Coil Parameters Research Articles

Effect of Coil Parameters on Layered DD Coil for Efficient Wireless Power Transfer

Inductive wireless power transfer technology (WPT) is gaining momentum recently for wide range of applications. This ranges from charging of portable electronic devices to static and dynamic charging of electric vehicles. It is enabled by the use of magnetic coils wound in certain shapes and dimensions. In order to gain optimal wireless power transfer, coil parameters such as the wire spacing and the core area, are critical. A less optimal selection of values for these parameters can lead to destructive or constructive interaction between the generated fields. In this letter, some coil parameters such as the inter-layer and turn spacing of the Layered DD (LDD) coil are investigated to determine how they influence the inductance which influences the WPT efficiency. It was deduced that the start radius of the LDD coil is directly proportional to the inductance. The inter-layer distance and change in radius exhibit an inversely proportional relationship.

Design Method of Multiwavelength EMATs Based on Spatial Domain Harmonic Control.

Conventional electromagnetic acoustic transducers (EMATs) are generally only used to generate and detect guided waves with a single wavelength, which increases their sensitivity at that particular wavelength but limits their application scenarios and the accuracy of defect assessment. This article proposes a design method for multiwavelength EMATs based on spatial-domain harmonic control. First, the EMAT model is analyzed, where it is then outlined that the eddy-current density distribution of the specimen is equivalent to the spatial low-pass filtering of the coil-current density distribution. This shows that the multiwavelength guided waves can be achieved as long as the spatial distribution of the coil-current density contains those multiple harmonics that are desired. It is then proposed that the structure of the EMAT coil is equivalent to the spatial sampled pulse sequences of a spatial signal. The coil parameter design based on pulse modulation technology is proposed. Taking a dual-wavelength EMAT design for Lamb waves as an example, details of the coil parameter design are presented. The simulation and experiment with the dual-wavelength EMAT proved the correctness of the proposed method. Finally, an experiment with a three-wavelength EMAT demonstrated the feasibility of the proposed method in designing multiwavelength EMATs.

Design of filamentary planar spiral coils with enhanced channel model for magnetic induction based underground communication

AbstractEarlier researches have proved that the magnetic induction (MI) communication has better performance compared to the electromagnetic (EM) wave propagation in underground (UG) medium as it provides low signal attenuation using small MI coils. In general, non‐planar coils are employed as transceivers in the MI UG communication and their performance is dependent on coil parameters. The disadvantages of non‐planar coils are their bulkiness and limited transmission distance. In this article, a novel idea of using compact filamentary planar spiral coils for MI UG communication is proposed to achieve higher received power at greater transmission distance. An enhanced MI channel model is also proposed to study the medium's influence on MI performance accurately by considering different soil characteristics. Performances of the circular and square coils in the MI system are evaluated based on mutual inductance, path loss, received power, and signal‐to‐noise ratio. The performance comparison suggests that the filamentary planar spiral square coil MI system achieves 9.22% higher received power than the filamentary planar spiral circular coil MI system. Moreover, the lateral and angular misalignment study shows that square coils are more tolerant to misalignments. For the proposed filamentary planar square spiral coil (FPSSC) MI system, the influence of coil parameters, channel parameters, and coil misalignment on the received power was carried out and its least sensitive and most sensitive parameters were identified for further optimization. The performance comparison between the proposed FPSSC MI system and the traditional non‐planar MI coil system suggests that the received power of the proposed system is improved by 47‐49 dBm thus extending the achievable transmission distance.

PCB Planar and Filamentary Planar Spiral Coils based Underground Magnetic Induction Communication with Enhanced Channel Model

A novel idea of using compact filamentary and printed circuit board (PCB) planar spiral coils for the magnetic induction (MI) based underground (UG) communication to achieve high received power and enhanced transmission distance is proposed. In the existing system, non-planar coils were employed as transceivers which lost their function due to their huge size and deployment difficulty. An enhanced MI UG channel model is proposed to accurately investigate the UG medium’s influence on the MI system performance by considering various soil properties that were considered negligible in the earlier models. An analytical approach to calculate self-inductance and mutual inductance of circular and square coils of filamentary planar and PCB planar spiral coils are described from which the communication parameters such as received power, path-loss, and signal-to-ratio are derived. The simulation results reveal that in both filamentary and PCB planar spiral coil, the square shape coil performs better than the circular coil. The filamentary planar spiral square coil (FPSSC) achieves 26.15% higher received power than the PCB planar spiral square coil (PPSSC) due to the former coil’s low resistance and strong mutual coupling. Further, the influence of coil parameters, coil misalignment, and soil properties on the received power is studied for both FPSSC and PPSSC systems, and their major performance influencing parameters are identified. The received power of the proposed FPSSC system exhibits a significant improvement of 31.24% as compared to the traditional non-planar MI coil system.

Numerical study of crosshole electromagnetic tunnel detection

Electromagnetic tunnel detection is studied numerically using a 3D analytic infinite lossy homogeneous space solution to magnetic dipole radiation and scattering from an infinite cylinder, in a crosshole context. At low frequencies, this serves as a model for a transmit coil radiating a time-varying magnetic field that is then detected from the open-circuit voltage induced on a receive coil. Numerical simulations illustrate how various parameters influence the signal strength and the ability to discern the scattered signal. Tunnel detection is achieved at relatively high frequencies (but below typical ground-penetrating radar frequencies) for fresh water-saturated sand and for weathered granite, which are lower loss media; for the coil and tunnel parameters used here, the optimum frequencies appear to be between 100 kHz and 1 MHz. Tunnel detection for fresh water-saturated clay, a much more lossy medium, can be achieved at a quite low frequency, with an optimum frequency between 1 and 10 kHz. These results suggest that, when a resonant coil system is used, tunnel detection may be possible in a wider range of earth media than previously reported, when the best-suited choice of frequency is used.

Analysis of Coil Parameters and Comparison of Circular, Rectangular, and Hexagonal Coils Used in WPT System for Electric Vehicle Charging

In this paper, the major factors that affect the performance of wireless power transfer systems, such as coil inner radius and coil number of turns, are discussed. A comparison of three coil shapes covering the coreless case, the case with ferrite, and the case with ferrite and aluminum is also carried out. Another comparison is proposed by addressing the combination of different coil shapes in the wireless power transfer (WPT)system. The analysis covers the coupling coefficient, the mutual inductance, and the self-inductance. Due to the complexity of calculating these parameters, the finite element analysis (FEA) method is adopted by using the Ansys Maxwell software. An introduction to the typical WPT system for electric vehicle charging is also presented.

Graphene acoustic transducers based on electromagnetic interactions

Graphene acoustic transducers have high sensitivity in receiving mode. However, they are used in transmitting mode with low radiation performance. A graphene acoustic transducer with high sensitivity and radiation performance is proposed in this study. The transducer is composed of graphene diaphragm, an insulating layer embedded in a copper planar coil, and a bottom layer plated with copper. The proposed capacitive transducer is driven by electrostatic and electromagnetic excitation. The sensitivity and radiation performance of the transducer are analyzed by transceiver theory and simulation models. The results demonstrate that the proposed capacitive transducer has excellent acoustic performance with sensitivity of −42 dB and the sound pressure level of 106 dB at 4 kHz with a 20-turn coil that is more than doubled compared without a copper coil. In addition, the radiation performance of the transducer is discussed by the coil parameters including coil turns and coil current, which can provide a theoretical basis for further experiments.

Design of a Rectangular Pickup Coil Fabricated on a PCB Using WBG Power Semiconductor in Discrete Package

Power semiconductors based on wide bandgap (WBG) devices are capable of fast switching and have low on-resistance. Accordingly, a fast sensor with a higher bandwidth is required for circuit inspection based on switch current measurements. Thus, it is necessary to have a current sensor in the printed circuit board (PCB) circuit for diagnosis and protection of the surface mount device (SMD) type circuit system. Accordingly, a pickup coil with the advantages of a high degree of sensor configuration freedom, wide bandwidth, and low cost can be a good alternative. This study analyzes the influence of coil shape and parameters on sensor design as a guideline for embedding a pickup coil in an SMD-type PCB circuit of a WBG power semiconductor-based, half-bridge structure. The mutual inductance and self-inductance values of the coil are considered large variables in the design of a sensor coil for simultaneously maintaining high bandwidth and sensor sensitivity. Therefore, magnetic and frequency response analyses were conducted to verify the correlation with inductance, the influence of coupling capacitance, and the influence of the magnetic field formation via the current flowing through the external trace inside the PCB. The coil model is verified and discussed through simulation and double pulse tests.

Parameter Analysis of Pulsed Eddy Current Sensor Using Principal Component Analysis

Pulsed eddy current (PEC) technique provides a means to inspect structures without surface contact. It is particularly useful when the structure's surface is rough or inaccessible, such as insulated pipes in pipeline. Probe parameters of a PEC system, especially the sensing and excitation coil diameters, can significantly affect the PEC system's performance. Thus, detailed analysis of these parameters is paramount in developing a PEC system. Currently, this is accomplished by establishing the trend of features with respect to the analyzed variables, e.g. sample thicknesses. However, prior to extracting these features, a number of configuration parameters have to be determined. For this reason, analyzing PEC performance over a range of coil diameter values is rather time-consuming as both the sensing and excitation coil diameters significantly affect the received signals. Principal component analysis (PCA) is proposed as an alternative to the feature extraction. The work here analyzes the trends contributed by the PCA scores for different values of sensing and excitation coil parameters. Results from both numerical simulations and experiments suggest that the sensitivity of the PEC probe is highly correlated with the excitation coil diameter, while the excitation-sensing coil distance is not significant in determining the sensitivity of the PEC probe. These findings are consistent with those reported in the literature, suggesting the potential of adopting PCA for an automated PEC performance analysis process.

Electromagnetic‐Thermal Characteristics Analysis of Dry‐Type Core Reactor and Optimization Design Based on the Particle Swarm Algorithm

In this paper, a fluid‐thermal coupled finite element model is established based on the design parameters of dry‐type core reactor, the detailed temperature distribution results are given, and the heat transfer process of the layer coils was analyzed. Meanwhile, the electromagnetic characteristics of core reactor have been analyzed, it shows that the structure parameters adjustment of layer coils have little effect on the inductance of reactor. Taking the metal conductor usage of coils as the optimization object, the heat dissipation process between the layer coils and air ducts is equivalent to the vertical pipe, the calculation method of temperature rise is given, and the thermal efficiency optimization method of dry‐type core reactor is proposed based on the particle swarm optimization algorithm, which can obtain the optimal structure parameters of coils. According to the optimization design results, the metal conductor usage of coils is only 80% compared with the initial parameters, and the correctness is verified by the simulation results. Thus, the optimization method can significantly improve the thermal efficiency and reduce the metal conductor usage of core reactor. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Investigation on Electromagnetic Vibration Energy Harvesting in Water Distribution Control Valves

Control stations of a water distribution system monitor several variables such as the pressure, the flow, and the quality of water. For these monitoring tasks, wireless sensor networks with ultra-low power consumption powered by vibration-based energy harvesters as an alternative to the usage of batteries or wired connections might be a suitable option in these facilities. This article investigates the potential applicability of an electromagnetic vibration energy harvester prototype in different control valves of a water distribution system in the province of Barcelona by means of experimental measurements and numerical simulations. The low-amplitude vibration with random excitation is measured with piezoelectric accelerometers in three control valves under normal operating conditions to process each signal and determine the dominant frequency in the complete spectrum, which is found to be in the order of magnitude of kHz, and the dominant frequency in the range of 10 to 100 Hz, where commercial harvesters normally operate. Numerical simulations of the harvester prototype are conducted in all cases with the same materials, geometries, and coil parameters, generating a maximum RMS load voltage and output power when the harvester's natural frequency matches the dominant frequencies of each vibration signal. The maximum output power estimated in these simulations is 1573.04 nW with a corresponding RMS load voltage of 53.6 mV and optimal load resistance of 1830 Ω.

Optimization and design of wide-band and low-noise air-core coil sensor for TEM system

The effective bandwidth and background noise of the sensor are important factors to the performance of TEM, especially in the detection of urban underground space. The limitation of the size of coils further reduces the bandwidth and sensitivity of the sensor, resulting in the distortion of high-frequency signal from ultra-shallow and the loss of weak signal from deep. In order to solve this problem, by establishing the physical model of the induction air-core coil sensor, a method of winding wire which reduces the parasitic parameters of the air-core coil is proposed to improve the bandwidth and sensitivity of system. Combined with theoretical simulation, the components of noise and parasitic parameters of the air-core coil sensor were analyzed, and the system was optimized. An air-core coil sensor with an effective bandwidth of 783 kHz and an equivalent noise of about 2.45 nV/ was obtained. The new sensor effectively improves the detection capability of TEM system for high-frequency secondary field signal, which has positive significance for the application of TEM in urban underground space.

Investigation on Key Parameters of NI HTS Field Coils for High Power Density Synchronous Motors

As global environment regulations are gradually strengthened, active research has been conducted on electric propulsion applications. High power density is one of the major research interests, as well as a machine's efficiency for a high-performance propulsion system. Among various electric propulsion technologies under development, a motor incorporating the no-insulation (NI) high-temperature superconducting (HTS) winding has the advantages of high current density and robustness to external disturbances, which are suitable for high specific power. However, still, there is little research on the motor with NI HTS coil. Therefore, as basic research, we investigated the potential application of the NI HTS motor, then derived required machine parameters and NI HTS coil designs in this paper. For that, first, basic parameters of the existing propulsion motors were investigated, then the target application and performance of the NI HTS motor were determined. Based on the target performance, conceptual designs of a motor with NI HTS coil were obtained by changing key design parameters including rated power, main dimensions, operating temperature, and width of air-gap. Calculated parameters were numerically compared, and expected design requirements and challenges were suggested.

Effects of stainless steel thickness and winding tension on electrical and thermal characteristics of metal insulation racetrack coils for 10-MW-class HTS wind generator

Experimental results on the electrical and thermal characteristics of GdBCO racetrack coils co-wound with stainless steel (SS) tapes of various thicknesses and winding tensions are presented in this paper. The SS thickness and winding tension are identified as the factors affecting the charging time and thermal stability of metal insulation (MI) coils. To verify these characteristics, three types of MI-SS racetrack coils were fabricated with various SS thicknesses and winding tensions: 100-μm SS thickness and 10-kgf winding tension; 100-μm SS thickness and 5-kgf winding tension; and 50-μm SS thickness and 10-kgf winding tension. Further, three MI-SS racetrack coils were characterized by sudden discharging, charging, and overcurrent tests. The sudden discharging and charging tests were performed in a steady state to investigate the decay time constant of the center magnetic field discharging the coils and the delay time of the magnetic field charging the test coils, respectively. To estimate the thermal stability of the three MI-SS coils, overcurrent tests were conducted in a transient state at 1.1 times the critical current (Ic) and 1.05 Ic. Based on the experimental results of three small-scale test coils, the total contact resistance between the layers of the test coils was calculated and applied to design a field winding using a second-generation high-temperature superconducting (HTS) tape for a 10-MW-class HTS generator used in an offshore wind turbine environment. Subsequently, an equivalent electrical circuit model was proposed to analyze the electromagnetic response and thermal stability characteristics of three HTS field coils of a 10-MW-class HTS generator with the key parameters of the HTS field coils, which were obtained using electromagnetic finite-element analysis. Finally, the charging delay time and thermal stability of the three HTS field coils were compared and analyzed in detail.

Equivalent Capacitance Model of Segmented Induction Coil in Electromagnetic Exploration System for Deep Resources

The study on fixed-wing electromagnetic induction coil device is conducted according to the characteristics and requirements of deep resources aerial electromagnetic measurement system. In order to detect resources with different structures and forms, the system needs to support the measurement of varying magnetic field signals in a wide frequency range. The induction coil, as the information search probe, its equivalent capacitance parameter plays a key role in the frequency response bandwidth of the detection system. In this article, an analysis model of multi-segment coil is proposed. Through the calculation and analysis of the structural parameters of multi-segment coil, the distributed capacitance parameters of multi-segment coil can be effectively estimated to improve the design efficiency of the electromagnetic induction system. In addition, the key parameters that affect the equivalent capacitance parameters of multi-segment coils are summarized, and the key parameters of coil structure are compared and improved. Finally, the expansion of frequency response bandwidth of induction coils is realized. Through the comparative analysis of actual measurement, the working response bandwidth of the improved two structural coils is 1.29 and 1.19 times that of the original structural coils respectively, and the receiving sensitivity is also improved, which verifies the effectiveness of the proposed analytical model. The analysis shows that the equivalent capacitance parameters of the coil can be controlled more flexibly through the reasonable design of segment spacings and choosing the materials with suitable dielectric constant as the coil framework, so that the designed induction coil can be characterized by good frequency domain response.

Optimized finite-build stellarator coils using automatic differentiation

A new stellarator coil design code is introduced that optimizes the position and winding pack orientation of finite-build coils. The new code, called flexible optimized curves in space using automatic differentiation (AD) and finite build (FOCUSADD), performs gradient-based optimization in a high-dimensional, non-convex space. The derivatives with respect to parameters of finite-build coils are easily and efficiently computed using AD. FOCUSADD parametrizes coil positions in free space using a Fourier series and uses a multi-filament approximation to the coil winding pack. The orientation of the winding pack is parametrized with a Fourier series and can be optimized as well. Optimized finite-build coils for a Wendelstein 7-X (W7-X)-like stellarator are found, and compared with filamentary coil results. The final positions of optimized finite-build W7-X-like coils are shifted, on average, by approximately 2.5 mm relative to optimized filamentary coils. These results suggest that finite-build effects should be accounted for in the optimization of stellarators with low coil tolerances.

Analysis and Research on High Speed On-off Valve Electromagnets with Different Electromagnetic Drive Forms

Abstract As a typical hydraulic component of digital hydraulics, high speed on-off valves are widely used in vehicle braking and high-pressure common rail injectors. Different electromagnetic drive forms have different effects on the discontinuous drive control effect of digital hydraulics. In order to compare the effects of the two electromagnetic drive forms of moving-coil type (MCT) and moving-iron type (MIT) more pro-foundly, this paper conducts the two electromagnetic drive forms. Through comparative analysis, the superiority of MCT electromagnetic drive in response time is obtained. First, the principles of the two drive forms are explained separately, and the magnetic circuit analysis of the two electromagnetic drive forms is carried out. Then, assuming that the coil parameters are the same, the electromagnetic simulation software is used to measure the magnetic field and electromagnetic function parameters of the MIT and the MCT. Finally, through the analysis and comparison of electromagnetic force, inductance, current and other parameters, it was found that the response speed of the MCT drive was better than that of the MIT. The magnitude of the two forms of steady-state electromagnetic force depends on the position of the initial working air gap of MIT. This phenomenon is explained in terms of electrical time attempts and inductance. It provides ideas for the design and improvement of electromagnetic drive of high speed on-off valves.

An Axial Foilless Diode Guided by Composite Magnetic Field for the Production of Relativistic Electron Beams

Foilless diode are widely used in high-power microwave devices, but the traditional foilless diodes have large volume, heavy weight, and high power consumption, which are not conducive to the application of high-power microwave system on mobile platform. In order to reduce the size of the foilless diode, improve the transmission efficiency of electron beams, and reduce the weight and power consumption of the guiding magnetic field system, an axial foilless diode with a composite guiding magnetic field system is developed in this paper. By adjusting the structure size and magnetic field parameters of solenoid coil, permanent magnet, and soft magnet, the configuration of the composite magnetic field is optimized. The diameter of the anode tube is about 40% smaller than that of the original structure, and the weight and power consumption of the guiding magnetic system are about 40% lower than that of the original system when the same axial magnetic field intensity in the uniform region is generated. When the magnetic field strength of the permanent magnet is set as 1.4 T and that of the solenoid coil is in the range of 0.5 T∼1 T, the electron beam transmission efficiency is 100%, and the diode impedance is adjustable in the range of 100 Ω∼240 Ω. The experimental results verify the correctness of the simulation analysis. The experimental results show that when the magnetic field strength of the solenoid coil is 0.98 T (0.5 T) and that of the permanent magnet is 1.4 T, the transmission efficiency of the high-current annular electron beam with a peak voltage of 636 kV (590 kV) and a peak current of 3.3 kA (2.6 kA) is 100%, and the diode impedance is about 194 Ω (220 Ω).

A Method for Comparing the Metrological Properties of Eddy Current Probes

This article describes a method for comparing the metrological properties of air-cored and solid-cored coils designed as eddy current probes. The approach suggested in this article assumes that a pair of equivalent parameters of an ideal filamentary coil can be assigned to any contact coil so that the impedance variations in both coils are identical. These two parameters include the coil radius and its distance from the surface of a test piece. The experiments performed demonstrate that for equivalent parameters defined in such a way, impedance variations in a real and filamentary coil are the same for a broad frequency range of excitation current and conductivity of the material being tested. Therefore, comparisons between parameters of eddy current probes such as sensitivity, depth of penetration, or inspection coverage can be made with the use of a simple model of an ideal filamentary coil defined by only two parameters. The solution proposed in this article substantially simplifies the calibration process of the measuring instrument, the adjustment and optimization of parameters for newly designed probes, and the development of efficient and reliable mechanisms to eliminate undesired effects (e.g., lift-off).

Magnetic Field Energy Harvesting From Current-Carrying Structures: Electromagnetic-Circuit Coupled Model, Validation and Application

Magnetic field energy harvesters (MFEHs) from current-carrying structures/conductors are usually modelled as decoupled electromagnetic and electrical systems. The current-carrying structures may affect the performance of MFEH through the generation of the eddy current and the alteration of the magnetic reluctance. Moreover, the load circuit affects the current generated in the coil and therefore the flux density and eddy current generated. The effects of the current-carrying structure and the load circuit cannot be fully described by the decoupled models. This work develops a finite element model (FEM) that fully couples the electromagnetic and electrical systems by simulating both the magnetic field and eddy current distribution of an MFEH connected to an electrical circuit. The FEM first simulates the coil inductance and resistance of a magnetic field energy harvester (MFEH) placed close to a current-carrying structure exemplified by a rail track. The FEM then simulates the outputs of the MFEH connected to an electrical circuit consisting of a compensating capacitor and optimal load resistor determined by the first step. An MFEH was fabricated and tested under a section of current-carrying rail track. Both experiment and simulation show an increase of both coil resistance and inductance when the MFEH is placed close to the rail track. The good agreement between experimental and simulation results validates that the FEM can predict the full-matrix performances of the MFEH, including the coil parameters, power output and magnetic flux density under the influence of the current-carrying structure and the load circuit. Simulation results reveal that in addition to the permeability of the magnetic core, the electrical conductivity and magnetic permeability of the current-carrying structure considerably affect the performance of the MFEH, which cannot be predicted by decoupled models.