Device 2 or 3, wherein {HEAD ~ said grid} further comprises {TAIL ~ at least one return connection} , linking together two sides of said frame , the grid being made from an electric conducting material 
comprises
Device 2 or 3 , wherein { HEAD ~ said grid } further comprises { TAIL ~ at least one return connection } , linking together two sides of said frame , the grid being made from an electric conducting material
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH