| The purpose of this study is to propose and implement a new type of high-frequency single-element annular transducer (SEAT) with increased bandwidth. Such a broadband transducer can be used to improve the axial resolution and/or to perform contrast and tissue harmonic imaging. Compared with the conventional single element uniform thickness (SEUT), the SEAT has an annular geometry with the thickness of the piezoelectric material increasing from the center to the outside. The SEAT consisted of six subelements, whose thickness ranged from 60 £gm to 110 £gm. Note that each side of annular pattern is electrically connected by a single electrode. For comparisons, both SEAT and SEUT transducers were designed and fabricated. The mean center frequencies of the SEUT and SEAT were 41.3 MHz and 42.4 MHz, respectively. The -6 dB fractional bandwidths were 69% for the SEUT and 82% for the SEAT. The two-way insertion losses of the SEUT and SEAT were 16.4 dB and 19.5 dB, respectively. The measured -6 dB lateral beam widths were 92 £gm for the SEUT and 108 £gm for the SEAT. The depth of field of SEAT was increased by 33.5 % as compared with the SEUT. Fabrication methods for such transducers were successfully developed and implemented. The SEAT enhanced the overall bandwidth and with a tradeoff of slight degradation in sensitivity. Finally, this type of transducers can also be used for multiple band imaging. |