Paul M. Weaver

Piezoelectric and ferroelectric materials and structures for energy harvesting applications

This review provides a detailed overview of the energy harvesting technologies associated with piezoelectric materials along with the closely related sub-classes of pyroelectrics and ferroelectrics. These properties are, in many cases, present in the same material, providing the intriguing prospect of a material that can harvest energy from multiple sources including vibration, thermal fluctuations and light. Piezoelectric materials are initially discussed in the context of harvesting mechanical energy from vibrations using inertial energy harvesting, which relies on the resistance of a mass to acceleration, and kinematic energy harvesting which directly couples the energy harvester to the relative movement of different parts of a source. Issues related to mode of operation, loss mechanisms and using non-linearity to enhance the operating frequency range are described along with the potential materials that could be employed for harvesting vibrations at elevated temperatures. In addition to inorganic piezoelectric materials, compliant piezoelectric materials are also discussed. Piezoelectric energy harvesting devices are complex multi-physics systems requiring advanced methodologies to maximise their performance. The research effort to develop optimisation methods for complex piezoelectric energy harvesters is then reviewed. The use of ferroelectric or multi-ferroic materials to convert light into chemical or electrical energy is then described in applications where the internal electric field can prevent electron–hole recombination or enhance chemical reactions at the ferroelectric surface. Finally, pyroelectric harvesting generates power from temperature fluctuations and this review covers the modes of pyroelectric harvesting such as simple resistive loading and Olsen cycles. Nano-scale pyroelectric systems and novel micro-electro-mechanical-systems designed to increase the operating frequency are discussed.

Integrated sustainability assessment: What is it, why do it and how?

This paper describes a new conceptualisation of sustainability assessment as an integrative and active process at the science-policy-society interface and its implementation as exemplified in case studies within the Methods and Tools for Integrated Sustainability Assessment (MATISSE) project. Integrated Sustainability Assessment (ISA) is defined within the MATISSE project as a cyclical, participatory process of scoping, envisioning, experimenting and learning through which a shared interpretation of sustainability for a specific context is developed and applied in an integrated manner in order to explore solutions to persistent problems. ISA is strategic, sustainability-oriented, constructive and potentially transformative. Its key role is to explore the opportunity-creation and problem-solving potential of framing contexts other than those in place, such as alternative institutions, technologies, spatial and temporal arrangements, price relations and associated policy regimes.

An environmental life cycle optimization model for the European pulp and paper industry

Will paper recycling reduce the environmental impact of the European pulp and paper sector? If so, is maximal paper recycling the best policy to optimize the life cycle of the pulp and paper sector? We explore these questions using an approach that combines materials accounting methods and optimization techniques. Environmental impact data are inputs for a linear programming network flow model to find optimal configurations for the sector. These configurations consist of a mix of different pulping technologies, a geographical distribution of pulp and paper production, and a level of recycling consistent with the lowest environmental impacts. We use the model to analyse scenarios with different recycling strategies. Recycling offers a reduction in environmental impact in regions with a high population and a large production of paper and board products. Regions with a large production of graphic products should focus on cleaner virgin pulp production with energy recovery. We conclude that relocation of paper production also offers a reduction in environmental impact. However, the severe effects on the economy make this policy less attractive than a combination of recycling, cleaner pulp production and energy recovery.

Composite corrugated structures for morphing wing skin applications

Composite corrugated structures are known for their anisotropic properties. They exhibit relatively high stiffness parallel (longitudinal) to the corrugation direction and are relatively compliant in the direction perpendicular (transverse) to the corrugation. Thus, they offer a potential solution for morphing skin panels (MSPs) in the trailing edge region of a wing as a morphing control surface. In this paper, an overview of the work carried out by the present authors over the last few years on corrugated structures for morphing skin applications is first given. The second part of the paper presents recent work on the application of corrugated sandwich structures. Panels made from multiple unit cells of corrugated sandwich structures are used as MSPs in the trailing edge region of a scaled morphing aerofoil section. The aerofoil section features an internal actuation mechanism that allows chordwise length and camber change of the trailing edge region (aft 35% chord). Wind tunnel testing was carried out to demonstrate the MSP concept but also to explore its limitations. Suggestions for improvements arising from this study were deduced, one of which includes an investigation of a segmented skin. The overall results of this study show that the MSP concept exploiting corrugated sandwich structures offers a potential solution for local morphing wing skins for low speed and small air vehicles.

Optimization of Long Anisotropic Laminated Fiber Composite Panels with T-Shaped Stiffeners

A method to optimize long anisotropic laminated fiber composite panels with T-shaped stiffeners is presented. The technique splits the optimization problem into two steps. At the first step, composite optimization is performed using mathematical programming in which the skin and the stiffeners are characterized by lamination parameters accounting for their membrane and flexural anisotropy. Skin and stiffener laminates are assumed to be symmetric or midplane symmetric laminates with 0-, 90-, 45-, or -45- deg ply angles. The stiffened panel consists of a series ofskin-stiffener assemblies or superstiffeners. Each superstiffener is further idealized as a group of flat laminated plates that are rigidly connected. The stiffened panel is subjected to a combined loading under strength, buckling, and practical-design constraints. At the second step, the actual skin and stiffener layups are obtained using a genetic algorithm and considering the ease of manufacture. This approach offers the advantage of introducing numerical analysis methods such as the finite element method at the first step, without significant increases in processing time. Furthermore, modeling the laminate anisotropy enables the designer to explore and potentially use elastic tailoring in a beneficial manner.

Minimum mass vascular networks in multifunctional materials

A biomimetic analysis is presented in which an expression for the optimum vessel diameter for the design of minimum mass branching or vascular networks in engineering applications is derived. Agreement with constructal theory is shown. A simple design case is illustrated and application to more complex cases with branching networks of several generations discussed. The analysis is also extended into the turbulent flow regime, giving an optimization tool with considerable utility in the design of fluid distribution systems. The distribution of vessel lengths in different generations was also found to be a useful design variable. Integrating a network into a structure is also discussed. Where it is necessary to adopt a non-optimum vessel diameter for structural integration, it has been shown that small deviations from the minimum mass optimum can be tolerated, but large variations could be expected to produce a punitive and rapidly increasing mass penalty.

Adaptive Structures: Engineering Applications

List of Contributors. Preface. 1 Adaptive Structures for Structural Health Monitoring (Daniel J. Inman and Benjamin L. Grisso). 1.1 Introduction. 1.2 Structural Health Monitoring. 1.3 Impedance-Based Health Monitoring. 1.4 Local Computing. 1.5 Power Analysis. 1.6 Experimental Validation. 1.7 Harvesting, Storage and Power Management. 1.8 Autonomous Self-healing. 1.9 The Way Forward: Autonomic Structural Systems for Threat Mitigation. 1.10 Summary. Acknowledgements. References. 2 Distributed Sensing for Active Control (Suk-Min Moon, Leslie P. Fowler and Robert L. Clark). 2.1 Introduction. 2.2 Description of Experimental Test Bed. 2.3 Disturbance Estimation. 2.4 Sensor Selection. 2.5 Conclusions. Acknowledgments. References. 3 Global Vibration Control Through Local Feedback (Stephen J. Elliott). 3.1 Introduction. 3.2 Centralised Control of Vibration. 3.3 Decentralised Control of Vibration. 3.4 Control of Vibration on Structures with Distributed Excitation. 3.5 Local Control in the Inner Ear. 3.6 Conclusions. Acknowledgements. References. 4 Lightweight Shape-Adaptable Airfoils: A New Challenge for an Old Dream (L.F. Campanile). 4.1 Introduction. 4.2 Otto Lilienthal and the Flying Machine as a Shape-Adaptable Structural System. 4.3 Sir George Cayley and the Task Separation Principle. 4.4 Being Lightweight: A Crucial Requirement. 4.5 Coupling Mechanism and Structure: Compliant Systems as the Basis of Lightweight Shape-Adaptable Systems. 4.6 Extending Coupling to the Actuator System: Compliant Active Systems. 4.7 A Powerful Distributed Actuator: Aerodynamics. 4.8 The Common Denominator: Mechanical Coupling. 4.9 Concluding Remarks. Acknowledgements. References. 5 Adaptive Aeroelastic Structures (Jonathan E. Cooper). 5.1 Introduction. 5.2 Adaptive Internal Structures. 5.3 Adaptive Stiffness Attachments. 5.4 Conclusions. 5.5 The Way Forward. Acknowledgements. References. 6 Adaptive Aerospace Structures with Smart Technologies - A Retrospective and Future View (Christian Boller). 6.1 Introduction. 6.2 The Past Two Decades. 6.3 Added Value to the System. 6.4 Potential for the Future. 6.5 A Reflective Summary with Conclusions. References. 7 A Summary of Several Studies with Unsymmetric Laminates (Michael W. Hyer, Marie-Laure Dano, Marc R. Schultz, Sontipee Aimmanee and Adel B. Jilani). 7.1 Introduction and Background. 7.2 Room-Temperature Shapes of Square [02/902]T Cross-Ply Laminates. 7.3 Room-Temperature Shapes of More General Unsymmetric Laminates. 7.4 Moments Required to Change Shapes of Unsymmetric Laminates. 7.5 Use of Shape Memory Alloy for Actuation. 7.6 Use of Piezoceramic Actuation. 7.7 Consideration of Small Piezoceramic Actuators. 7.8 Conclusions. References. 8 Negative Stiffness and Negative Poissons Ratio in Materials which Undergo a Phase Transformation (T.M. Jaglinski and R.S. Lakes). 8.1 Introduction. 8.2 Experimental Methods. 8.3 Composites. 8.4 Polycrystals. 8.5 Discussion. References. 9 Recent Advances in Self-Healing Materials Systems (M.W. Keller, B.J. Blaiszik, S.R. White and N.R. Sottos). 9.1 Introduction. 9.2 Faster Healing Systems - Fatigue Loading. 9.3 Smaller Size Scales. 9.4 Alternative Materials Systems - Elastomers. 9.5 Microvascular Autonomic Composites. 9.6 Conclusions. References. 10 Adaptive Structures - Some Biological Paradigms (Julian F.V. Vincent). 10.1 Introduction. 10.2 Deployment. 10.3 Turgor-Driven Mechanisms. 10.4 Dead Plant Tissues. 10.5 Morphing and Adapting in Animals. 10.6 Sensing in Arthropods - Campaniform and Slit Sensilla. 10.7 Developing an Interface Between Biology and Engineering. 10.8 Envoi. Acknowledgements. References. Index.

Measurement techniques for piezoelectric nanogenerators

Electromechanical energy harvesting converts mechanical energy from the environment, such as vibration or human activity, into electrical energy that can be used to power a low power electronic device. Nanostructured piezoelectric energy harvesting devices, often termed nanogenerators, have rapidly increased in measured output over recent years. With these improvements nanogenerators have the potential to compete with more traditional micro- or macroscopic energy harvesting devices based on piezoelectric ceramics such as lead zirconate titanate (PZT), polymers such as polyvinylidene fluoride (PVDF) or electrostatic, electret or electromagnetic kinetic energy harvesters. Power output from a nanogenerator is most commonly measured through open-circuit voltage and/or short-circuit current, where power may be estimated from the product of these values. Here we show that such measures do not provide a complete picture of the output of these devices, and can be misleading when attempting to compare alternative designs. In order to compare the power output from a nanogenerator, techniques must be improved in line with those used for more established technologies. We compare ZnO nanorod/poly(methyl methacrylate) (PMMA) and ZnO nanorod/poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) devices, and show that despite an open-circuit voltage nearly three times lower the ZnO/PEDOT:PSS device generates 150 times more power on an optimum load. In addition, it is shown that the peak voltage and current output can be increased by straining the device more rapidly and therefore time-averaged power, or time-integrated measures of output such as total energy or total charge should be calculated. Finally, the internal impedance of the devices is characterised to develop an understanding of their behaviour and shows a much higher internal resistance but lower capacitive impedance for the ZnO/PMMA device. It is hoped that by following more rigorous testing procedures the performance of nanostructured piezoelectric devices can be compared more realistically to other energy harvesting technologies and improvements can be rapidly driven by a more complete understanding of their behaviour.

Multi-stable composite twisting structure for morphing applications

Conventional shape-changing engineering structures use discrete parts articulated around a number of linkages. Each part carries the loads, and the articulations provide the degrees of freedom of the system, leading to heavy and complex mechanisms. Consequently, there has been increased interest in morphing structures over the past decade owing to their potential to combine the conflicting requirements of strength, flexibility and low mass. This article presents a novel type of morphing structure capable of large deformations, simply consisting of two pre-stressed flanges joined to introduce two stable configurations. The bistability is analysed through a simple analytical model, predicting the positions of the stable and unstable states for different design parameters and material properties. Good correlation is found between experimental results, finite-element modelling and predictions from the analytical model for one particular example. A wide range of design parameters and material properties is also analytically investigated, yielding a remarkable structure with zero stiffness along the twisting axis.

On feasible regions of lamination parameters for lay-up optimization of laminated composites

The stiffness tensors of a laminated composite may be expressed as a linear function of material invariants and lamination parameters. Owing to the nature of orienting unidirectional laminae ply by ply, lamination parameters, which are trigonometric functions of the ply orientation, are interrelated. In optimization studies, lamination parameters are often treated as independent design variables constrained by inequality relationships to feasible regions that depend on their values. The relationships between parameters enclose a convex feasible region of lamination parameters which is generally unknown. The convexity properties allow the efficient optimization of laminated composite structures where lamination parameters are used as design variables. Herein, a two-level method is presented to determine the feasible regions of lamination parameters where potential ply orientations are a predefined finite set. At the first level, the feasible region of the in-plane, coupling and out-of-plane lamination parameters is determined separately using convex hulls. At the second level, a nonlinear algebraic identity is used to relate the in-plane, coupling and out-of-plane lamination parameters to each other. This general approach yields all constraints on the feasible regions of lamination parameters for a predefined set of ply orientations.