DEVELOPING AN FDTD SIMULATION TOOL TO EVALUATE THE USE OF MAGNETIC INDUCTION ACROSS AN AIR-WATER INTERFACE

Abstract

Traditional underwater communication technology includes either the propagation of energy in the form of acoustic pressure waves or extremely low frequency electromagnetic radiation. Although today’s acoustic technology is mature and robust, it is not able to transmit information across the air-water interface without the aid of additional electronics hardware. Extremely Low Frequency (ELF) electromagnetic radiation technology overcomes this problem; however, the low frequencies (30 - 300 Hz) require the use of very large antenna structures. The size of the ELF antenna makes this RF-based technology impractical for many applications requiring compact antenna structures including subsea oil and gas exploration, military, Underwater Internet of Things (UIoT) sensor networks, marine animal tracking, search and rescue, fishing, and environmental surveying, amongst others.

In this thesis, a simulation tool is developed to evaluate an underwater communication system which includes an air-water interface. The simulator evaluates Maxwell's equations using the Finite-Difference Time-Domain (FDTD) method. The custom FDTD simulator is designed using a 2D geometry for increased computational time, and is easily configurable such that the medium properties, coil position and orientation, and problem geometry can be user-defined. The simulator also considers the circuit properties of the transmitter and receiver using the lumped parameters of an RLC circuit model. Because the FDTD is a time domain simulation, it allows for a variety of input signals including single tones, broadband pulses, and modulated signals. Stability and convergence ar successfully confirmed by running the simulation with decreasing cell size using a built- in convergence test feature. The accuracy has also been validated by comparing it against existing analytical models. The simulation tool predicts feasible transmitter depths up to 3 meters, with a receiving coil 1 meter above the air water interface, with channel capacities above several tens of kilobits per second.