Surface acoustic (Rayleigh) waves (SAWs) are highly sensitive to surface mass loading. Traditionally SAWs have been considered unsuitable for liquid sensing applications due to the large attenuation. However if the liquid volume is small, SAWs can provide a powerful tool for investigating the dynamics of viscous liquid spreading. In this work we report experiments in which small droplets of viscous oil were allowed to spread into the path of a SAW device. In all data the SAW signal initially increases while the liquid is still outside the SAW path. This is followed by a rapid attenuation in SAW amplitude as the liquid spreads across the SAW path. In data for larger volume drops the SAW amplitude is observed to pass through a minima. For drops of smaller volume, small features are observed superimposed on the overall attenuation.
- Surface acoustic wave (SAW)