Passive and remote polymer-coated Love wave chemical sensor

This paper presents a passive and remote polymer- coated Love wave chemical sensor. A ST-90degX quartz was used as the substrate, which provides a shear horizontal surface acoustic wave (SH-SAW) with high shear velocity and larger piezoelectricity. A layer of polymethylmethacrylate (PMMA) was considered as the guiding layer owing to its lower shear velocity. The dispersion relationship of the Love wave propagation was described. Also, to extract the optimal design parameters, a theoretical model on response mechanism of polymer-coated Love wave chemical sensor was established. A 440MHz Love wave reflective delay line was fabricated as the wireless chemical sensor element. Single phase unidirectional transducers (SPUDTs) and three shorted grating reflectors are used to structure the SH-SAW device, and a Teflon AF 2400 thin film sensitive to CO2 gas deposited onto PMMA surface between reflectors. The fabricated Love wave device was wirelessly characterized by network analyzer. Adsorption of CO₂ gas onto the sensitive film induced a large phase shifts of the reflection peaks depending on the CO₂ concentration. The obtained sensitivity was 7deg/ppm.