High-Sensitivity Photoacoustic Gas Sensor With Ultrawide Dynamic Range Using Active Frequency Tracking Technology

To achieve highly sensitive and ultra-wide dynamic range gas detection, a dual-mode gas sensor was proposed using cavity enhanced photoacoustic spectroscopy (CEPAS) and active resonant frequency tracking (ARFT) technology. Cavity enhanced photoacoustic cell with double resonance of optical and acoustic can greatly enhance the detection sensitivity of the sensor. Moreover, a new sensing mechanism based on the relationship between gas concentration and acoustic resonant frequency was studied. As an example, we developed an acetylene (C<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>H<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>) sensor, achieving a normalized noise equivalent absorption (NNEA) coefficient of 9.86×10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-11</sup> cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup>‧W‧Hz<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1/2</sup> and an unprecedented dynamic range of nearly nine orders of magnitude (10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup>−10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> ppm). This new measurement tool will provide crucial additional capabilities to gas monitoring with improved sensitivity and dynamic range.