Retrodirective transponder array with universal on-sheet reference for wireless mobile sensor networks without battery or oscillator

A rotating shaft in a wheel, a motor and a turbine uses sensors to measure torque, vibration, and acceleration for better control and maintenance of a machine. Such data is currently acquired in a laboratory and utilized for tuning the machine. For adaptive control and failure prognosis in future, the data need to be collected by the sensors on the fly. Connecting the moving sensors by wire and a brush to a microcontroller leaves reliability issues due to mechanical wear and electrical noise. A wireless data link with small form factor and low maintenance cost is needed. Bluetooth consumes large power and requires external parts such as a battery and a crystal. RFID loses connectivity when the sensors move into the shadow of a radio wave from a transponder. Continuous sensing on all sides is needed as the direction to be sensed is not determined.