ELECTRONICAL LY RECONFIGURABLE FS S - INSPIRED TRANSMITARRAY FOR TWO DIMENS IONAL BEAMSTEERING FOR 5G ANDRADAR APPL ICATIONS AT 2 8 GHZ

In this dissertation, the author’s work on a 28 GHz transmitarray capable of antenna beamsteering for various wireless applications, is presented. Such device allows for the adjustment of the radiation pattern of an antenna by changing its main lobe direction, without the need of any mechanical means. A unit-cell based on a square-slot Frequency Selective Surface (FSS) is designed, simulated and optimised through several full-wave simulations, using an electromagnetic solver (CST MWS). Subsequently, the unit-cell was extended to a 10x10 array configuration in order to enable Two-dimensional (2D) beamsteering. This work yielded the fabrication of a prototype composed of four passive transmitarray lens, which were experimentally tested and characterised. Finally, a novel unit-cell based on a double square-slot intended aiming at active beamsteering was also studied and optimised in simulation environment. From this work, it was demonstrated that transmitarray can be seen as feasible alternative to many traditional beamsteering techniques, such as phased antenna arrays, while reducing the RF burden of the overall system using only a single radiation source. This fact, allied with it’s ease of integration, reduced cost and low-profile characteristics make transmitarrays a desirable solution for 5G and RADAR applications, among others

Recent Progress in Far-Field Optical Metalenses

In this chapter, a review of the recent advances in optical metalenses is presented, with special emphasis in their experimental implementation. First, the Huygens’ principle applied to ultrathin engineered metamaterials is introduced for the purpose of giving curvature to the wavefront of free-space wave fields. Primary designs based on metallic nanoslits and holey screens occasionally with variant width are first examined. Holographic plasmonic lenses are also explored offering a promising route to realize nanophotonic components. More recent metasurfaces based on nano-antenna resonators, either plasmonic or high-index dielectric, are analyzed in detail. Furthermore, 2D material lenses in the scale of a few nanometers enabling the thinnest lenses to date are here considered. Finally, dynamically reconfigurable focusing devices are reported for creating a scenario with new functionalities

Broadband Terahertz Metasurfaces

The terahertz frequency range spans from 0.1 THz to 10 THz and presents unique potential for medical imaging, material characterisation, non-destructive evaluation, and wireless communications. In recent years, various functional devices have been developed to harness the potential of terahertz waves, however mostly with limited bandwidth and efficiency. The thesis presents diverse broadband terahertz metasurfaces for wavefront control and polarisation manipulation. The concept of metasurfaces along with rigorous design approaches yields terahertz components with bandwidth and efficiency superior to existing devices. Such properties are much needed for terahertz technology to leverage vast available bandwidth with moderate source power. This thesis comprises nine chapters in total that are divided into four major parts. Part I introduces relevant research background and fundamental theories. Specifically, Chapter 1 presents the definitions of terahertz technology and metasurfaces, while Chapter 2 details the fundamental theories involved in this doctoral research. Part II concerns terahertz reflectarray bandwidth enhancement. A single-layer stubloaded resonator is proposed in Chapter 3 for constructing broadband reflectarrays. As a proof-of-concept, a terahertz reflectarray is designed, fabricated, and experimentally characterised to focus an incident plane wave to a focal spot at a finite distance. Part III involves terahertz transmitarrays for antireflection and polarisation manipulation. Each transmitarray employs three metallic layers to realise a complete control over the electric and magnetic responses, so that an arbitrary transmission phase together with high transmittance can be produced. Chapter 4 introduces a broadband semi-analytical approach that is developed on the basis of an existing narrowband method. The broadband approach involves network analysis combined with a genetic algorithm to determine the optimal frequency-independent circuit parameters, so that the desired transmission coefficients can be achieved over a wide bandwidth. In order to illustrate and verify the functionality of this broadband design approach, a wideband and highly efficient antireflection transmitarray is systematically designed based on this approach. Chapters 5 and 6 detail a quarter- and half-wave transmitarray, respectively, which are designed using the same procedure. The measured results confirm the functionality of the proposed quarter- and half-wave transmitarrays and suggest that they provide superior bandwidth and efficiency over the notable existing designs. Lastly, Chapter 7 shows a terahertz circular polariser with enhanced bandwidth, which is designed with the assistance of the broadband semi-analytical approach. The circular polariser is capable of transmitting circularly polarised waves of one handedness while blocking the other. Importantly, the three-layer circular polariser possesses frequency tunability obtained by adjusting the air spacers. Moreover, by rotating the top or bottom metallic layer, the circular polariser can be reconfigured to function as a transmissive quasi-half-wave plate. Part IV focuses on ultra-wideband absorber design. Chapter 8 presents a non-resonant absorber that is developed by etching air cavities into moderately doped silicon. In the realised absorber, inverted pyramidal air cavities are etched into doped silicon using a wet-etching technique, so as to realise impedance matching between the lossy silicon and free-space. The measured results demonstrate that a high absorption can be maintained over an ultra-wide bandwidth that spans nearly the entire far-infrared spectrum. The presented absorber far outperforms the existing resonance-based perfect absorbers in terms of achieved fractional bandwidth. Lastly, Chapter 9 concludes the thesis and gives an outlook of terahertz metasurfaces for practical applications. This thesis introduces technical advancements to metasurfacebased terahertz devices for wavefront control and polarisation manipulation. The developed and experimentally validated functional devices can be incorporated into compact terahertz systems, and they address the bandwidth and efficiency limitations associated with the existing designs.Thesis (Ph.D.) -- University of Adelaide, School of Electrical and Electronic Engineering, 202

Multifunction full space graphene assisted metasurface

In recent years, there has been notable advancement in programmable metasurfaces, primarily attributed to their cost-effectiveness and capacity to manipulate electromagnetic (EM) waves. Nevertheless, a significant limitation of numerous available metasurfaces is their capability to influence wavefronts only in reflection mode or transmission mode, thus catering to only half of the spatial coverage. To the best of our knowledge and for the first time, a novel graphene-assisted reprogrammable metasurface that offers the unprecedented capability to independently and concurrently manipulate EM waves within both half-spaces has been introduced in the THz frequency band

Reconfigurable Reflectarrays and Array Lenses for Dynamic Antenna Beam Control: A Review

Advances in reflectarrays and array lenses with electronic beam-forming capabilities are enabling a host of new possibilities for these high-performance, low-cost antenna architectures. This paper reviews enabling technologies and topologies of reconfigurable reflectarray and array lens designs, and surveys a range of experimental implementations and achievements that have been made in this area in recent years. The paper describes the fundamental design approaches employed in realizing reconfigurable designs, and explores advanced capabilities of these nascent architectures, such as multi-band operation, polarization manipulation, frequency agility, and amplification. Finally, the paper concludes by discussing future challenges and possibilities for these antennas.Comment: 16 pages, 12 figure

Design, Concepts and Applications of Electromagnetic Metasurfaces

The paper overviews our recent work on the synthesis of metasurfaces and related concepts and applications. The synthesis is based on generalized sheet transition conditions (GSTCs) with a bianisotropic surface susceptibility tensor model of the metasurface structure. We first place metasurfaces in a proper historical context and describe the GSTC technique with some fundamental susceptibility tensor considerations. Upon this basis, we next provide an in-depth development of our susceptibility-GSTC synthesis technique. Finally, we present five recent metasurface concepts and applications, which cover the topics of birefringent transformations, bianisotropic refraction, light emission enhancement, remote spatial processing and nonlinear second-harmonic generation

Analog Computing Using Graphene-based Metalines

We introduce the new concept of "metalines" for manipulating the amplitude and phase profile of an incident wave locally and independently. Thanks to the highly confined graphene plasmons, a transmit-array of graphene-based metalines is used to realize analog computing on an ultra-compact, integrable and planar platform. By employing the general concepts of spatial Fourier transformation, a well-designed structure of such meta-transmit-array combined with graded index lenses can perform two mathematical operations; i.e. differentiation and integration, with high efficiency. The presented configuration is about 60 times shorter than the recent structure proposed by Silva et al.(Science, 2014, 343, 160-163); moreover, our simulated output responses are in more agreement with the desired analytic results. These findings may lead to remarkable achievements in light-based plasmonic signal processors at nanoscale instead of their bulky conventional dielectric lens-based counterparts