Fabry-Pérot-Based Thin Film Structure Used as IR-Emitter of a NDIR Gas Sensor: Ray Tracing Simulations and Measurements
Sprache des Vortragstitels:
SPIE Smart Sensors, Actuators, and MEMS V
Sprache des Tagungstitel:
Non-dispersive infrared (NDIR) gas sensors make use of the specific infrared absorption of particular gas molecules in
order to measure their distinctive gas concentration. The main parts of such a NDIR gas sensor are: an IR-emitter, a
chamber containing the sample-gas, and an IR-detector with a filter for the characteristic absorption wavelength. The
effectiveness of the IR-source for the total system is characterized by its temperature and the emissivity (i.e., the
difference to blackbody radiation) of the device surface. Due to the fact that conventional metal surfaces provide a rather
low emissivity, their emitting temperature must be set very high to generate sufficient IR-radiation for this kind of
sensors. We developed an IR-source consisting of a stack of thin films with a much higher emissivity. Its main part is a
combination of two mirrors and a dielectric layer which represent a Fabry-Pérot structure.
The obtained emission of the Fabry-Pérot structure and the consequences for the performance of the whole NDIR gas
sensor system were simulated with the enhanced transmittance matrix approach and a 3D ray tracing model. As an
example, CO2 was considered as sample gas where the major characteristic absorption occur around 4.26 ?m. The
theoretical results are validated by comparing them to experiments obtained with prototype devices.