High Sensitivity Resonant Infrared Light Sound Gas Sensor

Infrared gas sensor has the advantage of high sensitivity, high selectivity and rapid response speed, it has attached more importance. High sensitive miniaturized infrared opto-acoustic gas sensor basing on former system is designed, it made further enhancement in sensitivity and SNR.The major contributions of this article are the bellows:1. Discovered a new resonant mode and put forward new design method of the resonant cavity and the buffer cavity.It analyzed the relationship between the output signal and the chopping frequency, a new resonant mode that is different from the report of other papers was found. Not only 2550Hz but also 3450Hz is also a peak. The sensitivity and SNR performance were obviously enhanced, by comparison, with sensitivity by 1.5 to 2.3 times and SNR by 2.1 times and detection limit from 20 ppb to less than 10 ppb. This article believes the new resonant mode stems from the resonance of the buffer cavity. In order to verify this verdict and to optimize the test system, it adjusted the length of the buffer cavity, the outcome demonstrated that the high frequency peak moves to low frequency direction along with the length of the buffer cavity increasing. Thus we conclude the sensitivity and SNR will enhance notably if the resonant frequency of buffer cavity equals with resonant cavity’s resonant frequency.2. The sensitivity and SNR of the system are enhanced by improving the opto-acoustic gas sensor.It is discussed that the relationship between the structure of the microphone output cavity and the signal. It’s found that the signal can be amplified by increasing the length of the output cavity. It is also discussed that the affect if the reflecting film is added in the joint of the right buffer and the light passage. At 2550Hz the film can enhance the signal obviously but at 3450Hz the signal of film adding structure is not as high as the signal without the film. It demonstrated that the resonance of the buffer cavity disappeared with the film added.3. The gas ethylene which marks the ripeness of fruits and nerve poison gas DMMP were detected using developed opto-acoustic system.The test system that used for testing DMMP is designed in this article. Due to the density of the standard DMMP gas which we bought were inaccurate, it analyzed the reason and found the correct distribution method on the spot, acquired DMMP standard gas with different trace density. The study demonstrated the system can be used to detect nerve poison gas like sarin.