This thesis investigates electro-mechanical generator systems which harvest energy from an
aquatic environment. Such systems are needed to create maintenance-free sensor platforms for
use in autonomous wireless sensor networks which have applications in water quality monitoring.
Many energy harvesting mechanisms specific to an aquatic environment already exist but the
majority of them have been developed for use in renewable energy generation schemes for large-scale
electrical power generation. Energy harvesting, however, remains focused on the miniature
scale aiming to generate enough power to run a wireless sensor node. This work therefore
focuses on the identification, analysis, prototyping and miniaturization issues of existing marine
wave-based energy converters. The analysis of different possible energy harvesting mechanisms
is performed and their power densities are investigated as a function of their size.
In order to be able to maximize the power density of the chosen energy harvester under all
operating conditions, expressions have been derived for a generalized load impedance which
optimizes the generator damping and resonant frequency, through changes in load resistance
and reactance. Within this maximization, an AC/DC H-bridge converter is simulated as an
interface between the harvester and its load. This converter is designed to mimic the required
generalized load impedance and tune it so that the entire system adapts to the external working
frequency. A prototype of the energy harvester was designed and tested.
Based on the observation of a natural whistle made of a doubly clamped blade of grass that
produces sounds when it is blown on, a MEMS harvester extracting energy from vortex-induced-vibrations
was designed. The study of its feasibility as an energy harvester and the determination
of its dimensions at a microscopic scale are interesting as it presents a new way of extracting
energy using an electromagnetic transduction mechanism and a manufacturing advantage. A
prototype of a generator harvesting energy from Vortex-Induced-Vibrations was developed using
conventional engineering processes.