Radio accessible SAW sensors for non-contact measurement of torque and temperature

Surface acoustic wave (SAW) based sensors can easily be interrogated by low power radio signals. They therefore are ideally suited for non-contact measurement of torque and temperature on rotating shafts. It is advantageous to use lithium niobate as a substrate material because of its linear temperature response and its high electro-mechanical coupling efficiency. With this material, however, the sensitivities of temperature and torque measurement are strongly different: a small change in temperature of only a few Kelvin will cause a sensor signal of the same amount as the nominal torque of a typical shaft. It is experimentally demonstrated that, despite the strong temperature sensitivity of the sensors, exact measurements of both torque and temperature can be accomplished over a wide temperature range from 0°C to more than 70°C, while the resolution of torque measurement is well below 1%. Deviations from linearity are small, so that a third order polynomial in temperature and torque is sufficient to describe the sensor response characteristics