A Japanese research team developed the "wireless power transmission method using two parallel wire lines," which can wirelessly supply electricity to a moving device, electric vehicle (EV), etc.
The research team consists of a laboratory headed by Minoru Okada, professor at Nara Institute of Science and Technology (NAIST), Graduate School of Information Science, and Daihen Corp.
The method is a kind of wire line-type wireless power transmission technology based on the magnetic resonance method. But it does not lay out many power transmission coils as power transmission devices and uses two parallel conductive lines. The ends of the lines can either be connected or unconnected.
This method realizes wireless power transmission capability because the research team found matching conditions under which impedance matching can be achieved for the entire system including load when a power reception coil approaches. Specifically, it proved that the parallel wire lines and the equivalent circuits of the antenna on the power reception side and load at the time of magnetic coupling are equivalent to a high-pass filter (HPF) having a specific impedance.
The HPF works as an impedance converter that matches the impedances of power supply and load.
The impedance matching conditions for a system with a power receiving device moving above the wire lines depend on the position of the power reception coil in addition to the diameter of and distance between the lines. Therefore, the research team expects to actively match the impedance of the system by using a matching box embedded in the power supply.
We interviewed Takeshi Higashino, associate professor at NAIST, who found the matching conditions, etc, on the potential of the new wireless power transmission system.
Q: Why did you develop the power transmission device?
Higashino: Conventional line-type wireless power transmission systems that lay out coils for power transmission are vulnerable to position aberration. So, we considered solving the problem by using parallel wire lines. Currently, they produce the standing wave of current density, and their "belly" and "knot" have different amplitudes, meaning different transmittable power. But we consider that this issue can be solved by, for example, making improvements to the shape of the wire lines.
Q: There have already been several line-type wireless power transmission technologies. How is your technology different from them?
Higashino: While a research group headed by Takashi Ohira, professor at the Department of Electrical and Electronic Information Engineering, Toyohashi University of Technology, uses electric field coupling (See related article), our technology uses magnetic coupling.
Wireless power transmission technologies using magnetic coupling are also being developed by a research group led by Toshio Ishizaki, professor at the Department of Electronics and Informatics, Ryukoku University, and Ryutech Corp, respectively. But the designs of their power transmission antennas are different from that of ours. And they use traveling waves, not standing waves.
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