| dc.description.abstract | This thesis describes my research into the highly tuned naturally occurring
3D photonic structures that are present on a selection of insects. The experimental
and theoretical work presented in this thesis was performed in
both the optical and microwave regimes.
The work performed in the optical regime included both the geometric and
optical characterisation of the native photonic structures present on the
beetle Eupholus magni cus and the butter
y Parides sesostris. The native
photonic structures of these organisms were probed in order to determine
their photonic responses and also to ascertain their geometries and structural
classes. In cases where the geometry of a photonic crystal system has
been determined, I have performed additional theoretical analysis of the
structure to establish how it might be optimised for a particular optical
function. The overall aim of the work performed in the optical regime is to
further the understanding of the photonic structural designs present on a
selection of beetles and butter
ies, by both identifying and characterising
their underlying structural geometries and consequent photonic responses.
Eupholus magni cus is a species of weevil that produces its coloured appearance
from photonic structures that are present on its outer wing casing,
producing a striped coloured pattern. The photonic structures that I discovered
were present on this weevil were found to be contrasting in structural
order. I used a wide-ranging variety of experimental and theoretical
techniques in order to perform an extensive electromagnetic and structural
characterisation of these contrasting structures. The two contrasting photonic
mechanisms employed by E. magni cus were found to produce a similar
optical response in terms of angle-independent colour whilst re
ecting
di erent coloured hues.
Parides sesostris is a species of butter
y that uses a gyroid photonic crystal
structure, contained within scales, to produce green coloured patches
on the dorsal side of its wings. In addition to this, P. sesostris uses embellishments
to its scale morphology in order to produce a highly tuned
angle-independent optical response. The optical e ects brought about by
these structural embellishments were investigated with optical experimental
techniques and they were found to di usely scatter light and aid iridescence
suppression. In addition to this, theoretical modelling was performed on a
variety of gyroid geometries. The gyroid photonic structure found in the
wing scales of P. sesostris was determined to be highly optimised to re
ect
the largest range of frequencies possible from this geometry, also aiding iridescence
suppression. In addition to this, the arrangement of gyroid arrays
within each scale was determined to produce the highest intensity possible
by using the smallest possible number of unit cells.
In addition to the optical characterisations of the organic naturally occurring
photonic structures found on these organisms, I also synthetically
replicated the three fundamental naturally occurring triply periodic bicontinuous
cubic photonic crystal structures for experimental and theoretical
electromagnetic characterisation in the microwave regime. The microwave
regime was selected to perform the characterisation as a high-resolution
fabrication method can be employed in order to produce millimetre-scale
structures, suitable for probing in this wavelength regime. A high resolution
fabrication method is an absolute requirement for accurately replicating
the complex geometries of constant mean curvature structures and retaining
a high level of detail. I have electromagnetically characterised these
three structures with the aim of gaining a better understanding of their
polarisation-dependent photonic stop-band responses. Speci cally, I have
identi ed the origin of, and the dispersion of, photonic stop-bands produced
by each unique structural geometry. I have principally focused on the characterisation
of the electromagnetic responses of these structures, how they
di er from each other and also why a linear polarisation dependence arises
from these 3D photonic structures. In addition to this I have related the
electromagnetic responses of these structures to analogous optical structures
that naturally occur on the wings of the butter
y P. sesostris and elytra of
the weevil E. magni cus. With this I aimed to gain a better understanding
of the origin of the optical e ects they provide the host biological system.
This includes the characterisation of the gyroid photonic crystal structures,
chosen to mimic that found in P. sesostris wing scales. The results from
this were also subsequently used in the optical optimisation examination
performed on the P. sesostris gyroid.
Finally, I have investigated a dynamic aspect of the 3D gyroid photonic crystal,
formed from a constant mean curvature surface. A compliant gyroid
structure was fabricated for analysis in the microwave regime and a systematic
compression force applied to it. I have measured the electromagnetic
response of this compliant gyroid at each compression distance. Alongside
this, I used theoretical modelling to electromagnetically characterise
an analogous system under compression. In doing this I have identi ed the
origin of the novel and complex photonic band-shifting behaviour produced
by this 3D geometry. | en_GB |
