For example, the characteristic length may be a side length or a diagonal length when {HEAD ~ the transmission surface} has {TAIL ~ a square shape}, or may be a diameter when the transmission surface has a circular shape 
has
For example , the characteristic length may be a side length or a diagonal length when { HEAD ~ the transmission surface } has { TAIL ~ a square shape } , or may be a diameter when the transmission surface has a circular shape
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH