High-Sensitivity AlN-Based Surface Acoustic Wave Strain Sensor with Strain–Temperature Decoupling Method

To address the urgent demand for high-sensitivity and anti-interference strain sensing in structural health monitoring under extreme environments, this study proposes a surface acoustic wave (SAW) strain sensor based on a trench structure, along with a dual-channel temperature–strain decoupling strategy. Finite element simulations were employed to optimize the trench parameters and enhance strain sensitivity. By utilizing two sensor units with distinct strain sensitivities, a linear sensitivity equation system was established to achieve real-time decoupling of temperature and strain signals. Specifically, the two sensor channels were arranged along the wavelength and aperture directions, respectively, to exploit their different responses to directional strain—strain along the wavelength direction induces a positive frequency shift, while strain along the aperture direction causes a negative frequency shift. In contrast, temperature variations produce synchronous frequency shifts in both channels. Based on this principle, a sensitivity matrix was constructed to enable high-precision, real-time decoupling measurements. Experimental results demonstrate that thinning the substrate to 200 µm yields a strain sensitivity of 194 Hz/µε, more than twice that of conventional unthinned sensors. The grooved structure also reduces temperature sensitivity to 6.1 kHz/°C, representing a 57% decrease compared to similar studies. Through the dual-channel decoupling algorithm, the system achieves a strain measurement error of 7.5 µε (RMSE) and a temperature error of 0.21°C, enabling precise sensing. This research offers a highly reliable solution for wireless and passive strain monitoring in extreme conditions such as high temperatures and intense radiation.