Researchers at Sandia National Laboratories have created a device made out of common materials that can convert heat into electrical power. The rectenna, short for rectifying antenna, catches and converts heat waste into electrical power. (Photo via Sandia National Laboratories)
It’s easy to convert electrical power to heat. We do it on a daily basis without even recognizing it. For example, it happens in your toaster. But when you try to do the opposite – converting heat into electrical power – that’s when things get tricky. Now, researchers from Sandia National Laboratories may have found a way to ease the process. They have developed a tiny silicon-based device that harnesses waste heat and turns it into DC power.
The device is small, smaller than a pinkie nail at 1/8 inch by 1/8 inch, and is made of common materials, like aluminum, silicon, and glass combined in unlikely ways that make the device work. Aluminum covers the top of the device and is etched with stripes roughly 20 times smaller than the width of a human hair. The pattern is too small to see with the human eye, yet it acts as an antenna to catch the infrared radiation.
Once the radiation is trapped, the glass creates super faster electrical oscillations, estimated to be 50 trillion times a second. This process pushes electrons back and forth between the aluminum and the silicon in an asymmetric manner. This step is known as rectification, and it generates net DC electrical currents.
The team calls the device an infrared rectenna, that’s a mashup of rectifying antenna. The device is solid state meaning there are no moving parts to jam, bend, or break. It doesn’t even have to directly touch the heat source, which can cause thermal stress. Since the device the made using the same processers used by the integrated circuit industry, it’s easily scalable. Joshua Shank, an electrical engineer who worked on the project, says “We’ve deliberately focused on common materials and processes that are scalable. In theory, any commercial integrated circuit fabrication facility could make these rectennas.”
So not only is the device inexpensive, yet solid, it can be integrated into different industries. But the device itself wasn’t easy to make. One of the biggest challenges the team faced was placing small amounts of other elements into the silicon so it would reflect infrared light like a metal. Rob Jarecki, fabrication engineer, says “Typically you don’t dope silicon to death, you don’t try to turn it into a metal, because you have metals for that. In this case, we needed it doped as much as possible without wrecking the material.”
The team admits there’s still a lot of work to do, especially if they want the device to be an alternative for solar panels as a source of grid-scale power. They also want to improve the power output by improving the design and the conversion efficiency. In the long run, they hope to use the rectenna to power sensors for space missions that don’t get enough direct sunlight. It could also be a good alternative to RTGs for compact power supplies. For now, they believe the antenna will be useful for applications that require something to work reliably for long periods of time.
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