Overlapping metal arms shaped like a bowtie form a ‘rectenna’ that captures renewable infrared energy. Source: Atif Shamim, KAUSTOverlapping metal arms shaped like a bowtie form a ‘rectenna’ that captures renewable infrared energy. Source: Atif Shamim, KAUSTInfrared radiation is ubiquitous, with natural emissions estimated to be millions of gigawatts per second. Such radiation is viewed as an energy resource by researchers from King Abdullah University of Science and Technology, who developed a device that can harness infrared’s power potential as well as waste heat from industrial processes.

Infrared heat can be harvested 24 hours a day by treating it as high-frequency electromagnetic waves. Using appropriately designed antennas collected waves are sent to a rectifier, typically a semiconductor diode, that converts alternating signals to direct current charge for batteries or power devices. However, infrared emissions have very small wavelengths and require micro- or nanoscale antennas that are not easy to fabricate or test. Infrared waves also oscillate thousands of times faster than a typical semiconductor can move electrons through its junction.

The research team turned to quantum tunneling for a solution. Tunneling devices, such as metal-insulator-metal (MIM) diodes, rectify infrared waves into current by moving electrons through a small barrier which is only a nanometer thin. The MIM diodes can therefore handle high-frequency signals - 28.3 THz or 10.6 μm - on the order of femtoseconds.

A bowtie-shaped nano-antenna that sandwiches the thin insulator film between two slightly overlapped metallic arms was designed to produce the intense fields needed for tunneling. The structure is assembled with metals featuring different work functions, enabling the MIM diode to capture the infrared waves with zero applied voltage, a passive feature that switches the device on only when needed. Experiments with infrared exposure revealed the bowtie successfully harvested energy solely from the radiation and not from thermal effects, as evidenced by a polarization-dependent output voltage.

The research is published in the journal Materials Today Energy.

To contact the author of this article, email shimmelstein@globalspec.com