Investigation of Novel Surface Acoustic Wave (SAW) Gas Sensor Used in Sensor Network

Mobile communications, e.g., cellular phones, have become very widespread. A new concept called \Sensor Network has been proposed with the development of such commu- nications system. Sensed signals from many sensor nodes installed in a wide area are gathered to a center node by technology similar to that used in mobile communications. Home/o-ce circum- stance control, environment monitoring and protection can be conducted based on the collected data. We propose a new SAW subtle-gas sensor, which can be used in these sensor nodes. The new sensor structure removes a limited selection for piezoelectric crystal substrates, while only Quartz crystal substrates have been used in conventional SAW gas sensors. The sensing dynamic range was widely extended by utilizing both fundamental and 3rd-harmonic frequency SAWs. Moreover, our sensors are also designed to be combed with 2.4-GHz ZigBee, which has been regulated by IEEE802.15.4, and ZigBee Alliance as a wireless-communications medium for the \Sensor Network. It is predicted that our network system will possibly provide hydrogen-gas leakage sensing for future fuel-cell cars and environmental-pollution gas sensing.