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 fluid 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. Initially the SAW signal increases while the liquid is outside the SAW path. This is followed by a rapid decrease in SAW amplitude as the liquid spreads across the SAW path; significant features are observed superimposed on the overall attenuation.
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