Broadband wireless radio frequency power telemetry using a metamaterial resonator embedded with non-foster impedance circuitry

Wireless powering of implantable biomedical devices and smart radio frequency identification (RFID) tags with very low profile antennas is desired. We propose a low profile electrically small antenna for near-field wireless power telemetry employing a metamaterial Split Ring Resonator (SRR) antenna. SRRs can be designed for operation over wide frequencies from RF to visible. However, they are inherently narrowband making them sensitive to component mismatch with respect to external transmit antenna. Here, we propose an embedding of a non-foster impedance circuitry into the metamaterial SRR structure that imparts conjugate negative complex impedance to this resonator antenna thereby increasing the effective bandwidth and thus overcoming the fundamental limit for efficient signal coupling. We demonstrate the concept through extensive numerical simulations and a prototype system at the board level using discrete off-the-shelf components and printed circuit SRR antenna at 500 MHz. We show that the power transfer between SRR receive antenna and the external transmit loop antenna is improved by more than 8 dB over a wide frequency band (from 525 MHz to 635 MHz), before and after non-foster circuit activation. (C) 2015 AIP Publishing LLC.