A transmit beamformer includes multiple transducers, each responsive to a respective transmit waveform to produce a respective transducer waveform. A transmit waveform generator generates the transmit waveforms, and the transmit waveforms each include multiple frequency components. Progressively higher...http://www.google.fr/patents/US6122222?utm_source=gb-gplus-shareBrevet US6122222 - Ultrasonic transmit and receive system