Photoacoustic gas detection using a cantilever microphone and III–V mid-IR LEDs

The cantilever enhanced photoacoustic trace gas detection in the mid-infrared 3–7 μm wavelength range has been combined with light emitting diode (LED) technology. Mid-IR LED output power was modulated by pulse driving current with frequency high enough to avoid acceleration and acoustical noise. Methane (CH4), propane (C3H8), carbon dioxide (CO2) and sulphur dioxide (SO2) gases have been used for preliminary evaluation of the method sensitivity. The lowest detection limit of 6 ppm was observed for propane employing a LED with a center wavelength 3.3 μm and with 1 s sample integration time.