Optimisation of Broadband Energy Harvesters Using Bistable Composites

This proposal will develop optimum broadband energy harvesters at the large/meso-scale by creating an optimisation methodology. This will be achieved by bistable composite laminates with piezoelectric materials converting mechanical vibration to electrical energy.

Energy harvesting is an active research area developing ways of capturing energy from the external environment to power low energy electronics such as wireless sensor networks. One source of energy is vibration and piezoelectric materials are commonly used to convert mechanical vibration to electrical energy. The current state-of-the-art devices are designed to capture electrical energy at resonant frequencies. Whilst this works well in a well-controlled frequency environment, the harvesting performance falls dramatically outside the resonant frequencies and the resonant frequencies of a structure can quickly become unattainable as a device becomes small or large. This limits the application areas where vibratory energy harvesting devices can be used.

The proposed bistable composite mechanism has recently been discovered by Inman (Co-I) to have an excellent harvesting performance over a range of frequencies due to its nonlinear dynamics. Bistable composite plates have an inherent bistability arising from anisotropic material properties of an asymmetrical layup. These bistable composites have been extensively studied in the context of piezo-actuated morphing structures in recent years and Kim (PI) and Bowen (Co-I) introduced the first and the only optimisation methodology for bistable composites in 2011. The project combines these expertise together with mixed signal electronics of Clarke (Co-I) to develop broadband energy harvesters suitable for ambient vibration. The National Physical Laboratory (NPL) and Perpetuum will support this project via their experimental expertise, facilities and data on the industrial and customers' needs.

The complex physics of nonlinear bistable composites is difficult to understand and design, and the optimisation methodology for bistable composites recently developed by the applicants offers a systematic exploration of the design space to find the optimum combination of size, thickness and stacking sequence of fibre orientations. Building on from this foundation, the project will develop static and dynamic models of bistable enegy harvesting composites supported by experimental investigations and formulate an optimisation methodology which will be used to design and build demonstrators based on real world applications.

There are three main challenges which will be addressed in this project:
(1) The nonlinearity of the system behaviour, multiple equilibrium states of bistability, piezoelectric configuration and discrete composite lay-ups all present significant scientific challenges. The proposed research takes a novel approach of optimisation to account for the complex interaction of physics and offers engineers a methodology for designing bistable broadband energy harvesters for any given requirements.
(2) No research to date has studied the role of nonlinearities in bistable energy harvesting. We will explore this in the modelling of energy harvesting performance including dynamic nonlinearity with experimental characterisation of coupled electromechanical properties.
(3) One popular mechanism for generating bistability is via an external electromagnetic field which can be cumbersome and obtrusive to the surrounding system and the electrical components. Bistability is inherent to asymmetrical composite laminates, therefore the resulting system can be more compact and easily installed.

(1) Engineering Industry
The proposed research will bring a real opportunity to pioneer new areas for vibratory energy harvesting technology by developing a compact broadband system and offering an optimum design methodology. This will maximise the efficiency and economy of harvesters and significantly reduce the complexity of design and the time to market. The proposed broadband system has a potential to dramatically widen the application areas. The broadband nature of energy harvesting together with advances in low power electronics can widen the beneficiaries to industries such as aerospace, automotive, construction and medical engineering as well as military sectors. We will work closely with Perpetuum to produce technology demonstrators addressing the real customers needs to maximise the impact.

The underlying science which will be developed in this project has direct relevance in multifunctional structures and smart materials. Multifunctional structures have a potential to bring a transformative change to the design of light weight structures at a fundamental level. This will have significant impact on aerospace, automotive, robotics and military sectors. Defence Technology Strategy for the Demands of the 21st Century [MoD] specifically identifies smart materials and active structures as a priority emerging cross-cutting technology. The proposed research is critically timely for UK to maintain the competitiveness as the interests in smart multifunctional structures are growing internationally.

(2) Economy and Society
With increasingly scarce resources, the concept of energy harvesting from ambient environment and eliminating the need for a power source is unquestionably relevant to the wider society. Energy harvesting industry is currently $0.7Billion size market and is estimated to grow to $4.4Billion in 2021, of which a quarter is predicted to be piezoelectric-based [Energy Harvesting Market Analysis Report by IDTechEx, 2011]. Today, $13.75Million is being spent on energy harvesters for wireless sensors alone. Although over 50% of the current energy harvesting market is concentrated on consumer electronics, the application areas are set to diversify and interests in vibratory energy harvesting are growing. Taking a long-term view (>10 years) our research will benefit customers through low operating cost, and ultimately benefit the environment through low carbon emissions, a reduction in the use of batteries with toxic chemicals and resource efficiency. A fast transition of the technology into industry is ensured by the active dissemination plans. This will ensure that the ultimate benefits to the economy and security of the society are realised in a timely manner.

Harvesting energy through smart adaptive structures can capture people's imagination, exemplified in our previous bistable composites projects which was successfully exhibited at the Science Museum London and the invitation to be presented at the House of Commons. It is an excellent tool to engage the public in research of science and engineering and can have an important impact on the society's future by attracting talented young people to the profession of science and engineering.

(3) Investigators and PDRA
The potential of high impact scientific research represented in this project provides an opportunity for the researchers to become world leaders by making significant contributions in the relatively young research field of broadband energy harvesting. The project will lead to the identification of new challenges in research and open up new opportunities to secure future funding. Working closely with industrial partners provides a route for the researchers to make a direct impact in engineering industry and the society.