We present the development and characterization of a fiber-optic colorimetric gas sensor combined with the electronic
circuitry for measurement control and RFID communication. The gas sensor detects ammonia using a 300 μm polyolefin
fiber coated with a gas-sensitive polymer film. The spectral and time-dependent sensitivity of various polymer films was
tested in transmission measurements. Light from a standard LED at λ = 590 nm was coupled into the polyolefin fiber
through the front face. A prototype of the gas sensor with the direct coupling method was tested under realistic
measurement conditions, i.e. battery-driven and in a completely autonomous mode. The sensor system showed good
sensitivity to the ammonia concentrations and response times in the order of minutes. The achievable power
consumption was below 100μW.The films contained the pH-sensitive dyes bromocresol purple or bromophenol blue
embedded in either ethyl cellulose or polyvinyl butyral, and optionally tributyl phosphate as plasticizer. The
bromophenol blue based films showed a strong reaction to ammonia, with saturation concentrations around 1000 ppm
and response times of about 15 seconds to 100ppm. The colorimetric reaction was simulated using a simple kinetic
model which was in good agreement with the experimental results.
The work presented here focuses on the investigations of metallo-porphyrins and their gasochromic behavior.
Gasochromic materials change their color while they are exposed to a certain gas. So they offer the possibility to develop
very selective chemical gas sensors. In the focus of this work is the metallo-porphyrin 5, 10, 15, 20-
tetraphenylporphyrin-zinc (ZnTPP). When embedded into a polymeric matrix (PVC) the color change to the toxic gas
NO<sub>2</sub> can be detected. During exposure to NO<sub>2</sub> the dye changes its color from bright purple to yellow. To develop a standalone
gas sensor, the ZnTPP/PVC matrix is deposited onto a planar optical waveguide. The color change of the porphyrin
dye, due to the gas exposure, can be detected in the evanescent field of the optical waveguide. Therefore the light of a
high power LED is coupled into the waveguide. The color change of the porphyrin is detectable with photodiodes as
variations of the decoupled light intensity. The sensor shows no cross-sensitivities to other gases like CO<sub>2</sub>, NH<sub>3</sub>, EtOH,
CO or water vapor. NO<sub>2</sub> is detectable with a limit of 1 ppm.
A novel micromachined thermal emitter for fast transient temperature operation is presented. Compared to most
commercial available thermal emitters, the one here presented, is able to operate in a pulsed mode. This allows the use of
lock-in techniques or pyrodetectors in the data acquisition without the use of an optical chopper for light modulation.
Therefore, these types of thermal emitters are very important for small filter photometers. Several spider type hotplate
concepts were studied in order to find a design with excellent mechanical stability and high thermal decoupling. The
thermal emitters are fabricated using silicon on insulator (SOI) technology and KOH-etching. The emitters are heated
with Pt-meanders. For temperature determination an additional Pt-structure is deposited onto the hotplates. The emitters
are mounted in TO-5 housings using a ceramic adhesive and gold wire bonding. The used operation temperature is
750°C. In pulsed operation it's important to have a large modulation depth in terms of thermal radiation intensity in the
needed spectral range. The maximal reachable modulation depth ranges from ambient temperature to steady state
temperature. A modulation frequency of 5 Hz still allows using nearly the maximum modulation depth.