Fractional Electromagnetic Field Theory and Its Applications

Fractional electromagnetic field theory describes electromagnetic wave propagation through the complex, nonlocal, dissipative, fractal and also recent artificially engineered materials know as fractional metamaterials. In this theory using the fractional Maxwell equations we are also able to consider the well-known effect of electromagnetic memory. In this review we present some applications of the powerful theory of fractional electrodynamics.Comment: First version of the short lecture on "Fractional Electromagnetic Field Theory and Its Applications

Active and Fast Tunable Plasmonic Metamaterials

Active and Fast Tunable Plasmonic Metamaterials is a research development that has contributed to studying the interaction between light and matter, specifically focusing on the interaction between the electromagnetic field and free electrons in metals. This interaction can be stimulated by the electric component of light, leading to collective oscillations. In the field of nanotechnology, these phenomena have garnered significant interest due to their ability to enable the transmission of both optical signals and electric currents through the same thin metal structure. This presents an opportunity to connect the combined advantages of photonics and electronics within a single platform. This innovation gives rise to a new subfield of photonics known as plasmonic metamaterials.Plasmonic metamaterials are artificial engineering materials whose optical properties can be engineered to generate the desired response to an incident electromagnetic wave. They consist of subwavelength-scale structures which can be understood as the atoms in conventional materials. The collective response of a randomly or periodically ordered ensemble of such meta-atoms defines the properties of the metamaterials, which can be described in terms of parameters such as permittivity, permeability, refractive index, and impedance. At the interface between noble metal particles and dielectric media, collective oscillations of the free electrons in the metal particles can be resonantly excited, known as plasmon resonances. This work considered two plasmon resonances: localised surface plasmon resonances (LSPRs) and propagating surface plasmon polaritons (SPPs).The investigated plasmonic metamaterials, designed with specific structures, were considered for use in various applications, including telecommunications, information processing, sensing, industry, lighting, photovoltaic, metrology, and healthcare. The sample structures are manufactured using metal and dielectric materials as artificial composite materials. It can be used in the electromagnetic spectrum's visible and near-infrared wavelength range. Results obtained proved that artificial composite material can produce a thermal coherent emission at the mid-infrared wavelength range and enable active and fast-tunable optoelectronic devices. Therefore, this work focused on the integrated thermal infrared light source platforms for various applications such as thermal analysis, imaging, security, biosensing, and medical diagnosis. Enabled by Kirchhoff's law of thermal radiation, this work combined the concepts of material absorption with material emission. Hence, the results obtained proved that this approach enhances the overall performance of the active and fast-tunable plasmonic metamaterial in terms of with effortless and fast tunability. This work further considers the narrow line width of the coherent thermal emission, tunable emission, and angular tunable emission at the mid-infrared, which are achieved through plasmonic stacked grating structure (PSGs) and plasmonic infrared absorber structure (PIRAs).Three-dimensional (3D) plasmonic stacked gratings (PSGs) was used to create a tunable plasmonic metamaterial at optical wavelengths ranging from 3 m to 6 m, and from 6m to 9 m. These PSGs are made of a metallic grating with corrugations caused by narrow air openings, followed by a Bragg grating (BG). Additionally, this work demonstrated a thermal radiation source customised for the mid-infrared wavelength range of 3 μm to 5 μm. This source exhibits intriguing characteristics such as high emissivity, narrowband spectra, and sharp angular response capabilities. The proposed thermal emitter consists of a two-dimensional (2D) metallic grating on top of a one-dimensional dielectric BG.Results obtained presented a plasmonic infrared absorber (PIRA) graphene nanostructure designed for a wavelength range of 3 to 14 μm. It was observed and concluded that this wavelength range offers excellent opportunities for detection, especially when targeting gas molecules in the infrared atmospheric windows. The design framework is based on active plasmon control for subwavelength-scale infrared absorbers within the mid-infrared range of the electromagnetic spectrum. Furthermore, this design is useful for applications such as infrared microbolometers, infrared photodetectors, and photovoltaic cells.Finally, the observation and conclusion drawn for the sample of nanostructure used in this work, which consists of an artificial composite arrangement with plasmonic material, can contribute to a highly efficient mid-infrared light source with low power consumption, fast response emissions, and is a cost-effective structure

Recent Advances in Metasurface Design and Quantum Optics Applications with Machine Learning, Physics-Informed Neural Networks, and Topology Optimization Methods

As a two-dimensional planar material with low depth profile, a metasurface can generate non-classical phase distributions for the transmitted and reflected electromagnetic waves at its interface. Thus, it offers more flexibility to control the wave front. A traditional metasurface design process mainly adopts the forward prediction algorithm, such as Finite Difference Time Domain, combined with manual parameter optimization. However, such methods are time-consuming, and it is difficult to keep the practical meta-atom spectrum being consistent with the ideal one. In addition, since the periodic boundary condition is used in the meta-atom design process, while the aperiodic condition is used in the array simulation, the coupling between neighboring meta-atoms leads to inevitable inaccuracy. In this review, representative intelligent methods for metasurface design are introduced and discussed, including machine learning, physics-information neural network, and topology optimization method. We elaborate on the principle of each approach, analyze their advantages and limitations, and discuss their potential applications. We also summarise recent advances in enabled metasurfaces for quantum optics applications. In short, this paper highlights a promising direction for intelligent metasurface designs and applications for future quantum optics research and serves as an up-to-date reference for researchers in the metasurface and metamaterial fields

A Finite Difference Time Domain Study on the Design of Microwave Catheters

.An investigation of the design aspects along with proposed improvements in the construction of microwave ablation catheters are reported in this thesis. The computational methods used to carry out this research include an in-house created cylindrical coordinate rotationally symmetric Finite Difference Time Domain (FDTD) scheme. Firstly, a systematic means of modelling and designing microwave catheters is proposed. The method capitalizes on the rotationally symmetric nature of the microwave catheter and reduces the design from three dimensions to a two-dimensional problem. Secondly issues related to resonant frequency and leaky waves, an inherent property of microwave ablation, are investigated and subsequent solutions are proposed. For the issue of resonant frequency, the addition of a terminating cap halves the catheter’s resonant frequency allowing for acceptable return loss, less than -10 dB, at a resonant frequency of 2.7 GHz without a sleeve choke and 2.45 GHz with a choke. Several designs are investigated in order to eliminate the power coupled into waves travelling along the coaxial feedline’s exterior. The proposed catheter design with the sleeve choke is successful at eliminating surface waves whilst attaining a return loss of -14.61 dB at resonance. The internally matched catheter is equally as effective and attains a return loss of -49.39 dB at resonance while the catheter with a floating sleeve only partially reduces the amplitude of surface waves whilst achieving a return loss of -39.08 dB at resonance. The effectiveness of adding a dielectric cylinder around the monopole in order to improve return loss, bandwidth and overall Specific Absorption Rate (SAR) distribution is also investigated. Near to far field transformations are implemented and the far field pattern of the catheter is shown to be that of a dipole, at resonance. Furthermore, a dispersive FDTD algorithm is developed to incorporate a metamaterial plug. The effects of this are shown to be highly dependent on the dielectric properties of the metamaterial and act to lower the resonant frequency allowing for overall length reductions. Finally, the bioheat equation is investigated and is implemented in the context of microwave catheters by analyzing temperature rise at varying radial distances from the catheter