The primary goals of this research are to design, construct and test a new class of wideband, non-resonant, high efficiency ultrasound piezoelectric transducers based on modern materials. The transducers will be designed to work at clinically useful frequencies and will be suitable interfaced with commercially available ultrasound machines. In contrast to conventional piezoelectric ceramic or composite transducer design in which the bandwidth is controlled by the thickness resonance frequency of the active element, this design will use a non-resonant transducer structure. This will be achieved by using PVDF polymer or copolymer as an active piezoelectric material. This material will improve transducer manufacturability and reduce production costs and is well suited to fabricate novel ultrasound transducers with at least twice as wide bandwidth as that obtained with conventional (bandwidth limited) probes made of piezoelectric ceramics. The implementation of the wideband transducer design proposed makes use of coded multilayer approach in which the bandwidth is determined by the thinnest active PVDF film and the sensitivity is increasing with the number of active polymer layers, i.e. the length of the code. In such approach, the transducer will operate well below its resonance frequency and will be optimized to cover frequency bandwidth from 1 to 10 MHz relevant for clinical imaging. Such design will allow bandwidth enhancement, and, at the same time, will provide overall sensitivity comparable to that available with conventional piezoelectric materials. This bandwidth enhancement provides improved signal-to-noise ration in image analysis methods such as those based on Split Spectrum Processing (SSP) approach. In addition, increased bandwidth will reduce speckle noise in the frequency compounding method of imaging. Another immediately useful aspect of wide bandwidth transducers is that it allows frequency changing for conventional narrow band operation without changing the transducer. The ability is needed in intracavitary probes and is desirable for clinical convenience with all probes. The ultimate goal of the development of wideband pulse-echo polymer transducer is to interface it with modern ultrasound diagnostic machines and have the assembly used for improved tissue characterization.
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