Fabrication of focused poly(vinylidene fluoride-trifluoroethylene) P(VDF-TrFE) copolymer 40–50 MHz ultrasound transducers on curved surfaces

Abstract

Copolymer films such as poly(vinylidene fluoride-trifluoroethylene) P(VDF-TrFE) have lower acoustic impedance compared to their ceramic counterparts, allowing for a better acoustic match to tissues in the human body. Because of this, copolymer ultrasonic transducers are capable of yielding the desirable characteristics of broad bandwidth and short pulse duration that allow better image resolution to be achieved. In the past, such transducers in the frequency range from 40 to 80 MHz have frequently been fabricated by spin coating the copolymer film onto a flat substrate and then applying the film to a curved backing using an adhesive layer. The adhesive layer may cause spurious signals at these frequencies, in addition to the film damage that may occur as a result of such processing. In order to avoid these problems, a copolymer film can be directly spin coated onto a curved substrate. The resulting devices had an operating frequency of over 40 MHz and approximately a 75% bandwidth. The potential of several approaches that could be further explored to increase the level of performance of such devices is also discussed.

Piezoelectric materials for high frequency medical imaging applications: A review

“…P(VDF-TrFE) co-polymer has been shown to have a higher electromechanical coupling coefficient (k t ∼ 0.20-0.30) [10] than PVDF and can be polarized by applying an electrical field at elevated temperatures. This material therefore has proven to be useful in the production of simple, yet very effective, high frequency single element and annular array transducers [21,22].…”

Photoacoustic imaging of biological tissue with intensity-modulated continuous-wave laser

“…In pulsed mode, the piezoelectric transducer, which must have a broad bandwidth, typically has an insertion loss 19 of the order of 20 dB. This loss is due to either the low electromechanical coupling coefficient K of piezoelectric material or the high acoustic impedance Z because no piezoelectric material can yet provide both high K and low Z.…”

Ultrasonic properties of all-printed piezoelectric polymer transducers

“…2,17 They were pooled by using an AC voltage with frequency of 0.25 Hz over 10 periods. A Sawyer-Tower circuit was used to monitor the poling of four typical transducers samples of type T1 to T4 (also used further in the ultrasonic characterization).…”

“…Ferroelectric polyvinylidenefluoride (PVDF) and its copolymer PVDF trifluoroethylene [P(VDF-TrFE)] are widely used for making ultrasonic sensors and transducers applied to nondestructive evaluation (NDE), underwater acoustic and medical imaging. [1][2][3][4][5][6][7][8][9] Although piezoelectric polymers have a considerable weaker piezoelectrical coupling than comparable ceramics, they have advantages in terms of being flexible, easy to process, and providing a relatively good acoustic match to water, human tissue, and many polymer materials. A large number of techniques have been explored for processing ferroelectric polymers into flexible film, such as spin coating, hot pressing, stamping, and spraying.…”

“…A large number of techniques have been explored for processing ferroelectric polymers into flexible film, such as spin coating, hot pressing, stamping, and spraying. [1][2][3][4][5][6][7] Electrodes can also be attached to the film surface by various methods, as, for example, sputter coating, vapor deposition, and printing. 4,6,[9][10][11][12][13][14] Some of the printing methods (e.g., screen-printing, ink-jet printing, and laser ablation) also facilitate electrode printing directly onto the backing substrate, with a potential reduction in processing steps and fabrication time.…”