the control circuit causes alternately the first and second combinations to vibrate, and causes alternate transmission of {HEAD ~ 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 alternate transmission of { HEAD ~ 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 OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH