Tiny device could lead to waste heat reuse for space missions and car engines

A device smaller than the nail on your little finger and currently incapable of powering a calculator could one day help power space missions, its creators have claimed.

Based at Sandia National Laboratories in New Mexico, researchers developed the tiny silicon-based device known as the infrared rectenna, which can harness waste heat and turn it into DC power.

Short for rectifying antennas, the devices could utilise waste heat from car engines and reuse the energy. Physicist and principal investigator Paul Davids said they could also eventually replace radioisotope thermoelectric generators (RTGs), which are used for powering sensors on space missions that do not get enough sunlight for solar energy.

“We need to continue to improve in order to be comparable to RTGs, but the rectennas will be useful for any application where you need something to work reliably for a long time and where you can't go in and just change the battery,” said engineer and first author Joshua Shank.

The rectenna uses tiny stripes on a layer of aluminium as an antenna to “catch” infrared radiation from hot sources. The radiation is then “trapped” in an incredibly thin layer of silicon dioxide – only about 20 atoms thick – sandwiched between the aluminium and a silicon layer. The radiation oscillates at about 50 trillion times per second, pushing electrons back and forth between the layers and generating electrical current.

Although the device only generates eight nanowatts of power per square centimetre with radiation from a specialised heat lamp – a typical solar-powered calculator uses five microwatts, meaning it would need a sheet of rectennas larger than a piece of A4 paper to work – its creators said it is “readily scalable”.

Plans for improvements include using a thinner silicon wafer to minimise power loss from resistance and changing the antenna’s pattern to absorb infrared light with different polarisations.

“We've been whittling away at the problem and now we're beginning to get to the point where we're seeing relatively large gains in power conversion,” said Davids. “I think that there's a path forward as an alternative to thermoelectrics… It would be great if we could scale it up and change the world.”

The team has been issued a patent for the infrared rectenna and have filed several additional patents. Their work was recently published in Physical Review Applied.

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