA), and experimental validation. The study investigates key design aspects, including magnetic core selection, coil sizing, and contact geometry, under strict dimensional and thermal constraints. An analytical model is first used to predict electromagnetic force and current dynamics, and is subsequently validated using FEA. A prototype contactor is then constructed and experimentally tested to verify the predicted performance. Results show strong agreement between analytical, numerical, and experimental approaches, with force prediction errors below 10% across the operating range. The findings confirm the suitability of simplified analytical models for initial design stages and highlight the impact of material selection and inductance on actuation speed. The proposed workflow provides practical design guidelines for developing compact, efficient, and reliable contactors for high-current automotive applications operating under extreme conditions. Full article

With the increasing demand for higher efficiency and power density, innovative winding techniques have become crucial in modern electric machines. Hairpin windings are increasingly used in electric machines, particularly in high-current applications. A novel analytical model is proposed to estimate slot leakage inductance in hairpin windings. Traditional models are limited to random windings, which fail to capture the complex mutual inductance between multiple coil layers. This paper derives a generalized model to estimate specific permeance and total mutual specific permeance for the hairpin windings, which are key factors in determining slot leakage inductance. The proposed model is also valid for fractional-pitch windings. The derived analytical model is validated through finite element analysis (FEA) on an electric motor similar to that employed in Tesla Model S. In addition, experimental validation is performed to further validate the proposed model. Furthermore, parametric analysis is conducted to analyze the influence of slot geometry and conductor dimensions on the slot leakage inductance. This paper contributes an accurate method for predicting slot leakage inductance in hairpin windings; this provides electrical machine designers with a valuable tool for precise modeling and optimization for improved efficiency and performance in various applications. Full article

To address dependence on external power and the limited capability of conventional hydroelectric units to detect low-amplitude vibrations, this work introduces a self-contained, highly accurate monitoring device. The design incorporates a magnetically levitated configuration, with triboelectric films placed on both the upper and lower faces of the floating magnet. Under minor oscillations, magnetic repulsion increases the relative displacement between the friction layers, producing a substantial voltage that permits low-level vibration sensing. A surrounding induction coil responds to the levitated pole’s vertical motion; this motion intersects the magnetic flux, generating a current that provides stable energy for wireless data transmission. Experimental outcomes confirm a detection limit of 0.1 mm. At an amplitude of 1 mm and a load of 1000 Ω, the system achieves a maximum output of 9 mW and a power density of 1.587 W/m², ensuring reliable power. This configuration provides a new pathway for monitoring vibrations in hydroelectric turbine generators. Full article

To address the severe shielding of conventional electromagnetic signals by metallic pipelines and the inherent design trade-off under fixed-voltage excitation, whereby increasing coil size suppresses current and limits magnetic field intensity, this study proposes an independently parallel-fed multistage coil enhancement scheme for the transmitter of through-wall magnetic induction communication. Based on electromagnetic theory and COMSOL6.3 simulations, a coupled analysis framework for multistage coils was established to systematically evaluate the effects of axial partitioning, radial partitioning, nonuniform turn allocation, and magnetic-core loading on branch-current amplitude and phase consistency as well as spatial magnetic field intensity. The results show that, under in-phase, equal-frequency excitation, the resultant magnetic field intensity increases approximately linearly with the number of partitions. The partition scheme significantly alters the mutual inductance distribution among sub-coils, thereby affecting current synchronization and magnetic field synthesis efficiency. The introduction of a high-permeability magnetic core markedly improves the amplitude and phase consistency of the radially partitioned structure and enhances output stability. Considering magnetic field output, current synchronization, and engineering feasibility, the axial–radial hybrid four-partition structure with a magnetic core was identified as the preferred configuration. These findings provide a theoretical basis and structural guidance for transmitter design in low-frequency through-wall magnetic induction communication under metallic shielding conditions. Full article

This work presents wirelessly interrogated microelectromechanical system (MEMS) capacitive sensors for continuous intraocular pressure (IOP) monitoring. The sensor uses a passive inductor–capacitor (LC) tank circuit comprising a fixed, on-chip spiral inductor and a pressure-sensitive, variable-gap capacitor with parallel-plate membrane electrodes and side anchors. The membrane is designed with dimensions of 500 µm × 500 µm × 2 µm and a capacitive transducer gap of 2.5 µm. Applied pressure deflects the top membrane, producing a corresponding capacitance variation that changes the frequency and phase response of the LC tank circuit, enabling real-time and continuous IOP monitoring over a target detection range of 0–50 mmHg and beyond. Mutual inductive coupling between the sensor and the external readout coil is investigated as a reliable readout mechanism. Full article