Lateral displacement amplitude distribution of water-filled ultrasonic bio-separation resonators with laser-interferometry and thermochromatic foils

The displacement amplitude distribution of the piezo-ceramic, the reflector and the side-walls of a water-filled ultrasound cuvette resonator were measured with a heterodyne laser-interferometer. The resulting displacement amplitude distributions at the piezo-ceramic and the reflector suggest evidence of superposition of longitudinal wave fields with transverse wave fields, all polarised in the direction of sound propagation. Elevated amplitudes of the longitudinal wave field were found at the reflector in an area corresponding to the size and position of the piezo-ceramic. Thermochromatically-determined intensity distributions in the water layer confirmed such findings throughout the depth of the water layer; elevated amplitudes over the area of the piezoceramic were observed. This amplitude distribution superposes with a highly regular amplitude distribution pattern corresponding to, and caused by, transverse wave fields measured at the surface of the cuvette.