| dc.description.abstract | Over the last century the electromagnetic (EM) spectrum has become ever
more accessible with advances in technology. As a result, EM filters (or Frequency Selective Surfaces (FSSs)) have been developed for many applications. Such filters have been used on satellites and radomes. In this thesis,
novel single layer and dual layer FSS have been studied and characterised,
experimentally and using Finite Element Method (FEM) modelling, showing very good agreement between the data and models. The interesting
transmission properties of these structurally complicated FSS are explained
and the physics of the resonant modes that mediate transmission is explored.
Enhanced transmission through an array of sub-wavelength apertures close
to the diffraction limit has been a popular area of physics for many years.
In addition enhanced reflection from metal patch arrays has been of great
interest. This thesis studies original extensions of conventional FSS. The
work is split into two main sections: single layer FSS and dual layer FSS.
In the first experimental chapter (chapter 5) two new single layered FSS
comprising complementary elements tessellated into composite arrays are
explored (a connected array and a disconnected array). The behaviour of
these arrays is compared with that of arrays of the constituent elements
that either exhibit enhanced transmission or enhanced reflection phenomena. The behaviour of the connected composite array can be inferred from
the behaviour of arrays of the constituent elements. Interestingly for the
disconnected composite array, the behaviour can not be inferred from the
constituent elements as without one or the other of the elements in situ, the
modes supported on the composite array are not supported for the arrays
of constituent elements.
The second and third experimental chapters (Chapters 6 and 7) explore the
transmission through dual layer arrays composed of either capped holes or
capped annuli. Despite the holes being capped with a metal disc, the array
exhibits a remarkably high transmission, mediated by the annular cavity
formed between the caps and apertured metal sheet. In Chapter 7 concentrically nested annular patches above annular slots are used to achieve
multiple transmission pass bands.
For many applications it is often desirable to miniaturise resonant elements.
Developing this concept further, chapter 8 explores the resonant frequency
of a structured capped aperture. The internal structure of metal inclusions,
give control over the resonant frequency of the cavity, reducing it's resonant
frequency significantly and miniaturising the size of the cavity compared to
the incident wavelength. | en_GB |
