Monolithic Crystal Filter for Application in Viscosity Sensor

Monolithic crystal filter (MCF) on AT-cut quartz for application in viscosity sensor was developed. After proper matching, at a frequency of $\sim 3.6$ MHz, insertion loss in air of $\sim 1.6$ dB was obtained. The linear coefficient of frequency of about −5 ppm/°C and changes of the insertion loss of $\sim 0.5$ dB, in the temperature range of 10°–80°, were obtained. To eliminate errors caused by the longitudinal acoustic wave generation, MCF should be immersed in a measured liquid or proper amount of liquid should be inserted into the sensing window. Using water and glycerin solutions, insertion loss changes against dynamic viscosity of the MCF were measured. In a viscosity range from about 1 to 1000 $\textrm {mPa}\cdot \textrm {s}$ , an insertion loss change of $\sim 24$ dB was obtained.