Electroactive polymers, design and validation of new concepts in energy harvesting

This article-based thesis comprises a collection of six articles, each of which constitutes a chapter written and formatted in pre-print manuscript form. The thesis deals with new concepts and technologies employed in the field of the electro-mechanical transducers, devices that are able to convert mechanical energy into direct current electricity and vice-versa. They can be employed as sensors (to measure strains and vibrations), actuators (i.e. artificial muscles and volumetric pumps) or generators (as power-take-off system in wave energy application). The thesis focuses on two main technologies used to develop new transducers, the almost classic field of the dielectric elastomers and the emerging class of liquid electroactive polymer. In the current work, both of them are mainly employed in the generation mode, i.e. to convert an oscillating mechanical energy source into direct current electricity. Compared to conventional electro-mechanical transducers the electroactive polymers class allows to design solutions with a simplified architecture; they feature lower mass density and a reduced number of heavy and bulky mechanical components, which potentially leads to higher reliable and lower cost devices. Electroactive polymers transducers are also undoubtedly more compliant with respect to a potentially unstructured environment, which allows them to be employed in a wider range of scenarios. The research outline comprises: a state of the art of the available materials that are suitable for the transducer construction; a material characterization from both chemical and mechanical point of view through specifically designed tests; static and dynamic models that provide the electro-mechanical response and highlight the operating limits of the transducers; experimental tests to validate the proposed concepts and related models. Successful energy conversion has been proved, with promising performance in terms of energy density (with respect to the volume of dielectric material employed) and efficiency (ratio between input and output energy source). Despite the encouraging figure of merits obtained, the results achieved can be considered as a starting point for further development aimed at bringing the electroactive polymers transducers at a higher technology readiness level. Several aspects need to be improved, e.g. the dielectric material viscosity and electrical losses should be reduced; the electro-mechanical material fatigue has not been completely investigated, yet; the power electronics, especially at the larger scales, must be designed; the control of the energy conversion cycle is open to improvement; the manufacturing of transducers of big dimensions is an open problem to date.