Ray tracing simulations of the IR-emission of a Fabry-Perot-based thin film structure for NDIR gas sensors
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NDIR (non-dispersive infrared) gas sensors utilize the specific infrared absorption of particular gas
molecules (e.g., CO2) for measuring their distinctive concentration. One of the main parts of an NDIR gas sensor is the IR-source. The emitted wavelength characteristics of such an IR-source are characterized by two parameters: emissivity and emission temperature. To obtain a large emissivity a stack of thin films representing a Fabry-Perot structure are utilized. To simulate the characteristics of such a structure in relation to the total NDIR gas sensor system two simulation steps are implemented. At first we simulate the
angle-dependent infrared emission using the so-called enhanced transmittance matrix approach. In a second step we apply a 3D ray tracing model using a Monte-Carlo method for calculating the gas-specific
behavior of the entire sensor system. Finally, we compare the simulated sensor response with a similar
sensor system featuring a simple thermal emitter instead of the Fabry-Perot device.