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