Design, development and characterization of wideband polymer ultrasonic probes for medical ultrasound applications.

摘要

This dissertation deals with the design, development and characterization of non-resonant polymer ultrasonic probes for medical ultrasound applications. Both single element and multielement imaging transducer design having single layer and multilayer configuration were developed with the primary goal of minimizing the trade off between resolution and penetration depth.; The simultaneous improvement in the transducers' pulse-echo sensitivity and bandwidth was achieved by employing a multilayer structure made of thin piezopolymer films and utilizing the concept of Barker code. The results of the experiments indicated that the multilayer Barker code transducers provided the widest bandwidth in comparison with the imaging transducers made of conventional piezoelectric ceramic material. Also, they exhibited enhanced sensitivity compared to a single layer piezopolymer transducer. Specifically, the results indicated that the −6 dB fractional bandwidth extending over 2 decades (20 MHz) could be achieved in the case of non-resonant transducers, whereas the conventional resonant design imaging transducer could provide only about one half of the bandwidth. The polymer array transducers also showed uniform acoustic response from element to element, which is desirable in order to obtain high quality ultrasound images.; The double layer hydrophone probes used for characterization of the imaging transducers were fabricated using dissimilar thickness of PVDF polymer film. This technique ensured simultaneous enhancement of sensitivity and bandwidth. Also, a measurement procedure employing planar scanning technique was developed to calibrate the hydrophone probes below 1 MHz for adequate characterization of acoustic field produced by the imaging transducers.; The results of this work indicate that the new class of transducers developed features significantly enhanced bandwidth. Such transducers hold promise to be capable of operating at clinically relevant frequencies and suitable for use at fundamental, subharmonic and higher harmonics imaging. It is expected that this non-resonantly operating imaging transducer would become a useful clinical tool in medical imaging and could improve diagnostic efficacy.