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