The Microwave Response Of Ultra Thin Microcavity Arrays

Abstract

The ability to understand and control the propagation of electromagnetic radiation underpins a vast array of modern technologies, including: communication, navigation and information technology. Therefore, there has been much work to understand the interaction between electromagnetic waves and metal surfaces, and in particular to design materials the characteristics of which can be tailored to produce a desired response to microwave radiation. It is the objective of this thesis to demonstrate that patterning metal surfaces with sub-wavelength apertures can afford hitherto unrealised control over the reflection and transmission characteristics of materials which are an order of magnitude thinner than those employed historically.

The work presented herein aims to establish ultra thin cavity structures as novel materials for the selective absorption and transmission of microwave radiation. Experimental and theoretical approaches are used to elucidate the mechanism that allows such structures to produce highly efficient absorption via the excitation of standing wave modes in structures that are two orders of magnitude thinner than the operating wavelength. Also considered is how this same mechanism mediates transmission of selected frequencies through similarly thin structures.

Later chapters focus on ultra thin cavity structures which, through higher-order rotational symmetry, exhibit resonant absorption which is almost completely independent of incident and azimuthal angle and polarisation state. A detailed studied of the absorption bandwidth of these devices is also presented in the context of fundamental theoretical limitations arising from the thickness and magnetic permeability of the structure.