Coupling Coils Research Articles

Coupling Analysis and Research of Multistage SICL Based on Crowbar Circuit

In this article, the influence of multistage synchronous induction coil launcher (SICL) coupling on diode advance conduction was analyzed. The coil current and launching performance of the SICL which is based on the crowbar circuit was also investigated. The thyristor was connected before diode in this multistage SICL system circuit. First, the precise mathematical model for this two-stage SICL was theoretically deduced. The model was to analyze the effects of coils coupling under different trigger timings on diode advance conduction and coil current. Second, the derivation of the model was based on applying the precise mathematical methods of coils coupling to the process of SICL launching. From this analysis, the effects of coils coupling under fixed trigger timing on coil current and launching performance can be obtained. By comparing the MAXWELL finite-element simulation with MATLAB numerical calculation, we were able to estimate the correctness of the precise mathematical model. Finally, experiments were carried out and the results were well consistent with the simulation results.

A Design Method for Magnetically Coupled Resonant Coils Considering Transmission Objectives and Dimension Constraints

This paper proposes a coil design method for the magnetically coupled resonant wireless power transfer (MCR-WPT) system. Based on the Biot–Savart law, the magnetic flux density at the observation point was derived, and the magnetic flux of the observation plane generated by the exciting coil was deduced to build the calculation model of power transfer efficiency (PTE) and power delivered to the load (PDL). The PTE and PDL curves via coil parameters could be fitted in minutes using numerical calculation. The coil was designed according to transmission objectives and dimension constraints. In addition, the calculated PTE and PDL were compared with those from finite element analysis to verify the credibility of the method. Finally, the actual curves of PTE and PDL were achieved, which showed a strong positive correlation with the corresponding curves from the calculation model. The relative average deviations of PDL curves were less than 6.11%. Meanwhile, coils designed with the numerical calculation could realize 309.80 W and 88.51%, which achieved the objectives under the constraints. The results demonstrate that the proposed method can realize a rapid and accurate coil design under constraints. It can also be applied to other coil structures or circuit topologies with strong universality.

Design and Analysis of Magnetic Coils for Optimizing the Coupling Coefficient in an Electric Vehicle Wireless Power Transfer System

Although the wireless power transfer (WPT) system for electric vehicles (EVs) provides numerous advantages, there is still a low coupling coefficient and the misalignment between the primary coil and the secondary coil needs to be solved. In this paper, the transmission efficiency and transmitted power were calculated based on Series-Series (SS) compensation topology. The coupling coefficient is related to the coil parameters and misalignments. A simulation study was carried out to explore the variation in the coupling coefficient for different coil configurations under different air gaps and coil misalignments. Moreover, the influence of the internal parameters of the square coil on the coupling coefficient was further studied. Finally, this paper discusses the influence of ferrite cores with a square coil on the coupling coefficient. The results of this paper show that designing the optimal internal parameters of the square coil and the ferrite core can increase the coupling coefficient between the coils, which can also provide guidelines for the design and optimization of the magnetic coupling coils for a wireless charging system for electric vehicles.

Calculation model of mutual coupling between two ferrite-cored square coils in wireless power application for electric vehicles

Wireless power transfer (WPT) devices have been widely accepted by more and more industrial producers and consumers due to their safe, convenient, and high-efficient features. Square coils with ferrite cores are usually utilized as magnetic coupling devices by WPT systems for electric vehicles (EVs). However, the research on coupling coils often depends on three-dimensional finite element analysis (3-D FEA) tools such as ANSYS Maxwell or HFSS, which are troublesome and time-consuming. This paper explores a calculation model of mutual coupling between two square coils with ferrite cores based on magnetic mirror method. With this model, accurate results and fast operation speed can be obtained, and 3-D FEA tool is used to compare and verify the performance of this work.

Automatic tuning of the Class E power amplifier applied in inductive links during coil separation variations

In this paper, a new approach is proposed for the automatic tuning Class E power amplifier (PA) to compensate the effect of the coupling distance variation in wireless power transfer (WPT) systems. In WPT, coupling distance variations change the reflected impedance, causing Class E PA to operate under nonoptimal switching conditions. Here, a model-based approach is proposed to estimate the coil separation distance in real-time. Knowing the separation distance, the mutual inductance and reflected impedance are computed, and the Class E is retuned online by saturable reactors. A design example of Class E PA with proposed closed-loop control method is given. The results indicate that the proposed method could perfectly retune the Class E to operate under optimum conditions and compensate power delivered to the load (PDL) reduction during coupling distance variations. It can be seen that there is a closed agreement between the measured PDL when the PA is closed-loop controlled and the measured PDL when the PA is manually optimized during each coupling distance. The measurement results show that by using the proposed method, the PDL increased by 14.47%, 25.51%, 15.92%, and 12.88% at coil coupling distances of 15 mm, 20 mm, 25 mm and 30 mm, respectively.

Offset-tuned Bilateral-side Inductively Coupled RF Coils for Preclinical MRI at 15.2 T

A small coverage of magnetic flux density (B₁) and its inhomogeneity are intrinsic problems of conventional surface coils. Therefore, offset-tuned bilateral-side inductively coupled radiofrequency (RF) coils have been specifically designed to overcome these problems. Herein, we proposed bilateral-sided wireless coils for improving the B1-field uniformity by simultaneously adding a supplemental secondary coil (s-coil) to the primary coil (pcoil) in the orthogonal direction. The offset-tuned frequency of the s-coil was evaluated and compared from 0 to +60 MHz with a +10 MHz interval at the Larmor frequency of the p-coil. Using mathematical EM modeling, we optimized the +60-MHz offset-tuned s-coil at 15.2 T. Thus, a combined coil configuration with p-coil of 655 MHz and two s-coils of 710 MHz was obtained. This combined coil configuration can overcome the B₁-field inhomogeneity of p-coils in 15.2 T small animal magnetic resonance scanner and can be extended to overcome the volume coil array inhomogeneity.

Displaying images on a plane of rotation via mutual inductance coupling wireless controls

This work presents an innovative display technique, which renders the image displaying capability to the plane of rotation by installing a rectilinear LED array. Basing on the persistence of vision of human eyes, the rotating scan of LEDs generates the stable display of images under the timing control. Because of the cyclic motions during the rotating scan, the timely display control signals have to be received wirelessly. Further considering the desire for long-time usages, the electricity supply is also required to be achieved through wireless energy harvest. As per these requirements, we present an implementation scenario based on the mutual inductance coupling of coaxial coils. During the rotation, the noncontact coils maintain the relative positions unchanged, thus preserve the reliable transmission of control signals and power supply in a stable electromagnetic environment. Also benefited from the mutual inductance coupling design, the construction of wireless communications is achieved by using a primitive micro-controller circuit. The hardware simplicity enables the setting up of ad hoc screens via a convenient refit of rotatable objects (e.g., vehicle wheels and propellers), and realizes fashionable and customizable consumer electronics with the additional information broadcasting function.

Pareto optimal solutions of a wireless power transfer system

Electrical vehicles have to be periodically recharged. Currently, they are plugged to power station by cables. Wireless Power Transfer (WPT) Systems could be used instead of traditional cable connection to charge the batteries of electric vehicles. These systems are based on a couple of coils, one on the vehicle bottom and one under the road connected to a power station. Nevertheless, these systems are affected by the magnetic characteristic of the coupling coils, so that these devices should be carefully designed. In this paper, a pair of faced pancake coils equipped with ferrite core is considered. The possible geometries of the coils are designed using genetic optimization algorithms searching for optimal mutual inductance and saving in copper. This paper presents the analysis of the Pareto solutions obtained using automatic design strategy.

Multi-coupled commutation analysis in EAST poloidal field quench protection circuits based on fuse model

Abstract The poloidal field (PF) power supply (PS) system provides megawatt controllable energy to 14 PF coils in Experiment Advanced Superconducting Tokamak (EAST). The quench protection (QP) circuit in PF power supply system is designed to implement the superconducting coil protection in case of quench. A fuse employed in QP circuit plays an important role in diverting the coil current into the discharge resistor. However, the fuses in 12 QP circuits may turn off at different time due to different self-inductance of coils and initial current. Moreover, the PF circuits are quite complex due to the mutual coupling among the superconducting coils. This means that in fuse melting time the current variation in one of the coupled circuits may produce undesired current rising on the other PF circuits. This phenomenon has been found in experiment with the shot number 82,248. To analyze the multi-coupled commutation in QP circuit, a detail fuse model is necessary. This paper presented a detail fuse model at first. The fuse model consists of a two-dimensional pre-arc model considered the cooling effect of sand and a zero-dimensional arc model. Then the fuse model is integrated with the commutation circuit equations and the mutual coupling coils model. All described models are coded in a parallel computing program. Finally, the proposed integrated model is validated by comparing to an engineering test experiment data without plasma on EAST. The computed value is close to the experiment data, and the current rising phenomenon found in experiment is explained by the combined affection of time lag of fuses turn-off time and mutual coupling. The presented model is utilized to analyze the quench protection circuit response in a large variety of different conditions to ensure the safety of coils in quench scenarios. Furthermore, it might be applied in fuse design

Design of UAV wireless power transmission system based on coupling coil structure optimization

With the development of unmanned aerial vehicle (UAV), it has been used in many fields, such as aerial photography, military, and transportation. However, it is a challenge for charging due to its short battery life. Wireless charging has been considered as a good UAV solution. In this paper, we proposed a wireless power transmission system (WPT) through inductive coupling and analyzed the power efficiency of the inductive coupling. The WPT included a charging station, which can provide energy through an induction coil array, and a portable energy receiving device mounted on the base of the UAV. Moreover, the power efficiency was analyzed though the equivalent circuit of WPT and the mathematical model of the power efficiency was established. The results showed that the WPT can transfer energy to UAV with high power efficiency within a 30 mm lateral displacement range.

An implantable wireless powered light source

A wireless powered small volume light source composed of light emitting diode (LED) array is developed for implantation. According to the volt-ampere characteristics of LED and the load characteristics of coil coupling power supply, the light power and work distance of implant LED-array are optimized by changing the number and series-parallel connection mode of LEDs in receiver. The wireless powered implant can provide 5.4 mW light. The entire implant is seamlessly packaged within parylene, a biocompatible material, coating by chemical vapor depositing. The volume of the implant is 9 mm×4 mm×3 mm, the weight of which is only 0.25 g. The device can work continuously for more than three weeks in 0.9% saline and the prime prototype of the device has been validated by animal implantation.

Mutual Inductance Behavioral Modeling for Wireless Power Transfer System Coils

In this article, we derive low-complexity behavioral analytical models of the mutual inductance between the coupling coils of wireless power transfer systems (WPTSs), as functions of their reciprocal position. These models are extremely useful in the characterization and design optimization of WPTSs. Multiobjective genetic programming algorithm is adopted to generate models ensuring an optimal tradeoff between accuracy and complexity. The training and validation datasets needed for the generation of the models are here obtained by performing numerical full 3-D electromagnetic simulations. The resulting behavioral models allow the accurate and fast evaluation of the WPTS coils mutual inductance, over a wide range of misalignment conditions, enabling easier system analysis and optimization.

Mode Conversion and Structure Optimization of Quadrature Coils for Electric Vehicles Wireless Power Transfer

With the rapid growth of the electric vehicles (EVs) market all over the world, wireless power transfer (WPT), as an emerging way of charging batteries, has drawn the attention of researchers, manufactures, and customers recently. Various magnetic coupler configurations, which are essential in WPT systems, have been proposed and analyzed. However, the misalignment tolerances of the existing magnetic couplers are pretty small, which results in a remarkable decrease in the transmission power and efficiency when there is misalignment between two coupling coils. In order to solve this problem, novel quadrature coils and a converting circuit are proposed, which could adjust the coupler structure according to the relative position of the coils on both sides so that the transmission power and efficiency are optimal. The structure of quadrature coils is first optimized with a three-dimensional finite element analysis (3-D FEA) tool ANSYS MAXWELL. On the basis of the optimized parameters, a 3.5 kW WPT experiment platform is constructed. When the horizontal misalignment reaches 150 mm, the input and output power is 2.256 kW and 2.126 kW respectively, thus an efficiency of 94.22% is achieved. The experimental results verify the correctness of the theoretical analysis.

An FDM-Based Simultaneous Wireless Power and Data Transfer System Functioning With High-Rate Full-Duplex Communication

This article proposed a novel scheme integrating full-duplex communication into high-power wireless power transfer systems. The power and data are transferred through the same inductive link. A pair of coupling coils with taps are employed to omit the trap inductors that are widely employed in former simultaneous wireless power and data transfer (SWPDT) systems. The proposed scheme can reduce the system cost and size and improve the power transfer efficiency. The power and bidirectional data are transmitted using carriers of different frequencies. Frequency division multiplexing technique is utilized for full-duplex communication. The duplexer is carefully designed to separate the transmitted and received data signals. The circuit model of the system is built to analyze the power and data transfer performance. The crosstalk between the power and data transfer is also discussed. To improve the performance of data transfer, the method to determine the optimal coil tap position is proposed. A 300-W SWPDT prototype with a full-duplex data rate of 500 kb/s was built to demonstrate the feasibility of the proposed system.

Analysis of Primary Field Shielding Stability for the Weak Coupling Coil Designs

As an electromagnetic field conversion tool in the transient electromagnetic method (TEM), the weak coupling coils reduce the mutual inductance of its transmitter and receiver coils by special structural optimization, so the detection signal can be protruded from the primary field interference generated by the transmitter coil; thus, this kind of coil design can significantly improve the signal-to-noise ratio. However, with the popularity of drag or aerial TEM exploration, the structural stability problem caused by bumps or windage leads to non-negligible primary field leakages, thereby reducing the detection reliability. This paper incorporates the primary field shielding stability as a key indicator of the weak coupling designs and proposes a calibration scheme for this stability assessment, based on which the shielding stability of five typical weak coupling coil designs is quantitatively compared, and the relationship between the primary field density and the shielding stability explored in this study may contribute to the selection and improvement of TEM coils.

Wireless Power Transfer under Wide Distance Variation Using Dual Impedance Frequency

A dual-impedance operation, where coil impedance is controlled by operating frequency selection, is proposed to maintain optimum reflected impedance across coupling variation. More specifically, this work focuses on how high coupling between coils presents excessively high reflected resistance to transmitter (Tx) inverters, degrading the efficiency and output power of the inverter. To overcome this problem, the proposed system is equipped with dual-impedance coil and selects high- or low-impedance coil based on the ability to operate both at 200 kHz and 6.78 MHz frequencies. The reactive impedances of 6.78 MHz coils are designed to be higher than that of 200 kHz coils. Since the reflected resistance is proportional to the coil impedances and coupling squared, at close distance with high coupling coefficient, 200 kHz coils with low coil impedances are activated to prevent an excessive rise in reflected resistance. On the other hand, at large distance spacing with low coupling coefficient, 6.78 MHz coils with high coil impedances are activated so that sufficient reflected resistance is obtained even under the small coupling. The proposed system’s advantages are the high efficiency and the elimination of bulky mechanical relay switches. Measured efficiencies are 88.6–50% across 10 coupling variations.

Optimal Design of a 3-Coil Wireless Power Transfer System for Deep Micro-Implants

This paper presents a design methodology for a 3-coil magnetic resonance wireless power transfer (WPT) system with a long transfer distance (up to 20 cm) and a small implanted receiver (RX) (2mm in diameter) at a specific frequency. The methodology aims to find out the optimal value of dimensional parameters (i.e., coil diameter, gap interval and coil turn number) of the transmitter (TX) coils to maximize the magnetic field strength at the target distance while keeping the coil self-resonant frequency (SRF) twice of the target operational frequency. Firstly, the circuit model of the TX circuits is developed, which include a single-turn coupling coil and a multi-turn primary coil. Secondly, the co-dependences between the dimensional parameters are analyzed, which shows the dominant factors and secondary factors of each dimensional parameter, and how the optimal values of dimensional parameters are changed by these factors. Based on the analysis, design flow of the TX circuit is proposed to decide the optimal values of dimensional parameters given the transfer distance, source voltage, operational frequency and wire diameter. Using the design flow, optimal values of dimensional parameters are predicted for 20-cm transfer distance and 16-cm transfer distance and are verified with finite element analysis (FEA) software COMSOL Multiphysics. With the optimal TX design, the power received by a 2-mm ferrite core solenoid RX is calculated. At 20 cm transfer distance, up to 4.3 mW can be achieved in air, and 0.8 mW can be achieved in conductive human tissue.

Maximizing Transfer Distance for WPT via Coupled Magnetic Resonances by Coupling Coils Design and Optimization

The technology of wireless power transfer via coupled magnetic resonances (CMR-WPT) has a good transfer performance in the “middle range”, but it is far from satisfying the application requirements in practice. To achieve a longer transfer distance, coils are usually complicatedly designed, making the system unwieldy and costly. Based on the intuitive and easily adjustable coil parameters, a design and optimization method was proposed in this paper, which can realize the minimum size coil that meets the requirements at 6.78 MHz. First, an equivalent model of the CMR-WPT system was developed, and the influences of coil parameters on the effective transfer distance and power transfer efficiency (PTE) were analyzed, indicating that the effective transfer distance and PTE were not always proportional to the coil radius, the number of turns or the pitch. Then, the coil impedance and the quality factor of different coils were calculated. In addition, the influence degree of coil parameters on the transfer performance was also compared using variable control. Finally, an experimental platform was built, and experimental results agreed well with the simulation results.

Multiphase Resonant Inverter With Coupled Coils for AC–AC Induction Heating Application

In this article, a multiphase resonant inverter with vertical aligned coupled coils is proposed for an induction heating application, in which the proposed phase-shift control strategy improves the system power capability. The model for an $n$ coil arrangement is developed using the impedance matrix approach, which allows a circuit representation by means of dependent sources. Each coil is part of a series resonant tank fed by a half-bridge inverter. In particular, the developed converter is evaluated for an $n=2$ case, which is composed by two coils, whose commutation states and the typical waveforms for zero voltage switching operation are addressed in detail. Extensive SPICE simulations are accomplished for validating the analytical model under switching frequency, and duty cycle and phase-shift modulations are contrasted. The model parameters of the coils are obtained applying a nonlinear regression from the experimental data provided by an impedance analyzer. Afterwards, the system feasibility is corroborated using a 2-kW prototype with 97% maximum efficiency under wide load conditions for the aforementioned modulations.

Wireless intravesical device for real-time bladder pressure measurement: Study of consecutive voiding in awake minipigs.

Traditional urodynamics have poor correlation with urological symptoms. Ambulatory urodynamics may improve this correlation but the need for a transurethral catheter and the time-consuming nature of this examination limits its use. Therefore, the objective of this study was to develop a wireless real-time bladder pressure measurement device for repeated and prolonged-term measurement of bladder behavior in awake pigs. The Bladder Pill is an intravesical device with a pressure microsensor and a 3-dimensional inductive coupling coil for energy supply. A corresponding external coil provides wireless power transmission and real-time communication of bladder pressure data. To test the correlation between the pressure data measured by the device and by standard methods, we compared static water column pressures with this device and water-filled urodynamic catheter systems. In vivo assessment of awake voiding by the pill was done by introducing the bladder pill into the bladder of Göttingen minipigs. An air-charged urodynamic catheter was introduced transurethrally as control for pressure measurements. The optimal physical configuration of the pill was investigated to maximize the containment in the bladder. We used two versions of external signal receivers (one waistband and one rectangular frame) to test the optimal external signal capture. Next to that, we performed short-term and medium-term comparative pressure studies. The in vitro static pressure measurement demonstrated a mean difference of less than 1 cm H2O between the methods. The optimal design of the pill for maximal retainment in the bladder proved to be a pigtail configuration. The bending of the device during bladder contractions caused offset of 2.7 +/- 1.4 cm H2O (mean +/- SD) on the pressure measurements. The rectangular frame performed signal capture during 5 consecutive voids with a good correlation of the pressure measurements. The device can be inserted through the urethra and is retrieved using string or endoscopic extraction. In conclusion, wireless long-term measurement of bladder pressure is demonstrated and yields comparable results to current available catheter methods of measurement in a pig model.