Robotics Reference
In-Depth Information
capacitance the electronic tongue takes advantage of the fact that the
plastic films are sensitive to the substances responsible for various tastes.
Each sensor responds differently to different tastes, acting as a kind
of human taste receptor. A composite detector that incorporates all four
types of sensor therefore produces an electronic “fingerprint” of the taste.
The electronic tongue can correctly distinguish between different types
of coffee, different brands of orange juice and different types of milk. In
some tests it has outperformed most humans when discriminating be-
tween various brands of mineral water, between samples of a particular
type of wine taken from different wineries, and even between the same
type of wine from the same winery but from different years. It easily dis-
tinguishes among the five basic human taste patterns: sweet, salty, bitter,
sour and umami,
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even in concentrations that cannot be perceived by
humans. The electronic tongue can also sense low levels of impurities in
waterandcanspotsugarandsaltinconcentrationsthatarefartoolow
for human detection.
Instead of using plastic sensors scientists in Texas have taken a differ-
ent approach to taste recognition. John McDevitt and his team at the
University of Texas in Austin have developed a silicon chip with micro-
scopic wells etched into its surface, each well acting as a tiny taste-bud.
Each well holds a minute plastic bead made of polyethylene glycol and
polystyrene, coated with sensitive chemicals that change colour accord-
ing to the taste of the molecules that touch them. Each bead is equipped
with a sensor for a particular class of chemicals, corresponding to a par-
ticular taste sensation. The colour changes are detected by placing the
silicon chip in front of a light source and measuring the red, green and
blue patterns. Each of the different colour patterns corresponds to a dif-
ferent taste.
The large number of chemically sensitive micro-sensors on the chip
serve as artificial taste buds. They can be prepared a billion at a time, al-
lowing for the creation of a sufficient supply for the entire world's needs
for specific substances, such as the AIDS virus, anthrax spores or choles-
terol. In one field study, in Botswana, conducted by researchers from
Harvard and the University of Texas, tongues employing the technol-
ogy of these chips were used successfully to detect HIV in villagers, with
the results being processed in minutes, not days or weeks, and without
having to send blood samples to another location for testing.
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The taste of monosodium glutamate.
