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A magnetic resonance wireless power transfer (MR-WPT) system with a reconfigurable planar receiver (Rx) to optimize transfer efficiency (TE) for laptop application has been investigated. The proposed MR-WPT system consists of a general four-coil system: a source coil and a transmitter Tx) coil in a Tx part and an Rx coil and a load coil in an Rx part. To enable performance comparison, the Rx coil uses either a rectangular loop resonator or a slit ground resonator (SGR) and both resonators are connected with a p-i-n diode to reconfigure and optimize the MR-WPT system’s TE along the transfer distance between the Tx and Rx parts. Mobile devices, including laptops, need a ground plane for practical use; therefore, the Rx coil is replaced by only an SGR, which operates as both a resonator and a ground. This letter, experimentally and theoretically proves that a reconfigurable MR-WPT system with an SGR has sufficient efficiency without the ferrite sheet typically used in practical MR-WPT applications.

In this paper, we miniaturized the loop and coil in magnetic resonance wireless power transfer(MR-WPT) system for application to the small mobile device. The proposed disk type double coil resonator was designed to cause resonance at 6.87 MHz. It is composed of thin copper on both-side of acrylic substrate structured 2 mm width, 1 mm pitch and 8 turns. The outer radius of spiral coil pattern is 9 cm. And the proposed loop was made of the copper wire 5 mm diameter of cross-section. The size of loop is 10 cm diameter. For resonance at 6.87 MHz, the capacitor with 3,300 pF was connected in series on the loop. We rearranged the resonators and organized several WPT systems which is rearranged by resonators. The highest transfer efficiency of miniaturized WPT system was 35.67 %. This proposed design of spiral double coil will contribute to make resonator smaller for appling small and thin mobile device.

This paper presents a magnetic resonance wireless power transfer (WPT) system that uses three coils, a planar receiver and operates at 6.78 MHz,. Effective power transfer is ensured by establishing an impedance matching condition for this WPT system. A metamaterial (MTM) array having dimensions of 20 cm Ⅹ 30 cm is also positioned near the load coil to concentrate the magnetic field and enhance the transfer efficiency. The result is a maximal improvement of 27% in the transfer efficiency at a transfer distance of 50 cm. The impact of a ground plane on the transfer efficiency is also examined. By utilizing the MTM array, making slits on the ground plane and increasing the gap between the ground plane and the load coil, it is possible to mitigate this impact. The highest transfer efficiency improvement is about 55% at a distance of 20 cm with the ground plane. A practical laptop model is fabricated to verify the impact of the load coil angle and position on the transfer efficiency. The result shows that the maximum transfer efficiency with the laptop model is 47.58% with the load coil angle of 90 degree.

In this letter, the effect of the human body in a magnetic resonance wireless power transfer (MR-WPT) system for wearable and implantable devices is studied. To implement the experiment, muscle-mimicking liquid is configured with parameters similar to those of the human body. The transmitter part is located outside the human body (in the air), and the receiver part is implanted in the liquid. The proposed 3-coil MR-WPT system, which operates at 6.78 MHz shows effectively higher transfer efficiencies compared with a 4-coil MR-WPT system at near transfer distance which is the predicted position for a pacemaker. The results indicate that the proposed system with optimized receiver using air-pocket has potential applications in off/in-body devices that benefit from remote energy harvesting, especially at near distances such as pacemakers.

In this study, we suggested optimal design of in-body resonator by capacitance and air gap. We proposed magnetic resonance wireless power transfer (MR-WPT) system consisted of three resonators and was therefore called a three-resonator MR-WPT system. The proposed power transfer occurs between a wearable transmitter in the air and an implantable receiver in the fabricated muscle-mimicking liquid. According to the analysis of measurement results, the muscle-mimicking leads blocking on the H-field of MR-WPT system. This phenomenon has an affect the decreasing transfer efficiency that could be explained by the change in resonant frequency of the receiver resonator due to the impact of the dielectric constant and the conductivity of the MML liquid. To solve this problem, we suggested utilizing either an optimal capacitor or an air pocket to prevent the MML liquid from having this effect. These solutions improved the transfer efficiency of the MR-WPT system.

Wireless power transfer (WPT) system has been studied and four-coil WPT is the standard form in indirect-fed magnetic resonance WPT (MR-WPT). In this research, we fabricated small copper coil and transparent electrode coil. The electrode was deposed IZTO/Ag/IZTO as a multilayer film structure. Load loop and source loop were optimized using capacitors. The efficiency was measured in distance from 1 cm to 5 cm. The optimized efficiency of the MR-WPT with capacitance was 81% using a copper coil and 57% using a transparent coil (IZTO/Ag/IZTO) at 1 cm.

In this study, a wireless power transfer (WPT) system including three coils and working at 6.78 MHz is investigated. By employing a 2 × 3 metamaterial (MTM) array, the efficiency of the proposed WPT system is significantly enhanced. Experiments show that with the MTM array, a maximum efficiency improvement of 27 % is achieved at transfer distance of 35 cm. The impact of ground plane on the transfer efficiency is also studied. Several methods to reduce this impact are discussed and measured.

We investigate the indirect-fed magnetic resonant wireless power transfer system by rearranging the loops and coils used in the conventional wireless charging system for mobile devices. Three rearranged configurations (Out-Out, Out-In, In-In) have been considered and experimentally investigated by using hollow pipe copper loops (coils) and wire copper loops (coils). The power transfer efficiencies for the three configurations were similar. The highest measured efficiency of 82.5% was achieved at 35 cm distance between the Tx and Rx coils. We also investigated the practical application of the mobile device (note-pc), by rotating load loops and the Rx coil vertically, L-shape. The highest efficiency of the L-shape system, was 64.5 % at 45 cm distance between the Tx and Rx coils.