Mass density sensor for liquids using ZnO-film/Al-foil Lamb wave device

An application of A/sub 0/ mode Lamb wave devices employing ZnO-film/Al-foil composite structures to mass density sensors for liquids is discussed. By using the variational technique, the effect of liquid-loading upon A/sub 0/ mode Lamb wave propagation in the device is analyzed, and a simple relation between the A/sub 0/ mode Lamb wave velocity and physical conditions is derived. The results suggest that the mass density sensor could be realized by measuring the fractional change in A/sub 0/ mode Lamb wave velocity. It is experimentally shown that the center frequency of the fabricated A/sub 0/ mode Lamb wave device distinctly shifts due to various liquid-loading. The fractional change in the velocity is almost proportional to the mass density of liquids. The error of the measured mass density for seven different liquids is within about 5%.<
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