A wireless passive SAW sensor based on three one-port resonators and capable of simultaneous torque and temperature measurement is presented. The sensing element is made on Y+34° cut quartz substrate and the resonant frequencies are in the range from 433 to 437 MHz. Interrogation of the sensor is performed through an RF rotary coupler by short RF pulses. A microprocessor in the interrogation unit analyses the spectrum of SAW responses and calculates a temperature compensated torque value. Experimental results show that the temperature measurement error is within ±1° at any angle of the shaft and the torque measurement error does not exceed ±1% of full scale within the range from -40° to +125°C.Contactless torque sensor, SAW resonator, wireless sensor, temperature sensor, calibration

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A novel plate torque transducer based on UHF SAW resonant sensing elements has been developed allowing an easy aftermarket installation of passive wireless torque sensors on large diameter shafts by means of clamping. A design of a large diameter RF rotary coupler for wireless interrogation of the transducer was proposed that had a gap of 20 mm between the stator and the rotor and was insensitive to axial and radial misalignment as well as the rotation angle. The two plate transducers and the RF coupler were installed on a high-speed shaft of a wind turbine gearbox. The torque sensor accuracy achieved after calibration on a test shaft was better than 1% full range within the temperature range from +20°C to +80°C.