{TAIL ~ A longer characteristic length} of the transmission surface causes {HEAD ~ the ultrasonic wave} to less spread 
{ TAIL ~ A longer characteristic length } of the transmission surface causes { HEAD ~ the ultrasonic wave } to less spread
TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH