Development of practical surface acoustic wave liquid sensing system and its application for measurement of Japanese tea

In this paper, we report on the development of a practical compact and stable sensing system with a shear horizontal surface acoustic wave (SH-SAW) sensor for liquid. First, the oscillation circuits for the liquid-phase sensor based on the SH-SAW device is discussed. Two sensor outputs, i.e., frequency and amplitude, are required for evaluating the liquid properties. To monitor the amplitude, an automatic gain control amplifier (AGC amp) is utilized in the oscillation circuit. The developed sensing system has a low standard deviation of noise that is less than the temperature coefficient of the frequency of the dual SH-SAW sensor and from which the detection limit is estimated. The dynamic range of the developed SH-SAW sensing system is also estimated. The system is applied for the measurement of Japanese tea. The results indicate that the slight differences among teas can be detected by the SH-SAW liquid sensing system.