OptoAcoustic Gas Sensor Technology (Patent US 7,213,444 B2)
Gas molecules have the ability to absorb infrared radiation at wavelengths characteristics to their chemical structure. The proprietary gas sensor technology (Patent US 7,213,444 B2) is based on generating acoustic pressure waves as result of gas irradiation with suitably modulated light. The OptoAcoustic Gas Sensor contains a light source, a measurement & absorption cell, a membrane, an infrared band pass filter, a microphone and an electrical circuit for operating the light source and evaluating the microphone output signal. The intensity-modulated light first passes through the optical band pass filter whose spectral band corresponds to the absorption band of the target gas, and then illuminates the volume of the measurement cell. When the gas is in the vicinity of the sensor, the gas diffuses through the membrane into the measurement cell and there absorbs the light emitted.

The absorbed radiation, which for very short time (few microseconds) is stored as intermolecular vibrational rotational, is quickly released by relaxation to translational energy during numerous collisions occurring between the gas molecules. Translational energy is equivalent with heat, and since the measurement (absorption) cell is almost sealed, this will cause the pressure to rise. If the incident light is modulated at a given frequency, a periodic pressure change is generated in the measurement cell. At the edge of the measurement cell, a microphone captures the pressure modulation, which is then amplified and converted into an electrical signal directly related to the gas concentration.