Kenichiro Ogawa

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 study of efficiency improvement of wireless power transfer by impedance matching

In wireless electric power transmission employing magnetic resonant coils, objects or debris in the vicinity of the coil cause impedance mismatching. The mismatching will decrease the transmission efficiency at the frequency for performing electric power transmission. We have investigated the efficiency improvement by impedance matching adjustment using variable lumped capacitors. In the present work, a loop is employed to excite the resonance coil, and a set of variable capacitors are added to the loop on the power transmission side to adjust the matching. For the test against a small object, a small aluminum plate was put close to the transmission coil, and the input impedance of the coil on the transmission side was adjusted by the variable capacitors. The test measurement showed that the adjustment of the input impedance substantially improved the efficiency at the power transfer frequency.

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.

Wireless power transfer system minimizing an influence of a desk

A wireless power transfer system using both a resonant coil and a loop element has been reported. In this report, both a transmitter and a receiver are composed of a resonant coil and a loop element. In another report, only a loop element is employed for a receiver, and the configuration of the receiver is simplified. If there is a mutual coupling between the resonant coil and a surrounding object, a resonant frequency of the resonant coil is shifted. In particular, when a material of the surrounding object is a metal, the resonant frequency of the resonant coil is shifted significantly. When a frequency of the transmitter is restricted in narrowband, the transfer efficiency of the system becomes small. For example, when the transmitter of a wireless power transfer system for a mobile terminal is put on a steel desk, the transfer efficiency of the system becomes small. In this paper, a wireless power transfer system is proposed to minimize the influence of the desk. A transmitter of the proposed system is put on the desk. A receiver of the proposed system is put on the transmitter. Exploiting its thinness, a receiver of the proposed system is installed in a mobile terminal. The effectiveness of the proposed system is confirmed by the measurement data.