J. Phys. D: Appl. Phys. 34 (2001) R125–R149
Function and applications of gas sensors
Dieter Kohl
Institute of Applied Physics, University of Giessen, Holbeinring 16, D-35390 Giessen,Germany Received 3 April 2001Published 18 September 2001Online at stacks.iop.org/JPhysD/34/R125 Abstract
Gas sensors directed to high-volume applications are discussed. Mainly
semiconductor sensors cover this sector, but the merits of competing devices
are shown in comparison. Chemical and physical function is elucidated by
spectroscopic results and molecular calculations. Important applications,
e.g. monitoring of combustibles, especially methane, and the early detection
of fires, are presented as illustrations. Progress in microelectronics has
enhanced the development of electronic noses. An early example of such
noses, the identification of solvents and also the present state of food aroma
detection are described.
are usually more application oriented, e.g. ‘Sensoren undMesssysteme’ in Germany (www:http://www.vde.com/itg). A book series with yearly updates has covered the state of sen- sor chemistry, physics and technology to a large extent for a 2.2. Conductance response to beams of CO and O2 The following review focuses on gas sensors for high- volume applications. Semiconductor sensors are prevailing in 2.3. Different types of surface oxygen differ in this sector because they are cheap to produce. The basics of chemical and physical function are elucidated by spectroscopic 2.4. Specivity dependence on the metal atom results and molecular calculations. Important applications are 2.5. Spillover effect and ‘sensor sleep mode’ Within the last decade the availability of microcontroller 2.6. Electron transfer between metal cluster and chips with prices below US$1 have stimulated more complex gas sensor systems, usually tagged as electronic One of the first successful applications, the identification of solvents by a set of electrochemical cells, is still available as an optional module of the ‘Lennartz 5.1. Sensor arrays for on the spot identification of Moses II’, electronic nose (http://www.lennartz-electronic.de), also featuring semiconductor and microgravimetric gas sensors [2]. Besides a description of this historical landmark, recent results from food aroma analysis by gas sensors are reported.
1. Introduction
2. Function
Periodic international sensor conferences are devoted pre- First a short summary of gas sensor operating principles shall dominantly to fundamental research, for example Trans- ducers/Eurosensors (http://www.transducers01.de/) and SGS Microcalorimetric gas sensors (pellistors) burn com- (semiconductor gas sensors, http://zeus.polsl.gliwice.pl/∼zm/), bustible gases with the surrounding air on the surface of a smallPITTCON ball or film of a catalytically active metal [3]. The catalyst, e.g.
http://www.pittcon.org/exhibitor.htm). National conferences Pt, Pd or Rh, is kept at 500–600 ◦C. The heat of combustion in

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