Far field wireless power transfer for IoT applications enabled by an ultra-compact and highly-efficient Huygens rectenna

Far field wireless power transfer technology is very attractive for the future Internet-of-Things (IoT) applications, realizing a betteryless and sustainable wireless system. An ultra-compact and highly efficient Huygens rectenna is introduced that is suitable for powering IoT devices with small footprint. The rectenna is the seamless integration of an ultra-compact Huygens antenna and a highly efficient rectifier circuit. The Huygens antenna consists of two metamaterial-inspired near field resonant parasitic (NFRP) elements as the Egyptian axe dipole (EAD) and a capacitively loaded loop (CLL). As an antenna, it exhibits the cardioid-shaped (Huygens) pattern and the peak realized gain at the resonant frequency 915 MHz reaches 4.58 dBi. As a rectenna, it shows an inductive impedance that conjugately matches to the capacitive value of the rectifier. The peak AC to DC conversion efficiency is up to 87.8%. The entire rectenna is designed on a single piece of PCB substrate with the ka value less than 1 (electrically small). Finally, a wirelessly powered light detection sensor was successfully demonstrated based on the developed rectenna.