Wide-band Circular Ultrasonic Transducers

The second harmonic modality is intensively implemented in the new generation of the ultrasonographic imaging equipment. The important reduction of the side lobes is the main gain in lateral resolution and consequently, in contrast dynamic range. Effective use of the second harmonic mode requires the wide bandwidth of the ultrasonic transducer, enabling transmission at the fundamental frequency and reception at the second harmonic. One way of extending the bandwidth of the radiating system is fabrication of the transducer having the thickness changing gradually in function of its radius.

In the paper, the method of modeling and designing wideband circular transducers is described. The piezoelectric transducer including the quarter-wave length matching layer will be modeled as a set of adjacent annular elements using for each annuli of different thickness (different resonant frequency) Mason's equivalent circuit. On the electric ports all elements are connected as a parallel set of piezoelectric rings, and on the acoustic ports as a set of equivalent circuits connected in series, respectively. Optimization of the transducer bandwidth requires finding the thickness range as well as the function describing thickness changes along the transducer radius.