Development of Shear Horizontal Surface Acoustic Wave Sensor for Detecting Methanol Concentrations in a Direct Methanol Fuel Cell

摘要

A liquid phase sensor is realized by using a shear horizontal surface acoustic wave (SH-SAW). The SH-SAW sensor can detect density and viscosity product, conductivity and relative permittivity of liquid. Sensor sensitivity depends on a piezoelectric substrate used. When a 36° rotated Y-cut, X propagating LiTaO_3 is used for the substrate, high sensitive detection of electrical properties is possible. In this paper, the SH-SAW sensor is applied to a methanol (MeOH) sensor. First, frequency dependences of the SH-SAW sensor are discussed. The results indicate that the responses of high frequency sensor agree with the perturbation theory. The application of the SH-SAW sensor is MeOH concentration detection in a direct methanol fuel cell (DMFC). As a formic acid is produced during electrode reactions in the DMFC, real fuel becomes binary-mixture solutions of MeOH and formic acid. In this paper, the solutions are also measured. It is found that influence of the formic acid can be neglected by using high frequency SH-SAW sensor. This means that the MeOH concentration is determined from phase shift.