Noriaki Oodachi

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 method to improve the correlation coefficient and the mutual coupling for diversity antenna

Wireless LAN systems employ diversity antennas to reduce the effects of multipath fading. When several antennas are provided in close proximity, the radiation patterns becomes similar to one another and the diversity gain decreases. Moreover, the radiation efficiency decreases due to mutual coupling between antennas. In order to increase the diversity gain, a method to improve the correlation coefficient among the antenna elements by mutual coupling between antenna elements has been reported (Sawaya, K. et al., 1982). However, this leaves the problem of a decrease in the radiation efficiency caused by mutual coupling. The paper proposes a new method to improve the correlation and the mutual coupling between antennas simultaneously. A slit is provided on a finite ground plane with antennas. The slit changes the current distribution on the ground plane. This change of current distribution causes differences between antennas in the radiation pattern and a pattern diversity effect is achieved. This diversity effect improves the correlation coefficient without applying mutual coupling. Additionally, by changing the current distribution, the mutual coupling is improved and the radiation efficiency increases under low correlation conditions.

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.

Modified beamspace adaptive array employing eigenvector beams

This paper proposes a modified interference signal suppression algorithm for beamspace adaptive array antenna when the SIR is low. Notably, the algorithm does not require the arrival angle of the desired signal. The proposed algorithm utilizes the two outputs of the eigenvector beamspace adaptive array (EBAA). The combined weights for the proposed algorithm have been properly obtained under the typical severe condition.

Broadband folded notch antenna with a parasitic notch

This paper proposes a new broadband folded notch antenna with a parasitic notch on a rectangular conductive board. The parasitic notch can provide current distribution on a folded notch antenna similar to current distribution on an axially symmetric self-complementary antenna, which has an extremely broadband characteristic. In the simulation, frequency bandwidth of the folded notch antenna is increased by 1.5 times by the use of the parasitic notch.