New Wireless Power Transmission Method Improves Efficiency of Entire System

Dec 4, 2012
Hiroki Yomogida, Nikkei Electronics
This was prototyped to demonstrate the "direct-current resonance method." Electricity is transmitted between the coils to power the LEDs.
This was prototyped to demonstrate the "direct-current resonance method." Electricity is transmitted between the coils to power the LEDs.
[ If it clicks, the expanded picture will open ]

Murata Manufacturing Co Ltd developed a wireless power transmission technology that drastically improves the power transmission efficiency (power efficiency) of an entire system.

The technology realizes a power efficiency (from a direct-current voltage to a load via a wireless zone) 20 to 30 points higher than traditional technologies. For example, when a power of about 75W is directly supplied from a direct current power source to a load several tens of centimeters away, it is possible to transmit power with a power efficiency of 70% or higher.

With traditional systems using high-frequency alternating currents, a large power loss occurs when a direct-current voltage is converted into a high-frequency alternating current. As a result, the power efficiency of an entire system becomes 15-30%. Murata expects that the new technology will be used for various applications including miniature electronic circuits, mobile devices and electric vehicles (EVs).

Murata calls the technology "direct-current resonance method." The concept of transmitting power by using an electromagnetic field resonance between opposed coils is similar to methods that other companies propose. The difference is that the new method directly transmits power by using a direct-current voltage instead of using a high-frequency alternating-current source.

With the traditional methods, a high-frequency alternating-current source such as a 50Ω type is made by using a power source to transmit power to a coil. In this case, a large power loss occurs at the time of converting to a high-frequency alternating current. Also, another large power loss is caused by a matching circuit used for the matching of a resonance circuit

The new method directly generates an electromagnetic field that changes at resonant frequencies by using a direct voltage and a switching technology and connects a power transmission circuit to a power reception circuit. Its switching frequency is about 10MHz.

Because the new technology eliminates the need for a circuit that converters to a high-frequency alternating current and a matching circuit, the power efficiency of an entire system can be drastically increased, Murata said.

However, this technology requires a field effect transistor (FET) that can deal with a certain degree of power and operate at high speeds as a switching device. The performances of GaN semiconductor and other power semiconductors functioning as switching devices are improving, and they can now be used for the new technology, the company said.