It's only a $100 toy--an aquarium of swimming robotic fish developed by the Eamex Corporation in Osaka, Japan. What makes it remarkable is that the brightly colored plastic fish propelling themselves through the water in a fair imitation of life do not contain mechanical parts: no motors, no drive shafts, no gears, not even a battery. Instead the fish swim because their plastic innards flex back and forth, seemingly of their own volition. They are the first commercial products based on a new generation of improved electroactive polymers (EAPs), plastics that move in response to electricity.

For decades, engineers who build actuators, or motion-generating devices, have sought an artificial equivalent of muscle. Simply by changing their length in response to nerve stimulation, muscles can exert controlled amounts of force sufficient to blink an eyelid or hoist a barbell. Muscles also exhibit the property of scale invariance: their mechanism works equally efficiently at all sizes, which is why fundamentally the same muscle tissue powers both insects and elephants. Something like muscle might therefore be useful in driving devices for which building tiny electric motors is not easily accomplished.

   
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