Resonantly coupled antennas for passive sensors

Wireless resonant coupling can enhance the performance of wireless passive sensors. Very efficient transfer of both energy and information is possible. Resonant coupling implies that a weak wireless coupling is compensated by resonance. In ideal situations power conversion efficiencies of 10-50 percent can be achieved from the transceiver to the sensor. The cost is a limited bandwidth and an increased sensitivity to relative positional - especially angular - variations. The limited bandwidth is hardly a problem for most sensor applications. An analysis based on the theory for coupled circuits is presented. The capabilities and deficiencies are quantified by simple analytical and numerical calculations.