An ultrasonic imaging system includes a linear array of transducers of which a group of successively arranged transducers is selected and successively shifted to the next by at least one transducer. The transducers of the selected group are successively activated at respective delay times to transmit...http://www.google.com/patents/US4368643?utm_source=gb-gplus-sharePatent US4368643 - Ultrasonic imaging by radial scan beams emanating from a hypothetical point located behind linear transducer array
