Design Of Temperature Control Solution For Condensing Surface Acoustic Wave Gas Sensor

In the twenty-first century,terrorist activities surface from time to time both at home and abroad.With the use of improvised explosive device,suicide bombings and bus bombings are the mean forms of terror.Therefore,high-sensitivity explosive detectors with low false alarm rates have become a hot research target in recent years.As a highly sensitive gas detection technology,surface acoustic wave(SAW)gas sensing technology has great potential applications in the detection of explosives.The traditional SAW gas sensor needs to be coated with sensitive film on the piezoelectric substrate or film,which has led to low integration,slow response,low sensitivity,cross-interference and other technical problems.In this topic research,sensitive films are no longer used.Instead,we use low temperature to make gas molecules condensed on the SAW device surface,constituting a condensing SAW gas sensor.The new SAW gas sensor is said to increase the sensitivity of the traditional SAW gas sensor by a factor of 1000.For the condensed SAW gas sensor,accurate temperature control technology is the key.This paper starts with the precise temperature control technology in the condensed SAW gas sensor.This paper first reviews the current development of SAW gas sensor technology,introduces the working principle of temperature control technology and analyses the influence of temperature fluctuation on the frequency drift and the amount of condensate adsorption of the SAW device.The temperature control mode adopted in the related literature is summarized.And the commonly used temperature control elements,the semiconductor thermoelectric cooler(TEC)and the temperature sensor are introduced in detail.Besides,the high precision temperature control technology based on TEC is studied in this paper.In this paper,the design of temperature control includes two aspects.One is the design of a high-precision temperature control circuit.As the SAW gas sensor is extremely sensitive to the temperature on the surface,the constant temperature accuracy and temperature stability is two important indicators of the temperature control circuit.I made a hardware circuit design based on the TEC control chip MAX1978 and the micro-control unit STC89C52.The hard ware circuit is capable to adjust the temperature from 10? to 30? and keep the deviation within ± 0.03?.The temperature can be kept stable no upper or lower than 0.05? in 20 seconds.Only 3 seconds is needed to reduce the temperature on the surface of SAW gas sensor in the enclosed chamber from 27°C to 15°C.The other aspect is the improved designs for the integration of temperature control circuit and the SAW gas sensor readout circuit,for better air purging methods and for air chamber structures.I designed an open chamber and a closed chamber.Because of the difficulties in the procurement and synthesis of explosives,I only tested the baseline of the condensed surface acoustic wave gas sensor when the temperature was stable.By comparing the sensor baselines at the constant temperature and the ambient temperature,I made a conclusion that the stability of the sensor baseline is higher and the stability speed is faster under the condition of temperature control.