At the moment, Powercast has two chips: One works best at close range and puts out up to 4.2 volts of continuous electricity for directly powering a very low-power device or charging a battery. The other can be used at longer distances from the transmitter to create an intermittent pulse of up to 5.25 volts for directly powering a low-power device.
These chips can grab small amounts of usable power -- from microwatts to low milliwatts -- out of thin air. That's not enough to run an MP3 player or phone, but it is sufficient for a device that uses very little power, like a Kindle e-book reader, according to Ostaffe.
Rather than developing systems for consumer electronics products, however, Powercast focuses on powering the various sensors that monitor our world, from temperature and pressure sensors in oil refineries to smoke alarms in homes and offices. The typical office today might have a door-position sensor that's part of its security system, a smoke detector, and a motion sensor to turn off the lights if nobody's in the room -- all of which could be powered wirelessly with Powercast's technology.
The company's goal is to eventually develop technology that can extract usable amounts of power from ambient sources such as Wi-Fi signals. But for now its system needs a transmitter to work, which means it's subject to range limitations, Ostaffe says.
"Our biggest enemy is the inverse square law," he jokes. This fundamental law of physics describes how energy radiating outward from a point source -- such as light or in this case radio waves -- is dissipated over distance. The energy available for the receiver falls off very quickly the farther you get from the transmitter.
"Right now, our usable range is about 40 to 45 feet," he says. That's long enough to cover part of a house or a few offices in a building. The typical office facility would probably need 10 or 15 transmitters per 40,000 square feet of floor space, set up around the building's periphery with antennas aimed toward the center.
NIST's Seiler agrees that RF-to-DC power has potential for certain kinds of devices. "It's promising but is limited by range and the amount of power an RF wave can hold. But it could power many smaller devices," he says.
Beam forming: The ability of a wireless communication device to adjust its antenna parameters and tailor its signal directly at the receiver for greater speed and reliability.
Electroencephalography (EEG): The monitoring of the electrical activity of the brain with several electrodes placed on the scalp.
Functional magnetic resonance imaging (fMRI): An offshoot of magnetic resonance imaging, this technology can pinpoint areas of the brain that are being used during an activity.