Inexpensive wireless device harnesses "lost" energy from microwave signals

Our local environment is full of invisible and until now, unusable, energy in the form of microwaves and WiFi signals, but most of it is lost to us.

But a new type of power-harvesting device developed at Duke University has been able to capture and convert microwave signals into usable direct current that could charge small electronic devices.

Researchers at Duke's Pratt School of Engineering have configured a wireless power-harvesting device made with inexpensive materials to be able to recapture some of this 'lost' energy and turn it into a viable power source for gadgets. The new device uses a series of conductors connected together on a circuit board, and can put out about 7.3V of electrical energy (compare with a small USB charger with a 5V output).

According to Duke, this wireless energy-harvesting device has an efficiency "similar to that of modern solar panels".

“We were aiming for the highest energy efficiency we could achieve. We had been getting energy efficiency around 6 to 10 percent, but with this design we were able to dramatically improve energy conversion to 37 percent, which is comparable to what is achieved in solar cells." - Allen Hawkes, Duke undergraduate engineering student

Possible uses for the technology could include a coating applied to the ceiling of a room that could recover the lost energy in the omnipresent WiFi signals in our modern buildings, or used to improve appliance energy efficiency by capturing and recovering the power currently lost during their operation.

“It’s possible to use this design for a lot of different frequencies and types of energy, including vibration and sound energy harvesting. Until now, a lot of work with metamaterials has been theoretical. We are showing that with a little work, these materials can be useful for consumer applications." - Alexander Katko, Duke graduate student

Additional future uses for the device could include the integration of the metamaterial into cellphones, which would allow it to recharge wirelessly when not being used, or to power remote sensors in the field by capturing the signals from passing satellites.