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MEMS-based thermal emitters and beyond

Components and investigations for miniaturised NDIR systems
: Hildenbrand, Jürgen
: Wöllenstein, Jürgen; Korvink, Jan Gerrit

Tönning: Der Andere Verlag, 2010, XIV, 168 pp.
Zugl.: Freiburg/Brsg., Univ., Diss., 2009
Microsystem Simulation, Design and Manufacture, 2
ISBN: 978-3-86247-011-2
Fraunhofer IPM ()
Infrarotabsorption; MEMS

This thesis is focused on the development of components for NDIR absorption spectroscopy. Such a system consists of a broad band infrared source, a measurement cell and a detection unit. The system performance is determined by the right combination of suited components, Therefore, novel thermal emitters were developed within this thesis with improved spectral emission and optimised for fast transient operation, respectively, The developed designs were investigated theoretically by numerical simulation (finite element method) before the emitter fabrication. The characterisation processes comprise both the electro- thermal investigations and spectral measurements of the emitted radiation and the determination of the optical power. Scanning electron microscopy was used for the structural investigations e.g. after high temperature treatment. Another important component of a NDIR system is the measurement cell. Here, a White cell configuration was used to develop a small absorption cell with a multiple folded optical path. The configuration and its coupling optics were optimised using optical ray tracing, An alternative version made of plastic was also developed and compared to the aluminium White cell. Additionally, an accumulating method for sensitivity enhancement for non-continuous measurements was worked out and tested. The advantage of this method lies in the possibility of micro integration using MEMS technologies. Finally, a system for ethylene monitoring for fruit ripening in store-houses was developed. The system is based on the developed broadband emitter and the White cell. During the system development, anti-reflection coatings for the mid infrared region on silicon Fresnel lenses were developed.