Beschreibung:
A surface acoustic wave (SAW) strain sensor based on an acoustic Fabry-Pérot resonator is presented. A theoretical analysis is proposed to estimate the frequency sensitivity to strain of cavity resonance peaks and to predict strain distributions in a SAW Fabry-Pérot resonator bonded to a tapered cantilever beam. The frequency stability of cavity resonance peaks for SAW Fabry-Pérot resonators of different cavity length are measured and compared to the stability of a single interdigital transducer (IDT) device. Cavity resonances demonstrate superior stability, improving with cavity length up to 10 mm, where the stability is 32× greater than the single IDT device. The measured frequency sensitivity to strain of the cavity resonances of a resonator 10 mm in length was found to be -103.2 ± 0.2 Hz/με and the frequency stability was found to be 12.1 Hz. By considering a minimum signal to noise ratio (SNR) of 3 dB, the device exhibits a minimum strain resolution of 234 nε, 50× better than that of an equivalent single IDT device. The frequency of a cavity resonance of a SAW Fabry-Pérot resonator exhibits excellent stability and its shift in response to strain is both highly sensitive and linear, making the SAW Fabry-Pérot resonator a promising design for SAW strain sensors