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Abstract A novel use case for two data‐driven models, namely, a Transformer and a convolutional graph neural network (CGNN) is proposed. The authors propose to use these models for emulating the dynamics of electromagnetic (EM) propagation and scattering. The Transformer translates a past sequence into a future sequence by constructing representations from the past and using it to predict the future, taking all of its own previous predictions as input at each step of prediction. The CGNN updates the current state of attribute vectors of each node by passing it information (messages) from all of its neighbouring nodes. We train these models with FDTD simulations of plane waves propagating and scattering from PEC objects. The authors demonstrate that, within the bounds of computational resources, the Transformer can be utilised as a surrogate for EM dynamics, providing 14× speed‐up, while the CGNN can be utilised as a next‐frame predictor, providing 9× speed‐up. When comparing the accuracy of these two models with the authors’ previously developed Encoder‐Recurrent‐Decoder (ERD) model, it is observed that the error for both the Transformer and the CGNN remains within the same bound for the ERD model. To the best of the authors’ knowledge, this work is the first to utilise the Transformer as a surrogate for EM dynamics.

A novel use case for two data‐driven models, namely, a Transformer and a convolutional graph neural network (CGNN) is proposed. The authors propose to use these models for emulating the dynamics of electromagnetic (EM) propagation and scattering. The Transformer translates a past sequence into a future sequence by constructing representations from the past and using it to predict the future, taking all of its own previous predictions as input at each step of prediction. The CGNN updates the current state of attribute vectors of each node by passing it information (messages) from all of its neighbouring nodes. We train these models with FDTD simulations of plane waves propagating and scattering from PEC objects. The authors demonstrate that, within the bounds of computational resources, the Transformer can be utilised as a surrogate for EM dynamics, providing 14× speed‐up, while the CGNN can be utilised as a next‐frame predictor, providing 9× speed‐up. When comparing the accuracy of these two models with the authors' previously developed Encoder‐Recurrent‐Decoder (ERD) model, it is observed that the error for both the Transformer and the CGNN remains within the same bound for the ERD model. To the best of the authors' knowledge, this work is the first to utilise the Transformer as a surrogate for EM dynamics. [ABSTRACT FROM AUTHOR]

Abstract Fano resonance arises from the superposition of a narrow discrete resonance with a continuous state. In this paper, a Fano resonance‐based plasmonic refractive index sensor based on nanoscale metal‐insulator‐metal (MIM) waveguides is proposed and evaluated by applying the two‐dimensional finite‐difference time‐domain (2D FDTD) method. An MIM‐based single stub vertically attached to an MIM waveguide is considered as the unit cell of the waveguide system of the proposed structure. A transfer matrix of transmission and coupling complex coefficients is defined for the unit cell of the waveguide system of the proposed sensor, and the conditions for the authenticity of its modeling based on the transmission line theory are evaluated. A system of triplet coupled stub resonators (TCSRs) attached to an MIM waveguide is coupled with a disk resonator to induce Fano resonances in the transmission spectrum of the sensor. Fano resonance and its characteristics are utilized to improve the essential operating parameters of the sensor, such as full width at half maximum (FWHM) and figure of merit (FOM). In optimized conditions, for the system of TCSRs coupled to a disk resonator, a resonance with a sensitivity of 684 nm/RIU and an FOM of 621.8 1/RIU exhibited. Also, for the system of TCSRs coupled to a ring resonator, a resonance with a sensitivity of 3524 nm/RIU and an FOM of 35.24 1/RIU was achieved. Eventually, the numerically achieved results for the operating parameters of the sensor are validated using governing analytical methods.

Fano resonance arises from the superposition of a narrow discrete resonance with a continuous state. In this paper, a Fano resonance‐based plasmonic refractive index sensor based on nanoscale metal‐insulator‐metal (MIM) waveguides is proposed and evaluated by applying the two‐dimensional finite‐difference time‐domain (2D FDTD) method. An MIM‐based single stub vertically attached to an MIM waveguide is considered as the unit cell of the waveguide system of the proposed structure. A transfer matrix of transmission and coupling complex coefficients is defined for the unit cell of the waveguide system of the proposed sensor, and the conditions for the authenticity of its modeling based on the transmission line theory are evaluated. A system of triplet coupled stub resonators (TCSRs) attached to an MIM waveguide is coupled with a disk resonator to induce Fano resonances in the transmission spectrum of the sensor. Fano resonance and its characteristics are utilized to improve the essential operating parameters of the sensor, such as full width at half maximum (FWHM) and figure of merit (FOM). In optimized conditions, for the system of TCSRs coupled to a disk resonator, a resonance with a sensitivity of 684 nm/RIU and an FOM of 621.8 1/RIU exhibited. Also, for the system of TCSRs coupled to a ring resonator, a resonance with a sensitivity of 3524 nm/RIU and an FOM of 35.24 1/RIU was achieved. Eventually, the numerically achieved results for the operating parameters of the sensor are validated using governing analytical methods. [ABSTRACT FROM AUTHOR]

Abstract In this study, the implementation of different corona discharge models in a transient program for overhead multiconductor lines based on the implicit Crank‐Nicolson Finite Difference Time Domain method is presented. Among different corona models available in the literature, two empirical models (Gary's and Suliciu's models) and a physics‐based model (Malik's model) are discussed, which are broadly used in EMT programs, and their predictions under fast‐front lightning surges and slow‐front switching impulses are assessed. The authors critically review the dynamic capacitance approach in terms of numerical accuracy, when dealing with slowly varying voltages, and applicability, regarding dispersive models assuming a non‐instantaneous charge‐voltage relation. The alternative voltage‐controlled generator approach is proposed, which is successfully included in the implicit Crank‐Nicolson scheme. One of the objectives of this study is to show how different corona models may predict overvoltages with huge discrepancies, depending on the transient waveform and the propagation distance, despite the similarity of the q‐v hysteresis curves. More evident discrepancies between models under fast‐front voltage waves are reported, rather than for switching impulses. The consistency of these results in terms of the models' features and q‐v curves is analysed, highlighting the necessity for new engineering tools for corona simulation of general predictive capability.

Abstract The authors propose a nanoplasmonic structure based on metal–insulator–metal (MIM) waveguides which consists of a 3 db power splitter and a side‐coupled nanocavity placed between its two output ports. The proposed structure is analysed by the resonant theory and dispersion relation. Transmission spectra of the presented device are also extracted using the finite difference time domain method. Numerical simulations demonstrate that the structure operates as a band‐stop filter in each output channel. Moreover, the resonance wavelengths can be tuned by adjusting the geometrical parameters of the nanocavity. Meanwhile, the authors developed the cavity and added an extra stub to it to append a new stopband to the output spectrum. Each resonance wavelength can be easily manipulated by changing the widths of the nanocavity and the added stub. In the end, by choosing two different lengths for the side‐coupled cavities, the authors convert the power splitter into a wavelength division multiplexer. These introduced MIM, the authors proposed here, may have various meaningful applications in nanoscale high‐density photonic circuits such as optical switches, logic plasmonic circuits and slow‐light devices.

Abstract The uniaxial perfectly matched layer (UPML), an important link in the numerical calculation of the discontinuous Galerkin time domain (DGTD), truncates the size of the computational domain and absorbs the outward‐travelling waves. In traditional DGTD, tetrahedral meshes are used to divide the computational domain. These meshes are also used in UPML. As the scope of the computational domain is wide, many meshes will be generated after the UPML division wraps the external part of the domain, thereby resulting in inefficient computation. The use of a UPML in DGTD form based on hexahedral meshes is proposed. The internal propagation and UPML regions are divided by a tetrahedral element and a hexahedral element, respectively. Among the relevant numerical examples given, a few cases are analysed to demonstrate the feasibility of the proposed method: the high efficiency of the UPML with hexahedral mesh, attenuation of electromagnetic waves inside the UPML, and relative error of the electric field values at the observation points.

Abstract Semiconductor ring lasers have attracted remarkable interest as laser sources in photonic integrated circuits. They result in bidirectional laser owing to the rotation symmetry between the two counter‐propagating modes of the ring cavity. This symmetry can be broken embedding an S‐bend waveguide in the racetrack resonator, which generates an unbalanced loss mechanism and a non‐reciprocal gain between clockwise and counter‐clockwise direction beams. The propagating field along the resonator in the undesirable direction is evanescently coupled to the S element in correspondence of two coupling regions and converted into the preferred one. The authors examined how the field coupling coefficients of the couplers impact the resonator unidirectionality. In numerical simulations, the authors changed the coupler gap distance and the coupler length of the directional couplers to scan the full range of variability of the coefficients. The simulated performances of the resonator are discussed in terms of the extinction ratio between the clockwise and the counter‐clockwise modes as well as the power truly circulated in the two directions of the resonator net of all losses. The finite‐difference time‐domain method within Synopsys RSoft© suite was used to simulate the evolution of the counter‐propagating field along the racetrack.

Abstract The quantum Toffoli gate is one of the essential reversible universal logic gates widely used for optical data processing. Herein, a new scheme of developing all‐optical Toffoli gate using a two‐dimensional silicon–air photonic crystal is proposed. For the realization of the Toffoli gate, the principles of constructive and destructive interference of light are used. The Toffoli gate comprises two‐input–three‐output‐based optical AND gate, and a two‐input–one‐output optical XOR gate. Two Y junction power splitters have been used at the two inputs of the AND gate. The operating wavelength of the proposed Toffoli gate is 1550 nm along with the wafer size of 50 µm × 50 µm. The performance of the Toffoli gate has been analysed and simulated by the plane‐wave expansion method and finite‐difference time‐domain method. The response time and contrast ratios are also obtained from the simulation. The proposed Toffoli gate is intensity encoded with no non‐linear material within the crystal which shows significant improvement over other proposals.

Abstract An all‐optical half adder based on two‐dimensional photonic crystals is proposed. The proposed structure is composed of a triangular array of dielectric rods made of non‐linear optical material in air. The structure consists of four waveguides and one ring resonator which are formed by removing a number of dielectric rods. The structure has been simulated and analysed by the plane wave expansion method and the finite‐difference time‐domain method. The size of the proposed structure is small with dimensions of 17 μm × 14.8 μm, and the material of the rods and lattice constant are uniform across the structure. The proposed half adder has a minimum contrast ratio of 13.51 dB in the steady state, with a maximum time delay of 2 ps.

Abstract A new approach for using polynomial chaos‐based expansion finite‐difference time‐domain (PCE‐FDTD) is presented to calculate the uncertainty of electromagnetic wave propagation in dispersive materials. Based on the bilinear transform method, this approach performs polynomial expansion on random electromagnetic fields by PCE‐FDTD method. The proposed algorithm has a simple formulation and is very easy to extend to isotropic dispersive material. It has a general form for different types of random dispersive materials and can efficiently calculate the mean value and the SD of electromagnetic field components in a single run. Two examples of different dispersive media with two random variables are listed to show the generality of the algorithm, and a radar cross‐section of a perfectly conducting cylinder coated by a layer of random plasma is illustrated as an example to show the practicability of the approach. The results are validated by comparing it with the Monte Carlo method.

Underground cables such as pipe-type cables are widely used in urban power industry. In this study, an advanced thin-wire model of the pipe-type cables is 3D FDTD simulations. In this model, the multi-conductor cables are represented with two-level transmission line equations. A stabilising technique with a 1D spatial low-pass filter is proposed to maintain computational stability. Frequency-dependent losses are fully considered by using a vector-fitting technique. The proposed thin-wire model is validated with the multi-conductor transmission line theory analytically and the traditional FDTD method numerically. Good agreements are observed. It is found that the simulation maintains stability for 360,000-time steps. Compared to the traditional FDTD method, the memory space and computation time of the proposed model can be reduced by 73% and 98%, respectively. Induced lightning currents in a cable connection station are analysed. It is found that, without considering soil ionisation and soil stratification, the peak current in the metallic armour is 1.54 times as much as the one with considering these non-linear effects. It can be reduced by 9.04% and 18.6% if the cable is buried at depths of 1 m and 1.5 m, compared with the case of a 0.5 m buried depth. [ABSTRACT FROM AUTHOR]

This study aims at optimising the graphene coverage in a microresonator for the design of an efficient modulator by using a combination of graphene induced losses and phase shift. The graphene integration in the ring can provide tunability by means of altering the loss and coupling coefficient by changing the graphene coverage or its chemical potential. The fundamental parameters of graphene integrated all‐pass ring resonator are extracted based on the transmission characteristics using finite‐difference time‐domain method. As compared to conventional graphene‐oxide‐semiconductor straight waveguide, graphene integrated on an all‐pass ring resonator shows enhanced optical absorption and phase shift due to field enhancement factor. A modulator based on graphene tunable loss and phase shift is investigated taking into account the field enhancement factor. For 1.55 μm radiation and ring radius of 3.75 μm with 22% graphene coverage, a maximum modulation depth of 12.6 dB is demonstrated based on electrostatic control of graphene chemical potential. The proposed modulator can feature operational speed in the range of 10 GHz that is useful in a variety of electro‐optic applications. [ABSTRACT FROM AUTHOR]

A hybrid method combining the finite-element time-domain (FETD) method and transmission line (TL) equations (FETD-TL) is presented for evaluating the transient responses of a lossy TL in an apertured rectangular enclosure excited by electromagnetic pulses. First, the electric fields in the enclosure without the TL are calculated based on the Bethe's small holes theory and the mirror procedure. Then, the enclosure's electric fields are introduced into the second-order TL equation for current as the equivalent distributed sources. The transient currents induced on the TL are obtained by solving the second-order TL equation for current based on the FETD method with a single iteration variable. Finally, the transient voltages induced on the TL are computed by discretising the first-order TL equation. Compared with the method based on finite-difference time-domain (FDTD) method and TL (FDTD-TL) via several examples, the proposed hybrid method is proved to be correct and effective, which possesses much higher convenience and efficiency than FDTD-TL method in dealing with TL model terminated by complex lumped parametric networks. [ABSTRACT FROM AUTHOR]

In this Letter, the authors designed a photonic configurable logic block (pCLB) with 1×1 Mach–Zehnder modulator as a universal photonic gate (UPG) using electro‐optic mechanism. The UPG is capable of performing all the logical operations with the help of FPGA as a configuration controller. The functionality and its suitability is verified by forming a pCLB of ten UPGs, which finds applications in digital photonics. For the design of pCLB, traditional electronic design automation tools are used. The pCLB provides features namely scalability and modular approach, for the reconfigurable digital photonic integrated circuits. The photonic gate designed using a two‐dimensional finite difference time domain approach shows a crosstalk‐free operation with a negligible transmission loss of 0.18 dB and flexible switching control compared to the existing 2×2 MZI‐based photonic gate. [ABSTRACT FROM AUTHOR]

A novel InP#x02010;based metal#x02010;coated sidewall, hybrid plasmonic multimode interference (MCS#x02010;HP#x02010;MMI) power splitter has been proposed. Based on two methods of multimode interference self#x02010;imaging and finite difference time domain simulations, a 1 × 2 MCS#x02010;HP#x02010;MMI power splitter was numerically analysed and compared with an HP#x02010;MMI power splitter with the same specifications showing 70% reduction in length due to the negative Goos–Hänchen shift in the metal#x02010;coated sidewalls of the MCS#x02010;HP#x02010;MMI power splitter. The width and layer stack specifications of the device were optimised using response surface methodology to minimise the multimode interference length and maximise the optical power transmission. The total optical power transmission of 98% was achieved for an MCS#x02010;HP#x02010;MMI width and length of 662 and 190 nm, respectively, with a wavelength of 1550 nm. [ABSTRACT FROM AUTHOR]

The aim of this work is to design an integrated optical ring resonator to be implemented in LiNbO3 with a 2.5 mm radius and an operating wavelength of 1550 nm. Considering these ring parameters, a free spectral range of 71.54 pm and a quality factor of ∼5×105 were calculated. The authors apply results to improve the implementation of femtosecond laser writing in lithium niobate crystals. As it is well‐known finite difference time domain method requires large memory and time for processing circuits with large footprint (few square mm), in contrast, the beam propagation method allows to simulate large bends in a simple way. RSoft suite design tools commonly represent circles by closed polygons whose geometrical parameters are not optimised to obtain bending losses as least as possible, as suggested by coherent coupling theory. In this sense, the suitable determination of a splice angle (in this case 1.44°), shape and length for segments are key parameters in the ring design. For this purpose, an ad hoc software was implemented to overcome this drawback. In summary, a 250 sided polygon side showed a suitable coupling performance and established a new layout approach for middle range rings. [ABSTRACT FROM AUTHOR]

A novel implementation of the stretched coordinate perfectly matched layer (PML) is presented for the two‐dimensional (2D) transmission line modelling (TLM) method. The formulation offers a unified approach and is based on the mapping of the TLM node to a complex stretched domain for which the resulting transformation of the constituent RLC transmission line components is elaborated. The transformation is shown to modify the TLM connect‐scatter algorithm. The absorption performance is demonstrated by simulating a canonical waveguide test case. Unlike the existing split‐field based TLM‐PML implementations, which are better suited to lossless media, the numerical results obtained show the proposed PML formulation is effective in the termination of both lossy and lossless media. [ABSTRACT FROM AUTHOR]

A fourth‐order finite‐difference time‐domain (FDTD) scheme is proposed for the solution of Maxwell's equations in cold plasma (Drude medium), based on the multistage method of Jameson, Schmidt and Turkel, which was originally introduced in the framework of fluid dynamics. First, the system of governing differential equations is formed as a general first‐order, operator‐based approach, and then a four‐stage algorithm is established. The accuracy of the method is verified in benchmark problems compared with analytical solutions and with the conventional second‐order FDTD algorithm. [ABSTRACT FROM AUTHOR]

An efficient diagnosis method dedicated to embedded wiring network based on reflectometry technique is developed in this study. The proposed methodology is based on the two complementary steps. In the first step, the time‐domain reflectometry (TDR) method is simulated, by RLCG (R: resistance, L: inductance, C: capacitance and G: conductance) circuit model and the numerical finite‐difference time‐domain method, and at the same time the datasets are created. In the second step, the support vector machine (SVM) algorithm is combined with a principal component analysis to identify the faults on wiring network from the TDR response. Two types of SVM models have been used in the diagnosis procedure: SVM classifiers and SVM regression models. In order to illustrate the performances and the feasibility of the proposed approach, numerical and experimental results are presented. [ABSTRACT FROM AUTHOR]

Two‐dimensional (2D) metasurface integrated with strip waveguide in silicon‐on‐insulator (SOI) has been designed to achieve high coupling efficiency for 3.8 μm wavelength. The optimisation in period and radius has been achieved using 3D finite‐difference time‐domain (FDTD). The calculated coupling efficiency in the in‐plane waveguide for the out‐of‐plane surface illumination is over 90% with a bandwidth of 1 μm. The design is consistent with the available lithography using 400 nm thick SOI for mid‐IR applications. Finally, monolithic integration can be achieved using standard multi‐project wafer run. [ABSTRACT FROM AUTHOR]

In this study, a fast and accurate method to predict the radar cross-section (RCS) of large-scale and complicated shape targets is proposed based on a high-performance parallel finite difference time-domain (FDTD) numerical method. To this end, several most popular parallel computation methods [including OpenMP, graphics processing unit (GPU), and message-passing interface (MPI)] are discussed first. Based on this discussion, a novel MPI–OpenMP–GPU hybrid parallel computation scheme for FDTD is developed. Moreover, the corresponding load-balance parallel configuration is discussed as well. Since this hybrid parallel scheme combines the merits of existing parallel technologies, the computation performance is remarkably improved. The results show that the computation time of the RCS simulation of a large-scale target can be reduced from 3 days to 0.8 h, that is, ∼98.9% time saving.

The authors numerically analyse the performance of a mesoscopic photonic crystal (MPhC) waveguide that could be exploited to develop a new class of routing elements and a cascadable circuitry taking advantage of the spatial and spectral reconfigurability that this structure offers. The design of the MPhC was performed by means of the 3D plane wave expansion method (3D-MPB code), while the MPhC waveguide has been analysed by a 3D-FDTD code. The numerical results show that the MPhC waveguide exhibits minimal reflections at PhC input interfaces without either affecting the feasibility or the complexity of the structure, high transmission, strong mesoscopic self-collimation and discrete translational invariance. Moreover, the influence of the characteristics of the Gaussian source on the collimation phenomenon has been explored by considering different values of the waist radius.

In this study, a fast and accurate method to predict the radar cross-section (RCS) of large-scale and complicated shape targets is proposed based on a high-performance parallel finite difference time-domain (FDTD) numerical method. To this end, several most popular parallel computation methods [including OpenMP, graphics processing unit (GPU), and message-passing interface (MPI)] are discussed first. Based on this discussion, a novel MPI–OpenMP–GPU hybrid parallel computation scheme for FDTD is developed. Moreover, the corresponding load-balance parallel configuration is discussed as well. Since this hybrid parallel scheme combines the merits of existing parallel technologies, the computation performance is remarkably improved. The results show that the computation time of the RCS simulation of a large-scale target can be reduced from 3 days to 0.8 h, that is, ∼98.9% time saving. [ABSTRACT FROM AUTHOR]

In this study, the authors propose a hybrid computational model for the reliable simulation of electromagnetic‐wave phenomena emerging in graphene structures, which incorporates two variations of an unconditionally‐stable finite‐difference time‐domain algorithm. The new approach features: (a) a dispersive model that relies on the auxiliary differential equation technique and takes into consideration the graphene's surface conductivity, and (b) a modified discretisation algorithm implementing error‐optimised spatial approximations, which is appropriate for graphene‐free mesh nodes. The resulting update equations are devoid of time‐step restrictions, thus formulating a suitable and useful computational framework for the investigation of contemporary graphene‐based problems, which commonly call for densely‐sampled grids and/or prolonged simulations. After theoretically assessing the fundamental features of the proposed algorithm, the propagation properties of surface waves on graphene are extracted numerically and compared with analytical estimations, so that computational validation is provided. In addition, a realistic surface‐wave coupler configuration is simulated and its main characteristics are extracted accurately, exemplifying the method's robustness on more complex setups. [ABSTRACT FROM AUTHOR]

One of the main problems of the conventional meshless methods in the time domain is their conditional stability. Up to now, some algorithms have been introduced to remove the stability condition, like alternating‐direction‐implicit (ADI) and locally one‐dimensional (LOD) schemes. ADI meshless method has been investigated completely, but there is no report to exploit the full efficiency of the LOD meshless method. So, in this study, LOD scheme is employed to a meshless method for solving three‐dimensional transient electromagnetic problems. The initial form of the proposed meshless method solves time‐domain Maxwell's equations in three sub‐steps, so it is called LOD3. LOD3 meshless method has first‐order temporal accuracy. Moreover, LOD5 meshless method is introduced to upgrade temporal accuracy. Also, the results show that LOD5 meshless method is more accurate than ADI and LOD3 meshless methods. The accuracy of the proposed method is due to two main factors; Crank–Nicolson scheme and solving the equation in five sub‐steps instead of one sub‐step. Stability and accuracy of the proposed method are assessed through numerical experiment. Also, the unconditional stability of the proposed method is proved, analytically. [ABSTRACT FROM AUTHOR]

A compact plasmonic bandpass filter based on metal–insulator–metal plasmonic waveguides and a coupled U‐shaped cavity is proposed in this study. Air and silver are used as insulator and metal materials and silver is characterised by the Drude model in the simulations. By tuning the height of the designed cavity, it is found that the resonance wavelength can be easily adjusted. Furthermore, the quality factor of the designed filter can be increased by increasing the cavity numbers. One, two or three cavities can be used to generate single‐mode filters. Finally, by sweeping different structural parameters, the effect of them on transmittance spectrum is investigated. All results are obtained by the finite‐difference time domain method. The proposed structure due to its remarkable properties such as being a single‐mode filter, having a compact size, tunablity of the resonance frequency and its variable quality factor can be used in complex integrated optical structures such as demultiplexers and so on. [ABSTRACT FROM AUTHOR]

Monitoring of electromagnetic (EM) waves due to partial discharge (PD) is a promising tool for condition monitoring of cables. This study presents the development of a modelling scheme for simulation of EM wave propagation due to PDs occurring at cavities in the cross‐linked polyethylene (XLPE) insulation. Simulation models for generation and propagation of PD pulses through the cable geometry are developed. A finite element method (FEM)‐based model is developed to simulate the PD current along cylindrical voids in the cable insulation. The initial fields due to the PD currents in the voids are simulated by an FEM model. The propagated EM fields inside and outside the cable surface due to PD's occurring inside the voids are analysed by a finite‐difference time‐domain model. The analysis of propagated EM fields due to a Gaussian‐shaped PD pulse identifies the dominant components of propagated electric and magnetic fields along the cable geometry. Furthermore, the propagated EM fields at the cable sheath due to different void dimensions are simulated and experimental validation of the propagated magnetic field is conducted with measurement by an high‐frequency current transformer sensor installed around an earth wire from the sheath of an 11 kV XLPE cable. [ABSTRACT FROM AUTHOR]

Using a two‐dimensional photonic crystal lattice, a compact and simple structure has been introduced in the present study to construct an all‐optical half adder. The designed structure operates under the interference effect. The phase difference has been created in different states by putting the point defects and the difference in the length of the input waveguides. To do analyses, the finite‐difference time‐domain method and the plane wave expansion have been used. The advantages of this design include the small dimensions, high possibility of construction, compatibility with the silicon‐based technology, and equality of the output power in the logic states 0 and 1. The contrast ratio calculated for the port Sum and the port Carry has been equal to 9.3 and 8.22 dB. The response time has been equal to 0.22 ps, generating the data transfer rate of 4.55 Tbps. [ABSTRACT FROM AUTHOR]

The authors numerically analyse the performance of a mesoscopic photonic crystal (MPhC) waveguide that could be exploited to develop a new class of routing elements and a cascadable circuitry taking advantage of the spatial and spectral reconfigurability that this structure offers. The design of the MPhC was performed by means of the 3D plane wave expansion method (3D-MPB code), while the MPhC waveguide has been analysed by a 3D-FDTD code. The numerical results show that the MPhC waveguide exhibits minimal reflections at PhC input interfaces without either affecting the feasibility or the complexity of the structure, high transmission, strong mesoscopic self-collimation and discrete translational invariance. Moreover, the influence of the characteristics of the Gaussian source on the collimation phenomenon has been explored by considering different values of the waist radius. [ABSTRACT FROM AUTHOR]

UHF (ultra high frequency) method has been widely used in PD (partial discharge) detection for its high sensitivity. The resonance, distortion, and attenuation appearing in the propagation process of UHF signals in GIS (gas insulated switchgear) will influence the real situation of PD detection. Therefore, it is necessary to investigate the effect of GIS components such as disconnectors or high voltage conductors on the propagation characteristics of PD-induced UHF signals in various voltage classes GIS. The factors of PD signals propagation characteristics in axial and radial directions are both analysed to avoid the effect caused by placement of sensor in this paper. First, the simulation models of GIS are built based on FDTD (finite difference time domain) method. Then the propagation characteristics of PD-induced UHF signals are studied in the GIS with different disconnector gap lengths and different high voltage conductor radii. Finally, the reliability of the simulation results is verified by compared with laboratory tests. The disconnector gap and the change of conductor radii can both result in the signals attenuation which rises highest in the direction of 180°. The lower the GIS class voltage is, the larger the attenuation of signals after passing through disconnector gap is.

In this study, a compact plasmonic structure for realising plasmon‐induced transparency is proposed and numerically investigated by using the finite‐difference time‐domain method. The suggested device consists of double side‐coupled square ring resonators based on a metal–insulator–metal platform. The coupled mode theory is introduced to describe the spectral response of the proposed structure, which is verified by numerical simulations. By changing the geometrical and material parameters such as outer side length and width of square ring resonators and metal collision frequency, the transmission characteristics can be easily tuned. The simulation results show that the proposed plasmonic system is used as a sensor by filling the insulator region with different refractive index. The sensitivity and figure of merit of this sensor are calculated, 806 nm/RIU and 66 RIU–1, respectively. It is found that the slow light effect can appear in the proposed structure. By design optimisation, the maximum value of the group index is achieved close to 65. Meanwhile, the group index profile is obtained for different values of geometrical parameters like coupling aperture widths. The proposed structure provides a new way to utilise in nanosensor devices and slow light systems. [ABSTRACT FROM AUTHOR]

An impedance matching theory‐based methodology is presented in this study for designing/optimising photonic crystal‐based all‐optical AND gate. A basic architecture for the AND gate is projected first, and thereafter the same is optimised utilising the proposed methodology. Performance of the AND gate is evaluated based on several metrics that are calculated using a finite‐difference‐time‐domain simulation. The optimised AND gate has exhibited a high extinction ratio in the order of 6.9 dB, within a very small footprint of ≈110μm2. It also supports propagation of a high bit rate (≈1 Tb/S) and has a wide operational bandwidth (≈4 THz), which make the device suitable for different photonic integrated circuit applications. [ABSTRACT FROM AUTHOR]

In this study, the extended composite right/left handed (ECRLH) transmission line equations are solved by an unconditionally stable finite‐difference time‐domain algorithm. The results of the proposed algorithm are verified by the conventional one. Amplification matrix of the unconditionally stable algorithm is extracted. The results show that the spectral radius of the amplification matrix of the proposed algorithm is less than one and the proposed algorithm is unconditionally stable. To overcome the numerical dispersion, the complex phasor method is applied to the ECRLH equations. The new equations are solved by the proposed algorithm and results confirm the accuracy of the new equations. By using the complex phasor method and proposed algorithm, the CPU time is reduced about 98%, which shows the efficiency of the proposed method. [ABSTRACT FROM AUTHOR]

A dual‐gate aluminium gallium arsenide (GaAs)/GaAs pseudomorphic high electron mobility transistor is analysed based on the distributed modelling approach, wherein the transistor is considered as an active multi‐conductor transmission line. Discretisation of the governing matrix Telegrapher's equation is carried out using the implicit Crank–Nicolson‐finite‐difference time‐domain (CN‐FDTD) method. The results obtained from the proposed method are compared with the results of the conventional leap‐frog (LF) FDTD scheme. It is observed that the unconditionally stable CN method is in good agreement with the LF method even by increasing the time step size by the factor of 5000, leading to a dramatic decrease in the central processing unit time. [ABSTRACT FROM AUTHOR]

An efficient analytical model based on electromagnetic (EM) topology has been developed for predicting the EM field coupling with a lossless penetrated transmission line (TL) of which the termination loads are located in two enclosures, respectively, excited by an internal vertical monopole and an external plane wave of oblique incidence. Firstly, the electric fields generated by the plane wave are calculated based on Bethe's aperture coupling theory and scalar wave function method. Then, the topology network of the EM interaction is established according to the analysis of the interference paths and the coupling mechanism from sources to the TL. Finally, the electric current induced at the line terminations is obtained by combining the generalised Baum–Liu–Tesche equation and the Agrawal's model. The analytical model has been successfully verified by the finite difference time domain method over a broad frequency range, and costs less time and fewer computational resources than numerical methods, which provides guidance for the field‐to‐line coupling in complex multiple enclosures against different sources. [ABSTRACT FROM AUTHOR]

In this study, a novel ultra‐high frequency (UHF) sensor using an inner grading electrode inside an insulting spacer is employed to detect gas‐insulated switchgear (GIS) partial discharge (PD[AQ ID=Q1]). The simulation of the waveguide modes of the 252 kV GIS and the frequency response characteristics of this UHF sensor are performed by using the finite difference time domain (FDTD) method. Three kinds of typical defects are employed to investigate the PD detection characteristics of this UHF sensor. It is shown that the resonance frequencies of this sensor are extremely abundant below 3 GHz, and the major resonance frequencies around 0.5–1.2 and 2.2–3 GHz. The phase‐resolved PD (PRPD) images accumulated by using this UHF sensor present the typical PRPD images of defects. The main frequency spectrum of the metal protrusion on a high‐voltage conductor and floating potential defects are distributed below 1.5 GHz, which is consistent with waveguide mode simulation. A resonance frequency of a grading electrode UHF sensor appears at about 115 MHz, which is close to the simulation value of a resonance frequency at 140 MHz. The PD detection sensitivity of this sensor is much higher than that of an external sensor; however, it is a little lower than that of an internal sensor. [ABSTRACT FROM AUTHOR]

In this study, the authors investigated the effects of a single layer graphene as a coating layer on top of metal thin films such as silver, gold, aluminum and copper using finite‐difference time domain method. To enhance the resolution of surface plasmon resonance (SPR) sensor, it is necessary to increase the SPR reflectivity and decrease the full‐width‐half maximum (FWHM) of the SPR curve so that there is minimum uncertainty in the determination of the resonance dip. Numerical data was verified with analytical and experimental data where all the data were in good agreement with resonance angle differing in <10% due to noise present in components such as humidity and temperature. In further analysis, reflectivity and FWHM were compared among four types of metal with various thin film thicknesses where graphene was applied on top of the metal layers, and data was compared against pure conventional metal thin films. A 60 nm‐thick Au thin film results in higher performance with reflectivity of 92.4% and FWHM of 0.88° whereas single layer graphene‐on‐60 nm‐thick Au gave reflectivity of 91.7% and FWHM of 1.32°. However, a graphene‐on‐40 nm‐thick Ag also gave good performance with narrower FWHM of 0.88° and reflection spectra of 89.2%. [ABSTRACT FROM AUTHOR]

The aim of this study is to improve the performance of a wire fault diagnosis approach based on time‐domain reflectometry (TDR). In this approach, the TDR response collected from measurements for a given (faulty) coaxial cable network is used as a reference for the cable network model response computed by an accurate analytical transmission line (ATL) method. The ATL model is iteratively tuned according to the outcome of the optimisation algorithm proposed. The advantage of the proposed ATL method over the more classic finite difference time‐domain method is the extremely faster computational time which represents a significant factor for the diagnosis of faults in wiring networks. The proposed ATL method accurately provides the features of the resistance–inductance–conductance–capacitance‐based model of a RG‐58 coaxial cable employed as a device under test. The ATL model has been validated by comparison with measurement based and circuit simulations. Furthermore, seven experiments have been investigated in order to evaluate the performance of the ATL method for the diagnosis of wiring networks. The obtained results reveal that the ATL method together with the efficient optimisation algorithm is a reliable, efficient and fast method for the diagnosis of wiring networks. [ABSTRACT FROM AUTHOR]

A modified field‐to‐line coupling model for simulating the corona effect on the lightning induced voltages of the overhead multi‐conductor transmission lines is proposed in this study. Since the model is non‐linear, it is solved in an iterative way combining with the time‐domain finite‐element method and is validated by the measurements of Inoue's experiments. Furthermore, the unconditional stability of the numerical method is theoretically proved. The proposed model is a simplified method according to the method recently proposed by Thang et al., in which finite difference time domain (FDTD) is used to calculate the induced voltages. Compared with FDTD, the proposed model can achieve good efficiency because the transmission line theory is adopted instead of the electromagnetic solution. Both the effects of the corona and the lossy ground on the induced voltage are studied, furthermore, the relationship between the corona effect and the soil conductivity is discussed. The simulation results demonstrate that the corona effect will cause a rise time increase and waveform distortion of the induced voltage, and the magnitudes of induced voltages in the presence of corona discharge are larger than those computed without considering corona. [ABSTRACT FROM AUTHOR]

In this work, performance of dielectric inserted side contact multilayer graphene nanoribbon (Di‐side‐GNR) coupled interconnects using unconditionally stable finite‐difference time‐domain (USFDTD) technique has been investigated. The model developed for the same, overcomes the limitation of Courant stability criterion prevalent in the conventional finite‐difference time‐domain (FDTD) technique. The proposed model accurately analyses the crosstalk effect in copper (Cu), side contact multilayer graphene nanoribbon and Di‐side‐GNR interconnects. It is found that the crosstalk effect is least in Di‐side‐GNR amongst the three types of interconnect considered in this study. The proposed model and HSPICE simulation results match closely. Further, for transient analysis USFDTD technique based proposed model takes nearly 1.5 times lesser CPU runtime compared to the conventional FDTD technique. [ABSTRACT FROM AUTHOR]

The unconditionally stable alternating‐direction‐implicit finite‐difference time‐domain (ADI‐FDTD) method is extended for modelling anisotropic magnetised graphene sheets. In contrast to the conventional method for isotropic media, two additional sub‐stepping calculations are applied to incorporate anisotropic medium properties. The unconditional stability of the proposed extended method is examined numerically. The method is applied to study the transmission properties of graphene sheets. Numerical results show that the proposed method is more accurate than the recently developed locally one‐dimensional FDTD method. [ABSTRACT FROM AUTHOR]

A one‐step leapfrog weakly conditionally stable finite‐difference time‐domain method for modelling drude dispersive models is developed. Numerical results show that its stability condition remains invariant with respect to that in lossless media. The new algorithm is applied to efficiently investigate the transmission properties of a graphene sheet and a graphene‐based frequency selective surface. [ABSTRACT FROM AUTHOR]

A wavelength filter using a pair of one‐dimensional photonic crystal (1D‐PhC) waveguides incorporating cavity sections for one‐directional output is reported. The small number of holes for 1D‐PhC is used to attain distinct transmission peaks in the stop band. Two cavity sections are used to obtain peak with steep slope and widened top. The three‐dimensional finite difference time domain simulation results agree with the experimental result. [ABSTRACT FROM AUTHOR]

A semi‐implicit finite‐difference time‐domain thin‐wire (TW) scheme with a relaxed stability condition is proposed for modelling effective surface plasmons in waveguide metamaterials. Its formulation is based on introducing the Newmark‐Beta method into the TW formulation based on the contour‐path integral of Maxwell's equations around a wire. The resultant scheme is magnetically implicit. Its stability, accuracy and efficiency are assessed in the application to a wire‐added parallel‐plate waveguide perturbed with a small gap. [ABSTRACT FROM AUTHOR]

It is important to estimate the current magnitude and charge amount of a partial discharge (PD) in a gas-insulated switchgear (GIS). In this study, electromagnetic fields generated by a PD in an 84 kV-class three-phase GIS for testing have been measured with a voltage probe installed on the outer surface of an insulation spacer of the GIS tank, and the corresponding simulations have been carried out using the three-dimensional finite-difference time-domain (FDTD) method. FDTD-computed time-domain voltages across spacers agree reasonably well with the corresponding measured ones, and the current magnitude of PD and its charge amount have been estimated.

A versatile and straightforward human body model, comprising simple geometric structures, is consistently developed in this study for the precise electromagnetic field exposure assessment owing to mediated lightning strikes. The proposed model incorporates a realistic set of frequency‐dependent media, approximated by a 4‐Cole‐Cole scheme, while every body part is considered to be occupied by the most dominant medium. For the reliable evaluation of all related electromagnetic quantities, the featured implementation is systematically discretised by means of an efficient finite‐difference time‐domain algorithm and all results are compared to those of a circuit‐based approach, simulated via an electronic circuit software. Moreover, to minimise comparison errors, the most critical human body dimensions are carefully optimised. Finally, the model, so constructed, is employed for the study of a side flash impact and the investigation of a lethal electric discharge possibility through the disruptive effect technique. The benefits of the proposed realisation in the successful prediction of mediated lightning effects are thoroughly validated in terms of various real‐world scenarios, which, among others, reveal that the impact on humans is inversely proportional to its distance from the stroked object. [ABSTRACT FROM AUTHOR]

Via the auxiliary differential equation method, the authors propose a simple and efficient implementation of the stretched coordinate perfectly matched layer (SC‐PML) in this Letter. The proposal can successfully halve the number of auxiliary variables associated with the PML while maintaining the capacity of the original SC‐PML in terms of simple implementation. Thus, it can achieve a higher computational efficiency in the finite‐difference time‐domain simulations. The effectiveness of this new implementation is verified through an example carried out in a 3D Debye dispersive space. [ABSTRACT FROM AUTHOR]