In　order　to　realize　the　closed　loop　control　of　diphase　oppositing　giant　magnetostrictive　hydraulic　servo　salve　without　the　independent　displacement　sensor,　the　output　displacement　of　the　actuator　was　detected　by　measuring　the　change　of　the　driver　coil　voltage　drop,　based　on　the　characteristic　that　the　magnetic　permeability　of　magnetostrictive　material　changes　under　external　load　(inverse　magnetostriction).　A　magnetic　model　which　can　describe　the　dynamic　properties　of　the　material　was　established.　According　to　the　model,　a　new　self-sensing　technique　in　which　the　driver　function　and　the　sensor　function　shared　the　same　coil　was　presented.　A　self-sensing　circuit　was　designed　and　the　principle　was　analyzed.　Experimental　studies　showed　that　the　designed　circuit　can　successfully　detect　the　displacement　of　the　actuator　with　good　dynamic　characteristics.　©　2010　IEEE.