The Study Of New Technic Gas Sensor Based On Surface Acoustic Wave

Surface Acoustic wave (SAW) is elasticitive wave propagating along the object surface,external perturbation affect more or less viscosity,mass density,stiffness,electrical conductivity and permittivity, The extrinsic temperature and pressure affect also the change of propagating characteristic.At present,The sensor based SAW has been widely applied in many different fields.Surface Acoustic Wave gas sensor is a new kind of sensor which involved Surface Acoustic Wave theory, device technology, film theory, electromagnetic, detection technology and other new scientific fields. As it has the characteristics of high precision, high reliability and rapid dynamic response and is widely applied in the fields of environment protection and safety detection, the SAW gas sensor has the significant economic and social benefit.For SAW gas sensors, the propagation velocity of SAW can be changed by painting film to the delay line.The interaction between the film and the measured gas directly determines the sensitivity, selectivity and reversibility of the sensor.In this paper, we develop the five channel gas sensors of SAW including the design of IDT,the choice of substrate material and sensitive film and design of circuit. The main contents are listed as follows:1.Introduce the basis theory of SAW and the analytical model of SAW device.2.Introduce the selection of piezo-materical and compare the voltage of output IDT which the substrate are the diffent crystals or the diffent cut of the same crystal3.Developed a number of parallel IDT arrays which constructed multi-channel SAW sensors for delay and resonance types by adopting 1/4 and 1/8 wavelength interdigital splits, respectively.The center frequencies of the SAW sensors were selected as 100MHz,148.5MHz and 315MHz, respectively4.Analyze particularly the main physical properties of various films which adsorbed gases. The influence of the thickness of the films on the sensitivities of the sensors is derived theoretically, and the best thickness is obtained. The linear response region of the measured frequency is analyzed. Several kinds of commonly used sensitive films, such as copper phthalocyanine, indium oxide, zinc oxide and tin oxide thin films, are introduced. With the copper phthalocyanine film detected nitrogen dioxide gas, the sensitivity, repeatability, and the practicality of the circuit module are validated by using a dual-channel gas sensor. In addition, the responses of the sensor on the carbon monoxide and water vapor are experimentally investigated by using Quartz delay-line type and resonator type devices.5.Based on former literatures and dates,we desigen the frequency and amplitude detection ways and unify the tow seperated mathods so as to make it more scientific, reasonable, accurate.