A study of Love-wave acoustic sensors

Abstract

Love-mode acoustic devices are very promising as biosensors in gaseous and liquid environments because of their high sensitivity. An experimental studu of Love-wave devices based on SiO 2/ST-cut quartz, over a wide range of SiO 2 thickness, is presented in this paper. Devices with up to 7.3 μm thick SiO 2 guiding layers have been successully manufactured via an r.f. sputtering technique. Mass sensitivity, velocity, insertion loss, oscillation frequency stability and temperature coefficient of the frequency have been studied as a function of layer thickness. The sensitivity increases with increasing layer thickness and reaches a maximum at around 5.5 μm, for a wavelenght of 40 μm, in accordance with theory. Further increasing the thickness decreases the sensitivity dramatically. High sensitivity (≥ 300 cm 2 g −1) can be achieved at thickness between 3.5 and 6.5 μm. The Low-wave dual-channel delay-line oscilltors also demonstrate high frequency stability and low noise levels. The frequencies of the two channels track each other extremely well.