Flexible substrate rectenna devices for energy recovery

我的研究重点是利用刺绣电子设备在可穿戴系统中获取能量。研究的主要材料是PVDF(聚偏氟乙烯)，这是一种显示出压电、热释电以及光电和光伏特性的半结晶聚合物。材料性能的每一个方面都将被分析，重点是其纤维形式的压电性，但也会看看当用作薄膜时性能是如何变化的。这种薄膜形式的材料似乎最有可能成为光伏电池。哪种形式的热释电最适合用作热释电材料还有待研究。当材料经历机械变形(压缩、扭曲)并产生电压时，就会产生压电性。热释电是当材料被加热或冷却时，产生电压。这两种情况的发生都是由于材料的不对称结构，使得离子可以很容易地通过它。光伏是指电磁辐射照射到材料上，给电子提供能量，使其在材料内部运动。有许多论文致力于提高材料的效率，这似乎是一个漫长而昂贵的过程。我的目标是以一种商用的PVDF纤维为基础，开发一系列刺绣图案和机织面料，以研究如何最好地利用PVDF来获取能源，以及这些系统的实际应用。作为这项研究的一部分，将与其他团队开发的纤维进行直接比较。为此，我将模仿他们的挤出方法，包括熔融纺丝和纤维拉伸，并在相同的系统中使用它们，事实证明，由于商业上可以获得的纤维，它们是最有效的。为了支持这一点，将对纤维材料进行物理分析，以创建纤维之间哪些变化具有有价值的影响的基线。这将包括观察其晶体结构，并分析极化材料是否提高了效率，足以被认为是工业化开发的有价值的部分。这将使预测未来设计的结果变得更容易。关于压电性的一个已经被研究的应用是这种材料作为步态传感器的潜力，目的是检测医疗条件。这与EPSRC的医疗保健技术主题相吻合。作为自我供电系统的一部分，它也可能对运动员有潜在的应用，并作为个人健身系统中的计步器。如果证明它在机织织物中具有合理的效率，风能收集和服装应用是可能的。佩戴的自动供电系统将是个人传感器和设备领域的一项进步。如果这种材料被证明可以用作热释电材料，下一步将在许多实际用途中对其进行测试，例如将其纳入红外整流系统，从热的地方获取能量，包括汽车尾气。然而，作为一种聚合物，存在热降解的潜力。热收集和材料分解之间的平衡将是这项工作的一个关键点。材料的光伏方面被记录为效率低。为了提高效率，仍将对这一特性进行调查。如果这是可能的，而且这种材料也被证明具有热释电性质，那么将在一个系统中开发这两种性质的工作。PVDF已经被用作额外的一层来提高太阳能电池的效率。本项目的最终目标是开发实用的、可用于现实生活的利用PVDF的能量收集方法。

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.