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Name: Ian
Status: student
Grade: 9-12
Location: PA
Country: USA
Date: Summer 2011


Question:
Hello and thank you in advance. I have previously read of a material ( a kind of "rubber") that contracts when an electric current is applied.

My question is what is this material, how does it work/what is it made of? Thank you very much.



Replies:
Hi Ian, I believe the material you are referring to is a kind of piezoelectric rubber. Piezoelectric materials (usually they are special types of ceramics or crystals) produce an electrical voltage when compressed of otherwise subjected to stress. They also do the opposite... they slightly expand or contract when a voltage is applied.

But the amount they expand or contract is very small indeed. For example, one square meter of the recently discovered piezoelectric rubber materials typically contracts a mere 100 picometers for ever applied volt. Translated into everyday measurements, this means that if you apply a voltage of 1 Volt to a one foot long piece of this rubber, it will only contract less than half a billionth of an inch! Applying 100 volts will cause it to contract just under 50 billionths of an inch!

While technically interesting, you can see that this effect is rather limited! This material is made from a type of rubber that has a layer of piezoelectric crystals applied to one side. Its proposed use is to generate electrical current when stretched, which is the opposite effect that you are interested in (you are interested in it changing shape when an electrical current is applied).

Regards,
Bob Wilson.


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