Description

Motives – Objectives

The main purpose of the project is twofold, including the development of highly precise numerical methods as well as their application to novel realistic structures addressing metamaterials/metasurfaces, graphene setups or plasmonics, and micro-electromechanical systems (MEMS) for THz realizations. Also, the combination of the prior devices is extensively explored for advanced implementations with unique features.

The main methodology of ACMIMS is mainly based on finite-difference techniques. Specifically, the finite-difference time-domain (FDTD) method constitutes a popular choice for time-dependent electromagnetic phenomena, as it is simple to implement and quite efficient, especially within domains of moderate size. Nonetheless, the low-order accuracy of its classic rendition may become a limiting factor in electrically-large configurations or when extended time integration of Maxwell’s equations is required. To overcome this shortcoming, high-order extensions of space/time operators constitute valuable alternative choices. Furthermore, optimized versions of the latter schemes are known to ensure additional improvement, without augmenting the pertinent computational complexity, while the alternating-direction implicit (ADI) and the locally one-dimensional (LOD) FDTD algorithms can lead to simulation time-steps beyond the typical FDTD stability limit. On the other hand, the calculation of reliable numerical solutions with reasonable complexity has always been a matter of major concern. Contrary to the past, considerable computational power for scientific evaluations is nowadays available, thanks to parallelism by graphics processing units (GPUs), whose power originates from their highly parallel architecture. As a result, GPUs are ideal for rapidly solving data-parallel problems, as memory latency is practically hidden by the execution of more computations. GPU computing is now a simple task, due to the Compute Unified Device Architecture (CUDA) parallel programming environment. It is should be sterssed that the acceleration of calculations is crucial in realistic engineering simulations, where numerical operations are performed over several thousands of time-steps, within domains of considerable size. In the case of ACMIMS mathematical methodologies, the benefits from avoiding pure serial-coding realization are anticipated to be substantial.

First Research Axis: Design and Characterization of Metamaterial Configurations

A basic axis of the project is the formulation of precise homogenized surface susceptibility models of arbitrary metasurfaces for oblique wave incidence. The generalized matrix method obtains the particle polarizability matrix from the scattering parameters of incident plane waves and replaceσ each scatterer with suitable electric and magnetic point-dipoles, presuming solely its small electrical size. Morever, analysis deals with the design and fabrication of new planar bandwidth-enhanced ultra-thin wide-angle metamaterials (MTM) absorbers with near unity absorbance. Special attention is drawn on the interpretation of physical phenomena that govern wave interactions in the vacuum-MTM interface of the absorber. It is significant to emphasize that due to the extremely fine details, existing numerical schemes lack to provide acceptably accurate and fast simulations. Hence, the proposed algorithms are expected to play a critical role. A subsequent research topic is the analysis of nanomagnetic plasmonic media and their association with MTM configurations. The key motive for incorporating their study in the  project is the ability to replace typical microwave conductors in nanocircuits. For this aim, an algorithm based on the displacement (instead of the conductivity) current is introduced, exploiting the fact that it is the main electromagnetic interaction at optical frequencies. Actually, the design of elements with the behavior of a capacitor, an inductance or a resistor is achieved via the use of dielectric and plasmonic materials.

Second Research Axis: Modeling of Graphene Arrangements

ACMIMS also delves into the precise modeling of graphene sheets and graphene nanoribbons (GNRs). Based on the issue that future nanoelectronics will be facilitated only by providing the effective capability of connecting the nanometric devices to the circuit boards, our interest focuses on the accurate characterization of arbitrary graphene-oriented structures as well as the optimal design of high-speed nano-interconnects and MTMs by means of CNTs and GNRs. The objective is that graphene will be handled as a complex isotropic volume conductivity, whose dispersive nature is efficiently incorporated via an auxiliary differential equation algorithm to allow an explicit implementation. On the other hand, plasmonics can be a crucial ingredient for most MTM implementations, and thereby all the exciting phenomena that they support, including negative refraction, superlensing, and cloaking. Nonetheless, there is one impediment toward attaining these aims: noble metals, which are widely regarded as the best available plasmonic materials, are hardly tunable and exhibit enormous ohmic losses. This greatly motivates the exploration of plasmons and their losses in newly available materials with distinctive properties, such as the graphene. Therefore, the potential for a beneficial incorporation of the graphene plasmonics properties in advanced MTMs is explored. Particularly, the interaction between a single quantum emitter and single graphene surface plasmon is analyzed to show that the extreme mode confinement yields an ultrafast decay of the emitter into single surface plasmons of a proximal doped graphene sheet. So, ACMIMS attempts to theoretically and numerically verify the route, opened up by graphene, to quantum devices that have so far been difficult to accomplish via conventional noble-metal plasmonics.

Third Research Axis: Micro-Electromechanical Systems in the THz Regime

Concerning its third research axis, ACMIMS concentrates on the design of novel tunable MTM devices with enhanced bandwidth capabilities, exploiting the versatility of radio-frequency micro-electromechanical systems (RF-MEMS). Actually, RF-MEMS exhibit several potentials in fulfilling concurrent technological needs such as reduced power consumption, linear behavior, enhanced bandwidth, and fabrication through already established protocols. However, the impact of RF-MEMS components in the overall performance of a device is considered lumped, when embedded in filtering or radiating apparatuses. An alternative approach could be their combination with MTMs. Since the lack of the latter for wide bandwidths has been already spotted, the design of left-handed media with a controllable operating frequency is deemed important to circumvent the prior constraints. On the other hand, THz technology is a rapidly growing research area with a serious impact on future RF front-ends allowing broadband applications. Specifically, controllable THz radiators and waveguides, utilizing cantilever beams, comb drives and electrothermal actuators, are developed exhibiting wideband performance and flexibility, whereas periodic implementations are thoroughly investigated. The final aim of ACMIMS is related to the accurate numerical analysis and optimization of the bias networks for the above RF-MEMS devices. As the impact of these bias is considerable for the overall MTM performance and the achievement of advanced radiation attributes for THz antennas, effective designs along with the minimization of degradation factors are to be pursued.

Implementation Methodology

To fulfill the aforementioned aims, ACMIMS will follow the following methodology: 

• Development of the advanced computational techniques.
• Code parallelization and GPU-based optimization.
• Generalized methodology for MTM and metasurface homogenization.
• Design and fabrication of 3-D MTM components and absorbers.
• Analysis of nanomagnetic plasmonic media and nanocircuits.
• Efficient modeling of arbitrary graphene-based structures.
• Theoretical analysis of graphene plasmonics and low-loss realizations.
• Parametric design and characterization of advanced RF-MEMS.
• Applications of RF-MEMS in MTMs and the THz regime.