Modeling and testing of a highly sensitive surface acoustic wave pressure sensor for liquid depth measurements

The fluid depth/level measurement application extends from industry to domestic contexts. This article explores the underutilized potential of Surface Acoustic Wave (SAW) sensor-based devices for liquid depth and pressure measurements. Experiments conducted at room temperature address design challenges using a quartz Y34O cut single-port resonator. Theoretically predicted longitudinal strain sensitivity of −1.15 kHz/μStrain (−1.32ppm/μStrain) was reduced to −421 Hz/μStrain (-0.48 ppm/μStrain) due to adhesive layer thickness. Numerical simulations investigate the effect of adhesive thickness on strain transfer from a cantilever to the Surface Acoustic Wave (SAW) sensor's top surface. The sensor is tested on a cantilever and integrated into a 20 μm thick diaphragm-based depth gauge, achieving a depth sensitivity of 42 Hz/mm (0.048 ppm/mm). This sensitivity results from bending of the SAW sensor under hydrostatic pressure, causing compression at the top SAW surface, which was an interesting observation. Additional numerical investigations confirm this behavior, aligning well with experimental findings. The article summarizes the comprehensive study of the SAW resonator's performance and effect of adhesive thickness and provides a guide for designing thin diaphragm-based SAW pressure and depth sensors. It also identifies the device's high sensitivity compared to other sensors in the literature and outlines potential avenues for future research.