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2.4. Olfaction—The Sense of Smell 23
• Piezoelectric crystals. Crystals that expand and contract in response to
changes in an electric field. Work in this area has long been conducted
by the University of North Carolina [4].
• Shape memory alloy. Shape memory alloy wires and contract springs
contract when heated and then expand again as they cool. An inter-
esting haptic device based on this technology was developed at Har-
vard [10].
• Pneumatic systems. This type of system operates using air jets with an
array of air nozzles that can be grafted to a display device. For example,
the Rutgers Master II operates using pneumatic pistons which are posi-
tioned in the palm of the hand and can be activated to apply a force to
both the fingers and thumb ...