Transponder array system with universal on-sheet reference scheme for wireless mobile sensor networks without battery or oscillator

A rotating shaft with attached sensors is wrapped in a two-dimensional waveguide sheet through which the data and power are wire-lessly transmitted. A retrodirective transponder array affixed to the sheet beamforms power to the moving sensor to eliminate the need for a battery. A universal on-sheet reference scheme is proposed for calibrating the transponder circuit delay variation and eliminating a crystal oscillator from the sensor. A base signal transmitted from the on-sheet reference device is used for generating the pilot signal transmitted from the sensor and the power signal transmitted from the transponder. A 0.18-μm CMOS transponder chip and the sheet with couplers were fabricated. The coupler has three resonant frequencies used for the proposed system. The measured propagation gain of the electric field changes to less than ±1.5 dB within a 2.0-mm distance between the coupler and the sheet. The measured power transmission efficiency with beamforming is 23 times higher than that without it. Each transponder outputs 1W or less for providing 3mW to the sensor.