Multimaterial piezoelectric fibres

Abstract

A promising path for introducing rapid modulation into fibres would be through the piezoelectric effect [10][11] . Embedding piezoelectric domains would allow fibres to be electrically actuated over broad frequencies on the one hand, and to function as sensitive broadband microphones on the other. However, fibres for the most part have been made of materials in the disordered glassy state precluding the crystalline symmetry requirements necessary for piezoelectricity.Recent progress in drawing of fibres made of a multiplicity of materials 12 present new opportunities for re-examining this challenge. With this approach, fibre materials are drawn from 3 preforms in a regime dominated by viscous forces allowing for internal low viscosity domains to be arranged in non-equilibrium cross sections confined by viscous glassy boundary layers. In fact constructing a piezoelectric fibre could be accomplished in a straightforward manner by assembling a preform made of a piezoelectric material poly(vinylidene fluoride) (PVDF) 13-14 , with metal electrodes and an insulating polymer, which would be followed by a thermal draw.The stress present during the fibre draw should in principle induce the non-polar α to the ferroelectric β phase transition in the PVDF layer 13,[15][16] . The process should yield many metres of fibre with built-in internal electrodes which could be utilized to establish the large electric field necessary for poling the PVDF layer. However, upon detailed examination a number of significant challenges and seemingly conflicting requirements arise. The necessity to utilize crystalline materials both for the piezoelectric layer and the electrical conductors leads to the formation of multiple adjacent low viscosity and high aspect ratio domains. These domains undergoing a reduction in cross sectional dimensions are susceptible to capillary breakup and mixing during fibre drawing due to flow instabilities. Layer thickness non-uniformity either in the lateral or in the longitudinal directions [17][18] precludes the formation of the coercive field needed for poling. Moreover, even if capillary breakup were kinetically averted and uniform sections of fibres were to emerge they would not exhibit piezoelectricity because the stress and strain conditions necessary to induce the thermodynamic phase transition in PVDF cannot be sustained in the fibre draw process.To address these challenges we choose to focus our attention on the ability to maintain geometric coherence and layer thickness uniformity. A viscous and conductive carbon-loaded poly(carbonate) (CPC) is used to confine the low viscosity crystalline piezoelectric layer during 4 the draw process. The CPC layers exhibit high viscosity (10 5~1 0 6 Pa·s) at the draw temperature and adequate conductivity (1~10 4 ohm·m) over the frequency range from DC to tens of MHz, thus facilitating short range (hundreds of microns) charge transport on length scales associated with the fibre cross section. Then a piezoelectric polymer which crystallizes into the appropriate phase...

Linear stability analysis of capillary instabilities for concentric cylindrical shells

“…For example, concentric layers of different polymers and glasses can be drawn into a long fibre with submicron-scale layers that act as optical devices for wavelengths on the same scale as the layer thicknesses . Other devices, such as photodetectors , semiconductor filaments (Deng et al 2008(Deng et al , 2010, and piezoelectric pressure sensors (Egusa et al 2010) have similarly been incorporated into microstructured fibre devices. That work motivates greater theoretical investigation of multi-fluid geometries, and in particular the stability (or instability time scale) of different geometries is critical in order to predict whether they can be fabricated successfully.…”

Optimized design of a low-resistance electrical conductor for the multimegahertz range

“…At such frequencies, resistance is dominated by skin-depth effects, which prevent the current from being uniformly distributed over the cross section; this is typically combatted by breaking the wire into a braid of many thin insulated wires (litz wire 1 ), but the ∼ 10 µm skin depth at these frequencies makes traditional litz wire impractical (∼ 10 4 µm-scale strands). In contrast, we show that as few as 10 coaxial shells can improve resistance by more than a factor of 3 compared to solid wire, and thin concentric shells can be fabricated by a variety of processes (such as electroplating, electrodeposition, or even a fiber-drawing process [2][3][4]. Good conductors at these frequencies are increasingly important, e.g.…”

Alternative Resources for Renewable Energy: Piezoelectric and Photovoltaic Smart Structures

“…A multi-material piezoelectric fibre production has been reported by Egusa et al [41] however it was produced by a multi-process method where a copolymer of PVDF, P(VDFTrFE) and polycarbonates were used, which makes the fibre expensive and difficult to scale up for production. The first flexible piezoelectric fibre has been produced successfully by Siores et al [42] via a continuous process on a customised melt extruder.…”