Surface Acoustic Wave Viscosity Sensor with Integrated Microfluidics on a PCB Platform

This paper illustrates the extension of Rayleigh wave-based surface acoustic wave (SAW) viscosity and density sensor previously developed by the authors for integration with microfluidics and printed circuit board (PCB)-based electronics. The SAW device is first modeled with a microchannel and analyzed using finite-element method (FEM) software. Precise fabrication, alignment, and bonding of polydimethylsiloxane microchannels on diced Y-Z lithium niobate substrates are accomplished. A high-frequency PCB is built to obtain a better performance for SAW device testing. Low glycerin concentrations in deionized (DI) water are analyzed. The FEM simulation results and vector network analyzer measurements of the devices with the microchannel and PCB integration are presented. For low-frequency SAW sensor, a sensitivity of 171.9 Hz/(% glycerin) or 5.57 kHz/(kg/m²√s) in frequency shifts, 0.09°/(% glycerin) or 2.92°/(kg/m²√s) in phase difference, and minimum signal-to-noise ratio of 13.9 dB are achieved at peak frequency of 29.7 MHz. On the other hand, high-frequency (86.1 MHz) SAW sensor provides a sensitivity of 937.5 Hz/(% glycerin) or 37.15 kHz/(kg/m²√s) in absolute frequency shifts, 0.37°/(% glycerin) or 14.7°/(kg/m²√s) in phase difference, and minimum signal-to-noise ratio of 20.5 dB.