At CES 2009 I’ve seen some great product announcements and news on the showroom floor. But, some of the more interesting news is coming from behind closed doors after the show floor clears out. For example, I had the opportunity to hear about PowerBeams’ infrared power transmission system. The Powermitter can be used to deliver power to a system without the need for wires (see photo). It uses IR laser diodes to transmit power at distances up to 100 m. And Longer ranges are possible. It can send small amounts of power—from under 1 Watt to a kilowatt—the power density remains the same, but the beam area increases with the power requirement.
The Powmitter contains off-the-shelf IR laser diodes. Multiple diodes are used when more power is required. The Powceiver uses a custom diode chip array about 3.5 mm2 that generates up to 2.5 W at 6 V. Optical power density ranges from 1- to 8-mW/mm2. The photodiodes convert at 33% to 42% efficiency. For example, a 1,000-mm2 beam at 6 mW/mm2 and 33% efficiency supplies 2 W to the load. Multiple chips can be used at the receiving end as well. At the gross level, the IR power is sent from the Powmitter to the Powceiver. Line of sight is required and head on alignment is best but off angle alignment is possible. A range of optics including mirrors and prisms can be used depending upon the system requirements.
The more interesting part of this technology is related to its feedback control. This allows safe maximum power transmission. The Powmitter stops sending IR heat to the Powceiver if the beams are interrupted as when a hand is waved in front of the receiver. This trick is handled by a VGA camera in the Powmitter that detects an IR sensitive pattern around the periphery of the receiver. Power is turned off if the pattern is obscured. This means the power will be off before the obstruction hits the central part where the power beam is located. A microcontroller on the Powceiver tracks power reception and feeds back the status via an LED that the Powmitter can detect.
Systems where the beam may be interrupted will typically be built with a battery or capacitor to handle power requirements when the beam is interrupted. There are a host of applications that can benefit from remote power such as wireless speakers. Even powerful speakers typically have an average power requirement that is significantly less than its peak performance. For example, a 25-W speaker normally requires less than 4 W on average. Likewise, a system that is used only six hours a day can run with a system that delivers less than 1 W of power to charge the battery.