2.3 - Thermal modulation behavior of infrared emitters with cantilevered heating elements

AMA Conferences 2017
2017-05-30 - 2017-06-01
Nürnberg, Germany
Proceedings IRS² 2017
I2 - Spectroscopy and Gas Analysis
T. Ott, M. Schossig, G. Gerlach - Technische Universität Dresden (Germany)
774 - 778


In non-dispersive infrared (NDIR) gas analysis thermal infrared (IR) emitters and pyroelectric sensors are used together to utilize the absorption of IR radiation by gases at characteristic wavelengths. The infrared source has to provide alternating infrared radiation as pyroelectric detectors are only sensitive to changes of radiation and alternating electrical signals can be better processed. Because mechanical choppers prevent the miniaturization of the gas sensor and make the system susceptible, it is necessary to use an electrically modulated IR emitter. Under cyclic excitation the thermodynamic properties of the IR source affect the emitted infrared radiation and, in consequence, the sensor signal. Optimal gas sensor operations (e.g. with regard to gas measurement resolution) require to know which factors influence the thermodynamic properties of thermal emitters.

In this paper an analytical approach is introduced to determine the influence factors on the thermodynamic properties of IR emitters with cantilevered heating elements. The approach is based on the conservation of energy, which means that the electrical input power is completely dissipated into Joule heat, e.g. through radiation and heat conduction. To balance all dissipated heat fluxes, the first law of thermodynamics is applied. Following the Stefan-Boltzmann law the thermal heat flux radiated by the heating element of the IR emitter is dependent upon the fourth power of its thermodynamic (absolute) temperature. Thus, the thermal balance equation is a nonlinear differential equation of first order. As this equation cannot be solved analytically, a numerical solution process is applied. Finally, the model is validated by means of measured heating and cooling temperature curves of an IR emitter.