Abstract
The paper aims at discussing an application of A0 mode Lamb wave devices employing ZnO-film/Al-foil composite structure to mass density sensors in liquids.
By using the variational technique, theoretical analysis was made on the effect of liquid-loading upon A0 mode Lamb wave propagation in the device, and a simple relation between the A0 mode Lamb wave velocity and physical conditions was derived. The result strongly suggested that the mass density sensor could be realised: by measuring the fractional change in A0 mode Lamb wave velocity, mass density can be determined almost independent of acoustic wave velocities in liquids by making the ZnO-film and Al-foil very thin.
It was experimentally shown that the centre frequency (proportional to Lamb wave phase velocity) of the fabricated A0 mode Lamb wave device distinctly shifts due to various liquid-loading: the fractional change in the velocity is almost proportional to mass density of liquids. The error of the measured mass density for seven different liquids was within about 5%.
