The Small Volume Liquid Density Sensor Using Surface Acoustic Wave

Shear horizontal surface acoustic wave (SH-SAW) are generated and detected by interdigital transducers (IDT). When the viscoelastic liquid comes in contact with the delay path in a SH-SAW device, the viscous coupling action would effect on the wave propagation. Consequently the frequency, phase and propagating velocity of the SH-SAW are altered. In this paper the properties of the acoustic wave in a liquid overlay on a piezoelectric substrate are investigated. The theory analysis and initial experiment are presented. The result shows when signal frequency is 57.8 MHz, the SH-SAW can be excited effectively in the lithium niobate crystal. By measuring the phase change of the SH-SAW, the liquid density can be detected. Compared with traditional liquid density sensor, the SH-SAW liquid density sensor has the advantages of simple construction, high precision and little sample etc