Ambient backscatter: Energy for electronic devices – no wires, no batteries, no solar

Ambient backscatter devices
Ambient Backscatter devices (prototype)…..Credit: University of Washington

It’s true. There is now a way to power electronic devices without plugging them into the electrical grid (no wires), without solar panels, and without installing a battery. Engineers at the University of Washington (Seattle, USA) created a new wireless communication system that can interact with each other, powered by the energy they can absorb from (leach or more accurately piggyback on) the constant flow of TV, cellphone, and other radio frequency (RF) signals that surround us.

The researchers call it ambient backscatter. This means the devices – receiver and transmitter – pick up existing transmissions, typically TV because they tend to be high energy, and after inserting their own information into the signal, redirect or reflect it to another similar device. The antennas in the prototype devices (see picture above) currently tune to UHF TV signals (539 MHz in this case). On-board electronics uses the ambient energy and re-broadcasts it as its own signal. As one of the researchers put it, “We can repurpose wireless signals that are already around us into both a source of power and a communications medium.” Who said there is no free lunch?

Presumably, those who supply the energy, mostly commercial enterprises, have no complaint, since they simply broadcast into the ether and the new technique does nothing to disrupt or steal the content of the transmissions – it only piggybacks on the energy of the broadcast. (And yes, the researchers considered this potential problem and tested their devices for interference, but found the power levels are so low that even within 8 inches of a TV or radio, they have no effect.)

Of course, there are important limitations. The amount of energy available from a broadcast is very small; consequently, re-transmission has even less energy, which limits the range and speed of transmission. The current devices can operate up to 6 or 7 miles from a source (e.g. a TV tower) and transmission rates up to 1 kilobit per second when the devices are less than a meter (2.5 feet) apart. This means, to be effective, the devices must be linked into a very short range network. Still, the number of potential applications could be enormous – all the way from a communications network built into clothing to the most sophisticated and insidious spy sensor network. The main point is that such networks draw no detectable power, don’t have batteries to recharge or replace, and don’t need the sun or any unreliable energy source to operate. Theoretically, such networks could operate without the need for maintenance for years.

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