Electronic Nose Uses Standard Monitor
Daniel S. Burgess
An electronic nose under development at Linköping University in Sweden may be able to detect the odors of spoiled food in your kitchen before you catch a whiff of them. An offshoot of the scanning light pulsed technique, in which a scanning laser beam reveals localized changes in the surface potential of a chemically selective semiconductor, the chemical imager promises to be more economical and compact by using a standard computer monitor as its light source.
An electronic nose under development for consumer applications replaces the expensive and complex equipment in the scanning light pulsed technique with a standard computer monitor. Courtesy of Daniel Filippini.
To demonstrate the approach, Daniel Filippini and Ingemar Lundström employed a 17-in. Nokia cathode-ray tube monitor with a resolution of 1024 x 768 pixels and a refresh rate of 85 Hz. A metal-oxide semiconductor capacitor on which square, triangular and circular regions of 40-nm-thick palladium and 9-nm-thick platinum were deposited functioned as the detector, producing a photocurrent that changed in the presence of adsorbates or reaction products as the light from the monitor stimulated the structure. A current amplifier and a lock-in amplifier collected and displayed the electrical signals as images in another window on the screen as the system was exposed to hydrogen or ammonia at 1000 ppm in synthetic air.
Filippini said that the monitor-based setup performs as well as the scanning light pulse technique for simply detecting the presence of a chemical. Although the latter's higher accuracy enables its use as a local probe for research, he noted that it typically does not feature a resolution better than 200 µm in both the X and Y directions. In comparison, the pixel pitch of the monitor in the experiments was 250 µm.
To achieve this, Filippini said, the researchers could use data processing to digitally disentangle the images produced in the current setup, or they could introduce an array of collimating and focusing lenses. A preliminary investigation with disposable optics, he said, has yielded a resolution close to 200 µm.
Currently, they are working to commercialize the electronic nose for consumer applications, including testing the quality of food at home. In such cases, replacing the up to $10,000 of equipment in the scanning light pulsed technique -- an X-Y table, positioning controller, modulated laser source and accessories -- with something as ubiquitous as a cathode-ray tube or a liquid crystal display is key.
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