An experimental study of Love-wave acoustic sensors operating in liquids

It has been shown that properly designed Love-wave acoustic sensors are very promising for sensing in gaseous and liquid environments because of their high sensitivity. Since Love-wave devices do not incur a radiative loss when used in a liquid, they have many potential applications in biosensing. We have successfully manufactured a range of 40 μm wavelength Love-wave devices based on SiO₂/ST-quartz, with the SiO₂ thickness ranging from 0 to 7.3 μm. The relationship of the mass-loading sensitivity to the thickness of the SiO₂ layer has been obtained experimentally. High sensitivity (≥ 300 cm⁻² g⁻¹) is achieved at an SiO₂ thickness between 3.5 and 6.5 μm. The Love-wave oscillators have operated efficiently in various liquids with excellent stability and low noise. In this paper, we report the experimental results for the devices operating in various liquids. The mass sensitivity, insertion loss, oscillation frequency stability, noise level, liquid viscous loading and acoustoelectric coupling have been studied. The influence of the thickness of the SiO₂ layer on some of these properties has also been investigated.