My research is focused on the usage of embroidered electronics to harvest energy in a wearable system. The primary material of research is PVDF (poly(vinylidene fluoride)), a semi-crystalline polymer that displays piezoelectric, pyroelectric and both photoelectric and photovoltaic characteristics.
Each aspect of the materials properties will be analysed, with a focus on the piezoelectricity in its fibre form, but also a look at how the properties varies when used as a thin film. This film form is where the material appears to have the most potential as a photovoltaic. Which form is best for use as a pyroelectric is still to be investigated.
Piezoelectricity occurs when a material undergoes mechanical deformation (compression, twisting) which generates a voltage. Pyroelectricity is when a material is heated or cooled, and this generates a voltage. Both of these occur due to the asymmetric structure of the material that allows ions to move through it easily. Photovoltaics is when electromagnetic radiation hits a material, and gives energy to an electron, causing it to move within the material.
There are a number of papers working on the improvement of the materials efficiencies, which seems to be a lengthy and expensive process. I aim to use a commercially available PVDF fibre as my basis, to develop a series of embroidered patterns and woven fabrics to investigate how PVDF can best be used to harvest energy, and the practical applications of these systems. As part of this, a direct comparison will be undertaken with the fibres developed by other teams. For this, I will be mimicking their extrusion methods, both melt-spinning and fibre drawing, and using them in the same systems proved to be most efficient by the commercially available fibre.
To support this, physical analysis of the fibre material will take place, to create a baseline of what changes between fibres have valuable effects. This will include a look at its crystalline structure, and an analysis of whether poling the material increases efficiency enough for it to be considered a valuable part of developing it industrially. This will make it simpler to predict the results of future designs.
One application already being investigated with regards to piezoelectricity is the material's potential as a gait sensor, with an aim of detecting medical conditions. This fits in with EPSRC's theme of Healthcare Technologies. As part of a self-powering system, this could also have potential applications for athletes, and as a pedometer in personal fitness systems. If it proves to have a reasonable efficiency in a woven fabric, wind energy harvesting and clothing applications are possible. Worn self-powering systems would be an improvement for the field of personal sensors and devices.
If the material proves to have usage as a pyroelectric, the next step will be to test it in a number of practical uses, such as incorporation in an infrared rectenna system, to harvest energy from places of heat, including car exhausts. However, as a polymer, there is potential for thermal degradation. The balance of heat harvesting versus material breakdown will be a key point of this work.
The photovoltaic aspects of the material are recorded as being low in efficiency. This property will still be investigated, in the aim of creating an improvement in efficiency. If this is possible, and the material also proves to have pyroelectric properties, work will be done to develop both properties in one system. PVDF is already used as an additional layer to improve the efficiency of solar cells.
The final objective of this project is to develop practical and usable in real life methods of energy harvesting using PVDF.