Surface Acoustic Wave Strain Sensor With Ultra-Thin Langasite

Abstract

Langasite (LGS) surface acoustic wave (SAW) sensor is considered as an ideal wireless passive sensing technology application in complex environments. However, existing LGS-based SAW strain sensor has low strain range and its sensing accuracy is affected by temperature greatly as well as strain, which can not meet the application requirements. By exploiting ultra-thin substrate and a custom calibration algorithm, this paper proposes an ultra-thin 100 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> LGS SAW with (0°, 138.5°, 72°) Euler angle to extend strain range to 1200 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \varepsilon $ </tex-math></inline-formula> at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$500^{\circ }\text{C}$ </tex-math></inline-formula> , which is twice higher than the state-of-the-art. The ultra-thin SAW sensor has lower temperature coefficient and hysteresis loop effect, compared with thick LGS SAW. Aiming to improve sensing accuracy, the mechanism of temperature effects on strain sensitivity is investigated in different temperature stages, including thermal expansion mismatch effect and high-temperature glue strain transfer ratio effect. The mechanism can explain strain sensitivity curve under various temperature nicely. Based on the mechanism, a new calibration method is also developed to eliminate temperature effects. The testing results show that this calibration method can improve the measured strain accuracy effectively.