Hyunsun A. Kim

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.

Optimal configurations of bistable piezo-composites for energy harvesting

This paper presents an arrangement of bistable composites combined with piezoelectrics for broadband energy harvesting of ambient vibrations. These non-linear devices have improved power generation over conventional resonant systems and can be designed to occupy smaller volumes than magnetic cantilever systems. This paper presents results based on optimization of bistable composites that enables improved electrical power generation by discovering the optimal configurations for harvesting based on the statics of the device. The optimal device aspect ratio, thickness, stacking sequence, and piezoelectric area are considered. Increased electrical output is found for geometries and piezoelectric configurations, which have not been considered previously.

Morphing and shape control using unsymmetrical composites

Unsymmetrical carbon fiber/epoxy composites with bonded piezoelectric actuators are investigated as a means to shape or morph, the composite structures. Both a cantilever and unsupported laminate structure are examined along with their response to applied strains (from piezoelectric actuators) and applied mechanical load; with particular emphasis on the characterization of shape/deflection, the influence of externally applied mechanical loads and methods of reversing or promoting snap-through of these materials from one stable state to another. A variety of shape change/actuation modes for such structures have been identified namely, (i) reversible actuation by maintaining a constant stable state using piezoelectric actuation, (ii) an increased degree of shape change by irreversible snap-through using piezoelectric actuation and (iii) reversible snap-through using combined piezoelectric actuation and an externally applied load.

Shape memory alloy-piezoelectric active structures for reversible actuation of bistable composites

A study was conducted to introduce an actuation mechanism, called shape memory alloy-piezoelectric active structures (SMAPAS) that combined the advantages of the piezoelectric shape memory alloy (SMA) materials to achieve self-resetting bistable composites. The approach used piezoelectric actuation to provide a rapid snap-through with significant degree of control and a relatively slow, but high-strain SMA actuation to reverse the state change. A thin cantilever beam of carbon-fiber or epoxy material was used to demonstrate the two-way actuation. The composite lay-up procedure was a standard method for the manufacturing of carbon laminates through a standard cure cycle to a maximum cure temperature of 125°C and a pressure of 85 psi. A macrofiber composite piezoelectric actuator was used to conduct the investigations and it consisted of aligned piezoelectric fibers with an interdigitated electrode to direct the applied electric field along the fiber length.

Experimental analysis of the dynamical response of energy harvesting devices based on bistable laminated plates.

The use of bistable laminates is a potential approach to realize broadband piezoelectric based energy harvesting systems. In this paper the dynamic response of a piezoelectric material attached to a bistable laminate plate is examined based on the experimental generated voltage time series. The system was subjected to harmonic excitations and exhibited single-well and snap-through vibrations of both periodic and chaotic character. To identify the dynamics of the system response we examined the frequency spectrum, bifurcation diagrams, phase portraits, and the 0–1 test.

Modeling and characterization of piezoelectrically actuated bistable composites

This paper develops and validates a finite-element model to predict both the cured shape and snap-through of asymmetric bistable laminates actuated by piezoelectric macro fiber composites attached to the laminate. To fully describe piezoelectric actuation, the three-dimensional compliance [sij], piezoelectric [dij], and relative permittivity [εij] matrices were formulated for the macro fiber actuator. The deflection of an actuated isotropic aluminum beam was then modeled and compared with experimental measurements to validate the data. The model was then extended to bistable laminates actuated using macro fiber composites. Model results were compared with experimental measurements of laminate profile (shape) and snap-through voltage. The modeling approach is an important intermediate step toward enabling design of shape-changing structures based on bistable laminates.

Engineering design optimization using services and workflows

Multi-disciplinary design optimization (MDO) is the process whereby the often conflicting requirements of the different disciplines to the engineering design process attempts to converge upon a description that represents an acceptable compromise in the design space. We present a simple demonstrator of a flexible workflow framework for engineering design optimization using an e-Science tool. This paper provides a concise introduction to MDO, complemented by a summary of the related tools and techniques developed under the umbrella of the UK e-Science programme that we have explored in support of the engineering process. The main contributions of this paper are: (i) a description of the optimization workflow that has been developed in the Taverna workbench, (ii) a demonstrator of a structural optimization process with a range of tool options using common benchmark problems, (iii) some reflections on the experience of software engineering meeting mechanical engineering, and (iv) an indicative discussion on the feasibility of a ‘plug-and-play’ engineering environment for analysis and design.

Level Set Topology Optimisation of Aircraft Wing Considering Aerostructural Interaction

Topology optimisation is the most general form of structural optimisation, capable of calculating the optimal arrangement of material in a loaded structure. Low weight efficient structures are vital to aircraft performance making aerospace structures an ideal field for the application of topology optimisation. In this investigation 3D level set topology optimisation is developed to optimise the internal structure of an aircraft wing with coupled aerostructural interaction. The results suggest that an alternative configuration of I-beam like wing with columns may be an optimal solution for wing structures. They also show the importance of considering the relationship between the internal wing structure and its aerodynamic performance. The paper thus, demonstrates potential benefits of Aerostructural 3D level set topology optimisation for a design of aircraft wing.

Manufacture and characterisation of piezoelectric broadband energy harvesters based on asymmetric bistable cantilever laminates

In this paper a bistable asymmetric laminate is manufactured and coupled to a ferroelectric material for potential energy harvesting applications. A cantilever configuration is explored and the harvester response as a function of vibration frequency, vibration level and electrical load resistance examined. The harvester is characterised at low and high vibration levels where the device exhibits either single well oscillations (at low vibration amplitude) or snap-through events (at high vibration amplitude). As the vibration levels increase and the device approaches snap-through it exhibits ‘softening’ where the peak power moves to lower frequencies with differences in power levels during up-sweep and down-sweep of frequencies. Examination of the frequency dependence of power for a range of load resistances indicates a broadening of the harvester performance at higher vibration levels and during snap-through.

Structural Assessment of Advanced Composite Tow-Steered Shells

The structural performance of two advanced composite tow-steered shells, manufactured using a fiber placement system, is assessed using both experimental and analytical methods. The fiber orientation angles vary continuously around the shell circumference from ±10 degrees on the shell crown and keel, to ±45 degrees on the shell sides. The two shells differ in that one shell has the full 24-tow course applied during each pass of the fiber placement system, while the second shell uses the fiber placement systems tow drop/add capability to achieve a more uniform shell wall thickness. The shells are tested in axial compression, and estimates of their prebuckling axial stiffnesses and bifurcation buckling loads are predicted using linear finite element analyses. These preliminary predictions compare well with the test results, with an average agreement of approximately 10 percent.