Miniaturized anti-interference cantilever-enhanced fiber-optic photoacoustic methane sensor

Abstract

To realize all-optical passive detection of CH 4 in narrow spaces and harsh environments, a compact cantilever-enhanced fiber-optic photoacoustic sensor (CEFPS) resistant to electromagnetic and ambient noise interference is proposed. Through theoretical analysis and finite element simulation, a miniaturized photoacoustic cell (PAC) with diffusion holes has been designed and fabricated. The diffusion holes are used for the circulation of the gas to be measured and attenuate the external noise coupled into the PAC. The concentration information of CH 4 is obtained by demodulating the vibration amplitude of the built-in cantilever generated by the photoacoustic pressure. The design of the built-in cantilever structure avoids the possibility of mechanical damage and reduces the interference of external noise in the detection of photoacoustic signals. The experimental results and the Allan-Werle deviation analysis of the CH 4 signal show that the minimum detection limit (MDL) is 0.32 ppm with an integration time of 60 s. The normalized noise equivalent absorption (NNEA) coefficient is calculated as 2.44 × 10 −8 cm −1 W/Hz 1/2 . The developed CEFPS achieves performance comparable to conventional resonant photoacoustic spectroscopy CH 4 detectors, although the volume is two orders of magnitude lower. • A miniaturized all-optical anti-interference cantilever-enhanced photoacoustic methane sensor is presented. • The cantilever acoustic-sensitive element and miniaturized photoacoustic cell (PAC) adopt a built-in design. • The direct effect of environmental noise interference, wind disturbance and mechanical damage on the cantilever is avoided. • The sensitivity of the sensor reaches the traditional resonant photoacoustic spectroscopy trace gas detection technology. • At the same time, the volume of the built-in miniaturized non-resonant PAC is reduced by about two orders of magnitude.