Recycling Ambient RF Energy: Far-Field Wireless Power Transfer and Harmonic Backscattering

It all started with a spark. Let us rewind back to 1887, in Germany. The days were getting cooler in the garden of the Technische Hochschule in Karlsruhe as Heinrich Rudolf Hertz was setting up the first-ever far-field wireless power transmission with increasingly more power [1]. He was striving to demonstrate the wireless nature of electromagnetic waves and propagation. Moreover, as no high-frequency (nearly 100 MHz) voltmeter was available at that time for his experiment, he had to transmit enough power to generate a spark-hundreds of volts!-at the receiver to validate the famous theory of James Clerk Maxwell.