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26 Biomimetics: Biologically Inspired Technologies

U.S. signals piezoelectric foils were used with an electro-mechanical conversion factor, d 33 ,
ranging from 250 pC/N to 400 pC/N (Neugschwandtner et al., 2001). To demonstrate the simulation
of the bat capability the developed sensors were used to navigate robots. Current efforts are focused
on classifying landmarks, navigation in natural environments, making use of body movement, and
echo interpretation (Muller and Hallam, 2004).

1.7.5 Acoustic and Elastic Wave Sensors

Certain animal species are equipped with the ability to sense acoustic or elastic waves at great
distances. The elephant can rock its foot and emit vibrations that travel through the ground and are
felt and recognized by other elephants at a distance of several kilometers. The whale emits hyper-
low frequency sound that travels over great distances in the ocean and can be detected and identified
by other whales. Equivalent detectors made by humans include accelerometers used to detect
earthquakes and the sonar used in submarines. However, biological capability is still far superior
in terms of sensitivity, spectral response, and evaluation capability than any man-made detection
instrument.

1.7.6 Fire Monitoring

The jewel beetle (Melanophila) lays its eggs in the bark of freshly burned trees using its ability to
detect forest fires from a distance of about 80 km (http://www.uni-bonn.de). The sensory organ that
is used for this is located on the underside of the beetle, and consists of a pit that contains a large
number of receptors that are extremely responsive to the infrared (IR) radiation created by a forest
fire. Recently, zoologists at the University of Bonn have been trying to imitate this sensory
capability. The study by Schmitz and Trenner (2003) led to the development of a sensor that is
sensitive to infrared and automatically monitors large forest areas to trigger an early warning in the
event of fire. As biological imitation of the beetle’s cuticulas sensory organ, a polyethylene platelet
was developed, which absorbs thermal radiation with wavelength of 3 mm, which is the typical
radiation emitted by fierce force fires. This sensor was found to be two orders of magnitude more
sensitive than commercially available IR sensors. This new sensor is expected to be produced at
lower cost than commercial detectors and efforts to further improve its sensitivity are currently
underway.

1.7.7 Sense of Smell and Artificial Nose

The topic of smell sensing has reached a level of interest and progress that led in 2004, to the Nobel
Prize Award given to the researchers Buck and Axel (1991). The sense of smell is our analyzer
of chemicals of airborne molecules allowing us to determine presence of danger, hazardous
chemicals as well as gives us the enjoyment of good food and other pleasant odors. Using receptors
in our nose we continuously examine the content of the air we breathe, where the signals are sent
through stations called glomeruli that are located in the brain’s olfactory bulb. From there, the
signals are sent to the brain where patterns of smell memories are formed and compared with
previous ‘‘records.’’ The sense of smell alerts us of such danger as smoke from fire, leakage of
dangerous gases, as well as informs us of other relevant information, such as the presence of food or
even perfume from other individuals. The detectable chemicals need to be sufficiently small to be
volatile so that they can be vaporized, reach the nose, and then dissolve in the mucus. It is estimated
that our nose can distinguish between as many as 10,000 different smells.
Imitating the nose’s sensing capability offers important potential applications, and efforts to make
such sensors have been explored since the mid-1980s. There are several devices that have been built
and tested emulating the nose including some that use chemical sensor array (Bartlett and Gardner,