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