Wireless Power Transmission System Makes Sound Visible
Through wireless power transmission using sound, the Hirose-Tanikawa Group from the University of Tokyo are making sound beam routes visible.
This system uses a parametric speaker, which creates a narrow sound beam using ultrasound. The sound from the speaker is converted to electric power, which is used to light up LEDs.
"This speaker itself is a commercially available model, so it doesn't have much to do with our research. What we're researching is the design of the circuit that converts the sound from the speaker to electric power. This circuit doesn't have batteries; it consists of just the microphone and the board behind."
The output power is 10 mW at 50 cm, and 1 mW at 5 meters. So the system can deliver enough power to light up an LED 5 metres away.
"The method we're suggesting is to put a lot of these in a space like this, and supply enough power to light up LEDs in the space."
As sound waves can be easily reflected by any material, the transmission can be interrupted, rerouted, or broadened, and the effect of this and resulting level of power transmission can easily be seen with this system.
"Most conventional methods for wireless power supply use EM waves. For example, Suica and PASMO near field communication cards use RFID. Because EM waves aren't visible, Suica users can't detect where the power is being transmitted from. So it's necessary to indicate where you should touch a ticket gate, with a green light or an angle. But with this method for wireless power supply using sound, parametric speakers can be installed on the ceiling, so when you enter an area where sound is audible, you know that's the area where power is available. We think power supply using sound could be used to achieve a system that's very easy to understand."