A Compact Highly Sensitive Cone–Sphere Photoacoustic Spectroscopy Sensor for Real-Time Detection of Dissolved Acetylene in Transformer Oil

In this work, we report a compact and highly sensitive photoacoustic spectroscopy (PAS) system based on a cone–sphere coupled photoacoustic cell (CSC-PAC) for real-time detection of trace acetylene (C2H2) dissolved in transformer oil. The sensing module integrates a conical resonator with a spherical cavity, forming a hybrid structure that effectively enhances photoacoustic confinement and energy coupling efficiency. Finite element thermo-viscoelastic simulations were employed to optimize the cavity geometry and resonance conditions for maximum signal generation. Experimental results demonstrate a strong linear correlation between the photoacoustic signal and C2H2 concentration (R2 > 0.999), with a sensitivity of 2.45 µV·ppm−1. Allan deviation confirms a detection limit of 18.6 ppb is achieved at a 400 s averaging time, confirming excellent system stability. The miniaturized light-acoustic spectroscopy sensor, with a total volume of 7.5 mL and a rapid response time of 25.5 s, provides a high-performance and field-deployable platform for on-site monitoring of high-voltage power equipment and other industrial applications.