Xiangrong Li

In various types of surface acoustic wave (SAW) strain sensors, diverse piezoelectric substrates have recently been adopted to improve the operation temperature, strain detection range, and strain sensitivity. In this study, we propose a flexible SAW strain sensor based on a 100 μm thin langasite substrate with good linear strain range of 1-1800 με and strain sensitivity of 44.8 Hz/με at room temperature. In addition, the effect of temperature on the strain at temperatures 20-800 °C is measured. The results show that the sensor is affected by temperature at a fixed strain. In fact, varying temperatures or strains cause changes in the measured frequency. Furthermore, in environments wherein both temperature and strain change simultaneously, strain measurements given by changes in frequency are inaccurate. To accurately measure the strain, the interference of temperature should be eliminated. In this study, the intercept and slope are extracted from the curves of the relationship between strain and frequency at different temperatures, and the results are fitted. Therefore, the strain value in complex environments can be accurately estimated, with the proposed sensor being able to provide accurate strain sensing with a measurement error within ±5%.

In this paper, we present the design of an integrated temperature and strain dual-parameter sensor based on surface acoustic waves (SAWs). First, the COMSOL Multiphysics simulation software is used to determine separate frequencies for multiple sensors to avoid interference from their frequency offsets caused by external physical quantity changes. The sensor consists of two parts, a temperature-sensitive unit and strain-sensitive unit, with frequencies of 94.97 MHz and 90.05 MHz, respectively. We use standard photolithography and ion beam etching technology to fabricate the SAW temperature–strain dual-parameter sensor. The sensing performance is tested in the ranges 0–250 °C and 0–700 μԑ. The temperature sensor monitors the ambient temperature in real time, and the strain sensor detects both strain and temperature. By testing the response of the strain sensor at different temperatures, the strain and temperature are decoupled through the polynomial fitting of the intercept and slope. The relationship between the strain and the frequency of the strain-sensitive unit is linear, the linear correlation is 0.98842, and the sensitivity is 100 Hz/μԑ at room temperature in the range of 0–700 μԑ. The relationship between the temperature and the frequency of the temperature-sensitive unit is linear, the linearity of the fitting curve is 0.99716, and the sensitivity is 7.62 kHz/°C in the range of 25–250 °C. This sensor has potential for use in closed environments such as natural gas or oil pipelines.