Access Type

Open Access Dissertation

Date of Award

January 2013

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Mechanical Engineering

First Advisor

Chin An Tan

Abstract

This dissertation presents a novel, interdisciplinary research which addresses the potential of applying soft polymeric materials to strategically harvest biomechanical energy in a beneficial manner for use as a viable, low power source for on-board electronics. Of particular interest are electroactive polymers (EAP), which unlike other types of electromechanical smart materials such as piezoelectric ceramics, which are often brittle, have low elastic modulus and can exhibit large strains without substantial stress generations. One type of EAP, the dielectric elastomer (DE), which utilizes electrostatic forces built up across the dielectric polymer to convert between electrical and mechanical energy, is employed in this research. As with most EAPs, DE materials are highly nonlinear and require novel models to understand the electromechanical coupling and the effects of energy harvesting on the host structure which it is attached to.

Since energy harvesting fundamentally involves harnessing the dissipative energy in a system, this research specifically investigates the relationship between biomechanical damping and energy harvesting induced by DE thin films affixed to the knee and operated during walking. This research has three objectives: (1) energy harvesting characterization of composite electrode/DE polymers under uniaxial stretching and electrical loading by improved hyperelastic modeling and experiments; (2) development of relationships between energy harvesting and damping for the DE materials in uniaxial stretching and on a biofidelic knee model; and (3) investigation of the kinetic effects of beneficial DE energy harvesting during walking. Our empirical modeling leads to a more comprehensive constitutive relation for DE materials and allows a means to directly assess the effects of energy harvesting on the wearer. By selectively inducing damping through coordinated mechanical and electrical loading of the DE device, it is demonstrated through simulations that beneficial energy harvesting strategies that account for the various mechanisms of metabolisms and energy expenditure involved in walking can be archived.

This research is significant as it lays the foundation for future work in the integration of wearable technology using dielectric elastomers with sensing, actuation, and energy harvesting, and establishes a pathway for the integration of DE energy harvesting into a broad spectrum of applications where comfortable, inconspicuous, wearable devices can be designed to harvest energy in an unobtrusive manner.

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