Fundamental study for viscosity measurement utilizing circumferential shear-horizontal-mode acoustic waves in a c-axis parallel oriented ZnO film/silica glass pipe structure

Shear horizontal (SH) acoustic waves propagating along a solid surface are affected by the liquid loaded on the surface, which decreases their velocity and amplitude so that they can measure the liquid properties. The long-distance propagation of SH waves in the circumferential direction of a pipe increases the arrival time difference and amplitude change of the waves, resulting in a highly sensitive liquid sensor. In this study, circumferential SH waves were excited with an IDT electrode/ZnO film/silica glass pipe structure, and glycerol solutions were loaded on the outer surface of the pipe. The outer diameter of the pipe was 20 mm. The arrival time and amplitude at a liquid loading distance of 47.1 mm were measured from the time waveforms of the 133-MHz circumferential wave. When glycerol solutions with concentrations of 10, 20, 30, 40, and 50 wt.% were loaded, the arrival times were delayed by 0.3, 1.2, 1.9, 3.0, and 4.0 ns, respectively, compared to the pure water load. Additionally, the amplitudes decreased by −0.8, −4.7, −14.0, −16.4, and −25.8 dB, respectively. These results indicate an increase in the viscosity of the glycerol solution. Therefore, viscosity measurement of liquids using this pipe structure is expected.