Masakazu Taguchi

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.

Partial-response maximum-likelihood channel for mark edge recording on magneto-optical disks

We have developed a partial-response maximum-likelihood (PRML) read channel for mark edge recording on magneto-optical disks. In this paper, we report the results of a computer simulation and an actual experiment using this method and compare them with those of a conventional (level slice [bit-by-bit]) detection method in a leading/trailing-edge-independent reproduction. The PRML read channel can decrease the error rates of signal detection in terms of two factors (phase margin characteristics and error rate characteristics of the carrier-to-noise ratio [CNR]). We found that the PR(1, 1) ML detection method improved the CNR by 1.7 dB over the conventional detection method. With these improvements, we achieved a 30% phase margin at a density of 0.57 µm/mark ( 0.43 µm/bit). Therefore, we improved the capacity of MO disks using the PRML read channel, which decreased the error rates of signal detection for mark edge recording.

Jitter Characteristics of Mark Edge Recording on MO Disks

Edge shift and jitter characteristics have been examined using both conventional disks and an overwritable disk with three exchange-coupled layers. Edge jitter consists of random jitter, edge shifts dependent on data patterns (thermal interference), and edge shifts independent of data patterns (fluctuations of temperature or light spot control). Write compensation is an effective means of correcting shifts depending on data patterns. The shifts which are independent of data patterns can be rendered negligible in comparison with random jitter by using an edge detection method in which the leading and trailing edges are detected independently. The results were the same for the overwritable disk. The possibility of applying edge recording in magnetooptic disk systems was thus confirmed.

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).

Overwrite characteristics of magneto-optical disks by magnetic field modulation

We have been experimenting with overwriting by magnetic field modulation using flying magnetic heads and single-sided disks. We developed a new protective layer for the disks. This is a spin-coated polymer layer containing α-Fe203 powder. It holds lubricating oil well and increases durability. We obtained good read-write characteristics using the protective layer on a reflective structure disk.