Design, Optimization and Characterization of an Acoustic Plate Mode Viscometer

An acoustic plate mode (APM) device with shear horizontal (SH) displacements is reported. Unlike prior APM devices on ST-X quartz, -65deg rotated Y-cut (RYC) provides enhanced coupling to a single dominant mode via a leaky-SAW interaction with excellent temperature stability and good piezoelectric coupling. The sensor element has a very broad temperature range over which the selected mode is electrically dominant over the adjacent modes. The use of a resonator-delay line hybrid provides 6dB insertion loss in air. The loaded Q remains in excess of 1,000 with 14 dB of additional liquid losses (20 dB insertion loss). The present work details the design and operation of the sensor and support circuitry to implement a process control viscosity sensor. Data supports the ability to create reproducible devices operable over a broad range of environments. The critical role of surface roughness is indicated, as are molecular weight effects.