Department of Microsystems Engineering-IMTEK, University of Freiburg, 79110 Freiburg, Germany.
Fraunhofer Institute for Physical Measurement Techniques IPM, 79110 Freiburg, Germany.
Sensors (Basel). 2019 Feb 11;19(3):724. doi: 10.3390/s19030724.
Nitrogen dioxide (NO 2 ) is a poisonous trace gas that requires monitoring in urban areas. Accurate measurement in sub-ppm concentrations represents a wide application field for suitable economical sensors. We present a novel approach to measure NO 2 with a photoacoustic sensor using a T-shaped resonance cell. An inexpensive UV-LED with a peak wavelength of 405 nm as radiation source as well as a commercial MEMS microphone for acoustic detection were used. In this work, a cell has been developed that enables a "non-contact" feedthrough of the divergent LED beam. Thus, unwanted background noise due to absorption on the inside walls is minimized. As part of the development, an acoustic simulation has been carried out to find the resonance frequencies and to visualize the resulting standing wave patterns in various geometries. The pressure amplitude was calculated for different shapes and sizes. A model iteratively optimized in this way forms the basis of a construction that was built for gas measurement by rapid prototyping methods. The real resonance frequencies were compared to the ones found in simulation. The limit of detection was determined in a nitrogen dioxide measurement to be 200 ppb (6 σ ) for a cell made of aluminum.
二氧化氮（NO2）是一种有毒的痕量气体，需要在城市地区进行监测。在亚 ppm 浓度下进行准确测量是适合经济传感器的广泛应用领域。我们提出了一种使用 T 形共振腔的光声传感器测量 NO2 的新方法。使用了一个具有 405nm 峰值波长的廉价 UV-LED 作为辐射源，以及一个用于声学检测的商业 MEMS 麦克风。在这项工作中，开发了一种能够实现发散 LED 光束“非接触”馈通的池。因此，最小化了由于内壁吸收引起的不必要的背景噪声。作为开发的一部分，进行了声学模拟以找到共振频率，并可视化各种几何形状中的驻波模式。为不同形状和尺寸计算了压力幅度。通过这种方式迭代优化的模型为通过快速原型制造方法进行气体测量的构建提供了基础。将实际共振频率与模拟中找到的频率进行了比较。对于由铝制成的池，在二氧化氮测量中确定的检测限为 200ppb（6σ）。
