A High Performance Passive Wireless SAW Torque Sensor

Torque measurement presents challenges particularly in rotating structures, where traditional measurement methods are often limited. Surface Acoustic Wave (SAW) sensors, with their inherent wireless and passive characteristics, possess unique advantages in mechanical measurements of rotating structures. Currently, most of the existing resonant SAW mechanical sensors suffer from issues of short reading distances or poor signal quality, primarily due to the difficulty in achieving high Q factor of SAW resonators. Additionally, the problem of high temperature coefficient generally exists in the field of SAW sensors, which will seriously interfere with the measurement accuracy of the sensors. In this article, a SAW torque sensor with excellent wireless performance was proposed based on the X-112°Y LiTaO3 substrate due to its large electromechanical coupling coefficient ( ${K} ^{{2}}$ ) and favorable temperature characteristics. We investigated and simulated the characteristics of the sensing element including strain sensitivity, temperature coefficient, Q factor and electromechanical coupling coefficient, and designed SAW resonators on X-112°Y LiTaO3 substrates. The experimental results show that the proposed SAW sensor has higher signal-to-noise ratio (SNR) echo signal quality at the same wireless measurement distance compared with the case traditional high Q factor SAW sensor based on quartz substrate. Moreover, from temperature tests, the proposed SAW sensor has a linear temperature effect, which is beneficial to the compensation of temperature drift. Based on the manufactured SAW sensors, a SAW torque measurement system with wonderful linearity, repeatability, and hysteresis was developed. Our work provides a valuable and promising solution for wireless and passive measurement of mechanical quantities.