DEVELOPMENT OF WIDEBAND TRANSDUCERS FOR MEDICAL IMAGING

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The primary goals of this research are to design, construct and test a new class of wide-band, non-resonant, high efficiency ultrasound piezoelectric transducers based on modern materials. Based on the preliminary results, the design proposed is capable of operating in the frequency range 1 to 10 MHZ using one scan head only. The transducers will be designed for clinically useful frequencies and will be suited to interface 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 non-resonant transducer structure. This will be achieved by using PVDF polymer as an active piezoelectric material. This material is well suited to fabricate novel ultrasound transducers with at least twice the bandwidth as that obtained with conventional (bandwidth limited) probes made of piezoelectric ceramics. In particular, the proposed design makes use of a multi-layer approach in which the bandwidth is determined by the thinnest active PVDF film and the sensitivity is proportional to the number of active polymer layers. In such an approach, the transducer will operate well below its resonance frequency and will be optimized to cover the relevant clinical imaging frequency bandwidth from 1 to 10 MHz. Such design will allow bandwidth enhancement and, at the same time, will provide overall sensitivity on a par with that available with conventional piezoelectric materials. This bandwidth enhancement provides improve signal-to-noise ration in image analyses, such as those based on the Split Spectrum Processing Approach, and tissue scatterer analysis with spectral redundancy. Furthermore, wide bandwidth transducers will allow improved ultrasound tissue characterization utilizing cepstrum based deconvolution. In addition, increased bandwidth will reduce speckle noise in the frequency compounding method of imaging. Another immediately useful aspect of wide bandwidth transducers is the allowance of frequency changes for conventional narrow band operation without changing the transducer. This ability is needed in intracavitary probes and is desirable for clinical convenience with all probes. The ultimate goal of the development of the wide-band pulse-echo polymer transducer is to interface it with modern ultrasound diagnostic machines and have an assembly capable of improve tissue characterization at clinically relevant frequencies using only one scanhead.