The coupling of acoustic waves across interfacial boundaries depends u
pon the morphology of the surface and the orientation of the waves at
the boundary. The dependence of the wave propagation at the boundary a
s a function of the physical properties of the liquid is described. Th
e primary influence comes from the density and viscosity. However, the
electrical conductivity of the liquid may also contribute to the inte
ractions at such boundaries. The structure of the interface is an impo
rtant parameter in discriminating the influences of the density and vi
scosity of the liquid. It is possible to optimise the surface structur
e for sensitivity to either density or viscosity and to achieve a high
sensitivity to liquid densities despite samples with a broad range of
viscosities. The influence of surface morphology of the thickness she
ar mode resonator on the liquid properties is studied by using differe
nt structured electrodes to separate the density and viscosity of the
liquid. Finally, a sensor was developed to measure antifreeze concentr
ation in water.