2 Conductive Lines Fuction as Wireless Power Transmission Device (page 2)

Jan 7, 2014
Tetsuo Nozawa, Nikkei Electronics

Q: How much power transmission efficiency does your technology realize?

Higashino: When we prototyped a toy rail, it was possible to transmit 40W of electricity with an efficiency of a few percent or higher. However, we did not control the impedance of the power reception coil. In theory, if the impedance of the power reception coil is controlled, the efficiency can be improved up to about 85%, even in consideration of the loss caused by the electrical resistance of the wire line and eddy current. Without the loss, the theoretical efficiency is 100%.

The position aberration of the power reception coil in the transverse direction can be tolerated up to about 2cm when the distance between the lines is 4cm.

Q: What did you use for the power supply? Does the power transmission efficiency include the efficiency of the power supply?

Higashino: The power transmission efficiency does not include the efficiency of the power supply. At this point, we use a 50Ω power supply (such as a class A device), and the efficiency of the power supply is 50% or lower. This is because we are currently focusing on the improvement of the efficiency of the wireless transmission part.

Q: How about the frequency?

Higashino: With the prototype and in a theoretical calculation, it was 13.56MHz. Basically, we expect it to range from several megahertz to several tens of megahertz. With a low frequency, a large power reception coil is required. But with a high frequency, a different issue arises.

Q: What kinds of applications do you expect?

Higashino: We expect that the parallel wire lines will be installed on a sidewalk along a roadway to charge EVs, electric busses and bicycles, pedestrians' smartphones and so forth. It is possible that our first goal will be to supply electricity to industrial robots at manufacturing plants.

Daihen, which cooperates with us in the development, has excellent impedance control technologies and was responsible for the development of the matching box. We are considering having a field test with a large-scale system in the near future.