Abstract
The piezoelectric polymer PVDF and its copolymers have a long history as transducer materials for medical and biological applications. An efficient use of these polymers can potentially both lower the production cost and offer an environment-friendly alternative for medical transducers which today is dominated by piezoelectric ceramics containing lead. The main goal of the current work has been to compare the image quality of a low-cost in-house transducers made from the copolymer P(VDF-TrFE) to a commercial PVDF transducer. Several test objects were explored with the transducers used in a scanning acoustic microscope, including a human articular cartilage sample, a coin surface, and an etched metal film with fine line structures. To evaluate the image quality, C- and B-scan images were obtained from the recorded time series, and compared in terms of resolution, SNR, point-spread function, and depth imaging capability. The investigation is believed to provide useful information about both the strengths and limitations of low-cost polymer transducers.
Highlights
Scanning acoustic microscopy (SAM) is a widefield non-destructive and non-invasive technique that has been widely used over several decades for surface and subsurface microscopic imaging especially for industrial and biological specimens [1,2,3]
The lateral resolution in scanning acoustic microscopy generally depends on the acoustic wavelength and the f-number of the transducer [2]
We produced a small aperture P(VDF-TrFE) copolymer transducer appropriate for high-frequency imaging which was compared to a commercial Polyvinylidene difluoride (PVDF) transducer
Summary
Scanning acoustic microscopy (SAM) is a widefield non-destructive and non-invasive technique that has been widely used over several decades for surface and subsurface microscopic imaging especially for industrial and biological specimens [1,2,3]. The typical commercial transducers used in SAM are made up of ceramic, single crystals, or thin films of piezoelectric materials. Polyvinylidene difluoride (PVDF) and its copolymer with trifluoroethylene P(VDF-TrFE) are ferromagnetic materials that inherently possesses several benefits for an acoustic transducer. These are flexible materials which allow a high degree of physical focusing without lenses [7]. Polymer transducers typically offer wide bandwidth or short impulse response [8], and much a better acoustic impedance match to biological tissue than ceramic-based transducers. The copolymer P(VDF-TrFE) is commercially available in different mass mixing ratios where a ratio around 70 to 30 between PVDF and TrFE is known to produce the highest piezoelectric activity [9]. Ceramic-based transducers, on the other hand, normally have advantages in terms of a higher dielectric permittivity, higher electromechanical coupling, and lower loss factors
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