Highly Sensitive Photoacoustic Microcavity Gas Sensor for Leak Detection

Abstract

A highly sensitive photoacoustic (PA) microcavity gas sensor for leak detection is proposed. The miniature and low-cost gas sensor mainly consisted of a micro-electro-mechanical system (MEMS) microphone and a stainless-steel capillary with two small holes opened on the side wall. Different from traditional PA sensors, the designed low-power sensor had no gas valves and pumps. Gas could diffuse into the stainless-steel PA microcavity from two holes. The volume of the cavity in the sensor was only 7.9 μL. We use a 1650.96 nm distributed feedback (DFB) laser and the second-harmonic wavelength modulation spectroscopy (2f-WMS) method to measure PA signals. The measurement result of diffused methane (CH4) gas shows a response time of 5.8 s and a recovery time of 5.2 s. The detection limit was achieved at 1.7 ppm with a 1-s lock-in integral time. In addition, the calculated normalized noise equivalent absorption (NNEA) coefficient was 1.2 × 10−8 W·cm−1·Hz−1/2. The designed PA microcavity sensor can be used for the early warning of gas leakage.

Ppb-level detection of methane based on an optimized T-type photoacoustic cell and a NIR diode laser

“…It consists of a NIR DFB laser source, a high-speed spectrometer, an optical fiber collimator, an optimized T-type PA cell, a fiber-optic acoustic sensor, a superluminescent light diode (SLD), a circulator and a computer. In view of the cross interference with CO 2 and H 2 O, the characteristic spectrum line of 1650.96 nm was selected [ 42 ]. A 20 mW NIR DFB laser emitting at around 1651 nm was used as the PA excitation source.…”

Multi-mechanism collaboration enhanced photoacoustic analyzer for trace H2S detection

“…The p j ( r ) is the acoustic vibration mode, which is determined by the shape of the PAC. When the angular frequency of the photoacoustic signal is equal to the j th order resonance angular frequency ( ω = ω j ) of the PAC, the sound field amplitude can be expressed as [28] : Where p * j ( r ) is the complex conjugate of p j ( r ), V c is the volume of the resonance tube, ω j is the j th -order normal frequency, Q j is the acoustic resonance quality factor of the acoustic vibration mode p j ( r ).…”

Multi-mechanism enhanced photoacoustic spectroscopy H2S analyzer based on ultrasensitive fiber-optic acoustic sensor

“…The sound field in the photoacoustic cell is the superposition of a variety of different modes of sound waves. The amplitude of sound pressure can be expressed as [19]:…”