I know that this does not give dimensions, but it will give a general idea:-
http://en.wikipedia.org/wiki/Polish_mine_detector
There is also a thread on this Forum from way back in 2003 about this very item:-
http://www.mapleleafup.org/forums/showthread.php?t=424
Nigel Watson is still on the scene here, as is Cliff, so they should be able to help or suggest where you can get help.
Paul.