Robust and compact light-induced thermoelastic sensor for atmospheric methane detection based on a vacuum-sealed subminiature tuning fork
Zhijin Shang, Hongpeng Wu, Gang Wang, Ruyue Cui, Biao Li, Ting Gong, Guqing Guo, Xuanbing Qiu, Chuanliang Li, Lei Dong
Abstract
A compact light-induced thermoelastic spectroscopy (LITES) instrument incorporating a subminiature quartz tuning fork (QTF) was developed for atmospheric methane (CH 4 ) sensing. The QTF features prong dimensions of 1700 µm in length and 120 µm in width, which enable substantial thermoelastic expansion at the microscale, significantly enhancing the piezoelectric signal. The subminiature QTF was vacuum sealed to achieve a high quality factor of 20,511 and a temperature coefficient of frequency of − 0.91 ppm/℃, ensuring a high detection sensitivity and robustness for the LITES sensor. Under identical vacuum conditions, the subminiature QTF demonstrated a twofold signal enhancement compared to the standard QTF, resulting in a minimum detection limit (MDL) of 47 ppb with a 300-ms averaging time. Continuous measurements of atmospheric CH 4 levels over five days were conducted to evaluate the accuracy and robustness of the developed sensor for long-duration monitoring applications.