Reliable and consistent measurement of various gas molecules at low parts per million (low-ppm) concentration is an essential intermediary step towards low-cost versatile gas analysers. Here we demonstrate physical measurements of various low-ppm molecules by means of an acoustic standing wave-based resonating device with a speaker and a microelectromechanical microphone, using either the sound pressure level () at a fixed frequency, or alternatively, tracking the resonance frequency as gas molecules enter the acoustic device. Low-ppm gas molecules are measurable at frequencies near standing wave resonances, as slight shifts in the speed of sound result in a shift of the acoustic frequency response function. Since a chemical receptor layer on the sensing component is not required for the measurements, absolute physical quantities of the molecules are measurable, which coincide well theoretically with expected values for pure chemicals. Various conditions are tested using different low-ppm molecules to demonstrate the limit of detection (LOD), using a low-cost and portable acoustic setup. An LOD is determined to be in the order of several ppm for most molecules. Gas analysers based on a physical approach present new opportunities for mobile gas sensing in practical applications.

中文翻译：

---

低 ppm 浓度气体的声音传感

对低百万分之一 (低 ppm) 浓度的各种气体分子进行可靠、一致的测量是实现低成本多功能气体分析仪的重要中间步骤。在这里，我们演示了通过带有扬声器和微机电麦克风的基于声学驻波的谐振装置对各种低 ppm 分子的物理测量，使用固定频率的声压级 ()，或者跟踪谐振频率当气体分子进入声学装置时。低 ppm 气体分子可以在驻波共振附近的频率下测量，因为声速的轻微变化会导致声频响应函数的变化。由于测量不需要传感组件上的化学受体层，因此可以测量分子的绝对物理量，这在理论上与纯化学品的预期值非常吻合。使用低成本、便携式声学装置，使用不同的低 ppm 分子测试各种条件，以证明检测限 (LOD)。对于大多数分子来说，LOD 被确定为几个 ppm 的量级。基于物理方法的气体分析仪为实际应用中的移动气体传感提供了新的机遇。