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-Perot structure.
The obtained emission of the Fabry-Perot 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 μm. The
theoretical results are validated by comparing them to experiments obtained with prototype devices.
Every gas (e.g. CO2) absorbs IR-radiation at individual gas specific IR-wavelengths. Non-dispersive infrared (NDIR) gas
sensors exploit this property for gas monitoring. Such sensors are used in various applications, e.g. for control of air
quality in office buildings or cars. This is a big market for low cost sensors. A NDIR sensor consists basically of three
components: an IR-emitter, a chamber containing the sample gas, and an IR-detector with a filter for the observed
wavelength. Commercially available systems use broadband IR-emitters (e.g.: micro-lamps) in combination with
thermopile or pyroelectric detectors fabricated with a narrowband gas-specific IR-filter, e.g., an interference filter. We
devised a concept for a simple and cost-effective NDIR-gas sensor based on two non-symmetric Fabry-Perot absorberstructures
as IR-emitter and as IR-detector where no additional interference filter is needed. The presented sensor
combines thin layer technology with optical sensing techniques. The system was first analyzed using ray tracing models
based on a Monte Carlo method in order to model the response function of the system's sample chamber. For our results,
the sample gas is CO2 where the major absorption is centered around 4.26μm.