Pyroelectric Structures and Devices for Thermal Energy Harvesting

Abstract

Our daily infrastructure, safety, health and comfort relies on a continuous availability ofelectricity. Due to the volatile nature of electricity and the limited ability of storing electricalenergy, it is challenging to implement changes and improve energy efficiency, conversioneffectiveness and generator size and weight. In this regard, a wide range of sufficiently high,but currently unused, energy sources are available. Harvesting unexplored waste heat orabundantly available thermal energy sources such as industrial, solar, and geothermal wasteheat and abundantly available heat from friction or the human body enables local poweringof electronic device, extension of battery lifetime, and even provides accumulated base loadpower supplies, resulting in the recovery of otherwise unused thermal energy. For this reason,solid-state thermal to electrical energy conversion utilising the pyroelectric effect provides aconvenient and direct way of converting temperature fluctuations into an electrical potentialdifference available for discharge.In this thesis, the nature and the principles of pyroelectric energy harvesting are presentedin a complete review of materials, structures and devices for thermal energy harvestingapplications, followed by a detailed experimental set-up providing reproducible experimentalresults under constant laboratory test conditions. Introducing contactless and harmonic temperatureoscillations using a radiative heating lamp allows examination of energy harvestingdevices and helps to develop an geometrical optimisation approach.For radiative heating, a meshed micro- size electrode structure on polyvinylidene difluoride(PVDF) improves the pyroelectric conversion efficiency. The here presented photolithographicmanufacturing technique on a flexible substrate provides new device architecturesresulting in a 1050 % higher energy trade off. Further electrode modifications involve agraphene-ink based black body radiation absorber on flexible PVDF. With graphene-ink, alaminate structure introduces piezoelectric activity in response to the change in temperature.The inherent need of temperature oscillations for pyroelectric energy harvesting requiresan alternating heat flow. By linking the subject fields of heat transfer in oscillating heatpipes (OHPs) for high performance cooling, together with a pyroelectric energy harvestingdevice, the experimental system exploits a heat induced liquid-vapour transition of a workingfluid as a primary driver for a pyroelectric generator.

Date of Award	23 Nov 2016
Original language	English
Awarding Institution	University of Bath
Supervisor	Chris Bowen (Supervisor)