the control circuit causes alternately the first and second combinations to vibrate, and causes {HEAD ~ alternate transmission} of the ultrasonic wave with {TAIL ~ the second directivity} and that with the third directivity 
the control circuit causes alternately the first and second combinations to vibrate , and causes { HEAD ~ alternate transmission } of the ultrasonic wave with { TAIL ~ the second directivity } and that with the third directivity
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH