Akiyoshi Uchida

A numerical study of power loss factors in resonant magnetic coupling

We numerically studied the affect of power loss factors in a wireless power transfer system using resonant magnetic coupling. Resonant magnetic coupling is regarded as one of the most promising methods for mid-range wireless charging systems. To make this method practical, it is important to accurately estimate power transfer efficiency and effect of each loss factor in the device-designing stage. We conducted a numerical simulation using an equivalent circuit model and electromagnetic analysis for a mobile-device model. Resonance at 7 MHz between the transmitting and receiving coils was achieved using lumped capacitors attached at the coil ends. In addition to the skin effect, we consider various loss factors such as proximity effect, loss tangent of lumped capacitors, and so on. The results show that the proximity effect significantly decreases the power transfer efficiency of the system, and the loss tangent of lamped capacitor also decreases it by a few percentage points.

Phase and intensity control of multiple coil currents in resonant magnetic coupling

We studied the effects of the phase and intensity of multiple coil currents in a wireless power transfer system using resonant magnetic coupling. Resonant magnetic coupling is regarded as one of the most promising methods for mid-range wireless charging systems. For mid-range charging, the charging device can assume various positions and postures, and some of the conditions make wireless charging difficult. To solve this problem, we propose a method to control the phase and intensity of multiple coil currents. By performing numerical simulations using an equivalent circuit model and electromagnetic analysis, we confirmed that it had the desired effect.

Transfer efficiency control using switching devices in resonant magnetic coupling

The resonant magnetic coupling (RMC) method has advantageous features for mid-range wireless power charging. However, if a receiver is moved closer to a transceiver as transmission output remains fixed, excessive power is supplied to a load, which may cause considerable damage to the receiving device. In this paper, we propose a new efficiency control technique using nonlinear devices. Two switches with diodes are connected to the resonant capacitance in parallel and are turned on/off alternately at the transmission frequency. With this technique, receiving power control can be achieved without any communication between the transceiver and the receiver.

Power distribution control using switching devices for multiple charging system in resonant magnetic coupling

The resonant magnetic coupling (RMC) method has gained tremendous attention for its prospective features such as a large charging range or multiple device charging (multi-charging) application. In multi-charging systems, however, the receiving power ratio among the receivers is determined by coupling coefficient (k) or quality (Q) factor of each resonant coil. Therefore, it is difficult to supply appropriate power from single transmitter to plural receivers at the same time in various situations. To solve this problem, we apply a new efficiency control technique using non-linear devices. Two switches are connected to the resonant capacitance of receiving resonant coil in parallel and are turned on/off alternately at the transmission frequency. With this technique, receiving power ratio among the receivers can be controlled over a wide range at high efficiency.

Effect of load dependence of efficiency in a multi-receiver WPT system

Most batteries require constant voltage to charge; therefore, wireless charging receivers need a constant voltage circuit, commonly a DCDC converter (DDC). On the other hand, Resonant Magnetic Coupling enables multi-receiver charging. As a result, we need to design a wireless charging system for multi-receivers with a DDC. In cases of multi-receiver charging with different positions, the input voltage for a DDC in the stronger coupling receiver rises. Since there is a practical limit of DDC input voltage, we need to design the wireless charging system, not to exceed the limit. Through our work, we investigated the character of the load dependence of efficiency, and made clear that robustness to load variation determines the DDC input voltage by simulation and experiment. In conclusion, efficiency robustness to load variation is advantageous for single receivers, but not for multi-receivers in different coupling conditions.

Development of Signal Interpolated Phase Timing Recovery System for High Density Magneto-Optical Disks

We developed a new timing recovery system for magneto-optical disks (MO) with a higher recording density and higher transfer rate but it is difficult to achieve these without signal to noise ratio (SNR) degradation in the MO readout signal. Therefore, for signal processing, we have developed a turbo code technology, [rf1] which can obtain a high enough coding gain. However, as optimal phase to obtain the optimum performance of the turbo code must be detected, we developed a very precise phase timing recovery system that works under a degraded SNR in the MO readout signal. Moreover, as the turbo code is a kind of block code, which requires decoding by a turbo block unit, we also developed a system for detecting the start point for turbo decoding. We developed a new timing recovery system and, in this paper, we report architecture and performance evaluations of this system.

Read Channel with Turbo Decoding for Magneto-Optical Disks

Achieving high-density magneto-optical (MO) recording and a high transfer rate without degrading the signal-to-noise ratio (SNR) is not an easy task. Nonetheless, this is what we set out to do when we began developing a practical turbo decoding hardware description language (HDL) module for the MO read channel. To develop this module, we used a pipelined process to enable on-the-fly data reading, we optimized the system parameters, and we developed a time-sharing architecture to reduce the amount of required hardware. We tested the module using an HDL module simulator and an actual MO readout signal, and found that the SNR was improved by 3 dB compared to that required for partial response maximum likelihood (PRML) decoding.

Read channel with turbo decoding for magneto-optical disks

Blue lasers are indispensable for high-density recording on magneto-optical (MO) disks. Since the sensitivity of photodetectors decreases for blue laser light, it becomes difficult to obtain a sufficient signal-to-noise ration (SNR) for the MO readout signal. Turbo codes can provide a significant coding gain for both optical disks and magnetic disks. In this study, we used computer simulation to investigate the performance of turbo decoding for MO disks. We then develop a Verilog-HDL module based on our simulation results. The performance of turbo decoding was confirmed experimentally by evaluating the bit error rate for real MO readout signals as compared with the partial response maximum-likelihood (PRML).