{HEAD ~ A detection area} of {TAIL ~ an ultrasonic wave} depends on an area of a transmission surface and corresponding characteristic length of the transmission surface 
{ HEAD ~ A detection area } of { TAIL ~ an ultrasonic wave } depends on an area of a transmission surface and corresponding characteristic length of the transmission surface
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 OTH OTH