Resonant Coils Research Articles

3D‐spatial efficiency optimisation of MR‐WPT using a reconfigurable resonator‐array for laptop applications

In this study, magnetic resonant wireless power transfer (MR-WPT) system with a reconfigurable resonator using RF switches (PIN diodes) was studied to improve and optimise the transfer efficiency (TE) in a limited three-dimensional (3D) zone for laptop applications. Generally, the TE of the MR-WPT system is decreased by a 3D spatial variation (distance and location) in between the transmitter (Tx) source and the receiver (Rx) load . To improve and optimise the TE for this spatial variation, the authors utilised RF switches in a planar arrayed coils in the Rx. The TE was optimised by the status of the coil resonator (modes 1-6, open, and short) in the Rx. The average TE of the optimal mode increased >5% comparing with that of a certain mode in the whole range of the spatial variation ( x , y , z directions; 80 × 80 × 40 cm 3 ). In addition, they analytically and experimentally demonstrated the TE optimisation by the practical laptop model with the proposed MR-WPT system installed into a desk ( yz -plane) and the wall ( z -direction). Through this research, the proposed reconfigurable resonator with RF switches was shown to be possible for use as a reconfigurable efficiency optimiser in the MR-WPT system.

Radiofrequency magnetic resonance coils and communication antennas: Simulation and design strategies

Coils simulation and design is a fundamental task to maximize Signal-to-Noise Ratio in Magnetic Resonance applications. In the meantime, in the last years the issue of accurate communication antennas analysis has grown. Coil design techniques take advantage of computer simulations in dependence on the magnetic field wavelength and coil sizes. In particular, since at high frequencies coils start to behave as antennas, modern Magnetic Resonance coil development exploits numerical methods typically employed for antennas simulation.This paper reviews coil and antenna performance parameters and focuses on the different simulation approaches in dependence on the near/far field zones and operating frequency.

Transfer Efficiency and Cooling Cost by Thermal Loss based on Nitrogen Evaporation Method for Superconducting MAGLEV System

This paper presents the feasibility of technical fusion between wireless power transfer (WPT) and superconducting technology to improve the transfer efficiency and evaluate operating costs such as refrigerant consumption. Generally, in WPT technology, the various copper wires have been adopted. From this reason, the transfer efficiency is limited since the copper wires of Q value are intrinsically critical point. On the other hand, as superconducting wires keep larger current density and relatively higher Q value, the superconducting resonance coil can be expected as a reasonable option to deliver large transfer power as well as improve the transfer ratio since it exchanges energy at a much higher rate and keeps stronger magnetic fields out. However, since superconducting wires should be cooled indispensably, the cooling cost of consumed refrigerant for resonance HTS wires should be estimated. In this study, the transmission ratios using HTS resonance receiver (Rx) coil and various cooled and noncooled copper resonance Rx coils were presented under non cooled copper antenna within input power of 200 W of 370 kHz respectively. In addition, authors evaluated cooling cost of liquid nitrogen for HTS resonance coil and various cooled copper resonance coils based on nitrogen evaporation method.

Assembly and performance of a 6.4T cryogen-free dynamic nuclear polarization system.

We report on the assembly and performance evaluation of a 180-GHz/6.4T dynamic nuclear polarization (DNP) system based on a cryogen-free superconducting magnet. The DNP system utilizes a variable-field superconducting magnet that can be ramped up to 9T and equipped with cryocoolers that can cool the sample space with the DNP assembly down to 1.8K via the Joule-Thomson effect. A homebuilt DNP probe insert with top-tuned nuclear magnetic resonance coil and microwave port was incorporated into the sample space in which the effective sample temperature is approximately 1.9K when a 180-GHz microwave source is on during DNP operation. 13 C DNP of [1-13 C] acetate samples doped with trityl OX063 and 4-oxo-TEMPO in this system have resulted in solid-state 13 C polarization levels of 58±3% and 18±2%, respectively. The relatively high 13 C polarization levels achieved in this work have demonstrated that the use of a cryogen-free superconducting magnet for 13 C DNP is feasible and in fact, relatively efficient-a major leap to offset the high cost of liquid helium consumption in DNP experiments.

Conceptual Design and Operating Characteristics of Multi-Resonance Antennas in the Wireless Power Charging System for Superconducting MAGLEV Train

Recently super high-speed magnetic levitation (MAGLEV) using high-temperature superconducting (HTS) magnet has been expected as next-generation transportation since superconducting magnet can keep mighty levitation force. The superconducting magnet at MAGLEV train should be continually charged with high power in order to keep stronger and stable levitation force. Practically, since conventional power supply unit should be attached to HTS magnet in the MAGLEV, a large thermal loss is indispensably caused by power transfer wires and joints, those have been one of essential obstacles in the superconducting MAGLEV train. As the wireless power transfer (WPT) technology based on strongly resonance-coupled method realizes large power charging without any wires through the air, there are advantages compared with the wired counterparts, such as convenient, safety, and fearless transmission of power. From this reason, the WPT systems have started to be applied to the wireless charging for various power applications, such as transportations (train, underwater ship, electric vehicle). However, it has obstacles to commercialize, such as delivery distance and efficiency. To solve the problems, authors proposed the technical fusion using HTS resonance coil in the WPT system since the superconducting wire has merits a larger current density and higher Q -value than normal conducting wire. In this study, authors described the conceptual design of HTS receiver (Rx) coil with multi-copper antenna (Tx) coils. The priority characteristics of moving HTS receivers under multi-copper Tx coils are compared with and various copper Rx coils with radio frequency power of 370 kHz below 300 W.

Modeling of Dense Windings for Resonant Wireless Power Transfer by an Integral Equation Formulation

A full-wave integral equation scheme for modeling resonant coils applied in wireless power transfer systems is presented. An A - Φ formulation is applied with current and charge densities on the wire surface as unknowns. The method overcomes the limitation of the “thin-wire approximation” as it enables the unknowns to vary on the wire surface. Thus, proximity effects (that typically emerge when modeling dense windings) are taken into account. The numerical implementation of the formulation has smaller computation cost than, for example, finite element methods. The proposed scheme is tested against closed-form solutions and alternative simulations.

All-optical tunable delay line based on nonlinearities in a chalcogenide microfiber coil resonator

We propose an all-optical tunable delay line based on nonlinear effects in a two-turn chalcogenide microfiber coil resonator (MCR). Continuous rotation of light due to coupling between the two uniform MCR turns at the resonance induces a time delay. Using numerical simulation, we show the possibility of designing a continuously tunable all-optical and real-time delay line, taking advantage of the high Kerr nonlinear effect in a chalcogenide glass-based MCR. The threshold power for making the Kerr nonlinearity in the chalcogenide sulfide glass (Ge20Ga5Sb10S65, also known as 2S2G) MCR is less than 0.1 W. By selecting an appropriate pump power, one can adjust the time delay in the proposed MCR delay line as desired. Results of numerical simulations show that the time delay in an appropriately designed two-turn MCR can be tuned in the range of 24–147 ps with a bandwidth of ∼4.1 GHz. Pulse broadening and distortion related to group velocity dispersion (GVD) and the self-phase modulation (SPM) effect of the proposed microfiber coil delay line (MCDL) are also studied.

Inductively coupled small self resonant coil (SSRC) reader antennas for HF RFID applications

A new model of inductively coupled high frequency radio frequency identification (HF RFID) reader antennas is presented in this paper based on the idea of using the self resonance frequency (SRF) of a small multi turn coil. The introduced multi turn small self resonant coil (MT SSRC) antenna is mathematically analyzed in terms of SRF, number of turns, dimensions and dielectric characteristics of the insulation, where present. Based on the analysis, a compact planar version of MT SSRC antennas having two turns, the two turn planar SSRC (TTP SSRC), is investigated and the dependency of the SRF to the antenna dimension is observed. A TTP SSRC antenna operating at 13.56MHz is fabricated and is compared with an old model of HF RFID antennas; an optimized Q factor and a more uniform near field pattern is obtained for the new antenna. The benefits of the obtained optimized Q factor and uniform near pattern is explained for smart shelf application. Also, a number of TTP SSRC antennas operating at a distinct frequency, 13.56MHz here, are fabricated on different substrates and it is shown that the Q factor and dimension of the TTP SSRC antenna could be controlled and adjusted based on the dielectric characteristics of the substrate. The new antenna prototype has a beneficial application to smart shelf applications in HF RFID.

Excitation of piezoelectric device through resonant helical coil antenna-like structure

A resonant helical coil antenna-like structure has been explored for wireless excitation of piezoelectric devices. The basic idea behind this wireless excitation of piezoelectric device is electromagnetic resonance along with piezoelectric resonance. The analytical studies reveal that the maximum excitation occurs in the piezoelectric device when the operating frequency of the system coincides with its mechanical resonant frequency. It has been seen that the intensity of piezoelectric stimulation depends on the frequency of operation, air gap, relative position, electric load, and the generated electric field strength by the helical coil antenna-like structure. The analytical results are verified with the measured experimental results, and are found to be in well agreement. By adopting this proposed wireless excitation system the free actuation of the piezoelectric devices can be enabled as opposed to the confined motion for various potential applications.

A Magnetic Tank System for Wireless Power Transfer

This letter presents a tank system for wireless power transfer with magnetically coupled resonance. It contains two interconnected transmitting resonant coils placed perpendicular to each other and forms a magnetic resonant tank. Due to the combined effects of these two transmitting coils, there will always be magnetic flux that goes through the receiver regardless of axial misalignment between the transmitter and the receiver. The transfer efficiency thus improves and becomes less sensitive to axial misalignment than the conventional system. A prototype is fabricated on FR4 printed circuit boards and tested. Both the simulation and test results show that the proposed system can enhance power transfer performances over a relatively good distance and a large range of misalignment angles. The receiver is functional even when it is perpendicular to the transmitter. Therefore, the proposed system can serve as a good candidate for applications such as wireless power supply to underwater motors.

Wireless power transfer inspired by the modern trends in electromagnetics

Since the beginning of the 20th century, researchers have been looking for an effective way to transfer power without wired connections, but the wireless power transfer technology started to attract extensive interest from the industry side only in 2007 when the first smartphone was released and a consumer electronics revolution was triggered. Currently, the modern technology of wireless power transfer already has a rich research and development history as well as outstanding advances in commercialization. This review is focused on the description of distinctive implementations of this technology inspired by the modern trends in electrodynamics. We compare the performances of the power transfer systems based on three kinds of resonators, i.e., metallic coil resonators, dielectric resonators, and cavity mode resonators. We argue that metamaterials and meta-atoms are powerful tools to improve the functionalities and to obtain novel properties of the systems. We review different approaches to enhance the functionality of the wireless power transfer systems including control of the power transfer path and increase of the operation range and efficiency. Various applications of wireless power transfer are discussed and currently available standards are reviewed.

Design of rotating resonant magnetic perturbation coil system in the STOR-M tokamak

The interaction between resonant magnetic perturbations (RMP) and plasma is an active topic in fusion energy research. RMP involves the use of radial magnetic fields generated by external coils installed on a tokamak device. The resonant interaction between the plasma and the RMP field has many favorable effects such as suppression of instabilities and, under certain conditions, improvement of discharge parameters in tokamaks. The RMP technique has been successfully implemented in the STOR-M tokamak. A set of (m=2, n=1) helical coils carrying a current pulse was used to study the effects of RMP on magnetic islands, plasma rotation, and other edge plasma parameters. A new RMP system is being developed for the STOR-M tokamak. The system consists of a number of external saddle coils distributed in the poloidal and toroidal directions and powered by AC power supplies to generate a rotating RMP field. Numerical simulations have been carried out to calculate several parameters for the new RMP system such as the magnetic field and the dominant modes generated by the coils. The dominant mode generated by the new RMP coil system may be tuned to (2, 1) with significant contributions from (2, 3) and (2, 5) modes.

Flexible Induction Heating Using Magnetic Resonant Coupling

This paper proposes and implements the concept of flexible induction heating based on the magnetic resonant coupling (MRC) mechanism. In conventional induction heating systems, the variation of the relative position between the heater and workpiece significantly deteriorates the heating performance. In particular, the heating effect dramatically reduces with the increase of vertical displacement or horizontal misalignment. This paper utilizes the MRC mechanism to effectuate flexible induction heating; thus, handling the requirements of varying vertical displacement and horizontal misalignment for various cooking styles. Differing from a conventional induction heating, the proposed induction heating adopts one resonant coil in the heater and one resonant coil in the workpiece, which can significantly strengthen the coupling effect, and, hence, the heating effect. Both the simulation and experimental results are given to validate the feasibility and flexibility of the proposed induction heating.

Improvement of Transmission Distance by Using Ferrite in Superconductive Wireless Power Transfer

The wireless power transfer (WPT) characteristics between the transmitter and receiver coils according to the existence of ferrite were analyzed in this study to improve the transmission distance of superconductor resonance coils. To set the optimal reflection coefficient, the thickness increased by 1 mm, from 0 to 10 mm. It was found that the transfer efficiency improved with the lowest reflection coefficient at the thickness of 2 mm. The 2-mm-thick ferrite was applied to the transmitter coil, and the reflection coefficient was measured by the distance. As a result, the transfer efficiency with ferrite was highest at the distance of 2500 mm. Also, it was confirmed that the WPT characteristics were improved up to 500 mm by the application of ferrite. It is believed when the superconductive WPT system is organized using such advantageous ferrite, its transmission distance and efficiency improvement can be secured.

Design Methodology of a Printed WPT System for HF-Band Mid-Range Applications Considering Human Safety Regulations

A methodology for the design of printed magnetically coupled resonant wireless power-transfer (WPT) systems is proposed. The design methodology aims at a well-matched system with a maximized power-transfer efficiency for mid-range applications. The system consists of two identical resonant coils driven by high-quality factor loops. The proposed design criteria allows obtaining maximum achievable transfer efficiency and impedance matching at any defined distance without any external matching circuits connected to the driven loops. For validation purposes, a printed WPT system at 10 MHz is fabricated targeting 1-m distance between the transmitting and receiving sides. Its performances in terms of reflection and transmission coefficients, as well as in terms of generated electric and magnetic fields, have been characterized numerically and experimentally. The impact of human body presence on the system has also been investigated observing the splitting in two frequencies of the common resonant frequency of the coils. A dosimetric study has been conducted using a detailed high-resolution anatomical human body model and considering E 99 , J 1 cm 2 , and specific absorption rate (SAR) (local and whole body averaged SAR) as exposure metrics. It has been observed that peak exposure levels appear in different tissues depending on the body location. Compliance with the international commission on nonionizing radiation protection (ICNIRP) reference level as well as basic restrictions has been studied followed by computing the maximum allowable input power. It has been found that, with the body located 1 m away from the transmitting coil, the maximum allowable input power satisfying E 99 is in the order of MW, whereas it reduces to tens of kilowatt when considering SAR and J1 cm 2 . The latter has been noticed to be the most restrictive dosimetric quantity.

Characteristic comparison of different resonators to extend transfer distance in superconducting wireless power transfer for electric vehicle using high temperature superconducting resonance coil

AbstractThis paper presents the feasibility of technical fusion between wireless power transfer (WPT) based on resonance coupling system and superconducting technology to improve the transfer efficiency and spread the electromagnetic field widely in spite of small size coils. Until now, the various copper wires have generally been adopted in WPT system. From this reason, the transfer efficiency is limited since the copper wire keeps low Q intrinsically. On the other hand, as superconducting wires keep larger current density and higher Q value, the superconducting resonance coil can be expected as a reasonable option to deliver large transfer power as well as improve the transfer ratio since it exchanges energy at a much higher rate and keeps stronger magnetic fields out. In this study, we examined the transmission ratio using HTS and cooper wires in the antenna (Tx) or/and receiver (Rx) within input power of 500 W under various performances; copper Tx to copper Rx, HTS Tx to copper Rx, copper Tx to HTS Rx...

A Planar L-Shape Transmitter for a Wireless Power Transfer System

This letter presents a new planar L-shape transmitter for a magnetically coupled resonance wireless power transfer system. In it, a second transmitting resonant coil is added in the L-shape position to further improve the power transfer performance and to mitigate the adverse close-distance frequency splitting effects; it does not occupy space or block the path in between the transmitter and the receiver. A prototype is fabricated and tested. Both the simulation and test results show that the proposed system can significantly improve the power transfer performance over a relatively good distance with the maximum efficiency of 81.38% and the figure of merit of 0.97. In the overcoupled region, the power transfer efficiency maintains 75.02%, indicating the significant mitigation of the adverse frequency splitting effects. As a result, the proposed system is a good candidate for practical wireless power transfer applications.

Design of Maximum Efficiency Tracking Control Scheme for Closed-Loop Wireless Power Charging System Employing Series Resonant Tank

This paper presents a maximum efficiency tracking control scheme for a closed-loop wireless power charging (WPC) system for wireless charging of mobile devices. Generally, wireless charging systems need a precise output voltage and current with the highest possible efficiency. In an open-loop system, output voltage and efficiency depend strongly on the coupling coefficient and load condition. Alternatively, a closed-loop WPC system has a constant output voltage against coupling and load variations. Many studies have been carried out regarding closed-loop systems. However, those previous studies have the drawback of efficiency degradation. In this paper, we propose a maximum efficiency tracking control scheme to achieve the highest possible efficiency. Therefore, the proposed WPC system satisfies both the requirements of a constant output voltage and high efficiency. The proposed control scheme determines the current of the transmitter based on the data received by the receiver via Bluetooth. For validation, the proposed WPC system was implemented at 6.78 MHz using loosely coupled series–series resonant coils, and we verified that the proposed system can track the maximum efficiency while maintaining a constant output voltage.

Local measure of the electromagnetic field in magnetic resonance coils: How do simulations help to disentangle the contributions of the electric and magnetic fields?

The development of probes for Nuclear Magnetic Resonance (NMR) spectroscopy of metabolites, biomolecules or materials requires the accurate determination of the radio-frequency (RF) magnetic field strength, B1, at the position of the sample since this RF-field strength is related to the signal sensitivity and the excitation bandwidth. The Ball Shift (BS) technique is a commonly employed test bench method to measure the B1 value. Nevertheless, the influence of the RF electric field, E1, on BS is often overlooked. Herein, we derive, from Maxwell equations, an analytical expression of the BS, which shows the contribution of both the electric and magnetic energies to the BS value. This equation shows that the BS allows quantifying the B1 field strength only in regions where the electric energy is small with respect to the magnetic one. The numerical simulations of electromagnetic (EM) field and energy prove that this condition is fulfilled at 100.5MHz inside the electrically balanced coil of a double-resonance 1H/X 4mm Magic Angle Spinning (MAS) probe since for that circuit, the center of the coil is an antinode for the B1 standing wave and a node for the E1 one. We also show that the simulated BS values agree well with the experimental ones. Conversely, NMR experiments show that the contribution of the electric energy to BS becomes significant when the X channel of this probe is connected to a frequency splitter. In that case, the use of BS method to estimate the B1 value is compromised.

Time-Domain Analysis of Wireless Power Transfer System Behavior Based on Coupled-Mode Theory

In this paper, coupled-mode theory (CMT) is used to obtain a transient solution analytically for a wireless power transfer system (WPTS) when unit energy is applied to one of two resonators. The solutions are compared with those obtained using equivalent circuit-based analysis. The time-domain CMT is accurate only when resonant coils are weakly coupled and have large quality factors, and the reason for this inaccuracy is outlined. Even though the time-domain CMT solution does not describe the WPTS behavior precisely, it is accurate enough to allow for an understanding of the mechanism of energy exchange between two resonators qualitatively. Based on the time-domain CMT solution, the critical coupling coefficient is derived and a criterion is suggested for distinguishing inductive coupling and magnetic resonance coupling of the WPTS.