Underwater Acoustic Sensor Network with Energy Harvesting Nodes

This thesis explores the possibility of a self sustained and service free Underwater Acoustic Sensor Network (UASN). The network nodes are installed along a subsea three phase High Voltage Alternating Current (HVAC) power cable where a energy harvester utilizes the magnetic field surrounding the cable by an inductive coil placed in the time varying magnetic field. By exploring the fundamentals of electromagnetic induction, underwater sound and communication networks, a complete solution is presented. The energy harvester implements basic principles of electromagnetic induction, and it is found feasible to design a network which, in theory, eliminates the need of battery service. The inductive coil is tested through simulations carried out in this thesis and compared with external simulations. Results show the possibility of harvesting some tens of milliwatts of power from the magnetic field, depending on the cable current, given a coil of 1000 windings and a coil load of 500 Ohm. Optimal size and placement for the inductive coils are also found through the simulations together with the physical properties of the cable the coil is intended for. Features of underwater wireless communication based on ultrasound as the information carrier are explored in order to gain a thorough overview of the estimated energy consumption in such network. The resulting system simulator calculates communication range, energy consumption and battery charge time based on modulation scheme features, underwater acoustics, battery properties and battery charge current. The network described is based on the idea of a simple and robust network in order to ensure a low bit error probability. Combining the energy harvesting system with a UASN gives the possibility of self sustained and service free network nodes. Such network is useful in a number of underwater applications such as environmental and oceanographic studies, commercial monitoring and military surveillance. Cable properties such as temperature, relative node position and current flow can also be monitored to gain more information on in service effects on underwater HVAC power cables