Resonant Wireless Power Transfer Research Articles

高速スイッチング技術を利用した磁界共振型非接触給電の低次高調波における漏洩磁界低減

高速スイッチング技術を利用した磁界共振型非接触給電の低次高調波における漏洩磁界低減

New Magnetic Coupling Pad with Circular Geometry for Wireless Power Transfer Applications

In Resonant Inductive wireless power transfer systems (RIPT), the magnetic coupler plays a fundamental role. That assists in passing of power without wires. In wireless power transfer systems (WPT), couplers are designed to achieve various parameters such as power transfer efficiency, high power density, transferrable distance, and tolerant towards misalignment. In addition, minimizing leakage flux, low weight, less cost, and space occupied. To achieve these parameters, researchers proposed different types of coils with different shapes. Those circular coils are more popular due to their unique features. Compared to other coils, these coils lack in power transfer distance. In this paper, a distinct magnetic coupler with circular geometry proposed to preserve some extent of its features. In proposed, a circular quadrature coil added with two circular coils shaped to the circular coil. Proposed topology analyzed using ANSYS Maxwell Finite Element Analysis 3D simulation and compared with different combinations chosen better performing combination.

Performance Evaluation of Silicon and GaN Switches for a Small Wireless Power Transfer System

In the last few years, the wide diffusion of rechargeable devices has fueled the research interest in wireless power transfer (WPT) technology that offers advantages such as safety, flexibility, and ease of use. Different standards have been developed over the years but a significant part of the global interest is focused on the inductive resonant wireless power transfer. By increasing the resonance frequency, an improvement in the transfer efficiency between transmit and receive coils is generally observed, at the expense, however, of an increase in losses in the switching devices that constitute the transmitting and receiving circuits. This study concerned the performance evaluation of a WPT transmitting circuit built using Gallium Nitride (GaN) or conventional silicon (Si) switching devices, to assess their specific contribution to the overall efficiency of the system. The overall performance of two circuits, respectively based on GaN HEMTs and Si MOSFETs, were compared at frequencies of the order of MHz under different operating conditions. The theory and design choices regarding the WPT circuit, the coils, and the resonant network are also discussed. The comparison shows that the GaN circuit typically performs better than the Si one, but a clear advantage of the GaN solution cannot be established under all operating conditions.

Open-channel microfluidics via resonant wireless power transfer

Open-channel microfluidics enables precise positioning and confinement of liquid volume to interface with tightly integrated optics, sensors, and circuit elements. Active actuation via electric fields can offer a reduced footprint compared to passive microfluidic ensembles and removes the burden of intricate mechanical assembly of enclosed systems. Typical systems actuate via manipulating surface wettability (i.e., electrowetting), which can render low-voltage but forfeits open-microchannel confinement. The dielectric polarization force is an alternative which can generate open liquid microchannels (sub-100 µm) but requires large operating voltages (50–200 VRMS) and low conductivity solutions. Here we show actuation of microchannels as narrow as 1 µm using voltages as low as 0.5 VRMS for both deionized water and physiological buffer. This was achieved using resonant, nanoscale focusing of radio frequency power and an electrode geometry designed to abate surface tension. We demonstrate practical fluidic applications including open mixing, lateral-flow protein labeling, filtration, and viral transport for infrared biosensing—known to suffer strong absorption losses from enclosed channel material and water. This tube-free system is coupled with resonant wireless power transfer to remove all obstructing hardware — ideal for high-numerical-aperture microscopy. Wireless, smartphone-driven fluidics is presented to fully showcase the practical application of this technology.

Analysis of Symmetric Two and Four-coil Magnetic Resonant Coupling Wireless Power Transfer

This study examined the efficiency of power transfer for two-coil and four-coil spiral magnetic resonant coupling wireless power transfer (WPT) using distance to coil diameter (D/dm) ratio and reflection coefficient, S21 value. Adding resonators reduced the total resistance in the two-coil WPT system while increasing the S21 values of the whole system. A same-size spiral coil was proposed for the system and simulated using computer simulation technology (CST). A prototype with similar specifications for a four-coil design was implemented for verification. The proposed method yielded an optimal efficiency of 76.3% in the four-coil system, while the two-coil WPT yielded a 23.2% efficiency with a 1.33 D/dm ratio.

Compensation Optimization of the Relay Coil in a Strong Coupled Coaxial Three-Coil Wireless Power Transfer System

With regards to wireless power transfer (WPT) systems with relay coils, the power transfer distance, efficiency, and capacity can be effectively improved by tuning the relative position of the relay coil compared with a common two-coil WPT system. However, the cross-coupling between nonadjacent coils can cause the system to no longer resonate even when the compensation capacitors resonant with the corresponding coils. This will cause an increase in reactive power and additional losses in the coils. In this article, the optimal operating conditions of the coaxial fully resonant three-coil WPT system are analyzed first for achieving higher efficiency compared with the two-coil WPT system with the same load and the same power transfer distance, by adjusting the relative location of the source coil and relay coil. An optimization design method for further improving the efficiency of the three-coil WPT system by tuning the compensation capacitor of the relay coil is proposed subsequently. The experimental results show that for a given load (10 Ω in this article), the efficiency of the three-coil WPT system can be improved from 88.8% to 92.3% compared with the two-coil WPT system, and be further improved to 93.3% when the relay compensation capacitor is optimized.

Planar Omnidirectional Wireless Power Transfer System Based on Novel Metasurface

In this article, we propose a novel metasurface-basedmagnetic coupling resonant wireless power transfer (MCR-WPT) system to realize planar omnidirectional WPT at a mid-range distance. The resonator devices—dielectric-constant disks or planar helixes—are located on both sides of the metasurface, which comprises conducting wires placed in a planar sunburst pattern. Transmission efficiency of >40% is achieved on a circular plane with a diameter of ∼40 cm. In addition, the transfer efficiency is insensitive to the placement of a human hand near the proposed MCR-WPT system. The maximum permissible input powers for the coil and dielectric resonator versions of the proposed MCR-WPT system are 0.83 and 2.56 W, respectively, in compliance with the limit prescribed in the International Commission of Non-Ionizing Radiation Protection guidelines. The proposed design may help realize many potential WPT applications, especially for the desktop wireless charging of household devices, such as mobile phones, tablets, and LED desk lamps.

A Systematic Design Method for a Wireless Power Transfer System Based on Filter Theory

One of the major considerations for a short- or intermediate-distance wireless power transfer (WPT) system is its robustness against variations of the distance, displacement, misalignment between the transmitting and receiving coils, and variations of the loads. Designing such a robust system has not been easy since most methods require some forms of trial-and-errors or optimization that present different degrees of uncertainty. In this article, we propose a design method to overcome the above issue: we make the power transfer efficiency (PTE) function of the WPT equivalent to that of a modified filter. Then, we apply a well-established filter theory to develop a systematic WPT design method; it can keep the PTE stable within the specified ranges of the distance changes, displacements, misalignments, and load variations. We take the Chebyshev filter as an example to verify the proposed method and build and test the prototype. Experiments show that when distance and misalignments occur, the prototype can maintain the efficiency of around 90% with less than 5% in variations as predicted by the theoretical design. In comparison, the conventional magnetically coupled resonant WPT system can only maintain the efficiency of 82% with more than 20% in variations. Therefore, the proposed design method presents a new efficient and optimized way to develop a robust WPT system for practical applications.

Fully Implantable Neural Stimulator with Variable Parameters

Neural implantable systems have promoted the development of neurosurgery research and clinical practice. However, traditional tethered neural implants use physical wires for power supply and signal transmission, which have many restrictions on implant targets. Therefore, untethered, wireless, and controllable neural stimulation has always been widely recognized as the engineering goal of neural implants. In this paper, magnetically coupled resonant wireless power transfer (MCR-WPT) technology is adopted to design and manufacture a wireless stimulator for the electrical stimulation experiment of nerve repair. In the process of device development, SCM technology, signal modulation, demodulation, wireless power supply, and integration/packaging are used. Through experimental tests, the stimulator can output single-phase pulse signals with a variable frequency of (1–20 Hz), a duty cycle of (1–50%), and voltage. The average power is approximately 25 mW. The minimum pulse width of the signal is 200 μs and the effective distance of transmission is 1–4 cm. The stimulator can perform low-frequency, safe and controllable wireless stimulation.

Radially Periodic Metasurface Lenses for Magnetic Field Collimation in Resonant Wireless Power Transfer Applications

In this paper, a new procedure and topology of magnetic metasurface lens are proposed for improving the performance of Resonant Wireless Power Transfer systems. Firstly, three subwave-length unit cells are optimized in order to get negative magnetic permeability in the same frequency, each one with a different refractive index, and they are experimentally characterized. Then, the Transformation Optics technique is applied in order to find the unit cell arrangements which lead to the magnetic field focusing in a given direction. For this purpose, two coordinate transformations are proposed, and the effective electric permittivity and permeability that generate these profiles are calculated. It is shown from simulations and measurements that the refractive index gradient produced by the radial disposition of the unit cells can lead to a magnetic field manipulation similar to the optical converging and diverging lenses. Both metamaterials lenses are built, and the calculation of the magnetic flux density as a function of the measured induced voltage in a probe coil verifies their effects on the magnetic field. Finally, their performance in a resonant wireless power transfer system is tested, and improvements in terms of efficiency and range are presented. The proposed design method and the lenses that were developed demonstrate that metasurface lenses can improve efficiency without reducing the range, once these lenses are positioned close to the transmitter coil. Besides that, this method can reduce the losses due to misalignment between coils once the field can be collimated in a specific direction.

Novel compact coupled resonator wireless power transfer system at 1 GHz using nested open loop ring resonators

In this work, the wireless power transfer system employing nested open loop ring resonators at the ground plane is proposed. In the suggested design both the transmitter and the receiver are symmetric. The forward-facing view contains the transmission line. The ground plane contains number of 33 open loop ring resonators which are nested together. The system has a size of 40 × 40 mm2 with a transmission distance of 15 mm. The proposed design is investigated in two cases with and without the loading capacitor. Comparisons between the resonance frequency and the power transfer efficiency of the proposed design with and without the loading capacitor are presented. The coupled resonator system achieved an efficiency of 97% at 1.35 GHz while the system with the loading capacitor achieved an efficiency of 98.8% at 1 GHz. The proposed system is designed, simulated, and measured.

Research on Dual-LCC MCRWPT system based on controlled rectifier

Among many types of Wireless Power Transfer (WPT) technology, Magnetically Coupled Resonance Wireless Power Transfer (MCRWPT) technology has been studied more and more due to its stable transmission Power and strong anti-interference ability. In this paper, the operating characteristics of the Dual-LCC MCRWPT system based on the secondary side controlled rectifier are analyzed, and the variation of the system current with D, the phase relationship between the input voltage and current of the resonant network, the phase relationship between the output voltage and current of the resonant network, and the variation of the input and output load of the system are studied in depth. Through the simulation analysis of inverter MOSFET switching state, verify the effectiveness of the controlled rectifier control mode and the rationality of theoretical analysis, provide a solid theoretical basis for the optimization of the controlled rectifier control mode.

Genetic-Algorithm-Based Optimization of a 3D Transmitting Coil Design with a Homogeneous Magnetic Field Distribution in a WPT System

In magnetically coupled resonant wireless power transfer (MCR-WPT) systems, the nonhomogeneous magnetic field of the transmitting coil can lead to frequency splitting phenomena and lower efficiency. In this paper, a 3D transmitting coil (TX) with a homogeneous magnetic field distribution is proposed. The proposed coil structure consists of two layers with different numbers of turns per layer, i.e., with different current distributions. To achieve a homogeneous magnetic field distribution with a high magnetic field value and a low profile of the 3D coil structure, the optimal layer placement and current distribution were optimized using a genetic algorithm (GA). The prototype of the optimized coil was fabricated, and its magnetic field distribution was measured. The measurement results agreed more than 95% with the simulation results. The measured homogeneous area was at least 12.5% larger than reported in the literature. By using a different current distribution, the profile of the 3D coil structure was successfully reduced by 29% and the average magnetic field value was increased by 25% compared to our previous work.

Metamaterials for Improving Efficiency of Magnetic Resonant Wireless Power Transfer Applications

In this article, we investigate a compact metamaterial structure for enhancing a magnetic resonant wireless power transfer (WPT) system operated at 6.5 MHz. A thin magnetic metamaterial (MM) slab placed between the transmitter (Tx) and receiver (Rx) coil can improve WPT efficiency. The metamaterial unit cell is designed by a ten-turn spiral resonator (10T-SR) loaded with an external capacitor. The resonant frequency of MM unit cells can be easily controlled by changing the capacitor value. By using the optimization approach, we achieve a significant WPT efficiency improvement at a mid-range distance. The results showed an enhancement of the magnetic field in the WPT system when MM slab was present. This demonstrates the ability to amplify the evanescent wave of MM slab, thereby improving the WPT efficiency. The transmission coefficients of WPT system at 60 cm increased from 0.5 to 0.76 with MM slab, which corresponds to a 46% improvement.

Wireless power transfer system with enhanced efficiency by using frequency reconfigurable metamaterial

The wireless power transfer (WPT) system has been widely used in various fields such as household appliances, electric vehicle charging and sensor applications. A frequency reconfigurable magnetic resonant coupling wireless power transfer (MRCWPT) system with dynamically enhanced efficiency by using the frequency reconfigurable metamaterial is proposed in this paper. The reconfigurability is achieved by adjusting the capacitance value of the adjustable capacitor connected in the coil of the system. Finite element simulation results have shown that the frequency reconfigurable electromagnetic metamaterial can manipulate the direction of the electromagnetic field of the system due to its abnormal effective permeability. The ultra-thin frequency reconfigurable metamaterial is designed at different working frequencies of 14.1 MHz, 15 MHz, 16.2 MHz, 17.5 MHz, 19.3 MHz, 21.7 MHz and 25 MHz to enhance the magnetic field and power transfer efficiency (PTE) of the system. Frequency reconfigurable mechanism of the system with the frequency reconfigurable metamaterial is derived by the equivalent circuit theory. Finally, further measurement which verifies the simulation by reasonable agreement is carried out. PTE of the system by adding the metamaterial are 59%, 73%, 67%, 66%, 65%, 60% and 58% at different working frequencies. PTE of the system with and without the metamaterial is 72% and 49% at the distance of 120 mm and the frequency of 15 MHz, respectively.

Comparison and selection strategy of compensating topologies in two coil resonant wireless power transfer system

In this study comparisons of different compensation topologies are investigated for two coil resonant wireless power transfer systems. Compensation circuits are examined individually according to system parameters such as efficiency, equivalent impedance, frequency, load resistance, and phase angle. This paper aims to compares the system variables in order to address the constraints in the system applicability regarding the compensation topology selection in Wireless Power Transfer (WPT) systems. Topology selection schemes related to circuit parameters are given. The main motivation of this study is that it presents a suitable topology selection scheme and flow diagram according to applications with various voltages, currents, power and loads. Simulations performed for four main topologies under various load conditions concludes that choosing the proper compensation topology for appropriate load is essential. Simulation studies are carried out with the Simulink software. The results obtained from here are validated with both Matlab calculation codes and C # calculation codes. The analyses according to the frequency in various load conditions have shown that variation of efficiency depends on the compensation topology of the receiver side. Moreover, in this study, it has been revealed that the topology of the transmitter side only affects the equivalent impedance together with the amount of power drawn from the input hence it has no effect on the efficiency and load characteristics. Consequently in the case of working with low load resistance such as an electric vehicle or mobile phone charging, topologies with series compensation on the receiver side can be preferred. Correlatively, topologies with parallel compensation on the receiver side can be evaluated as suitable for high load resistance, low current, and low power operations such as biomedical appliance charging.

Geometry-Based Circuit Modeling of Quasi-Static Cavity Resonators for Wireless Power Transfer

Geometry-Based Circuit Modeling of Quasi-Static Cavity Resonators for Wireless Power Transfer

Optimization of Low-Frequency Magnetic Metamaterials for Efficiency Improvement in Magnetically Coupled Resonant Wireless Power Transfer Systems

With the extensive applications of magnetically coupled resonant wireless power transfer (WPT), improving the power transfer efficiency (PTE) of WPT systems is critical. Magnetic metamaterials (MTMs) can effectively improve the PTE. However, currently the design of MTMs is mainly based on microwave or optical theory, and their applicability in low-frequency WPT systems needs to be further explored. In this paper, a fast and effective method for the design and optimization of low-frequency MTM is provided. Firstly, based on circuit theory and mutual inductance calculation, the PTE of WPT systems is concluded in an equation that concerns the position of a 2-D MTM slab and added compensation capacitance of MTM unit coils. Two WPT systems with large differences in coil size of the transmitter (Tx) and receiver (Rx) or the same size are considered, and a directly separating variables method is proposed to optimize the MTM slab position and the compensation capacitance of unit coils to maximize PTE when the MTM slab position changes axially between Tx and Rx. It is found that the optimal MTM slab positions for the two systems are remarkably different, and the PTE impressively presents a capacitance splitting phenomenon with the change of compensation capacitance. Finally, two MTM-enhanced WPT systems are established to verify the theoretical calculation. The experiments show that the maximum PTE is significantly increased by 144% and 31% respectively by adopting optimized compensation capacitance compared with that without MTM for the two systems with different or same transceiver coil size.

Control of the near magnetic field pattern uniformity inside metamaterial-inspired volumetric resonators

In recent years metamaterial-inspired resonators, due to the ability to form desired near field patterns at subwavelength scale, have found application in various practical fields, i.e., magnetic resonance imaging or wireless power transfer. This paper proposes an approach for controlling the near electromagnetic field distribution inside the volumetric metamaterial-inspired structure based on a set of split-ring resonators or materials with high permittivity. We numerically and experimentally demonstrate how to precisely manipulate the near-field pattern’s uniformity by changing the number of resonant elements while maintaining the geometric dimensions of the structure. The effectiveness of the concept was also verified via a magnetic resonance imaging study. The optimized volumetric metamaterial-inspired resonator showed an increase in transmit efficiency and receive performance of the large body coil compared to the commercial dedicated radiofrequency coil.

Effects of Electro-Magnetic Properties of Obstacles in Magnetic Resonant Wireless Power Transfer

Magnetic resonant wireless power transmission (MRWPT) is a method of transmitting power over a long distance at a specific frequency. Because this system uses an alternating magnetic field, if an object with electrical/magnetic properties is placed between the transmit and receive coils, this will have a significant impact on the power transfer. In this paper, the effect of an obstacle located between two coils on the resonance frequency and transmission power is analyzed. A wireless power transmission system with a resonant frequency of 20 kHz was designed, and ferrite, aluminum, and carbon steel were selected as obstacles with permeability or conductivity. After simulating the system with finite element analysis (FEA) with these obstacles, the results were verified through actual experiments. The results show that the permeability of the obstacle decreases the resonant frequency, and the conductivity increases the resonant frequency and greatly reduces the output power. In addition, part of reduced output could be recovered by adjusting the frequency.