Nick Hiebert, a 23 year old male from the Internet asks on November 14, 1999,Is there a substance known to science that reacts to electrical impulses by contracting or changing its density?
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There may be many such things. One thing I'm aware of are piezoelectric materials that do this: salts, ceramics, and plastics. The chief polymer used for this is Polyvinylidene Fluoride (PVDF). If you do web searches on this, you will find much info. A good explanation can be found at http://www.ndt.net/article/yosi/yosi.htm
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