Seok Hyon Kang

Magnetic resonance wireless power transfer using three-coil system with single planar receiver for laptop applications

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.

Transparent and Flexible Antenna for Wearable Glasses Applications

This paper aims to design, fabricate, and analyze transparent and flexible monopole antennas for an application in wearable glasses. A multilayer electrode film composed of 100-nm-thick indium-zinc-tin oxide (IZTO)/Ag/IZTO (IAI), a type of transparent conducting oxide electrodes, is selected as the conductors of antennas and ground planes of the wearable glasses. The average transparency of the proposed antennas is measured to be 81.1% in the visible wavelength, and the electrical conductivity of the proposed antennas is measured to be 2 000 000 S/m. The proposed antennas are fabricated with physical vapor deposition process in high vacuum. Moreover, nontransparent antennas made of a 40-nm-thick silver (Ag) thin film are designed and fabricated to compare their performances with the transparent IAI antennas. To reduce the electromagnetic field absorption of the human head, we introduced and analyzed three configurations (types A-C) of monopole antennas having different directions of radiation patterns. The fabricated IAI antennas show the average efficiency of 40% and 4-dBi peak gain at 2.4-2.5 GHz. Furthermore, they have a specific absorption rate lower than 1.6 W/kg, which complies with the Federal Communications Commission standard, when the input power is 15 dBm, which is Google Glasss.

Magnetic Resonant Three-Coil WPT System Between Off/In-Body for Remote Energy Harvest

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.

Analysis of WPT system using rearranged indirect-fed method for mobile applications

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.

Wireless power transfer for mobile devices with consideration of ground effect

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.

Textile Resonators With Thin Copper Wire for Wearable MR-WPT System

This letter presents the comparison of performance of planar textile resonators (PTRs) with various forms of conductive patterns. The conductive materials of the conductive pattern included copper sheet and copper wires of three different thicknesses. The PTRs with thin copper wires were found to be flexible and stable for wearable applications. To verify the performance of PTRs in MR-WPT, a symmetrical four-coil system was measured. This study considered the normal and standard condition of PTRs without any forms of modification in physical. The results showed that thin copper wires, especially of 1.0 mm thickness, had the highest transfer efficiency of 75.66% because the thickness of copper sheet is not sufficient for skin depth and the current was over ampacity of copper sheet.

Transparent electrode resonators for MR-WPT

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.

Wearable and implantable magnetic resonant wireless power transfer

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.