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Title: Efficiency and durability of wearable smart materials and structures
Author: Matsouka, Dimitroula
ISNI:       0000 0004 7231 2046
Awarding Body: University of Bolton
Current Institution: University of Bolton
Date of Award: 2018
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Piezoelectric polymer materials have been under investigation since the 1970’s starting with the discovery of the piezoelectric effect in PVDF films by Kawai. Since then the piezoelectric effect has been detected among other polymers in polyureas, polyamides, and polypropylene and their copolymers. While the investigation of the piezoelectric effect was largely carried out on the film form of the polymers since 2010 interest has developed into the production methods, properties and applicability of melt spun piezoelectric textile fibres made of these polymers. The application of piezoelectric fibres could have a significant impact in wearable textiles as sensors, actuators, or energy harvesting modules. Current research is mostly centred onto production methods and fibre crystallinity characterization. The research carried out in this PhD by publication project is concerned with piezoelectric textile fibres as electrically active elements. As such the research focused on the electrical behaviour of the fibres. The work carried out was threefold. Specifically, wearable textile materials undergo cleaning/ care treatments that are intrinsic to their function as wearables. These treatments may include washing, dry cleaning or sponging. Washing (cleaning treatment in a solution mainly containing water and an appropriate detergent at an elevated temperature or room temperature) is a common cleaning method. The effects of washing cycles on melt spun piezoelectric fibres remain under-investigated. For the first part of the research, piezoelectric melt spun fibres (PVDF, PP and PA-11) with two different cross sections (circular and rectangular), were mechanically stimulated by a rotating fin that impacted the fibres periodically. The resulting Vp-p (peek to peek voltage), was measured on the original fibres and on the fibres following one wash cycle (adapted BS EN ISO 105-C06), using an oscilloscope. Based on the results of this part of the research it was shown that the washing cycle effected the voltage response of the fibres depending on the fibre cross section and the fibre composition. The results of the research were presented in a paper titled “Investigation of the durability and stability of piezoelectric textile fibres” published in the Journal of Intelligent Materials Systems and Structures. For the second part of the research, it was noted that according to the existing literature the research approach for the determination of the electrical response of the fibres utilized exclusively the measurement of the voltage produced by mechanical excitation of the fibres, in open circuit conditions. This approach is not sufficient to satisfactorily characterise the electrical behaviour of the fibres as power generating elements. By contrast, a sufficient measurement is the power production of the fibres as this also includes a measurement of the current produced. In order to supply these measurements a testing apparatus/ methodology was developed. The apparatus consists of a measuring station where the voltage and current produced are measured, and a means for periodic mechanical stimulation of the specimens. The equipment was used to determine the power generated by piezoelectric melt spun fibres (PVDF, PP and PA-11) with two different cross sections (circular and rectangular). The results of the research were presented in a paper titled “On the Measurement of the Electrical Power Produced by Melt Spun Piezoelectric Textile Fibres” published in the Journal of Electronic Materials. Finally, considering the underlying premise of integration of fully textile based electronic components into textile substrates (e.g. wearable applications), 3D knitted fabrics that incorporated piezoelectric melt spun fibres were investigated with regards to their capacitive behaviour. Four different fabric structures were examined (different composition of the outside layers and different thickness). The capacitive behaviour of the samples was modelled based on the specific structural characteristics of the fabrics and the actual properties were determined using an Impedance Analyzer. Based on the results it was found that the theoretical model for the calculation of the capacitance of the samples appeared to be an acceptable approximation for the behaviour of the fabrics. Also, the ability to customise the required capacitance to suit the applications by specifying the dimensions of the 3D fabric and/or the density, the thickness or even the material of the interlaced fibres has also been shown to be possible. Moreover, reviewing the results of a resonance test for a purely textile based parallel LC circuit, it was shown that it is possible to implement resonant circuits that are convenient for basic electronic applications (i.e. oscillators, filters, etc.). The results of the research were presented in a paper titled “Three-dimensional weft-knitted textile fabrics-based capacitors” published in the Journal of the Textile Institute. This research project touched on some of the less thoroughly investigated research areas connected to the efficiency and durability of piezoelectric melt spun fibres and structures, with innovative results such as the development/ construction of the equipment that can be used for the measurement of the power produced by piezoelectric textile fibres as well as the investigation of the capacitive behaviour of the 3D knitted fabrics incorporating piezoelectric textile fibres and the conclusion that resonance is possible to achieve in a purely textile LC parallel circuit.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available