Abstract:
In this thesis the development of a single pass non-dispersive infrared (NDIR) CO2 gas sensor
with a path length of 30mm and with a lowest level CO2 detectivity of 20 ppm is described. A
single pass NDIR CO2 sensor was developed in order to better understand the effect of the
different sensor components i.e. the infrared source, thermal detector and the interference filter
has on the NDIR CO2 gas sensor’s sensing ability for the industrial gas sensing application. . The
study of various IR sources, detectors and filters has resulted in developing methodology that can
be used for characterising IR sources detectors and filters from an application point of view. The
obtained result from such application specific characterisation shows a more realistic measure of
the NDIR CO2 sensor’s individual components performance characteristic, than what is quoted
by the manufacturer of the IR sources, detectors and filters. The developed characterisation
methodology is novel in its own right as such methodology currently to the author’s knowledge
does not exist in the available literature.
In order to better understand the effect of different infrared (IR) source, detectors and filters four
different types of IR sources (microbulb, membrane type source, IR-LED source and ICX 2Dmetallo
photonic crystal sources/detector pair), three different type of IR detectors Pyroelectric
detectors, Thermopile detectors and 2D-metallo photonic crystal source/detector pair and two
interference filters were investigated. A new amplitude modulation (AM) scheme was developed
for driving the 2D-metallo photonic crystal device as a detector. This has resulted in an
improvement of the 2D-metallo photonic crystal devices detectivity by a factor of 102 compared
to the standard / conventional / recommended scheme. Demonstrations of the performance of the
developed NDIR CO2 gas sensor are also shown in this thesis.
