Near Infrared spectroscopy has become one of the main workhorses for fast, reliable and robust process applications. NIR spectroscopy is a main spectroscopic method in the e.g. pharmacy- , food- or chemical industry.
The possibility of usage of glass fibres, fast and rugged spectrometer systems favours the technology compared to others. A main drawback of the current NIR systems is their size and price.
One solution can be the miniaturisation of the spectrometer systems combined with low cost production based on MOEMS (micro optical electromechanical mirror system) technology.
Drawing of the micro- mechanical device with
the positioning of the grating and elements
of drive mechanism.
A NIR spectrometer system based on a Czerny Turner set-up was constructed and assembled based on the MOEMS technology by the Fraunhofer IPMS institute and is tested by the ICT Fraunhofer institute. Applications were performed using the MOEMS spectrometer and compared with conventional diode array spectrometer systems.
Identification of plastics and textiles, quality of tomatoes as well as on-line extruder measurements including prediction models (PLS) were done.
The miniaturized spectrometer is well suited for classification of materials recognizable for spectroscopic measurements. Measurement time lasts 1 sec to 3 sec whereby the system was connected with glass fibres and conventional reflection probes.
Extruder measuremts were done in transmission measuring different blend composition. The system was compared to a conventional spectrometer system (Carl Zeiss MCS 611). Despite the signal to noise ratio of the MOEMS spectrometer was lower compared to the ZEISS system the prediction results i.e. the RMSEP yielded slightly lower vlaues.
An extension of the concept is currently under inverstigation i.e. the designing of a two dimensional imaging system. The second axe of the mirror is utilized and the spectrometer system is used as a push broom imaging system. Such a system was developed and will be tested for plastic identification puposes in a research project whereby the objects are scanned when moving on a conveyor belt.
This development will enlarge the field of possible application tremendously. Combining the small size, low achievable prices and manifolded applications it will boost the MOEMS spectrometer system as it will meet the increasing demands of users and the market in the future.
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Wolfgang Becker, Fraunhofer Institut für Chemische Technologie, Pfinztal / Germany
Heinrich Grüger, Thomas Eggloff, Fraunhofer Institut für Photonische Mikrosysteme, Dresden /Germany
Fraunhofer Institut für Chemische Technologie (ICT)
Tel. ++49 (0)721 4640 154
Fax. ++49 (0)721 4640 111
Internet: http://www.ict.fraunhofer.de http://www.fhg.de