Athanasios N. Papadimopoulos, Stamatios A. Amanatiadis, Nikolaos V. Kantartzis, Theodoros T. Zygiridis and Theodoros D. Tsiboukis
Important statistical variations are likely to appear in the propagation of surface plasmon polariton waves atop the surface of graphene sheets, degrading the expected performance…
Abstract
Purpose
Important statistical variations are likely to appear in the propagation of surface plasmon polariton waves atop the surface of graphene sheets, degrading the expected performance of real-life THz applications. This paper aims to introduce an efficient numerical algorithm that is able to accurately and rapidly predict the influence of material-based uncertainties for diverse graphene configurations.
Design/methodology/approach
Initially, the surface conductivity of graphene is described at the far infrared spectrum and the uncertainties of its main parameters, namely, the chemical potential and the relaxation time, on the propagation properties of the surface waves are investigated, unveiling a considerable impact. Furthermore, the demanding two-dimensional material is numerically modeled as a surface boundary through a frequency-dependent finite-difference time-domain scheme, while a robust stochastic realization is accordingly developed.
Findings
The mean value and standard deviation of the propagating surface waves are extracted through a single-pass simulation in contrast to the laborious Monte Carlo technique, proving the accomplished high efficiency. Moreover, numerical results, including graphene’s surface current density and electric field distribution, indicate the notable precision, stability and convergence of the new graphene-based stochastic time-domain method in terms of the mean value and the order of magnitude of the standard deviation.
Originality/value
The combined uncertainties of the main parameters in graphene layers are modeled through a high-performance stochastic numerical algorithm, based on the finite-difference time-domain method. The significant accuracy of the numerical results, compared to the cumbersome Monte Carlo analysis, renders the featured technique a flexible computational tool that is able to enhance the design of graphene THz devices due to the uncertainty prediction.
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Michail G. Christodoulou, Antonios X. Lalas, Nikolaos V. Kantartzis and Theodoros D. Tsiboukis
Metamaterials have been utilised in several exciting configurations such as tuneable reflectors, reconfigurable absorbers, and programmable modulators, triggering intense research…
Abstract
Purpose
Metamaterials have been utilised in several exciting configurations such as tuneable reflectors, reconfigurable absorbers, and programmable modulators, triggering intense research efforts. Among them, the ability to steer the radiation pattern of a single antenna component by employing a metamaterial-based superstrate is considered crucial for the development of advanced beam forming applications. The purpose of this paper is to introduce an adjustable omega-inspired metamaterial module to facilitate the design of beam steering implementations, involving beam forming capabilities, as well.
Design/methodology/approach
A variable capacitive diode is properly positioned at the novel omega element, hence advancing the controllability of its electromagnetic performance and circumventing the requirement of extra bias networks. When an array of these particles is placed in front of an antenna, several negative refractive index profiles can be realised, allowing the manipulation of the beam direction. Furthermore, a pyramidal horn antenna, loaded with this complex medium superstrate, is thoroughly investigated in terms of programmable beam steering and beam forming attributes. Several numerical data derived via the finite element method unveil the merits of the featured configuration.
Findings
The proposed structure allows programmability of the electromagnetic behaviour, but also circumvents the necessity of complicated bias networks, while minimising interference. The numerical assessment of a standard gain pyramidal horn antenna, associated to the featured metamaterial superstrate, sufficiently proves the controllable beam steering and beam forming attributes. Several parametric studies clarify the principal characteristics of the proposed setup, facilitating the design of high-end systems.
Originality/value
Development of tuneable metamaterial, which utilises variable capacitive diodes to enable controllability. Incorporation of reconfigurable metamaterials into antenna technology. Design of a pyramidal horn antenna, loaded with a complex medium superstrate exhibiting programmable beam steering and beam forming attributes. The proposed device circumvents the necessity of complicated bias networks, while minimising interference.
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Theodoros Zygiridis, Georgios Pyrialakos, Nikolaos Kantartzis and Theodoros Tsiboukis
The locally one-dimensional (LOD) finite-difference time-domain (FDTD) method features unconditional stability, yet its low accuracy in time can potentially become detrimental…
Abstract
Purpose
The locally one-dimensional (LOD) finite-difference time-domain (FDTD) method features unconditional stability, yet its low accuracy in time can potentially become detrimental. Regarding the improvement of the method’s reliability, existing solutions introduce high-order spatial operators, which nevertheless cannot deal with the augmented temporal errors. The purpose of the paper is to describe a systematic procedure that enables the efficient implementation of extended spatial stencils in the context of the LOD-FDTD scheme, capable of reducing the combined space-time flaws without additional computational cost.
Design/methodology/approach
To accomplish the goal, the authors introduce spatial derivative approximations in parametric form, and then construct error formulae from the update equations, once they are represented as a one-stage process. The unknown operators are determined with the aid of two error-minimization procedures, which equally suppress errors both in space and time. Furthermore, accelerated implementation of the scheme is accomplished via parallelization on a graphics-processing-unit (GPU), which greatly shortens the duration of implicit updates.
Findings
It is shown that the performance of the LOD-FDTD method can be improved significantly, if it is properly modified according to accuracy-preserving principles. In addition, the numerical results verify that a GPU implementation of the implicit solver can result in up to 100× acceleration. Overall, the formulation developed herein describes a fast, unconditionally stable technique that remains reliable, even at coarse temporal resolutions.
Originality/value
Dispersion-relation-preserving optimization is applied to an unconditionally stable FDTD technique. In addition, parallel cyclic reduction is adapted to hepta-diagonal systems, and it is proven that GPU parallelization can offer non-trivial benefits to implicit FDTD approaches as well.
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Nikolaos V. Kantartzis, Theodoros K. Katsibas, Christos S. Antonopoulos and Theodoros D. Tsiboukis
A systematic, non‐orthogonal FDTD algorithm for the unified and fully dual construction of curvilinear PMLs in 3‐D lossy electromagnetic and advective acoustic problems, is…
Abstract
A systematic, non‐orthogonal FDTD algorithm for the unified and fully dual construction of curvilinear PMLs in 3‐D lossy electromagnetic and advective acoustic problems, is presented in this paper. Postulating a consistent mathematical formulation, the novel methodology introduces a set of general vector parametric equations that describe wave propagation in both media and facilitate the effective treatment of the remarkably complex, arbitrarily‐aligned (non‐uniform) source or mean flow terms, particularly at low frequencies. The discretization procedure is performed via accurate higher‐order FDTD topological concepts, which along with a well‐posed variable transformation, suppress the undesired lattice dispersion and anisotropy errors. Hence, due to these additional degrees of design freedom and their optimal establishment, the new stable PMLs (split‐field or Maxwellian) accomplish a critical attenuation of the evanescent, vorticity or elastic wave families by carefully accounting for every loss mechanism. Numerical investigation reveals the superiority of the proposed technique in terms of various open‐region, waveguide and ducted‐domain simulations.
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Georgios Pyrialakos, Athanasios Papadimopoulos, Theodoros Zygiridis, Nikolaos Kantartzis and Theodoros Tsiboukis
Stochastic uncertainties in material parameters have a significant impact on the analysis of real-world electromagnetic compatibility (EMC) problems. Conventional approaches via…
Abstract
Purpose
Stochastic uncertainties in material parameters have a significant impact on the analysis of real-world electromagnetic compatibility (EMC) problems. Conventional approaches via the Monte-Carlo scheme attempt to provide viable solutions, yet at the expense of prohibitively elongated simulations and system overhead, due to the large amount of statistical implementations. The purpose of this paper is to introduce a 3-D stochastic finite-difference time-domain (S-FDTD) technique for the accurate modelling of generalised EMC applications with highly random media properties, while concurrently offering fast and economical single-run realisations.
Design/methodology/approach
The proposed method establishes the concept of covariant/contravariant metrics for robust tessellations of arbitrarily curved structures and derives the mean value and standard deviation of the generated fields in a single-run. Also, the critical case of geometrical and physical uncertainties is handled via an optimal parameterisation, which locally reforms the curvilinear grid. In order to pursue extra speed efficiency, code implementation is conducted through contemporary graphics processor units and parallel programming.
Findings
The curvilinear S-FDTD algorithm is proven very precise and stable, compared to existing multiple-realisation approaches, in the analysis of statistically-varying problems. Moreover, its generalised formulation allows the effective treatment of realistic structures with arbitrarily curved geometries, unlike staircase schemes. Finally, the GPU-based enhancements accomplish notably accelerated simulations that may exceed the level of 120 times. Conclusively, the featured technique can successfully attain highly accurate results with very limited system requirements.
Originality/value
Development of a generalised curvilinear S-FDTD methodology, based on a covariant/contravariant algorithm. Incorporation of the important geometric/physical uncertainties through a locally adaptive curved mesh. Speed advancement via modern GPU and CUDA programming which leads to reliable estimations, even for abrupt statistical media parameter fluctuations.
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Nikolaos V. Kantartzis, Theodoros K. Katsibas, Christos S. Antonopoulos and Theodoros D. Tsiboukis
This paper presents a curvilinearly‐established finite‐difference time‐domain methodology for the enhanced 3D analysis of electromagnetic and acoustic propagation in generalised…
Abstract
This paper presents a curvilinearly‐established finite‐difference time‐domain methodology for the enhanced 3D analysis of electromagnetic and acoustic propagation in generalised electromagnetic compatibility devices, junctions or bent ducts. Based on an exact multimodal decomposition and a higher‐order differencing topology, the new technique successfully treats complex systems of varying cross‐section and guarantees the consistent evaluation of their scattering parameters or resonance frequencies. To subdue the non‐separable modes at the structures' interfaces, a convergent grid approach is developed, while the tough case of abrupt excitations is also studied. Thus, the proposed algorithm attains significant accuracy and savings, as numerically verified by various practical problems.
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George Bouzianas, Nikolaos V. Kantartzis and Theodoros D. Tsiboukis
The purpose of this paper is to conduct the accurate analysis and systematic characterisation of realistic generalised bi‐isotropic and lossy chiral metamaterial 3D applications…
Abstract
Purpose
The purpose of this paper is to conduct the accurate analysis and systematic characterisation of realistic generalised bi‐isotropic and lossy chiral metamaterial 3D applications at microwave frequencies.
Design/methodology/approach
An accuracy‐adjustable time‐domain methodology is developed. The technique uses a convex combination of optimal stencils along with an advanced wavefield decomposition to precisely model the highly dispersive, double negative nature of chirality and constitutive parameters. Furthermore, open‐region radiation or scattering problems are terminated through a pertinently modified perfectly matched layer (PML) of variable depth.
Findings
The paper reveals that the proposed algorithm is versatile in the generation of adaptive stencils that attain a very natural way of manipulating continuity conditions at material interfaces. Thus, when periodic structures with split‐ring resonators are to be modelled, the resulting schemes attain optimal precision and minimised dispersion errors. Numerical validation proves these merits via diverse demanding structures of curved shape and multiple layers.
Originality/value
The new technique introduces a family of piecewise polynomials and spatial discretization criteria which lead to additional degrees of freedom for the discrete vectors of the application. In this manner, grid dual is intrinsically embedded in the physical profile of the problem, without resorting to the simplified conventions of other approaches. Moreover, singularity points or demanding geometric discontinuities are properly manipulated, even via coarse lattice resolutions. Thus, the overall accuracy is significantly improved and the computational requirements remain in very logical and affordable levels.
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Antonios X. Lalas, Nikolaos V. Kantartzis and Theodoros D. Tsiboukis
Wireless power transfer (WPT) is deemed as an emerging technology with exciting applications, like wireless charging devices, and electric vehicles, whereas metamaterials exhibit…
Abstract
Purpose
Wireless power transfer (WPT) is deemed as an emerging technology with exciting applications, like wireless charging devices, and electric vehicles, whereas metamaterials exhibit exceptional properties. For every WPT system that occupies coupled magnetic resonances, it is also mandatory to involve resonators. The purpose of this paper is to introduce a new interdigitated split-ring resonator (I-SRR) as the basic part of a WPT system, pursuing advanced levels of efficiency.
Design/methodology/approach
A novel WPT system, which exploits I-SRRs as its elementary blocks, is comprehensively examined. The analysis investigates the distance between the modules, the distance between transmitting and receiving components as well as the geometrical features of the structure. Several numerical data derived via the finite element method unveil the merits of the featured configuration.
Findings
The proposed arrangement reveals a noteworthy enhancement of the power delivered to the load and a promising tuning of the operational frequency via the interdigitated topology. Several parametric studies clarify the principal characteristics of the proposed setup, facilitating the design of high-end systems. In particular, the distance between the resonators and the port loops affect the matching of the input and output ports, allowing optimisation of power efficiency, while the length of the I-SRR gap can determine the operational frequency.
Originality/value
Development of a WPT system, which utilises I-SRRs as its key elements. Incorporation of metamaterials into WPT technology. Efficiency enhancement of WPT systems and alternative design via geometrical modifications. The necessity of lumped elements to implement the WPT resonators is eliminated by utilising split-ring resonators components, enabling compactness in several implementations.
Details
Keywords
Antonios X. Lalas, Nikolaos V. Kantartzis and Theodoros D. Tsiboukis
Metamaterials are artificially tailored complex media with extraordinary properties, not available in nature. Due to their unique performance, they are considered as a crucial…
Abstract
Purpose
Metamaterials are artificially tailored complex media with extraordinary properties, not available in nature. Due to their unique performance, they are considered as a crucial component of modern radio-frequency technology, especially in the THz regime. However, their lack of wide spectral bandwidths introduce constraints for realistic applications. The purpose of this paper is to propose piezoelectric micro-electromechanical systems (MEMS) actuators to modify the shape of electric field-driven LC (ELC) resonators. A THz modulation capability is revealed by connecting/disconnecting the associated metal parts.
Design/methodology/approach
Piezoelectric MEMS actuators are proposed to provide the desired bandwidth enhancement along with THz modulation. Two setups with different degrees of freedom in altering the behaviour of the novel modulator are investigated. A variety of numerical data, acquired via the finite element method, substantiate the advantageous characteristics of the proposed structures.
Findings
The novel devices enable the modification of the structural features of an ELC-based complex medium, unveiling in this manner a significant THz modulation capability along with improved bandwidth tunability. Two discrete cases are presented involving different degrees of freedom to shape the overall performance of the metamaterial modulator.
Originality/value
Development of a THz modulator, which utilises metamaterials as its fundamental component. Incorporation of tunable piezoelectric metamaterials into THz technology allowing increased reconfigurability. Bandwidth enhancement of metamaterial systems and alternative design via multiple controllable gaps enabling more degrees of freedom for design purposes.
Details
Keywords
Nikolaos V. Kantartzis and Theodoros D. Tsiboukis
The paper seeks to investigate the precise time‐domain modelling and broadband performance optimisation of 3D EMC structures formed by composite left‐handed metamaterials.
Abstract
Purpose
The paper seeks to investigate the precise time‐domain modelling and broadband performance optimisation of 3D EMC structures formed by composite left‐handed metamaterials.
Design/methodology/approach
A frequency‐dependent alternating‐direction implicit finite‐difference time‐domain method is introduced. Developing a class of multi‐directional curvilinear schemes for double‐negative media, the unconditionally stable algorithm forms robust lattice tessellations and provides advanced models complicated media interfaces. Moreover, the erroneous refractions at the metamaterial boundaries are systematically analysed through dynamic stencil configurations and powerful perfectly matched layer absorbers.
Findings
The paper finds that the proposed technique leads to convergent discretisations that resolve all propagation bandwidths and enhances the design of promising periodical devices loaded by substrates of thin wires and split‐ring resonators. Furthermore, its versatile character subdues dispersion deficiencies far beyond the usual stability criteria. Numerical validation, addressing various up‐to‐date EMC devices like coupled antennas, waveguides, high‐pass filters and absorber linings in test facilities, confirms the merits of the algorithm.
Originality/value
The novel methodology offers an advanced nodal control process which drastically suppresses the serious dispersion errors of existing approaches as time‐step exceeds the Courant limit. The resulting grids can support coarse resolutions, while the general curvilinear framework, along with the ADI rationale, allows the accurate approximation of demanding permittivity and permeability constitutive profiles. Hence, high accuracy and confined computational overhead are achieved without the need of laborious assumptions.