Single Acoustic Channel SAW Sensor With Ladder-type Transducers

Abstract

This work presents the design, fabrication, and validation of a surface acoustic wave (SAW) sensor utilizing ladder-type interdigital transducers (LIDTs) and direct group delay measurements. By exploiting the LIDT multi-subchannel structure, sensing and reference channels are integrated into a single device, significantly reducing system complexity. Fabricated on an ST-cut quartz substrate, the device was selectively functionalized with a graphene oxide (GO) thin film. Sensor interrogation was performed using a NanoVNA to directly measure group delay. Fourier-domain analysis and time-domain gating were applied to suppress parasitic feedthrough and acoustic reflections, improving signal quality and enabling reliable feature extraction without complex hardware. Validated through water activity measurements using supersaturated salt solutions, the results show a stable reference subchannel and a clear monotonic dependence of group delay on water activity in the GO-coated subchannel. This approach combines a simplified architecture, low-cost instrumentation, and robust signal processing for scalable SAW-based sensing applications.