Attenuation of acoustic normal modes in piezoelectric plates loaded by viscous liquids.

Attenuation cac versus viscosity eta of adjacent liquid is measured for each normal mode n generated in 30 different plates of commercially available, piezoelectric crystals with thickness-to-wavelength ratio in the range h/lamda = 0.6 - 2.5.

New type of an acoustic plate mode: quasi-longitudinal normal wave.

A new type of an acoustic wave belonging to the family of the normal plate modes is discovered numerically and verified experimentally in ST, x-quartz plates with free surfaces. It exists within restricted bands of the normalized plate thickness H/lambda, where H is the thickness, lambda is the wavelength, separated by forbidden H/lambda-bands attributed to the common plate modes. Polarization of the wave over the whole plate thickness is almost longitudinal.