Weighted Conical Type Limited-Diffraction-Beam Transducers for High-Resolution Ultrasound Imaging

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The purpose of this research project is to develop a new type of limited-diffraction-beam transducer which has a conical radiation surface for high-resolution ultrasound imaging. The results obtained in this project are as follows :(1)Discretely weighted structures have been presented that will facilitate the fabrication of weighted conical transducers. Divided conical transducers composed of a segmented cone with discrete weighting can create sound fields almost the same as those for the continuously weighted complete conical transducers.(2)A simple and practical method of realizing weighted conical transducers have been examined that uses apodisation on the vibration area by forming narrow electrode strips of a uniform width spreading radially on the transducer.(3)A weighted conical transducer has been fabricated using a piezoelectric composite with 1-3 connectivity that has the electromechanical coupling coefficient larger than that of a PVDF film. It has been shown that the large electromechanical coupling coefficient of the piezocomposite material increases the transducer sensitivity by 7 dB or more.(4)It has been demonstrated through preliminary experiments with B-mode imaging that high resolution is maintained over a large depth.