Electronic Olfactory Systems Based on Metal Oxide Semiconductor Sensor Arrays
- PDF / 1,076,027 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 8 Downloads / 239 Views
Electronic Olfactory Systems Based on Metal Oxide Semiconductor Sensor Arrays
Matteo Pardo and Giorgio Sberveglieri Abstract In this article, we present the Pico electronic nose, an artificial olfactory system based on thin-film semiconductor sensors, and two applications: food-quality control (coffee analysis) and environmental monitoring (odors at a landfill site). For both applications, the electronic nose data correlated with that of panels of trained judges. For the coffee, a global index (called the hedonic index) characterizing the sensorial appeal could be predicted with the electronic nose, and for the landfill site, the intensity of odors could be quantified. In this article, we stress the importance of stable and sensitive sensors, such as metal oxide thin films produced by sputtering, and of multivariate data analysis for extracting knowledge (e.g., gaining selectivity) from the data. Keywords: chemical sensors, electronic nose, multilayer perceptrons, thin films, metal oxide semiconductors.
Introduction Electronic noses, in the broadest sense, are instruments that analyze gaseous mixtures to discriminate between different (but similar) mixtures and, in the case of simple mixtures, quantify the concentration of the constituents. Electronic noses consist of a sampling system (for a reproducible collection of the mixture), an array of chemical sensors, electronic circuitry, and data analysis software.1 The sampling system used depends on the sample type and its preparation. To prepare simple gas mixtures for testing, automated gas-mixing stations consisting of certified gas bottles, switches, and mass flow controllers are used. To sense complex odors like food odors, the volatile fraction (the so-called headspace) of the odor is allowed to form inside a vial containing a certain amount of the odor-emitting sample. The chemical sensors, which are the heart of the electronic nose system, can be
MRS BULLETIN/OCTOBER 2004
divided into three categories according to the type of sensitive material used: inorganic crystalline materials (e.g., semiconductors, as in metal oxide semiconductor field-effect transistor structures), organic materials and polymers, and biologically derived materials. Data analysis is a fundamental part of the electronic nose, as it is for any sensor system or analytical instrument. This is not the case for basic research on materials for gas sensing, where the focus is traditionally on single sensors, which give higher responses or higher sensitivity toward a single gas (possibly with minor interference). Analysis of results is done visually, by inspecting the response curves of single sensors at various concentrations. There is normally an absence of statistical validation. Electronic noses, meanwhile, take a step toward real-world experimental conditions. What matters is the difference between re-
sponses (selectivity), not the magnitude of the responses toward single gases (sensitivity). Since single sensors are normally not selective, arrays of sensors have to be used. Analysis
Data Loading...
