Extending Wireless Power Transfer Range for Self-Powered Micro Devices with mm-size Antenna

Abstract: The primary challenge in expanding the wireless power transfer range for miniaturized self-powered micro devices is the limited RF energy harvesting due to the small effective area and low gain of the mm-sized antennas used in these devices. This thesis introduces a method for extending the distance between an external energy source antenna (TX) and a micro-device antenna (RX) to more than 10 cm. This method employs various TX antennas, such as a conventional loop antenna, multiple patch antennas, and a rectangular cavity antenna, in conjunction with a 2-turn double-sided square loop RX antenna, sized 1.2mm x 1.2mm on an FR4 substrate, which can be mounted on a CMOS SoC. The wireless power transfer link's performance is assessed and contrasted under various conditions. In the 434 MHz ISM band, the highest peak power transfer efficiency of $-$20 dB and the highest harvested DC voltage of 4 V through an 8-stage Dickson RF-DC converter are achieved within a 49.6cm x 49.6cm x 30.4cm rectangular hollow cavity, serving as the TX, with an input TX power of 20 dBm. Moreover, the multiple patch antennas exhibit a power transfer efficiency of -39 dB and a harvested DC voltage of 2.5 V at a 10 cm distance with an input TX power of 37 dBm. The specific absorption rate for both scenarios remains under the limits set by IEEE. The feasibility of incorporating a rectangular cavity in backscatter communication is demonstrated in this study, although the cavity's filtering characteristics present certain challenges.