PMUT enhanced light-induced thermoelastic spectroscopy.

High-precision detection of acetylene (C₂H₂) concentration plays a vital role in industrial safety, environmental monitoring, and fault diagnosis of power equipment. This paper reports a highly sensitive light-induced thermoelastic spectroscopy (LITES) C₂H₂ sensor based on a piezoelectric micromachined ultrasound transducer (PMUT). The sensor employs an eight-cantilever PMUT structure at the micrometer scale as its sensing element, effectively converting minute thermal deformations into larger displacements to achieve enhanced mechanical amplification effects. The novel cantilever beam structure design increases the PMUT resonance frequency to a high frequency of 198.8 kHz while simultaneously enhancing the LITES signal by a factor of 45. A spot-concentrated miniature multi-pass cell designed for the novel PMUT structure further enhances detection sensitivity and stability by amplifying the optical path length by 70 times through optical folding. Experimental results demonstrate that the sensor exhibits excellent linear response (R² = 0.99936) and long-term stability for C₂H₂ concentration detection, achieving a minimum detection limit of 2 ppm (@64 s). Compared with existing C₂H₂ optical detection technologies, PMUT-based LITES C₂H₂ sensor not only demonstrates outstanding detection performance but also offers CMOS-compatible fabrication advantages, providing a novel approach for the development of highly sensitive, portable, easily integrated, and low-cost C₂H₂ detection systems.