Rx Coil Research Articles

A Quasi-Uniform Magnetic Coupling Array for a Multiload Wireless Power Transfer System with Flexible Configuration Strategies

The coupling problem between the transmitter coils (Tx) and receiving coils (Rx) is influenced by the transmission power and efficiency for a multiload wireless power transfer (WPT) system. In order to solve this problem, a novel array WPT system with quasi-uniform coupling (QC) is proposed in this paper. Owing to the comprehensive design of the Tx and its mutual positional relationship, the proposed system supports simultaneous activation of multiple and even adjacent Tx while maintaining QC. In addition, the structure of Tx is simple and can be obtained with a low-cost optimization procedure, and the compact Rx coil provides sufficient misalignment transmission tolerance for one or two Rx within the Tx and overlapping areas. Furthermore, a parity-time (PT) symmetry-based Rx position detection method is adopted to support flexible unit operation strategies without additional communication procedures. Each Tx unit is equipped with an ingenious dynamic compensation circuit to solve the frequency detuning problem caused by adjacent Tx cross-coupling. Finally, the effectiveness of the design is proved by the prototype; the Tx can provide a QC area that is 1.44 times or 4.44 times the Rx coil area for each receiver in independent and composite modes, and it can match the operation strategy to achieve optimal configuration of the charging area.

Model Decomposition-Based Approach to Optimizing the Efficiency of Wireless Power Transfer Inside a Metal Enclosure

This paper describes a numerically efficient method for optimizing the high power transfer efficiency (PTE) of a resonant cavity-based Wireless Power Transfer (WPT) system for the wireless charging of smart clothing. The WPT system under study unitizes a carbon steel closet intended to store smart clothing overnight as a resonant cavity. The WPT system is designed to operate at 865.5 MHz; however, the operating frequency can be adjusted over a wide range. The main reason behind choosing a resonant cavity-based WPT system is that it has several advantages over the competitive WPT methods. Specifically, in contrast to its Far-field Power Transfer (FPT) and Inductive Power Transfer (IPT) counterparts, resonant cavity-based WPTs do not exhibit path loss and significant PTE sensitivity to the distance between the Tx and Rx coils and misalignment, respectively. The non-uniformity of the fields within the closet is addressed by using an optimized Yagi-like transmitting antenna with an additional element affecting the waveguide mode phases. The changes in the mode phases increase the volume inside the cavity, where the PTE values are higher than 50% (the high PTE region). In the present study, the model decomposition method is adapted to substantially accelerate the process of finding the optimal WPT system parameters. Additionally, the decomposition method explains the mechanism responsible for extending the high PTE region. The generalized scattering matrices are computed using the full-wave simulator Ansys HFSS for three sub-models. Then, the calculated S matrices are combined to evaluate the system’s PTE. The decomposition method is validated against full-wave simulations of the original WPT system’s model for several different parameter value combinations. The simulated results obtained for a sub-optimal model are experimentally verified by measuring the PTE of a real-life closet-based WPT system. The measured and calculated results are found to be in close agreement with the maximum measured PTE, as high as 60%.

Determination and analysis of compensation capacitor for a robust distance-variable wireless power transfer system

Wireless power transfer (WPT) systems have been widely adopted for full autonomy in various fields due to their convenience. However, changes in the air gap between the Tx and Rx coils significantly affect efficiency. To overcome this challenge, this paper introduces the determination of a compensation capacitor for a distance-variable WPT system that is robust in varying air gap conditions. The proposed method was verified using theoretical analysis, simulation, and experimental measurement. The electrical circuit was modeled using a T-equivalent model in a series–series (SS) topology to calculate power transfer efficiency (PTE). Specifically, compensation capacitors were analyzed at distances of 10, 30, and 50 mm, considering different self-inductance values. These results are compared against varying load resistances to demonstrate the effectiveness of the proposed approach. Additionally, the PTE drop ratio was defined to facilitate comparison. The results show that the PTE drop ratio for the compensation capacitor at the farthest distance was consistently smaller than that for the capacitor at the nearest distance under varying air gaps and load resistances. In this research, the difference in the PTE drop ratio between 10 and 50 mm was measured, demonstrating that determining the capacitor at the farthest distance reduces the PTE drop ratio across a range of operational conditions.

A Wireless Miniature Injectable Device with Memory-Assisted Backscatter for Multimodal Animal Physiological Monitoring.

This paper introduces a wirelessly powered multimodal animal physiological monitoring application-specific integrated circuit (ASIC). Fabricated in the 180 nm process, the ASIC can be integrated into an injectable device to monitor subcutaneous body temperature, electrocardiography (ECG), and photoplethysmography (PPG). To minimize the device size, the ASIC employs a miniature receiver (Rx) coil for wireless power receiving and data communication through a single inductive link operating at 13.56 MHz. We propose a folded L-shape Rx coil with improved coupling to the transmitter (Tx) coil, even in the presence of misalignment, and enhanced quality factor. The ASIC functions alternatively between recording and sleeping modes, consuming 2.55 μW on average. For PPG measurements, a reflection-type PPG sensor illuminates an LED with tunable current pulses. A current-input analog frontend (AFE) amplifies the current of a photodiode (PD) with 30.8 pARMS current input-referred noise (IRN). The ECG AFE captures ECG signals with a configurable gain of 45-80 dB. The temperature AFE achieves 0.02 ̊C inaccuracy within a sensing range between 27-47 ̊C. The AFE outputs are sequentially digitized by a 10-bit successive approximation register (SAR) analog-to-digital converter (ADC) with an effective number of bits (ENOB) of 8.79. To improve the reliability of data transmission, we propose a memory-assisted backscatter scheme that stores ADC data in an off-chip memory and transmits it when the coupling condition is stable. This scheme achieves a package loss rate (PLR) lower than 0.2% while allowing 24-hour data storage. The device's functionality has been evaluated by in vivo experiments.

A small-loop double-coil decoupling transient electromagnetic device for high-sensitivity near-surface detection

Small-loop transient electromagnetic (TEM) devices, several meters in size, are increasingly applied to near-surface geophysical exploration in space-limited environments. But the transmitter (TX) coil significantly affects the early time data acquisition of the receiver (RX) coil during current turn-off, resulting in the loss of shallow signals and creating a significant blind zone problem. We report a double-coil decoupling TEM (DCDTEM) device to solve this problem. The novel DCDTEM device ensures a weak primary magnetic flux region between the two coplanar TX coils with the same current direction and different radii. Simulation results indicate that the transmitting field of the DCDTEM device is more focused than the traditional central loop device, ensuring a stronger coupling with the target. The 3D TEM forward-modeling results show that the DCDTEM device has the highest detection sensitivity, together with a relatively high lateral resolution compared with other small-loop TEM devices. We further carry out several physical experiments to test the response characteristics of the DCDTEM device with reference to the offset and the ratio of turns between the TX and RX coils. The experimental results ensure that the position of the zero magnetic flux point can be accurately calibrated and mitigate interference from TX coils. Our DCDTEM device is also applied in a field test on water pipe detection, demonstrating its practicality in near-surface detection.

Multiple-Split Transmitting Coils for Stable Output Power in Wireless Power Transfer System with Variable Airgaps

In this paper, a tunable multi-split transmitting (TX) coil for a wireless power transfer (WPT) system that accommodates a wide range of distances between the TX and receiving (RX) coils is proposed. This method enables the WPT system to maintain a stable and consistent output power supply to the load, regardless of variations in coupling coefficients caused by changes in the distance between the TX and RX coils. The tunable multi-split TX coil can operate in various modes depending on how the wire connections between each TX coil are configured. This approach adjusts the inductance value of the TX coil for different conditions, using the same amount of coil as a conventional single-loop TX coil. The results show that by adjusting the TX coil to three different modes as the airgap varies from 50 mm to 250 mm, consistent output power is achieved with smaller variations in the input current and voltage compared to those in a conventional system. A conventional system requires an input voltage increase of approximately 529.64%, while the proposed system requires only a 42.93% increase. The proposed system enhances the power transfer capacity of the WPT system, particularly when operating in an over-coupling state. This approach provides a stable output power supply with a standardized and simplified TX coil structure.

A Wirelessly Powered Scattered Neural Recording Wearable System.

This paper introduces a wirelessly powered scattered neural recording wearable system that can facilitate continuous, untethered, and long-term electroencephalogram (EEG) recording. The proposed system, including 32 standalone EEG recording devices and a central controller, is incorporated in a wearable form factor. The standalone devices are sparsely distributed on the scalp, allowing for flexible placement and varying quantities to provide extensive spatial coverage and scalability. Each standalone device featuring a low-power EEG recording application-specific integrated circuit (ASIC) wirelessly receives power through a 60 MHz inductive link. The low-power ASIC design (84.6 µW) ensures sufficient wireless power reception through a small receiver (Rx) coil. The 60 MHz inductive link also serves as the data carrier for wireless communication between standalone devices and the central controller, eliminating the need for additional data antennas. All these efforts contribute to the miniaturization of standalone devices with dimensions of 12 × 12 × 5 mm3, enhancing device wearability. The central controller applies the pulse width modulation (PWM) scheme on the 60 MHz carrier, transmitting user commands at 4 Mbps to EEG recording ASICs. The ASIC employs a novel synchronized PWM demodulator to extract user commands, operating signal digitization and data transmission. The analog frontend (AFE) amplifies the EEG signal with a gain of 45 dB and applies band-pass filtering from 0.03 Hz to 400 Hz, with an input-referred noise (IRN) of 3.62 µVRMS. The amplified EEG signal is then digitized by a 10-bit successive approximation register (SAR) analog-to-digital converter (ADC) with a peak signal-to-noise and distortion ratio (SNDR) of 55.4 dB. The resulting EEG data is transmitted to an external software-defined radio (SDR) Rx through load-shift-keying (LSK) backscatter at 3.75 Mbps. The system's functionality is fully evaluated in human experiments.

A birdcage transmit, 24-channel conformal receive array coil for sensitive 31P magnetic resonance spectroscopic imaging of the human brain at 7 T.

Phosphorus (31P) magnetic resonance spectroscopic imaging (MRSI) can serve as a critical tool for more direct quantification of brain energy metabolism, tissue pH, and cell membrane turnover. However, the low concentration of 31P metabolites in biological tissue may result in low signal-to-noise ratio (SNR) in 31P MRS images. In this work, we present an innovative design and construction of a 31P radiofrequency coil for whole-brain MRSI at 7 T. Our coil builds on current literature in ultra-high field 31P coil design and offers complete coverage of the brain, including the cerebellum and brainstem. The coil consists of an actively detunable volume transmit (Tx) resonator and a custom 24-channel receive (Rx) array. The volume Tx resonator is a 16-rung high-pass birdcage coil. The Rx coil consists of a 24-element phased array composed of catered loop shapes and sizes built onto a custom, close-fitting, head-shaped housing. The Rx array was designed to provide complete coverage of the head, while minimizing mutual coupling. The Rx configuration had a mean reflection coefficient better than -20 decibels (dB) when the coil was loaded with a human head. The mean mutual coupling ( ) among Rx elements, when loaded with a human head, was -16 dB. In phantom imaging, the phased array produced a central SNR that was 4.4-fold higher than the corresponding central SNR when operating the 31P birdcage as a transceiver. The peripheral SNR was 12-fold higher when applying the optimized phased array. In vivo 3D 31P MRSI experiments produced high-quality spectra in the cerebrum gray and white matter, as well as in the cerebellum. Characteristic phosphorus metabolites related to adenosine triphosphate metabolism and cell membrane turnover were distinguishable across all brain regions. In summary, our results demonstrate the potential of our novel coil for accurate, whole-brain 31P metabolite quantification.

Realization of an Optimum Load for Wireless Power Transfer System

Wireless power transfer (WPT) system has been an integral part of personal living since its regained interest, especially the magnetic resonance (MR) scheme. MR-WPT scheme suffers, however, change of the coil separation distance and various alignment errors. This paper reports a realization of optimum load for MR-WPT system, which can change the loading impedance accordingly for different coupling coefficients between the Tx and Rx coils. A simple varactor circuit is adopted to realize the optimum load curve. Usefulness of this is demonstrated through both the steady and transient analysis. The proposed realization relies on an open-circuit scheme, and hence it is suitable for scenarios with low-cost and small-size requirements.

Wireless Power Transfer with Magnetic Flux Concentrator and Its Equivalent Circuit

This paper proposes a novel loosely coupled transformer (LCT) with a planar magnetic flux concentrator (MFC) for the wireless power transfer (WPT) in smart grid, which can improve the power of the receiving (Rx) coil. The MFC is a planar copper plate with a radial slit and a center hole, which is made of a printed circuit board (PCB). A simulation model and an experimental platform are built to investigate the performance of the LCT with and without an MFC. The results show that in the case of the transmitting (Tx) side with an MFC, the power of the receiving (Rx) coil increase by 33.82%. Besides, we propose the equivalent T-circuit for the LCT with an MFC.

Maze-Based Scalable Wireless Power Transmission Experimental Arena for Freely Moving Small Animals Applications.

This paper presents an innovative T/Y-maze-based wireless power transmission (WPT) system designed to monitor spatial reference memory and learning behavior in freely moving rats. The system facilitates uninterrupted optical/electrical stimulation and neural recording experiments through the integration of wireless headstages or implants in T/Y maze setups. Utilizing an array of resonators covering the entire underneath of the mazes, the wireless platform ensures scalability with various configurations. The array is designed to ensure a natural localization mechanism to localize the Tx power toward the location of the Rx coil. The system is analyzed and modeled using ANSYS HFSS software to optimize design. The primary goal was to achieve uniform wireless power delivery throughout the mazes through a comparative study of different transmitter (Tx) array configurations, such as float, series, and parallel resonators. The calculated Specific Absorption Rate (SAR) in rat tissue model equals 1.7 W/kg at the power carrier frequency of 13.56 MHz. A prototype of the proposed maze-based WPT design, featuring 8 Tx resonators, a Tx coil and power amplifier, and a headstage power harvesting unit, is successfully implemented and its performance characterized for all three resonator configurations. The implemented T maze-based WPT system has a total length of 128 cm. In the overlapping Tx resonators configuration, a homogeneity of 94% is achieved for the measured power transfer efficiency at over 30%, while continuously delivering over 60 mW for series configuration.

Multifunctional coil technique for alignment-agnostic and Rx coil size-insensitive efficiency enhancement for wireless power transfer applications

This paper presents a multifunctional coil technique to enhance the transfer efficiency of an inductively-coupled wireless power transfer (WPT) system, regardless of the alignment condition and size ratio between the transmitter (Tx) and receiver (Rx) coils. The technique incorporates an auxiliary coil on the Tx side, where current is induced through coupling from the primary coil. Since the Tx coil consists of two coils, transmission to the Rx occurs through the coil with the higher coupling coefficient, determined by the misalignment state. Additionally, by controlling this current using a varactor placed on the auxiliary coil, an optimal magnetic flux is generated based on the alignment condition and/or the size of the Rx coil. In perfect alignment, the auxiliary coil focuses the flux from the Tx to the Rx coil, maximizing transfer efficiency. In misalignment scenarios, the current on the auxiliary coil is adjusted to shift the effective center of the Tx coil, achieving the strongest alignment of the magnetic flux traversing the Rx coil. This adjustment, which can be controlled adaptively based not only on the degree of misalignment but also on the size of the Rx coil, enables virtually null-free operation across varying misalignment conditions and for different Rx sizes. Furthermore, as this multifunctionality of the proposed system is achieved with a minimal number of additional components-just a single auxiliary coil and a single varactor-the impact on the overall quality factor (Q) of the system is minimized, contributing to the higher efficiency. In a size-symmetric system, where the Tx and Rx coils have the same size, the efficiency reaches 98.1% in perfect alignment and remains above 60% with up to 135% misalignment relative to the largest coil dimension. In a size-asymmetric system, with the Rx coil reduced to a quarter of the Tx coil, the efficiency is 96.1% in perfect alignment and remains above 60% up to 95% misalignment. Despite its enhanced practicality through a simple structure featuring only one auxiliary coil and an asymmetric configuration integrated solely on the Tx side, the proposed technique surpasses previous methods by delivering significantly superior performance. Moreover, it demonstrates unprecedented tolerance to both misalignment and smaller Rx coil sizes, which is frequently encountered in practical applications.

Electromagnetic Detection System with Magnetic Dipole Source for Near-Surface Detection.

This paper proposes a nondestructive, separate transmitter-receiver (TX-RX) electromagnetic measurement system for near-surface detection. Different from the traditional dual-coil integrated design, the proposed transient electromagnetic (TEM) system performs shallow subsurface detection using independent TX coil and movable RX coils. This configuration requires a large primary field so that the far-away secondary field is able to generate reliably induced voltages. To achieve this goal, a bipolar current-pulsed power supply (BCPPS) with a late resonant charging strategy is designed to produce a sufficiently large magnetic moment for the exciting coil with low source interference. The magnetic dipole source (MDS) with a large proportion of weight is separated from the field observation device and does not need to be dragged or transported during the detection process. This setup lowers the weight of the scanning device to 3 kg and greatly improves the measurement efficiency. The results of the laboratory test verify the effectiveness of the separate MDS and RX module system. Field experimental detection further demonstrates that the proposed system can realize highly efficient and shallow surface detection within a 200 m range of the MDS device.

Machine Learning Based Foreign Object Detection in Wireless Power Transfer Systems

As power electronics continue to drive advancement in electronic devices by managing the system's energy flow, it is advantageous to examine all areas of energy transfer. Wireless power transfer is one section seeing increased adoption in consumer, industrial, and healthcare applications. This consequently increases the concern for safety, reliability, and efficiency. Power transmission to any unintended load is a primary safety issue in high-power wireless power transfer applications, such as unmanned aircraft systems. Foreign object detection is utilized to selectively transmit power to only the intended target to mitigate this issue. This paper seeks to demonstrate a novel alternative method of using machine learning and artificial intelligence techniques for performing foreign object detection solely on the transmitter portion of the system by only monitoring the TX coil current. This method is first evaluated in SPICE simulation software. Then by transitioning to a closed-loop hardware-based testbed designed to be deployed in unmanned aircraft systems. During the test process for the novel FOD method, the aggregate detection accuracy achieved was 83%, including worst-case misalignment conditions with the RX coil. When the outlying worst-case conditions are excluded, the detection accuracy improves to 97%. To measure the FOD effectiveness in preventing temperature rise in a metallic object, the metallic object was placed at the peak power draw location on the transmitter coil. When the metallic object is left at this location for extended periods, the novel FOD method lowers the maximum temperature reached by 86.8°C when compared to no FOD being active. The primary advantage to this novel method is the simplistic hardware additions, which only require minimal alterations to a WPTS without any FOD implemented. Along with this, implementing this foreign object detection method in the transmitter would mitigate the need for a direct communication link between the receiver and transmitter. As a result, the entire system complexity would decrease, thus increasing the UAS power density while maintaining a safe, effective, and reliable wireless power transmission method.

Experiment and analysis of a high-efficient stacked multi-Tx WPT system with identical Tx currents

Conventional multiple-transmitter (multi-Tx) wireless power transfer (WPT) systems require cumbersome operation in that the Tx currents need to be adjusted to be proportional to the mutual inductance between transmitting and receiving coils for optimal efficiency. In addition, planar-arranged multi-Tx systems can hardly improve the transmission distance even with fine Tx-current control. In this paper, we disclose that when the ratio of the minimum value to the maximum value of mutual inductances between Tx coils and Rx coil is 0.5 or more, multi-Tx WPT systems with identical Tx currents can achieve near-optimal efficiency. That is, under this condition, the WPT system does not need to fine-tune Tx currents. Additionally, we suggest a stacked multi-Tx system with high mutual inductance ratios that satisfies the condition. For validation of the proposed scheme, COTS coils were used to implement the single series coil, and planar multi-Tx systems as well as the stacked multi-Tx system. The experiment confirmed that the stacked multi-Tx WPT system can dramatically improve the critical transmission distance without any tuning of currents or voltages.

Improvement in Power Transmission Efficiency of Wireless Power Transfer System Using Superconducting Intermediate Coil

We have demonstrated that using a high-quality-factor intermediate (IM) coil with a high temperature superconductor (HTS) wire improves the power transmission efficiency (PTE) of a wireless power transfer (WPT) system for long-distance power transmission. The IM coil is placed at the center of Cu transmitting (Tx) and receiving (Rx) coils and consists of a previously developed double-sided HTS coated conductor (CC) wire. A WPT system with the HTS IM coil was designed on the basis of the design theory for a third-order bandpass filter. The measured PTE of the system was compared with that of one with a Cu IM coil. The resonant frequencies of the Tx, Rx, and IM coils in both systems were each about 9 MHz. When the distance between the Tx and Rx coils was 160 cm, the PTEs of the systems were 49.7% and 17.5%, respectively, demonstrating that the PTE of a WPT system can be greatly improved by using an HTS IM coil rather than a Cu one.

Wireless Power Transfer System Using High-Quality Factor Superconducting Transmitting Coil for Biomedical Capsule Endoscopy

We experimentally investigated the power transfer efficiency (PTE) of a wireless power transfer (WPT) system for capsule endoscopy that uses a high-temperature superconducting (HTS) transmitting (Tx) coil and a small Cu receiving (Rx) coil. A high-quality factor Tx coil is needed to maximize the PTE of a WPT system. A previously developed high-quality factor coil using double-sided HTS coated conductor wire was used as the Tx coil to improve the PTE. The diameter of the coil was 235 mm. The Rx coil was φ10 × 20 mm. The measured quality factors of the coils were 13,007 and 105, respectively. That of the Tx coil was about 13 times that of a Cu one. We measured the PTE of the WPT system in the facing direction, axial misalignment, and angular misalignment. The measured PTEs of two systems, one with an HTS Tx coil and one with a Cu Tx coil, in the facing direction at a transfer distance of 15 cm were 48.6% and 15.3%, respectively. The PTE of the system with a HTS Tx coil under axial misalignment, and angular misalignment conditions showed sufficiently high robustness compared with a system with a Cu Tx coil. The measured quality factors of the HTS and Cu Tx coils with a liquid phantom were 1,350 and 382, respectively. That of the Tx coil was about 3.5 times that of the Cu one.

Design and Analysis of Misalignment Insensitive Wireless Power Transfer System Based on Multitransmitter for Constant Power

This paper proposes a multiple transmitting array wireless power transfer (MTA-WPT) system with constant output power charging for consumer electronics, such as tablets and mobile phones. Compared to conventional WPT systems, this proposed system can achieve constant output power by controlling the current phase shift of the transmitting (Tx) coils when the receive (Rx) coil is located at different positions and directions. The detailed circuit topology of the proposed system is modeled and analyzed to obtain the correspondence between the current phase shift and load output power. Furthermore, the excitation current distribution strategies for a system of three and four Tx coils at optimized efficiency are theoretically analyzed. The simulation demonstrates that the proposed system can achieve constant output power with modulating the phase shift at various Rx sites. Finally, an experimental prototype with four Tx coils is designed and carried out to prove the effectiveness of the phase shift modulation method and current distribution strategy. Besides, the superiority of the proposed MTA-WPT system is verified by comparison with other methodologies. The experimental results show that the output power of Rx at different positions is kept at roughly 41W with the transmission efficiency over 80% by the Tx current phase shift modulation.

Reconfigurable PCB Coil Array Loaded With PIN Diodes for Improving Transmission Efficiency in MCR-WPT Systems

In this letter, we propose a reconfigurable coil array by loading PIN diodes to solve the problem of transmission efficiency degradation due to lateral misalignment in magnetically coupled resonant wireless power transfer (MCR-WPT) systems. The reconfiguration of the coil array is achieved by changing the capacitance of the coil array through the ON/OFF of the PIN diodes, thus adjusting the magnitude of the induced current and achieving higher transmission efficiency. By specifying one of the four loaded PIN diodes in the transmitting (Tx) coil array as ON state by the relative position of the receiving (Rx) coil to the Tx coil array, a significant improvement in transmission efficiency with a wider area of strong coupling can be obtained compared to a conventional Tx coil array without loading PIN diodes. This can be used in high efficient multi-coil versus single-coil WPT systems to provide more positioning freedom for Rx coil.

A Study on the Optimal Magnetic Beam Forming of Coil Arrays for Long Distance Wireless Power Transmission.

Multiple-input multiple-output (MIMO) wireless power transfer (WPT) technology which employs multiple transmitter (TX) coils to simultaneously couple power to the receiver (RX) coil has proved to be an effective technique to enhance power transfer efficiency (PTE). Conventional MIMO-WPT systems rely on the phase-calculation method based on the phased-array beam steering concept to constructively combine the magnetic fields induced by the multiple TX coils at the RX coil. However, increasing the number and distance of the TX coils in an attempt to enhance the PTE tends to deteriorate the received signal at the RX coil. In this paper, a phase-calculation method is presented that enhances the PTE of the MIMO-WPT system. The proposed phase-calculation method considers the coupling between the coils and applies the phase and amplitude to calculate the coil control data. From the experimental results, the transfer efficiency is enhanced as a result of the transmission coefficient improvement from a minimum of 2 dB to a maximum of 10 dB for the proposed method as compared to the conventional one. By implementing the proposed phase-control MIMO-WPT, high-efficiency wireless charging is realizable wherever electronic devices are located in a specific space.