Rectennas for thermal-energy conversion

We demonstrated the conversion of thermal energy in the form of far- and mid-infrared using a micro rectenna, consisting of a spiral antenna coupled to an ultra-fast nanodiode, the so-called self-switching device (SSD). A maximum efficiency of 0.02 % was measured at a 973 K (700 °C) using a calibrated black-body radiator illuminating the rectenna. The relatively low efficiency was due to the impedance mismatch between the diode and the antenna, and can be reduced by designing a suitable matching structure. The fabrication of larger rectenna array could be exploited, for example, to harvest wasted thermal energy from exhaust pipes and industrial machinery.