Hiroki Kudo

Efficiency improvement of wireless power transfer via magnetic resonance using transmission coil array

The transfer efficiency between a transmission coil and a reception coil for wireless power transfer via magnetic resonance is a function of the orientation between the coils. When two coils share a single axis, the transfer efficiency is maximal, but otherwise the efficiency becomes lower. In this paper, a wireless power transfer system via magnetic resonance using a transmission coil array is proposed to improve the transfer efficiency. The transmission coils of the array are excited with appropriate phase weights by transmission circuit, according to the orientation among the transmission coils and the receiving coil. The effect of the proposed system is confirmed by simulation by a method of moment and measurement using a vector network analyzer.

A voltage ratio-based efficiency control method for 3 kW wireless power transmission

This paper presents a novel control method for wireless power transmission (WPT). The proposed method can maximize the power efficiency only by controlling the voltage ratio between the primary and the secondary side. Experimental measurement results of the prototype system with 3 kW power transmission show the efficiency difference between the proposed control method and the available maximum value is less than 0.3 % even with a large variation of coil-to-coil distance and load voltage. The automatic controller for the proposed method provides the load-following operation, maintaining both constant power and high efficiency, using a WLAN connection.

Detection of a metal obstacle in wireless power transfer via magnetic resonance

Wireless power transfer via magnetic resonance is a technique to realize higher transmission efficiency over a distance of several meters. However, if there are obstacles to the transmission coil, it is difficult to maintain high transmission efficiency. This is caused by variation of matching frequency for the transmission coil brought about by a metal obstacle. This paper evaluates the effect of the transmission performance via magnetic resonance for wireless power transfer when metal obstacles approach the transmission coil. In addition, this paper proposes a procedure for detecting metal obstacles via magnetic resonance.

Caching mechanisms towards single-level storage systems for Internet of Things

Internet of Things (IoT) involves coping with enormous number of distributed devices. This paper introduces three pieces of caching technology as steps towards single-level storage systems that can host and map numerous IoT devices on a single vast address space: 1) a caching mechanism for making solid-state storage appear as huge main memory, 2) speeding up access to resource-limited IoT devices by caching the address translation table of solid-state storage chips, and 3) ad hoc device-to-device data relay, which can be used as effective network caching for mapping IoT devices.