Influence of pulse drive shape and tuning on the broadband response of a transducer

The shape and symmetry of the pulser drive waveform and its interaction with the transducer and its tuning circuitry have a profound effect upon the pulse echo performance achievable from a medical transducer probe. Conventional wisdom has it that the shortest pulse obtainable, and subsequently the widest bandwidth achievable will come from the impulse response of the system. This study helps elucidate why an impulse generator may not always result in the shortest pulse and widest bandwidth. The pulse response is critically dependent upon the pulser drive symmetry, and its interaction with the reactance of the components making up the tuning topology. Unipolar pulses such as the spike impulse, or half wave square unipolar pulse drive, can create notches in the drive spectrum at the gold electrode that are deleterious, and significantly reduce available bandwidth. The transducer model used in this study is a 3.5 MHz 96 element sector phased array. In conjunction with a new innovative transducer acoustic design and optimized tuning, experimental results producing bandwidths of over 90% with clean, short pulse ringdown, have been achieved.