▁contract ▁when ▁the ▁field ▁is ▁removed , ▁the ▁rod ▁will ▁actually ▁" c raw l " ▁down ▁the ▁stat or ▁t ube ▁like ▁an ▁in ch w orm . ▁Re pe ated ▁propag ating ▁waves ▁of ▁magnetic ▁flux ▁will ▁translate ▁the ▁rod ▁down ▁the ▁t ube ' s ▁length , ▁producing ▁a ▁useful ▁stroke ▁and ▁force ▁output . ▁The ▁amount ▁of ▁motion ▁generated ▁by ▁the ▁material ▁is ▁proportional ▁to ▁the ▁magnetic ▁field ▁provided ▁by ▁the ▁co il ▁system , ▁which ▁is ▁a ▁function ▁of ▁the ▁electric ▁current . ▁This ▁type ▁of ▁mot ive ▁device , ▁which ▁features ▁a ▁single ▁moving ▁part , ▁is ▁called ▁an ▁el astic - wave ▁or ▁per ist alt ic ▁linear ▁motor . ▁( view : ▁Video ▁of ▁a ▁Mag net ost rict ive ▁micro ▁walk er ) ▁ ▁Adv antages ▁of ▁magnetic ▁actu ators ▁ ▁High ▁actu ation ▁force ▁and ▁stroke ▁( dis p lacement ) ▁ ▁Direct , ▁fully ▁linear ▁trans du ction ▁( in ▁the ▁case ▁of ▁elect rod ynamic ▁actu ation ) ▁ ▁Bi - direction al ▁actu ation ▁ ▁Contact less ▁remote ▁actu ation ▁ ▁Low - vol t age ▁actu ation ▁ ▁A ▁figure ▁of ▁mer it ▁for ▁actu ators ▁is ▁the ▁density ▁of ▁field ▁energy ▁that ▁can ▁be ▁stored ▁in ▁the ▁gap ▁between ▁the ▁rot or ▁and ▁stat or . ▁Mag net ic ▁actu ation ▁has ▁a ▁potentially ▁high ▁energy ▁density ▁ ▁Mag net ▁material ▁ ▁The ▁operation ▁of ▁the ▁magnetic ▁actu ator ▁depends ▁on ▁the ▁interaction ▁between ▁the ▁field ▁from ▁an