The first directivity is different from a second directivity of {HEAD ~ the ultrasonic wave} transmitted from {TAIL ~ single transmission element} 
transmitted from
The first directivity is different from a second directivity of { HEAD ~ the ultrasonic wave } transmitted from { TAIL ~ single transmission element }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL