Measurement Characteristics of Flow-Type Shear-Horizontal Surface Acoustic Wave Sensor for Direct Methanol Fuel Cells

Direct methanol fuel cells (DMFCs) offer promising future power sources. Operating DMFCs at ideal conditions, fuel concentration management is required, and therefore, devices for methanol concentration measurement are considered important to DMFC systems. Shear-horizontal surface acoustic wave (SH-SAW)-based methanol concentration sensors can be used as DMFCs offering advantages such as miniature size, mass-production ability, and reliability. The objective of this study was to develop and evaluate an easy to install SH-SAW sensor in a wide variety of DMFC systems. In this paper, we describe the detailed structure and measurement characteristics of the developed sensor system. The evaluations were focused on the linearity and response to methanol concentration change. Through the evaluations, theoretically predicted response linearity to the methanol concentration change was confirmed on the developed sensor. It was found that the response speed of the sensor was so quick that even a transient phenomenon of methanol spreading into water could be detected. These measurement abilities will be useful for accurate fuel control of DMFC systems, and should be able to extend the application range of SH-SAW sensors. (C) 2012 The Japan Society of Applied Physics