School of Science, Wuhan University of Technology, Wuhan 430070, China.
Liangyuan Institute of Science and Technology Information, Shangqiu 476000, China.
Sensors (Basel). 2023 May 14;23(10):4740. doi: 10.3390/s23104740.
Reconstruction of the acoustic relaxation absorption curve is a powerful approach to ultrasonic gas sensing, but it requires knowledge of a series of ultrasonic absorptions at various frequencies around the effective relaxation frequency. An ultrasonic transducer is the most widely deployed sensor for ultrasonic wave propagation measurement and works only at a fixed frequency or in a specific environment like water, so a large number of ultrasonic transducers operating at various frequencies are required to recover an acoustic absorption curve with a relative large bandwidth, which cannot suit large-scale practical applications. This paper proposes a wideband ultrasonic sensor using a distributed Bragg reflector (DBR) fiber laser for gas concentration detection through acoustic relaxation absorption curve reconstruction. With a relative wide and flat frequency response, the DBR fiber laser sensor measures and restores a full acoustic relaxation absorption spectrum of CO using a decompression gas chamber between 0.1 and 1 atm to accommodate the main molecular relaxation processes, and interrogates with a non-equilibrium Mach-Zehnder interferometer (NE-MZI) to gain a sound pressure sensitivity of -45.4 dB. The measurement error of the acoustic relaxation absorption spectrum is less than 1.32%.
重建声弛豫吸收曲线是超声气体传感的一种强大方法，但它需要了解在有效弛豫频率周围的多个频率下的一系列超声吸收。超声换能器是最广泛部署的超声波传播测量传感器，仅在固定频率或特定环境（如水）中工作，因此需要大量在不同频率下工作的超声换能器来恢复具有相对大带宽的声吸收曲线，这不能适应大规模实际应用。本文提出了一种使用分布式布拉格反射器（DBR）光纤激光器的宽带超声传感器，通过声弛豫吸收曲线重建来进行气体浓度检测。DBR 光纤激光传感器具有相对较宽和平坦的频率响应，通过在 0.1 到 1 大气压之间的减压气室测量和恢复 CO 的全声弛豫吸收光谱，以适应主要的分子弛豫过程，并使用非平衡马赫-曾德尔干涉仪（NE-MZI）进行询问，以获得-45.4dB 的声压灵敏度。声弛豫吸收光谱的测量误差小于 1.32%。
