Superheterodyne Metamaterials: Controlling the Scattering Frequency from Incident Waveforms

Since the conception of the Salisbury screen absorber in the 1950s, different types of absorbers such as Jaumann, Dallenbach and later metamaterial absorbers have been developed
and tested. These deliver different reflectivity responses, such as narrow or wide band effects
and the size of an absorber is characterised by the operating frequency. Because of this
fundamental characteristic, thicker and heavier absorbers are required to provide a desired
absorber effect at low frequencies. This is a problem many have tried to find a solution
to, with different methods and design techniques that have been developed throughout the
years.
A solution to solve this problem is presented in this thesis by implementing the superheterodyne concept to a metasurface through the connection of non-linear components to a
metamaterial to upconvert a low frequency, illuminating signal. This mixer surface is then
integrated into a metamaterial structure which contains a simple absorber to remove generated harmonics. It is through this effect, that the work presented in this thesis can be a key
step towards a future in building multilayered metamaterial absorbers that are thinner than
conventional low frequency absorbers.
To determine whether the aims of the project have been met, the overall performance of an
absorbing structure in terms of the reflectivity of an illuminating frequency, the thickness of
a structure and far field scattering of harmonics will be evaluated. This type of absorber and
the reduction of an illuminating signal in this manner expands the area of superheterodyne
metamaterials as earlier models have primarily focused on down-conversion as opposed to
the upconversion that is of interest in this project. The use of computer software also sets
this project aside from other state of the art metamaterials, as the superheterodyne concept
has not been simulated on metamaterials using modern computer software and as such, the
work performed in this thesis will set the standard in terms of the computer modelling of
superheterodyne metamaterials.
The operation of metamaterial structure and the evaluation of the key parameters that characterise it will be presented in both simulation and measurement to evaluate the feasibility
of designs and to discuss how a structure is operating in the context of solving the problem
that has been postulated. It is thought by offering the final design in this thesis that a brand
new type of metamaterial absorber that is made using low cost, off-the-shelf materials can
be seized upon to create a new type of metamaterial absorber.