In the power industry, sulfur hexafluoride (SF6) as an insulating gas is widely used in gas-insulated switchgears (GISs). Owing to the latent inner insulation defects of GIS, various SF6 gas decompositions are generated in the process of partial superheating and partial discharge (PD). The decomposition components and concentrations are different under different PD types. A number of gas sensors were reported for the detection of these decompositions. Photoacoustic spectroscopy (PAS) gas sensors have been developed for many applications owing to their high sensitivity and selectivity, such as gas pollutant detection, industrial process control, and non-invasive medical diagnosis. Due to the SF6 physical constants being different from that of nitrogen (N2) or air, the sensor structure should be redesigned. A detailed review of four different types of PAS-based gas sensors is discussed and compared.

Photoacoustic spectroscopy (PAS), as a nondestructive method, permits high sensitivity and selectivity in trace gas detection fields. Advances in differential PAS configurations have dramatically suppressed the background noise and triggered the detectivity improvement. A detailed review on the development of differential photoacoustic gas sensors is presented: using two identical cavity differential cells and optical path types provides good performance for coherent noise suppression, and differential mode excitation technique, which evaluates the signal ratios with two frequency excitations, suppresses the common mode noise and signal drifts generated by the light power or the responsivity of the PA system. An overview of the latest developments of the differential PAS sensors is reported. Distinguished results in terms of sensitivity, selectivity, and miniaturization are presented. The advantages and limitations of differential sensors with different photoacoustic sensing technologies are discussed.

Speckle correlation imaging (SCI) has found tremendous versatility compared with other scattering imaging approaches due to its single-shot data acquisition strategy, relatively simple optical setup, and high-fidelity reconstruction performance. However, this simplicity requires SCI experiments to be performed strictly in a darkroom condition. As background noise increases, the speckle contrast rapidly decreases, making precise interpretation of the data extremely difficult. Here, we demonstrate a method by refining the speckle in the autocorrelation domain to achieve high-performance single-shot imaging. Experiment results prove that our method is adapted to estimate objects in a low signal-to-background ratio (SBR) circumstance even if the SBR is about − 23 d B . Laboratory and outdoor SCI experiments are performed.

Acoustic detectors constitute a key factor of photoacoustic spectroscopy configuration, which is an ultrasensitive gas sensing method. This review aimed to discuss the recent development of acoustic detectors, including capacitive microphone, quartz tuning forks, and optical microphone. An overview of their applications for sensitive, selective, and quantitative trace gas detection was reported, and advantages and limitations of these detectors were presented.

No abstract