Trace Ammonia Detection Technology Based On Fiber-optic Cantilever Microphone Enhanced Photoacoustic Spectroscopy

In recent years,with the rapid development of science and technology,the further advancement of industrialization and modernization,a wide variety of gases play an important role in life.As a toxic gas with a pungent odor,ammonia can cause harm to the environment and the human body.Therefore,high sensitivity detection of ammonia is of great significance.In this paper,the detection of trace ammonia with high sensitivity is studied.The development of traditional ammonia detection scheme and photoacoustic spectroscopy?PAS?gas detection technology is introduced in detail.The types of acoustic sensors and the gas detection technology of PAS based on acoustic sensors are described in this paper.It is clear that the sensitivity of acoustic sensor is the key factor affecting the gas detection sensitivity of PAS.In order to improve the sensitivity of PAS gas detection system,a fiber optic acoustic sensor based on cantilever diaphragm is proposed.A rectangular cantilever beam with one fixed edge and three free vibration edges is fabricated on a stainless steel diaphragm with a thickness of 10 microns.The cantilever beam,as an acoustic sensor,combines with the flat end of the optical fiber to form an optical fiber cantilever microphone with the F-P interferometer structure.Compared with the traditional acoustic sensor,the optical fiber cantilever microphone has the advantages of small size,immune electromagnetic interference and high sensitivity.The near infrared tunable erbium-doped fiber laser amplified by erbium-doped fiber amplifier?EDFA?was used as the excitation source of photoacoustic signal,and a PAS trace ammonia detection system was built with a resonant photoacoustic cell.Wavelength modulation combined with second harmonic detection technology is used to extract photoacoustic signals sensed by fiber-optic cantilever microphone.Trace NH₃ measurement experiments show that when the central wavelength of excitation light is 1522.448nm,the PAS gas detection system described in this paper has a good linear response to ammonia gas in the concentration range of 0ppm-20ppm with a response degree of 660.5?v/ppm.When the integral time is 30s,the limit detection sensitivity of the system to ammonia gas is 3.2 ppb.