PVDF polymers: Imaging transducers and ultrasonic hydrophone probes

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Abstract
This paper presents practical applications of PVDF polymers in biomedical ultrasonics. The applications discussed entail both miniature hydrophone probes for sensing ultrasonic fields and a new generation of non-resonant pulse-echo imaging transducers, which use multilayer polymer films. The multilayer PVDF transducer structure discussed here represents a relatively unconventional approach to the pulse-echo imaging transducer design. The non-resonant design provides exceptionally wide bandwidth and is suitable for operation at the clinically relevant frequencies. The design described uses multiple active piezopolymer layers arranged according to a Barker code pattern and is adapted for pulse echo imaging. The operation principle of the switchable Barker code transducer (SBCT) is outlined and it is shown that not only SBCTs pulse-echo sensitivity is on a par with that achievable with the resonant PZT or PZT composite transducer design but also the bandwidth achievable with SBCTs is twice as large as that exhibited by the conventional imaging scanheads. Also, it is demonstrated that the SBCT can be driven by virtually any excitation signal. This allows a potential improvement in clinical diagnosis by optimizing image resolution at a given penetration depth. To verify the computer simulation results, several three and seven layer Barker code transducers were fabricated and tested. The experimental results were found to be in good agreement with the theoretical predictions.

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