| dc.description.abstract | The development of millimeterwave (MMW) and Terahertz (THz) technologies
for a wide range of wireless sensing and communication applications have been rapid due
to the unique characteristics of waves in these bands. Antennas are regarded as the core
of wireless applications, and its development for efficient operation within these bands
require the use of new carbon nanomaterials such as graphene. This is due to the
conductivity deterioration of conventional metals with increasing frequency. This work
focuses on improving the antenna performance parameters in the MMW and THz bands
based on the utilization of graphene. The employment of graphene requires mathematical
modelling and characterization of its surface impedance, which are frequency dependent.
The chemical potential (𝜇c) (doping) indicated a more significant effect compared to
other variables. Its values are influenced by electrical bias, magnetic bias, or chemical
doping. The 𝜇c = 0eV value is used as the non-doped graphene (ND-G) model, while (𝜇c
= 0.25eV and 𝜇c = 0.5eV) values are used for the doped graphene (D-G) models. D-Gs
were found to exhibit higher surface conductivities than ND-G, while the increasing 𝜇c
resulted in increased graphene conductivity. The material models of graphene (D-G and
ND-G) are then integrated onto the substrate and the microwave solver software CST
prior to simulations to determine the graphene based antenna (GBA) performance. These
GBA antenna models indicated significant performance improvement at THz frequencies
(1 THz, 1.29 THz, and 1.49 THz) compared to the copper-based antenna models. On the
contrary, the use of ND-G does not always show such significant improvements at MMW
frequencies (64GH), but is rather more concentrated on the bands beyond it. Two other
new techniques (coating and adhesives) are proposed as alternative fabrication methods
of graphene based antennas. These techniques indicated similar parameter improvements
to that of the direct deposition technique in the MMW (70GHz) and THz (1.71 THz)
bands. It was also discovered that antenna modeling using the adhesive technique
performs better than the direct deposition technique at MMW frequencies. Next, an
investigation to determine the critical frequency (CrFr) for the use of ND-G and copper
at MMW and THz spectrum (30GHz-3THz) was performed. This study considers
different topologies and performance parameters of ND-GBA to determine CrFr. The
curves of the performance parameters are plotted against frequency to facilitate
comparison between various GBA configurations. The CrFr is determined using the
intersections of the performance curves for copper-based and graphene-based antenna.
The investigation is also extended onto GBAs with graphene as ground or patch only.
The comparison for different antenna topologies, configurations, and parameters reported
different CrFrs, ranging from 0.130 - 0.240 THz, with an average of 0.147 THz. On the
other hand, the critical frequencies for the patch and ground only graphene-based
configurations ranged between 0.145 - 0.365 THz, with an average of 0.213 THz
indicating that the CrFr of ND-GBA depends on the antenna topologies and
configurations. | en_US |
