Infrared 'rectenna' generates electrical power from waste heat

July 09, 2018 // By Rich Pell
Infrared 'rectenna' generates electrical power from waste heat
Researchers at Sandia National Laboratories (Albuquerque, NM) have developed a small silicon-based device that can convert waste heat into direct current (DC) power.

Called a rectenna - short for "rectifying antenna" - the device is made of common aluminum, silicon, and silicon dioxide (or glass) using standard processes from the semiconductor integrated circuit (IC) industry. The device has no moving parts, and uses direct conversion of infrared (IR) radiation to generate power.

"We have developed a new method for essentially recovering energy from waste heat," says Paul Davids, a physicist and the principal investigator for the study. "Car engines produce a lot of heat and that heat is just waste, right? So imagine if you could convert that engine heat into electrical power for a hybrid car. This is the first step in that direction, but much more work needs to be done."

In the short term, say the researchers, they are looking to make a compact infrared power supply - perhaps to replace radioisotope thermoelectric generators (RTGs), which are used for application such as powering sensors for space missions that don’t get enough direct sunlight to power solar panels.

The infrared rectenna developed by the researchers is about 1/8 x 1/8 inch, and metallically shiny with an aluminum top and silicon bottom. Its aluminum top is etched with stripes roughly 20 times smaller than the width of a human hair - a pattern too small to be seen by eye, but which serves as an antenna to catch infrared radiation.

Between the device's aluminum top and silicon bottom is a very thin layer - about 20 silicon atoms thick, or 16,000 times thinner than a human hair - of silicon dioxide. The patterned and etched aluminum antenna channels the infrared radiation into this thin layer.

The infrared radiation trapped in the silicon dioxide creates very fast electrical oscillations - about 50 trillion times a second - which pushes electrons back and forth between the aluminum and the silicon in an asymmetric manner. This process, called rectification, generates net direct electrical current .

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