New modification of the acoustic Lamb waves and its application for liquid and ice sensing

• Lamb waves with elliptic polarization oriented parallel to the plate faces exist in crystal plates. • Particular polarization is maintained at any depth from free faces, for wide range of plate thickness. • The new waves are promissing for sensing liquid viscosity and liquid-to-ice phase transitions. Using quartz plates as an example existance of the new modification of the Lamb waves is demonstrated. The waves have small vertical displacement, large shear-horizontal and longitudinal components, and elliptic polarization which is oriented parallel to the plate faces. Numerical calculations of the surface displacements and depth profiles show the particular polarization is maintained at any depth from free faces and for all plate thickness in the range h/λ = 0–1.7 (h - thickness, λ - wave length). Results of the measurements accomplished for four new modes and three plate thickness h/λ confirm that radiation of the waves into adjucent liquid (which is proportional to vertical displacement) is small, while viscoelestic loss of the same the waves (which is proportional to in-plane components) is large. This property makes the modified waves suitable for sensing liquids and ices. In particular, responses of the waves towards liquid viscosity and water-to-ice transformation are larger than those are for common Lamb waves approaching 27 and 50 dB, respectively, at about 30 MHz, 1500 cP, and 10 mm propagation path.