A metasurfaces review: Definitions and applications

This paper is a critical review of metasurfaces, which are planar metamaterials. Metamaterials offer bespoke electromagnetic applications and novel properties which are not found in naturally occurring materials. However, owing to their 3D-nature and resonant characteristics, they suffer from manufacturing complexity, losses and are highly dispersive. The 2-dimensional nature of metasurfaces allows ease of fabrication and integration into devices. The phase discontinuity across the metasurface offers anomalous refraction, thereby conserving the good metamaterial properties while still offering the low-loss characteristics. The paper discusses salient features and applications of metasurfaces; wavefront shaping; phase jumps; non-linear metasurfaces; and their use as frequency selective surfaces (FSS)

Metamaterial

In-depth analysis of the theory, properties and description of the most potential technological applications of metamaterials for the realization of novel devices such as subwavelength lenses, invisibility cloaks, dipole and reflector antennas, high frequency telecommunications, new designs of bandpass filters, absorbers and concentrators of EM waves etc. In order to create a new devices it is necessary to know the main electrodynamical characteristics of metamaterial structures on the basis of which the device is supposed to be created. The electromagnetic wave scattering surfaces built with metamaterials are primarily based on the ability of metamaterials to control the surrounded electromagnetic fields by varying their permeability and permittivity characteristics. The book covers some solutions for microwave wavelength scales as well as exploitation of nanoscale EM wavelength such as visible specter using recent advances of nanotechnology, for instance in the field of nanowires, nanopolymers, carbon nanotubes and graphene. Metamaterial is suitable for scholars from extremely large scientific domain and therefore given to engineers, scientists, graduates and other interested professionals from photonics to nanoscience and from material science to antenna engineering as a comprehensive reference on this artificial materials of tomorrow

Miniaturized Microwave Devices and Antennas for Wearable, Implantable and Wireless Applications

This thesis presents a number of microwave devices and antennas that maintain high operational efficiency and are compact in size at the same time. One goal of this thesis is to address several miniaturization challenges of antennas and microwave components by using the theoretical principles of metamaterials, Metasurface coupling resonators and stacked radiators, in combination with the elementary antenna and transmission line theory. While innovating novel solutions, standards and specifications of next generation wireless and bio-medical applications were considered to ensure advancement in the respective scientific fields. Compact reconfigurable phase-shifter and a microwave cross-over based on negative-refractive-index transmission-line (NRI-TL) materialist unit cells is presented. A Metasurface based wearable sensor architecture is proposed, containing an electromagnetic band-gap (EBG) structure backed monopole antenna for off-body communication and a fork shaped antenna for efficient radiation towards the human body. A fully parametrized solution for an implantable antenna is proposed using metallic coated stacked substrate layers. Challenges and possible solutions for off-body, on-body, through-body and across-body communication have been investigated with an aid of computationally extensive simulations and experimental verification. Next, miniaturization and implementation of a UWB antenna along with an analytical model to predict the resonance is presented. Lastly, several miniaturized rectifiers designed specifically for efficient wireless power transfer are proposed, experimentally verified, and discussed. The study answered several research questions of applied electromagnetic in the field of bio-medicine and wireless communication.Comment: A thesis submitted for the degree of Ph

The design, simulation, and pattern synthesis of novel reflectarrays

The main focus of this thesis is on the development of both a comprehensive understanding and a thorough computational routine of the reflectarray metasurfaces designs, with focuses on a liquid crystal-based reconfigurable reflectarray metasurface and on the phase-retrieval/optimisation techniques for reflectarray-based pattern synthesis. A dielectric-based polarisation converting reflectarray metasurface is also presented, with the advantage of having a thinner profile over the traditional quartz-based half-wave plates. In the introductory sections, a thorough review of the state-of-the-art metasurfaces is presented, with a focus on applications to high-frequency wireless communications, as the motivation of this PhD is on the development of technologies that would facilitate the wireless communication challenges for the 5G-and-beyond frequency spectrum. In this section, a review of array antennas, including phased arrays, reflectarrays, transmitarrays, as well as metasurfaces utilising Mie-resonance, plasmonic resonance, geometric phase (Pancharatnam-Berry phase) and photoconductive material is presented. The following chapter on the theoretical background ensures the understanding of the fundamental mechanisms that will be applied to the study of reflectarray metasurfaces and optimisation routines. The high-frequency propagation associated with beyond-5G wireless communications brings many challenges to the current standards: some of the biggest problems are the much greater path loss and heavy non-line-of-sight signal attenuation. Traditionally, this has been dealt with in phased arrays. However, in the introduction part of this thesis, I show that this becomes impractical due to the requirements of enormous array sizes and expensive high-frequency phase shifters. Therefore, in our research, we have focused on reconfigurable reflectarrays as an intermediate solution to alleviate the tough propagation challenges faced by beyond-5G wireless communications. The reconfigurable reflectarray can either be designed to reflect off from a nearby mobile cell site to enhance the signal strength for non-line-of-sight areas, or it can include an integrated source to function independently, reducing the losses associated with power amplifiers and complex circuitries associated with the enormous array sizes. This thesis aims to produce a high-frequency tailored reconfigurable reflectarray design, which combines the conceptual advantages from state of-the-art lumped-element-based and liquid crystal-based reflectarrays. As shown in the literature review section, most recent researches on lumpedelement- based reconfigurable reflectarrays are designed for the sub 40 GHz frequencies; with higher frequencies, the intrinsic losses associated with lumped-elements such as PIN diodes make them unsuitable choices. On the other hand, liquid crystals have been used as a tunable material for different radio-frequency applications; however, most state-of-the-art designs of liquid crystal-based reflectarrays do not incorporate individual biasing control for maximum beam-control. There are also challenges faced with individually-biased reconfigurable reflectarrays. Traditionally, phased arrays can perform single beam-scanning or multiple beam-scanning with the control of multiple sub-arrays. We intend to achieve more complex beam-functionalities (such as vortex, null, and magnitude-specific beams) within the domain of manipulating one individual array. This is already possible with optimisation algorithms such as the genetic algorithm. However, traditional optimisers such as the genetic algorithm and particle swarm optimisation are far too slow to be implemented in an “online” mode, where the algorithm runs onboard the reflectarray to give low-latency solutions. The “online” optimisation mode would be very beneficial as it would reduce the channel occupation from the transmission of configuration information and thus increase channel capacity. In this thesis, I aim to develop an individually biased liquid crystal-based reconfigurable reflectarray for >100 GHz frequencies. I also aim to develop an algorithm that is sufficiently quick to have the potential to be practically utilised as an onboard pattern synthesis optimisation method. Additionally, using the same design principles, I have designed an all-dielectric-based reflectarray metasurface that acts as a polarisation-converting quarter-wave plate, which is much thinner than traditional quartz-based quarter-wave plates. In the Research Results and Publications chapter, a complete procedure for the design of LC-based reconfigurable and dielectric-based nonreconfigurable reflectarray metasurfaces is presented, where much of the content comes from the author’s own publications[52, 78, 50, 51]. This thesis provides details on the computational tools/programs used, cross-platform routines development with CST Studio Suite, MATLAB and VBA, and the pattern synthesis algorithm, whereby a genetic algorithm is employed for the global optimisation, and an improved Gerchberg-Saxton algorithm is developed and adapted to the application of faster local optimisation for the pattern synthesis. For the all-dielectric reflectarray metasurface, the further functionality of polarisation conversion (linear to circular and circular to linear) is demonstrated on top of the beam-manipulation capabilities of the reflectarrays. The reflectarray metasurfaces can be designed to beamform, beamsteer, beamsplit/multibeam, as well as achieve novel beam profiles such as the vortex profile. Originally, the idea was to completely focus on the liquid crystal-based study and to develop a down-scaled 28 GHz proof-of-concept, for which partial work had already begun (the simulation, optimisation and initial planning on the construction with collaborators from other departments); however, due to the pandemic and numerous other uncontrollable factors, this was later discarded and replaced by remaining on and extending upon the computational studies, to further understand and improve the pattern synthesis algorithms and the other types of phase-change metasurfaces

Antenna Design for 5G and Beyond

With the rapid evolution of the wireless communications, fifth-generation (5G) communication has received much attention from both academia and industry, with many reported efforts and research outputs and significant improvements in different aspects, such as data rate speed and resolution, mobility, latency, etc. In some countries, the commercialization of 5G communication has already started as well as initial research of beyond technologies such as 6G.MIMO technology with multiple antennas is a promising technology to obtain the requirements of 5G/6G communications. It can significantly enhance the system capacity and resist multipath fading, and has become a hot spot in the field of wireless communications. This technology is a key component and probably the most established to truly reach the promised transfer data rates of future communication systems. In MIMO systems, multiple antennas are deployed at both the transmitter and receiver sides. The greater number of antennas can make the system more resistant to intentional jamming and interference. Massive MIMO with an especially high number of antennas can reduce energy consumption by targeting signals to individual users utilizing beamforming.Apart from sub-6 GHz frequency bands, 5G/6G devices are also expected to cover millimeter-wave (mmWave) and terahertz (THz) spectra. However, moving to higher bands will bring new challenges and will certainly require careful consideration of the antenna design for smart devices. Compact antennas arranged as conformal, planar, and linear arrays can be employed at different portions of base stations and user equipment to form phased arrays with high gain and directional radiation beams. The objective of this Special Issue is to cover all aspects of antenna designs used in existing or future wireless communication systems. The aim is to highlight recent advances, current trends, and possible future developments of 5G/6G antennas

Antennas and Propagation

This Special Issue gathers topics of utmost interest in the field of antennas and propagation, such as: new directions and challenges in antenna design and propagation; innovative antenna technologies for space applications; metamaterial, metasurface and other periodic structures; antennas for 5G; electromagnetic field measurements and remote sensing applications

Antenna Design for 5G and Beyond

This book is a reprint of the Special Issue Antenna Design for 5G and Beyond that was published in Sensors

Intelligent Circuits and Systems

ICICS-2020 is the third conference initiated by the School of Electronics and Electrical Engineering at Lovely Professional University that explored recent innovations of researchers working for the development of smart and green technologies in the fields of Energy, Electronics, Communications, Computers, and Control. ICICS provides innovators to identify new opportunities for the social and economic benefits of society.　 This conference bridges the gap between academics and R&D institutions, social visionaries, and experts from all strata of society to present their ongoing research activities and foster research relations between them. It provides opportunities for the exchange of new ideas, applications, and experiences in the field of smart technologies and finding global partners for future collaboration. The ICICS-2020 was conducted in two broad categories, Intelligent Circuits & Intelligent Systems and Emerging Technologies in Electrical Engineering

Smart Surface Radio Environments

This Roadmap takes the reader on a journey through the research in electromagnetic wave propagation control via reconfigurable intelligent surfaces. Metasurface modelling and design methods are reviewed along with physical realisation techniques. Several wireless applications are discussed, including beam-forming, focusing, imaging, localisation, and sensing, some rooted in novel architectures for future mobile communications networks towards 6G

Waveguiding of electromagnetic waves and investigation of negative phase velocity in photonic crystals and metamaterials

Ankara : The Department of Electrical and Electronics Engineering and the Graduate School of Engineering and Science of Bilkent University, 2012.Thesis (Ph. D.) -- Bilkent University, 2012.Includes bibliographical references.Electromagnetic wave propagation is characterized in periodic dielectric and metallic structures: Photonic Crystals (PCs) and Metamaterials, respectively. The applications of these structures are demonstrated in the Microwave regime. In the first application, Graded Index (GRIN) PC is used to focus the incoming waves into a small spot. Speaking in terms of PC period a, for an incident beam with Full Width Half Maximum of 9.20a the power of the focusing behavior is quantified by looking at the spot size conversion ratio, which is around 3.9. PCs can act as an efficient input coupler for the PC Waveguide (PCW). The GRIN PC has been experimentally shown to yield a coupling efficiency of 5 dB over the single PCW at 18 GHz. This method can be applied to provide a solution for the input coupling losses between PC structures and other lightwave circuits. PCs can also be used to achieve dual-bandpass and bandstop spatial filtering by proper adjustments of the lattice parameters and the frequency range. For the plane-wave excitation, a wideband spatial filtering is shown to exist due to the specific Fabry-Perot type resonances, which are nearly independent on the angle of incidence. The effect of the finite angular distribution of the Gaussian-beam excitation is also demonstrated. The spatial filtering in the incidence and observation angle domains has been discussed both numerically and experimentally for the non-plane-wave excitations under the light of calculated iso-frequency contours. In addition to bandstop characteristics, the dispersion relation of the PCs can be modified with the proper arrangement, namely by employment of the dimer layer. This surface layer supports the surface waves and serves like a waveguide for the electromagnetic waves. At higher frequencies above the lightline, surface waves radiate into air in the form of backward leaky waves and frequency dependent steering is reported from 0 º to 70º for the outgoing beam. The leaky wave behavior and backward radiation is similar to that is seen in Left-Handed (LH) Metamaterials. Metallic fishnet layers are used to demonstrate negative refractive index (NRI) in conjunction with the left-handed behavior in this class of metamaterial. A wedge structure formed by fishnet layers is used to measure the NRI which was also verified by the retrieval analysis. The limits of homogenization are discussed. The dependence of the LH properties on the fishnet parameters is investigated parametrically. For example, the NRI changes from -1.8 to -1.3 as the interseperation distance of the layers varies from as=λ/10.5 (2mm) to as=λ/4.2 (4mm) at magnetic resonance frequency around 14.3 GHz (ωm). It is also shown that the fishnet layers behave as an LC resonator as well as a TEM waveguide and a 1D transmission line at ωm.Çolak, İlyas EvrimPh.D