SMART MATERIALS AS ENERGY TRANSDUCERS

Abstract

In this thesis two types of smart materials are investigated: piezoelectric materials and hydrogels. These materials have the property of transforming a specific energy into another. In particular, piezoelectric materials are capable of generating an electric potential, hence an electrical power, when strained, while hydrogels are capable of large deformations after the absorption of a solvent. In the case of piezoelectric materials the electrical power can be harvested through a resistive load which has to be accurately chosen to maximize the efficiency of the device. A specific application of such materials is the energy harvesting in a fluid-solid interaction. Indeed, wind and water currents provide free kinetic energy which can be converted using piezoelectric sheets immersed in fluid flows through. This problem involves several physics which are strongly coupled. In this thesis, a specific configuration of a bilayer structure composed of a piezoelectric sheet is investigated both experimentally and numerically. Moreover, some modeling issues of piezoelectric materials and the optimal load resistance are also discussed. On the other hand, hydrogels are material able to transform a chemical energy into an elastic energy. For this reason, they can be used as actuators which autonomously respond to environment changes. In this thesis, the shape control of hydrogel materials is investigated numerically and analytically. Moreover, since in general the response of hydrogel is slow, two high power mechanisms are described with an experiment and through some numerical simulations. Finally, the problem of residual strains due to the change of chemical conditions in the environment are tackled by means of a theoretical model. A list of submitted and published papers and proceedings included in this thesis are listed in the final chapter.