Development of an infrared absorption spectroscope based on linear variable filters
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Date
2009-05-15
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Abstract
The objective of this thesis is to develop a low-cost infrared absorption spectroscope
based on linear variable filter (LVF) technology for the automated detection of gases and
vapors, and the semi-automated detection of liquids. This instrument represents an
alternative to electronic-nose instruments based on cross-selective gas sensor arrays.
Instead, the proposed instrument uses the idea of computational “pseudo-sensors”,
whereby spectral lines in an analytical instrument are clustered into groups and used as
independent variables. We characterize the system on a number of performance metrics,
uncovering its detection limits and resolving power. We present calibration methods to
estimate the concentration of analytes in a matrix of absorbing species, as well as signal
processing techniques for spectral classification. Specifically, we validate the instrument
on a mixture calibration problem with simple and complex chemicals, and compare the
efficiency of different calibration methods to estimate the concentration of one analyte in
the matrix. Moreover, we demonstrate the use of the instrument on two real-world
applications in the foodstuffs domain: oil adulteration and trans fatty acid (TFA)
detection. The instrument, combined with signal processing techniques, is able to fully discriminate oils, as well as classify margarine and spreads onto high-TFA and low-TFA
groups. Despite operating at a low spectral resolution, our results show that the LVF
based spectroscope is a promising alternative to traditional analytical techniques for
selected niche applications.
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Keywords
Infrared spectroscopy, linear variable filter, signal processing