WAVE CHAOS STUDIES FOR TWO-DIMENSIONAL CAVITIES USING THE RANDOM COUPLING MODEL (RCM) AND OTHER HIGH FREQUENCY METHODS

Wave coupling within systems with irregular boundaries is a common phenomenon in many branches of science such as acoustics, vibrations, electromagnetics, and others. If the wavelength of the incident wave is small compared with the structure size, and the dynamics of the ray trajectories within the scattering region are chaotic, the scattering properties of the cavity will be extremely sensitive to small perturbations. These structures are then termed wave chaotic. Exact solutions of such systems are not feasible and various alternative methods are sought. In the first part of this dissertation, such alternative methods are used to calculate the power delivered to a port in a two-dimensional wave chaotic enclosure. These methods are the ray tracing (RT), the Dynamical Energy Analysis (DEA) and the Power Balance methods (PWB). Particularly, the RT and DEA are used to calculate power received at an aperture and are compared with the established PWB. These results indicate that the RT and DEA are equivalent methods. Additionally, RT is compared with direct numerical simulations of the wave fields and found to be accurate if the wavelength is sufficiently small. The Random Coupling Model (RCM) gives a statistical description of coupling of radiation in and out of large enclosures through localized and/or distributed ports. The RCM, in contrast to DEA, PWB, and standard RT, includes both amplitude and phase information. It combines both deterministic and statistical information and makes use of wave chaos theory to extend the classical modal description of the cavity fields in the presence of boundaries that lead to chaotic ray trajectories. In the second part of this dissertation, a correction to the RCM termed the Short Orbit Formulation (SOF) is used to calculate successfully the impedance of a two-port wave chaotic enclosure in two dimensions using RT. Also, a directed beam approach was used to launch energy in a wave chaotic enclosure to break the so called 'random plane wave hypothesis', a fundamental basis of the RCM formulations. Results show that launching of such directed beams lead to enhanced short orbit effects which make the RCM inapplicable

Wireless power distributions in multi-cavity systems at high frequencies

The next generations of wireless networks will work in frequency bands ranging from sub-6 GHz up to 100 GHz. Radio signal propagation differs here in several critical aspects from the behaviour in the microwave frequencies currently used. With wavelengths in the millimetre range (mmWave), both penetration loss and free-space path loss increase, while specular reflection will dominate over diffraction as an important propagation channel. Thus, current channel model protocols used for the generation of mobile networks and based on statistical parameter distributions obtained from measurements become insufficient due to the lack of deterministic information about the surroundings of the base station and the receiver-devices. These challenges call for new modelling tools for channel modelling which work in the short-wavelength/high-frequency limit and incorporate site-specific details—both indoors and outdoors. Typical high-frequency tools used in this context—besides purely statistical approaches—are based on ray-tracing techniques. Ray-tracing can become challenging when multiple reflections dominate. In this context, mesh-based energy flow methods have become popular in recent years. In this study, we compare the two approaches both in terms of accuracy and efficiency and benchmark them against traditional power balance methods