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In this paper, we theoretically and numerically demonstrate a tunable and polarization-dependent electromagnetically induced transparency analogy based on graphene terahertz metasurfaces. The unit cell of the metasurface consists of three-layer graphene strips embedded in a silicon grating. The dynamic adjustment of the transparent window can be achieved by changing the coupling distance between the graphene layers and the polarization direction of the incident lights. The operation mechanism behind the phenomenon can be attributed to the near-field interaction and electromagnetic coupling of modes in graphene strips. Furthermore, the full wave electromagnetic simulations obtained by the finite-difference time-domain method agree well with the theoretical fitting results based on the three-harmonic oscillator model. In addition, by changing the Fermi levels, it can not only realize the outstanding slow-light effects with a maximum group index of 3750 but also obtain the four-frequency asynchronous optical switch function in terahertz regions. Therefore, our proposed metamaterial device may have potential applications in image switching, optical switches, slow-light device, optical communication, and optical storage. [ABSTRACT FROM AUTHOR]

ZnO/g-C3N4 heterojunction modified with Ag nanoparticles (ZnO/CN/Ag) was synthesized by depositing ZnO nanorods/Ag nanoparticles onto g-C3N4 nanosheets. Under xenon lamp irradiation, 99% of Rhodamine B (RhB) was degraded by ZnO/CN/Ag-5% composite within 30 min, which was much higher than the degradation efficiency of ZnO and ZnO/CN. The synergistic effect of g-C3N4 and ZnO, along with the localized surface plasmon resonance effect of Ag NPs, contributes to the improvement of photocatalytic performance. Ag nanoparticle provides another charge transfer path from g-C3N4 to ZnO, which speeds up the separation of electron–hole pairs. Meanwhile, the catalyst had good stability and recyclability. Finite-difference time-domain method and the density functional theory were used to obtain the charge transfer process. The photodegradation process has been studied in depth. [ABSTRACT FROM AUTHOR]

The monolayer metamaterial that consists of graphene arrangement squares and four L-shaped graphene blocks is designed to achieve quintuple plasmon-induced transparency (quintuple-PIT). First, the accuracy of the results has been validated through finite difference time domain simulations and coupled mode theory, which show good agreement. Second, a quadruple-frequency asynchronous switch with amplitude modulation degree (AMD) values of 94.7%, 91.1%, 96.6%, and 77.4% and a sextuple-frequency synchronous switch with AMD values of 95.0%, 96.8%, 88.0%, 93.3%, 58.6%, and 71.5% have been proposed by dynamic control, respectively. It is worth noting that the number of PIT windows in the transmission curve can be freely adjusted from a quintuple-PIT to single-PIT mode by manipulating the Fermi level states of different parts of the structure. Finally, further investigations have demonstrated that the proposed structure exhibits excellent slow-light properties and is insensitive to polarized light, which indicates that the metamaterial structure possesses good stability and anti-interference capabilities under various polarization conditions. The metamaterial and results provide valuable insights and ideas for the design of optoelectronic devices. [ABSTRACT FROM AUTHOR]

We present an integrated magneto-photonic device for all-optical switching of non-volatile multi-bit spintronic memory. The bits are based on stand-alone magneto-tunnel junctions, which are perpendicularly magnetized with all-optically switchable free layers, coupled onto photonic crystal nanobeam cavities on an indium phosphide based platform. This device enables switching of the magnetization state of the bits by locally increasing the power absorption of light at resonance with the cavity. We design an add/drop network of cavities to grant random access to multiple bits via a wavelength-division multiplexing scheme. Based on a three-dimensional finite-difference time-domain method, we numerically illustrate a compact device capable of switching and accessing at least eight bits in different cavities with a 5 nm wavelength spacing in the conventional (C) telecommunication band. Our multi-bit device holds promise as a new paradigm for developing an ultrafast photonically addressable spintronic memory and may also empower novel opportunities for photonically driven spintronic-based neuromorphic computing. [ABSTRACT FROM AUTHOR]

A plasma refractive index sensor based on metal–insulator–metal waveguide-coupled analogy T-shaped with double-ring resonators was designed. The transmission characteristics of the waveguide were investigated using the finite-difference time-domain method with perfectly matched layer absorbing boundary conditions. By optimizing the structure parameters, the sensor obtained the maximum sensitivity (S) of 1110 nm/RIU and the maximum figure of merit of 1904. The results demonstrate that this new structure can generate dual Fano resonances and exhibit typical refractive index sensing functionality, which provides valuable insights into the design and optimization of plasma refractive index sensors. Additionally, by measuring the concentration of plasma solution and glucose solution, it has been proven that the structure has the prospect of practical application. [ABSTRACT FROM AUTHOR]

At present, optical anapole resonances in nanostructures have attracted increasing attention due to the strong field confinement and substantially suppressed scattering. This study provides the results of three-dimensional finite-difference time-domain simulations exhibiting the possibility of the anapole state in high refractive index dielectric nanohole array metasurfaces having different profiles of the holes (square, hexagon, and octagon). Behavior of the effective optical Kerr nonlinearity of the metasurfaces in the vicinity of the anapole state is investigated. Depending on the geometry, the absolute value of the effective nonlinear Kerr coefficient of the metasurface may be up to three orders of magnitude greater than that of the unstructured film. A square transverse section of the nanohole is preferable for the optical Kerr effect in the holey metasurfaces. The effect of the random rotation of the square holes representing the metasurface irregularity on the optical nonlinearity is examined. As a result, the dielectric nanohole array metasurfaces display a concrete possibility to have the anapole state with large enhancement of the optical nonlinearity. [ABSTRACT FROM AUTHOR]

In this paper, we introduce an entirely new solar absorber design—a multi-layer periodic stacked structure. Through coupling effects, this design has perfect ultra-wideband absorption characteristics. The absorber structure is composed of four absorption units with varying cycle lengths, which are cyclically stacked on the surface of the refractory metal Cr. Each cycle encompasses three-layer nanosheets of Ti–SiO2–GaAs. We verify through finite difference time domain method (FDTD) simulations that the absorber achieves an absorption efficiency of 97.8% within the wavelength range of 280 nm to 3000 nm, with an average efficiency of 96.6% under the AM1.5 standard solar spectrum. The absorber can achieve such a remarkable absorption effect because of surface plasmon resonance (SPR) and Fabry–Pérot resonance effects. At 1500 K, this structure exhibits a thermal radiation efficiency of up to 97.83%. Furthermore, the design is not affected by polarization and it is less affected by the incident angle of the light source. These absorption spectra remain consistent regardless of whether it is in the TE or TM mode. Even when the angle of incidence is increased to 60 degrees, the absorption efficiency remains high. Its unique structure and excellent performance characteristics provide higher solar energy efficiency. These outstanding features enable solar absorbers to have broad application potential in improving solar energy efficiency. [ABSTRACT FROM AUTHOR]

This paper presents the application and analysis of Z-domain modelled double optical ring resonator configuration as a biosensor. The output of the configuration is anlayzed using MATLAB environment and the configuration is modelled as biosensor using finite-difference time-domain (FDTD) numerical method. Because of the intense light-matter interaction in the coupled resonators, the presented configuration provides increased sensitivity. Sharper resonance peaks are obtained by the coupling, making even minor variations in the refractive index detectable. Its application as a biosensor has been analyzed for different cancerous-cell samples as well as for various concentrations of haemoglobin in the samples, obtaining high sensitivities of 902 nm per Refractive Index Unit (RIU) and 921 nm per Refractive Index Unit (RIU) respectively for both the cases. The simulation results demonstrate the resonator's ability to achieve precise shifts in resonance in response to changing refractive indices of samples for label-free biosensing. [ABSTRACT FROM AUTHOR]

This paper presents a perovskite solar cell with a distinctive multilayered structure, which includes an FTO anti-reflective glass layer, a TiO2 electron transport layer, a MAPbI3 perovskite absorber layer, a Spiro-OMeTAD hole transport layer, and an aluminum electrode. The core innovation lies in the absorber layer, which is embedded with core–shell Ni@SiO2@graphene nanoparticles with a 70 nm radius. This addition leads to a significant 81% increase in light absorption and a 77% rise in solar cell efficiency compared to traditional structures without nanoparticles. The study also explores the impact of nanoparticle arrangement and chemical potential adjustments, demonstrating the potential of nano-engineering to enhance solar cell performance through improved light trapping and absorption efficiency. [ABSTRACT FROM AUTHOR]

Crack depth detection is a technical challenge. The traditional detection method has the problems of insufficient accuracy and low detection efficiency. In addition, the conventional interpretation method of radar signal profile is easily disturbed by the noise signal generated by the complex structure inside the concrete. To solve these problems, this paper proposes a new concrete crack depth detection method and complex signal analysis technology based on the combination of indicator and radar. In this paper, the detection principle of tracer electromagnetic method and the principle of complex signal analysis are described in detail. The finite time domain difference method is used to simulate the numerical model, and the complex signal analysis technology is used to analyze the forward results. A high dielectric liquid indicator was prepared, deep crack and shallow crack depth detection tests were carried out by using the indicator. The crack depth information was determined by complex signal analysis. The test data were compared with the actual depth of the specimen to evaluate the effectiveness and accuracy of the method. Using the complex signal analysis technology, it is more convenient to clearly observe the crack morphology distribution and accurately locate the bottom position of the crack. [ABSTRACT FROM AUTHOR]

Wireless communication very often causes problems due to its quality. Problems with the network are very important when installing wireless networks inside buildings. The reason is the effects created during the propagation of electromagnetic waves inside rooms due to, among other factors, the construction of the walls and the building materials used. At the stage of network design, it is possible to use numerical methods, which allow for multivariate and fast analysis. This article presents a multivariate analysis of the impact of the variability in the electrical parameters of concrete and reinforced concrete on the propagation of electromagnetic waves and the value of the electric field intensity. The subject of the analysis was a wall composed of a homogeneous material (concrete) or non-homogeneous material (concrete with reinforcement). In the case of the homogeneous wall, the analysis was performed taking into account four electric permittivity values and a wide range of conductivity values. The analysis was performed at two frequencies used in wireless communication (2.4 GHz and 5 GHz). The analysis was performed using the time method based on Maxwell's equations—the finite difference time domain method (FDTD). The results of the numerical analysis were compared with the results obtained from the presented analytical relationships. In the next step, four models and calculations were obtained for systems with a reinforced concrete wall, taking into account the variability in the spacing between the bars, the diameter of the reinforcement and the number of rows of reinforcement. The analysis of complex systems was performed at a frequency of 2.4 GHz. The aim of the presented analysis was to check how the change in the value of the electric permittivity of concrete affects the values of the field intensity and its effect on the analysis of systems composed of concrete with reinforcement. In the case of concrete, it was observed that, for conductivity above 0.9 S/m, regardless of the electric permittivity, all characteristics had a similar course. For low concrete loss, the greatest differences in the electric field intensity were observed at a frequency of 2.4 GHz rather than at 5 GHz. On the other hand, the analysis of systems with reinforced concrete showed, among other aspects, that models with two rows of bars and spacing of 0.15 m, regardless of the reinforcement diameter, were characterized by lower values of the electric field intensity compared to the variants with one row of bars. [ABSTRACT FROM AUTHOR]

Aiming at the inefficiency caused by the optimal design of rotationally symmetric horn feed models, a fast modeling method for rotationally symmetric structures is proposed, which is used to deal with the mesh generation of rotationally symmetric structures and the rapid establishment of computational models. In this paper, the body-of-revolution finite-difference time-domain (BOR–FDTD) method is employed to investigate the radiation performance of the horn feed. Due to the rotational symmetry of the horn antenna, modeling only requires the establishment of a two-dimensional cross-sectional mesh of the horn feed. An optimized Delaunay triangulation algorithm combined with the projection intersection method is utilized to triangulate the horn cross-section of arbitrary polygons and establish the BOR–FDTD computational mesh. Results from both single-medium and multi-medium triangulation algorithms and computational models verify the accuracy of this modeling method. The radiation patterns of a smooth-walled horn were calculated and compared with the modeling time of MATLAB 2017 and the simulation time of CST. The results reveal that the algorithm presented in this paper aligns well with the simulation results from CST; furthermore, the modeling time amounts to only 6.78% of the MATLAB program's modeling time, while the total simulation time is 31.3% of CST, which demonstrates both the accuracy and efficiency of the proposed method. [ABSTRACT FROM AUTHOR]

An ultra-thin spiral diffractive lens (SDL) was fabricated by using focused ion beam milling on a fiber end-facet coated with a 100 nm thick Au film. Focusing vortex beams (FVBs) were successfully excited by the SDLs due to the coherent superposition of diffracted waves and their azimuth dependence of the phase accumulated from the spiral aperture to the beam axis. The polarization and phase characteristics of the FVBs were experimentally investigated. Results show that the input beams with various polarization states were converted to FVBs, whose polarization states were the same as those of the input beams. Furthermore, the focal length of the SDL and the in-tensity and phase distribution at the focus spot of the FVBs were numerically simulated by the FDTD method in the ultra-wide near-infrared waveband from 1300 nm to 1800 nm. The focal length was tuned from 21.8 μm to 14.7 μm, the intensity profiles exhibited a doughnut-like shape, and the vortex phase was converted throughout the broadband range. The devices are expected to be candidates for widespread applications including optical communications, optical imaging, and optical tweezers. [ABSTRACT FROM AUTHOR]

The double-ridge superimposed structures (DRSSs), formed by the superposition of a nano-ridged textured ZnO layer and a ternary organic active layer (PTB7:PC70BM:PC60BM) with self-assembled nano-ridged (SANR) structures, have been preliminarily examined experimentally for its positive effects in light-trapping for organic solar cells (OSCs). To obtain DRSSs with higher-performance light-trapping effects and enhance the light absorption of OSCs, the present work carried out prior theoretical simulations of the light-trapping characteristics of the DRSS using the finite-difference time-domain (FDTD) algorithm. The results show that the DRSS exhibits a significant light-trapping effect, with an active layer absorption peak around 530 nm due to the light-trapping effect. This helps the active layer capture more high-energy photons, significantly enhancing the photon utilization of the DRSS. Interestingly, the intensity of the light-trapping absorption peak is solely dependent on the height or width of the active layer ridges in the DRSS, while the position of the peak is jointly determined by both the ZnO and active layer ridges. By controlling the aspect ratio (W/H) of the dual ridges, the light-trapping absorption peak position can be fine-tuned, enabling precise light-trapping management for specific wavelength bands. It is certain that the outcomes of this work will provide theoretical foundations and practical guidance for the fabrication of light-trapping OSCs. [ABSTRACT FROM AUTHOR]

The integration of ground-penetrating radar (GPR) with unmanned aerial vehicles (UAVs) enables efficient non-contact detection, performing exceptionally well in complex terrains and extreme environments. However, challenges in data processing and interpretation remain significant obstacles to fully utilizing this technology. To mitigate the effects of numerical dispersion, this paper develops a high-order finite-difference time-domain (FDTD(2,4)) three-dimensional code suitable for airborne GPR numerical simulations. The simulation results are compared with traditional FDTD methods, validating the accuracy of the proposed approach. Additionally, a Kirchhoff migration algorithm that considers the influence of the air layer is developed for airborne GPR. Different processing strategies are applied to flat and undulating terrain models, significantly improving the identification of shallowly buried targets. Particularly under undulating terrain conditions, the energy ratio method is introduced, effectively suppressing the interference of surface reflections caused by terrain variations. This innovative approach offers a new technical pathway for efficient GPR data processing in complex terrains. The study provides new insights and methods for the practical application of airborne GPR. [ABSTRACT FROM AUTHOR]

The emission rate of atom-like photon sources can be significantly improved by coupling them to plasmonic resonant nanostructures. These arrangements function as nanoantennas, serving the dual purpose of enhancing light–matter interactions and decoupling the emitted photons. However, there is a contradiction between the requirements for these two tasks. A small resonator volume is necessary for maximizing interaction efficiency, while a large antenna mode volume is essential to achieve high emission directivity. In this work, we analyze a hybrid structure composed of a noble metal plasmonic resonant nanoparticle coupled to the atom-like emitter, which is designed to enhance the emission rate, alongside a corner reflector aimed at optimizing the angular distribution of the emitted photons. A comprehensive numerical study of silver and gold corner reflector nanoantennas, employing the finite difference time domain method, is presented. The results demonstrate that a well-designed corner reflector can significantly enhance photon emission directivity while also substantially boosting the emission rate. [ABSTRACT FROM AUTHOR]

This article introduces a one‐step leapfrog three‐dimensional (3D) split‐field finite‐difference time‐domain (SF‐FDTD) method designed for analyzing periodic structures under oblique incidence, aiming to improve computational efficiency. Initially, it introduces new variables to substitute the field components postsplitting. After that, it applies time‐centered approximate difference method to precisely adjust the time step for each iteration. It eliminates the need for empirical coefficients when performing calculations with lossy materials. Finally, it derives the implementation of the convolutional perfectly matched layer (CPML) for the proposed method. The proposed method is both easier to implement and more resource‐efficient, significantly cutting down CPU usage and memory consumption. Numerical results confirm its improved efficiency. [ABSTRACT FROM AUTHOR]

We propose a novel unstructured mesh finite‐difference time‐domain (FDTD) method for solving electromagnetics problems with complicated geometries. The method, which solves the TE‐mode reduced form of Maxwell's equations, can handle both material interfaces and anisotropic material. Using the transformation optics principle, which describes how fields and material tensors change under coordinate transformations, we locally transform each cell in the mesh to a reference unit‐square computational domain where the usual FDTD update is performed. This comes at a cost: employing unstructured grids and coordinate transformations requires more complicated data structures, a mesh orientation process, and potentially introduces an anisotropic material tensor at every mesh cell. Nonetheless, we find that the method maintains the same desirable properties of the classic FDTD method (explicit, divergence‐free B‐field, nondissapative, and second‐order accuracy) while also gaining conforming material interfaces and boundaries in complicated geometry. Even further, we prove that the method is stable under a Courant condition and a fairly nonrestrictive mesh condition, hence defeating the late‐time stability issue plaguing prior nonorthogonal FDTD methods. To verify the method, we conduct convergence studies on three electromagnetic cavity problems with known exact solutions. For these numerical studies, we find that the method maintains second‐order convergence and stability. [ABSTRACT FROM AUTHOR]

By using the finite‐difference time‐domain (FDTD) method and a two‐port network model, this letter investigates the response of a uniformly moving resistive sheet to illuminating electromagnetic plane waves, at normal incidence. The numerical Doppler frequency shifts and scattering matrix are matched with curve‐fitting expressions. The effects of motion on the impedance matrix, the chain matrix, and the continuity equations are analyzed. Moreover, the total energy of the transferred and reflected waves are studied for the cases of a resistive sheet moving toward or away from the plane wave source. [ABSTRACT FROM AUTHOR]

In this research, we propose a deep learning model employing gated recurrent units (GRUs) for the transmission spectrum prediction, and computational inverse designing of all-optical plasmonic devices (AOPDs), which may a crucial role in the precise fabrication process of photonic integrated circuits (PICs). This shift from a conventional simulation-based design to a GRU-based model offers a significant advantage in terms of accuracy and precision. The technique facilitates the intricate design process by simulating the propagation of Surface Plasmon Polaritons (SPPs) within the plasmonic structures of AOPDs. The forward modeling approach presented here demonstrates a substantial improvement in computational efficiency over the finite-difference time-domain method, adeptly forecasting transmission spectra characterized through the analysis of various geometrical parameters. The inverse modeling process infers the necessary design parameters to produce specific transmission spectra, markedly expediting the design process and eclipsing the time-intensive nature of traditional optimization methods. With a prediction loss (MSE) of 0.168 and 0.9217, this research substantiates the efficacy of GRUs in streamlining the forward and inverse design processes of AOPDs for integration into PICs. [ABSTRACT FROM AUTHOR]

Time domain finite difference methods have been widely used for wave‐equation modelling in exploration geophysics over many decades. When using time domain finite difference methods, it is desirable to use a larger time step so as to save numerical simulation time. The Lax–Wendroff method is one of the well‐known methods to allow larger time step without increasing the time grid dispersion. However, the Lax–Wendroff method suffers from more time consumption because there are more spatial derivatives required to be approximated by the finite difference operators. We propose a new finite difference scheme for the Lax–Wendroff method so as to reduce the numerical simulation time. Then we determine the finite difference operator coefficients and analyse the dispersion error of the proposed finite difference scheme for the Lax–Wendroff method. At last, we apply the proposed finite difference scheme for the Lax–Wendroff method to different velocity models. The numerical simulation results indicate that the proposed finite difference scheme for the Lax–Wendroff method can effectively suppress time grid dispersion and is more efficient compared to the traditional finite difference scheme for the Lax–Wendroff method. [ABSTRACT FROM AUTHOR]

In time domain to solve electromagnetic radiation and scattering problems, several numerical methods are available in literature. Among these numerical methods Finite Difference Time Domain (FDTD) method and Time Domain FEM (TDFEM) method are more popular. In the present work, we have proposed a quantity in continuum, which is conserved under certain boundary conditions. Additionally, we have also proposed a time marching scheme within edge element framework, which satisfy this conservation characteristic in algorithmic sense irrespective of the choice of time step. To facilitate this, we have used some conversion algorithm that transform nodal finite element data to edge finite element data. [ABSTRACT FROM AUTHOR]

Featured Application: our proposed method can perform numerical simulations in the full wavenumber range and can be applied to forward simulations in anisotropic media while maintaining high accuracy. The staggered grid finite difference method has emerged as one of the most commonly used approaches in finite difference methodologies due to its high computational accuracy and stability. Inevitably, discretizing over time and space domains in finite difference methods leads to numerical artifacts. This paper introduces a novel approach that combines the widely used Taylor series expansion with the least squares method to effectively suppress numerical dispersion. We have derived the coefficients for the staggered grid finite difference method by integrating Taylor series expansions with the least squares method. To validate the effectiveness of our approach, we conducted analyses on accuracy, dispersion, and stability, alongside simple and complex numerical examples. The results indicate that our method not only inherits the capabilities of the original Taylor series and least squares methods in suppressing numerical dispersion across small and medium wavenumber ranges but also surpasses the original methods. Moreover, it demonstrates robust dispersion suppression capabilities at high wavenumber ranges. [ABSTRACT FROM AUTHOR]

Accurately characterizing the internal porosity rate of thermal barrier coatings (TBCs) was essential for prolonging their service life. This work concentrated on atmospheric plasma spray (APS)-prepared TBCs and proposed the utilization of terahertz non-destructive detection technology to evaluate their internal porosity rate. The internal porosity rates were ascertained through a metallographic analysis and scanning electron microscopy (SEM), followed by the reconstruction of the TBC model using a four-parameter method. Terahertz time-domain simulation data corresponding to various porosity rates were generated employing the time-domain finite difference method. In simulating actual test signals, white noise with a signal-to-noise ratio of 10 dB was introduced, and various wavelet transforms were utilized for denoising purposes. The effectiveness of different signal processing techniques in mitigating noise was compared to extract key features associated with porosity. To address dimensionality challenges and further enhance model performance, kernel principal component analysis (kPCA) was employed for data processing. To tackle issues related to limited sample sizes, this work proposed to use the Siamese neural network (SNN) and generative adversarial network (GAN) algorithms to solve this challenge in order to improve the generalization ability and detection accuracy of the model. The efficacy of the constructed model was assessed using multiple evaluation metrics; the results indicate that the novel hybrid WT-kPCA-GAN model achieves a prediction accuracy exceeding 0.9 while demonstrating lower error rates and superior predictive performance overall. Ultimately, this work presented an innovative, convenient, non-destructive online approach that was safe and highly precise for measuring the porosity rate of TBCs, particularly in scenarios involving small sample sizes facilitating assessments regarding their service life. [ABSTRACT FROM AUTHOR]

Accidental fires have shown that fires can be of a spreading nature, burn for longer durations until the fuel has been exhausted, or be uncontrolled until fire fighter intervention. These observations limit the use of nominal fire curves for performance assessment of structural members during fire. In this article, a novel graphical user interface (GUI)-based computer program is developed to capture the spreading nature of fire. The temperature inside the compartment is evaluated by superposition of the temperature rise due to heat flux from flames and heat transfer from smoke. The temperature of the member is evaluated by solving the equation of heat conduction in space and time domain by the finite difference method. The smoke temperature, resultant temperature after collation, and temperature inside the concrete member are validated and a reasonable agreement is observed. A demonstration describing the application of the developed computer program has been discussed, which concluded that different locations inside a compartment are subjected to different temperature-time curves during the fire. This developed computer program can be applied to any occupancy in which fuel-controlled traveling fire can occur to predict the temperature distribution inside the concrete compartment as well as inside the concrete member during the fire duration. Additional features will be added in future to computer programs to perform structural analysis during fire. [ABSTRACT FROM AUTHOR]

Polaritons, arising from the strong coupling between excitons and photons within microcavities, hold promise for optoelectronic and all-optical devices. They have found applications in various domains, including low-threshold lasers and quantum information processing. To realize complex functionalities, non-intuitive designs for polaritonic devices are required. In this contribution, we use finite-difference time-domain simulations of the dissipative Gross–Pitaevskii equation, written in a differentiable manner, and combine it with an adjoint formulation. Such a method allows us to use topology optimization to engineer the potential landscape experienced by polariton condensates to tailor its characteristics on demand. The potential directly translates to a blueprint for a functional device, and various fabrication and optical control techniques can experimentally realize it. We inverse-design a selection of polaritonic devices, i.e., a structure that spatially shapes the polaritons into a flat-top distribution, a metalens that focuses a polariton, and a nonlinearly activated isolator. The functionalities are preserved when employing realistic fabrication constraints such as minimum feature size and discretization of the potential. Our results demonstrate the utility of inverse design techniques for polaritonic devices, providing a stepping stone toward future research in optimizing systems with complex light–matter interactions. [ABSTRACT FROM AUTHOR]

The article contains a numerical analysis of the effects of electromagnetic wave propagation in an area containing a non-ideal, non-uniform, and absorbing dielectric. The analysis concerned the influence of the structure of the building material and its electrical parameters on the electric field intensity. The analysis took into account the variability of the number of hollows in the brick, the width of hollows, as well as the arrangement of these hollows relative to each other using the example of two types of bricks. The article also provides the most commonly used values of electrical parameters for building materials (brick, plaster). For this reason, the article includes results for different values of conductivity (0–0.2 S/m). The FDTD (Finite Difference Time Domain) method was used for multivariate analysis. The aim was to verify the correctness of the numerical assumptions adopted. Using the example of the most commonly used wall structure in construction, the results obtained using the FDTD method were compared with values obtained using another numerical method, the finite element method (FEM). The influence of an additional layer of plaster on the considered wall on the electric field was also checked. The analysis showed that a symmetrical arrangement of bricks results in higher values of the electric field by an average of 20%. Of course, this depends on the length of the hollows and the number of holes. The highest field values occur at low conductivities (0–0.04 S/m). A brick wall with a larger number of hollows and a symmetrical brick arrangement shows the highest electric field intensity, especially for hollow sizes (0.009–0.015 m). [ABSTRACT FROM AUTHOR]

This article presents a numerical analysis of the effects related to the propagation of electromagnetic waves in an area containing a non-ideal, non-uniform, and absorbing dielectric. The analysis concerns the influence of electrical parameters, the structure of the building material, and the layering of the wall on the values of the electric field intensity. A multivariate analysis was carried out with different conductivity values. Homogeneous materials (e.g., solid brick) can be analyzed using the analytical method. In the case of complex materials containing, e.g., hollows (brick with hollows, hollow block), it is necessary to use the numerical method. The FDTD (finite difference time domain) method was used to assess the dependence of the electric field intensity on the layering, the length of hollows in bricks, and the material loss. In order to check the correctness of the adopted numerical assumptions, a series of tests related to the discretization of the model was carried out. The article also presents the influence of changing the length of hollows in bricks on the values of the electric field intensity at a frequency of 2.4 GHz. The instantaneous field distributions and maximum values of the electric field intensity are presented. In the model with a two-layer wall, regardless of the conductivity, the field values were the same for the two models, where the difference in the percentage of ceramic mass in the brick was 8%. A 12% decrease in the percentage of ceramic mass in the brick resulted in a 15% increase in the value of the area between a single-layer and a double-layer wall made of clinker bricks. At a conductivity of 0.04 S/m for a single-layer wall, the field values were similar for all brick variants. [ABSTRACT FROM AUTHOR]

Naked-eye 3D micro-LED display combines the characteristics of 3D display with the advantages of micro-LED. However, the 3D micro-LED display is still at the conceptual stage, limited by its intrinsic emission properties of large divergence angle and non-coherence, as well as difficulties in achieving large viewing angles with high luminous efficiency. In this work, we propose a double-layer metasurface film integrating functions of collimation with multiple deflections, constituting a micro-LED naked-eye 3D display system. The system is characterized through numerical simulations using the 3D finite-difference time-domain method. The simulation results show that the double-layer metasurface film restricts 90% of the emitted light of the micro-LED to the vicinity of the 0° angle, improving its spatial coherence. Subsequently, a large-angle, low-crosstalk outgoing from −45° to 45° is achieved, while providing a deflection efficiency of over 80% and a pixel density of up to 605. We believe this design provides a feasible approach for realizing naked-eye 3D micro-LED displays with a large field of view, low crosstalk, and high resolution. [ABSTRACT FROM AUTHOR]

This work reports on the plasmonic properties of an eccentric nanostructure consisting of a silver ring and a gold disk, in the frequency regime of several hundreds of tetrahertz. In the structure, a gold nanodisk is located in a silver nanoring, with the centers of the two metals being set apart. As the radius of the gold disk, the separation between the centers, the light polarization, and the refractive index of the surrounding dielectric material are respectively varied, the normalized scattering cross section of the system is numerically simulated, using the finite difference time domain method. Multiple plasmonic resonances are observed, the plasmonic coupling effect between the ring and the disk is revealed, and the corresponding electromagnetic field distributions are demonstrated. The resonance peak associated with the coupling is found to possess a Fano-like lineshape, and it is well fitted to a model that employs a Fano function. The resonance frequency, the spectral width, and the characteristic q factor are determined from the best-fit parameters, and the plasmonic characteristics of the eccentric nanostructure are quantitatively probed. The results in this work may be of significance in designs of plasmonic devices that are based on bi-metallic eccentric structures. [ABSTRACT FROM AUTHOR]

This paper presents a method to enhance the light absorption and power conversion efficiency of organic solar cells (OSCs) by embedding a plasmonic Ag nanocuboid array into the active layer. Numerical simulations based on the finite-difference time-domain method are conducted to compare the enhancement of short circuit current density (Jsc) caused by the Ag nanocuboid array with other types of plasmonic nanostructures such as nanocubes, nanospheres, nanorods, and nanocylinders. It is demonstrated that the nanocuboid array can lead to an enhancement of 25.5% in Jsc, much higher than that of other nanostructure arrays. Analyses of the photoelectric field and light absorption enhancement show that the enhancement in Jsc primarily results from the combined effects of localized surface plasmon resonance (LSPR) and optical interference within the devices. It is also revealed that the optical interference can improve or weaken the absorption-enhancing ability of the LSPR mode, which depends on the spectral position of the LSPR mode and the spatial position of the Ag nanocuboids in the optical electric field. Finally, we investigate the effects of light polarization and nanostructure size on Jsc enhancement of the OSC devices. The findings in the paper provide theoretical support for designing OSCs with thinner active layers and superior absorption performance. [ABSTRACT FROM AUTHOR]

With the development of body area network technology and brain neuroscience, the study of electroencephalogram signals has been increasingly emphasized by academics. However, more research on electrocorticography (ECoG) still needs to be carried out. In this study, the communication performance of ECoG signal transmission via the human body and the influence of port structure on their transmission are thoroughly investigated. First, we use the finite difference time domain method to model the head system accurately in conjunction with the electromagnetic properties of human tissues, which reveals the multipath propagation phenomenon in communication. Second, based on our previous research results, we compare the system bit error rate (BER) under phase shift keying (PSK) and frequency shift keying (FSK) modulation modes and further explore the link budget of the system under these two modulation modes. Finally, we analyze the potential impact of the transceiver structural parameters on the signal transmission characteristics. The results show that the power delay in the communication link exhibits a second-order exponential decay function distribution and that the inter-path delay and delay spread follow a Weibull distribution. Under certain BER conditions, PSK reduces the signal-to-noise requirement by 3.2 dB compared to FSK modulation, which is more suitable for head-end channel transmission. In addition, variations in the size and angle of the electrode disks at the transmitter and receiver have little effect on the transmission results. [ABSTRACT FROM AUTHOR]

Silver nanoparticles (AgNPs) are employed to utilize plasmonic effects in PM6:Y7 organic solar cell. Such enables utilization of wavelengths ranging from 400–490 nm and resonance tuning toward longer wavelengths. Inverted structure is employed with AgNPs incorporated into zinc oxide (ZnO) layer. 5–15% volume ratio concentrations of AgNPs were used. The results obtained indicated a 12.97% power conversion efficiency for AgNPs with 10% concentration in comparison to the device without AgNP incorporation. Finite-difference time-domain method (FDTD) simulation of AgNP indicated forward scattering as the most dominant mechanism for external quantum efficiency (EQE) enhancements for wavelengths ranging from 500-900nm. [ABSTRACT FROM AUTHOR]

Plasmonic materials have been extensively explored for surface-enhanced Raman scattering (SERS) due to their high tunability and excellent localized electric field enhancement. Most research for now has focused on noble metals, with limited investigation into corrosion-resistant materials for SERS effects. In this study, a photolithography process is firstly used to create a patterned dot array on a silicon substrate. Next, magnetron sputtering is employed to deposit molybdenum films, finally resulting in the molybdenum truncated cone array substrates for SERS applications. The fabricated truncated cone array experimentally facilitates the coupling of localized surface plasmon polaritons, consistent with simulation results obtained via the finite-difference time-domain method. The formation of hot spots between the cone unit cell arrays leads to the improved Raman signals and can act as traps for target molecules. This study demonstrates that molybdenum-based micro-nano structures can serve as reliable SERS substrates for sensitive molecular sensing applications in highly corrosive environments. [ABSTRACT FROM AUTHOR]

The September 2024 issue of the IETE Journal of Research contains forty papers covering various areas such as Communications, Electromagnetics, Computers and Computing, Electronic Circuits, Devices and Components, Instrumentation and Measurement, Medical Electronics, Power Electronics, and Opto-electronics. The papers discuss topics ranging from malware detection in 5G and IoT networks to the development of smart systems for antimicrobial susceptibility tests. Authors from diverse backgrounds contribute to research on advanced technologies and applications in the field of electronics and telecommunications. [Extracted from the article]

Plasmonics-based sensors have grown more popular in the biosensing sector because of their label-free detection feature, which not only makes the sensor easier to use but also eliminates the need for numerous antibodies, which is a requirement for enzyme-linked immunosorbent assays. In this paper, a plasmonic-based refractive index sensor is proposed consisting of a linear rectangular waveguide coupled with a semi-ring arc and a microring resonator on both sides separated by a coupling distance. The Finite Difference Time Domain method is used to study the transmittance characteristics of the sensor. The transmittance curve displays Quintuple Fano resonances, which show sensitivity of 1000, 1184, 1290, 1914, and 2372.1 nm/RIU at 1.037, 1.211, 1.323, 2.051, and 2.383 μm, respectively. Further investigation is carried out by varying structural and geometrical parameters, such as the microring resonator's radius and the coupling distance between the semi-ring arc and the microring resonator, which may arise due to fabrication intricacies. The performance of the sensor is investigated using the Figure of Merit, Q factor, and Detection limit producing a value of 30.41 RIU−1, 30.2, and 0.0328, respectively. The proposed sensor is further examined for its potential use in the detection of HSV, influenza A, HIV, and M13 Bacteriophage viruses. [ABSTRACT FROM AUTHOR]

In this paper, a stacked cylinder solar absorber with a bimetallic dielectric layer ( F e and A l 2 O 3 ) is proposed. Simulations using the finite-difference time-domain method reveal the proposed absorber can achieve an average absorbance greater than 90% in the visible to near-infrared wavelength range (455–3527 nm). Beyond this, in the solar radiation range of 280 ~ 4000 nm, under AM 1.5, the weighted average absorption is 96.36%. By exploring the mechanism of this absorption, we analyze the electromagnetic field distribution maps of the three peaks. It can be seen that the reason for the bandwidth absorption is that the depth of the bimetallic dielectric cylinder generates surface plasma of different wavelengths. The incident angle insensitivity and polarization independence of the absorber are also studied in detail. The simulation results show that the thermal emissivity is increased when the temperature goes up, a high thermal emissivity of 94.3% is obtained when the temperature is 1700 K. Due to the high-temperature resistance of Fe and A l 2 O 3 , the proposed model can be widely used in photothermal conversion and thermal radiators. [ABSTRACT FROM AUTHOR]

Electromagnetic problems with moving structures are considered. For objects moving at a uniform velocity, the most popular technique used in the literature consists of a change of the reference frame and the utilization of Lorentz transformation of Maxwell's electric and magnetic fields and Voigt-Lorentz transformations of space and time variables. In order to account for non-uniform motions, a numerical approach based on the finitedifference time-domain (FDTD) method is used. In this approach, Maxwell's equations are applied without modification and the motion of objects is implemented by changing their positions in the FDTD time loop. Three types of movements are considered: vibration, rotation, and acceleration. Full-wave numerical results are reported for different objects in motion: observer, source, and reflecting electromagnetic surface. In all the problems analyzed, interesting results are obtained and these results are discussed in detail. [ABSTRACT FROM AUTHOR]

Our latest study builds upon our previous research on multi-wall carbon nanotubes (MWCNTs) by exploring the photonic responses of regularly β-aligned arrays of these nanotubes. Through extensive calculations using the Finite Difference Time Domain Method, we determined that MWCNT-based photonic crystals possess significant Bragg reflections of up to 80% without experiencing substantial attenuation, even at wavelengths as low as 17 nm. This discovery is of great significance, as traditional materials have not been able to scatter UV photons within this frequency range efficiently. Following extensive research, we analyzed various model parameters such as lattice periodicity, inner and outer radii of MWCNTs, and the polarization (TM or TE) and direction (Γ-X or Γ-M) of the incident wave. Our findings present promising implications for advancing ultra-highfrequency photon manipulation in EUV applications, with potential developments ranging from UV laser mirrors to EUV lithography lenses, and beyond to UV spectroscopy collimators. [ABSTRACT FROM AUTHOR]

In this paper, a comparative analysis and numerical simulation of operation of two types of amplitude binary gratings (conventional and fork), both in the focal plane and near-field diffraction under illumination by mode beams with different polarization states, were performed. The simulation of the field formation in the focal plane was performed using the Richards–Wolf formalism. The diffraction calculation in the near-field diffraction was performed based on the FDTD method, considering the 3D structure of optical elements. The possibility of multiplying the incident beam in different diffraction orders of binary gratings and the polarization transformation associated with spin–orbit interaction at tight focusing were shown. In this case, various polarization transformations were formed in ±1 diffraction orders of the fork grating due to different signs of the introduced vortex-like phase singularity. The obtained results can be useful for the laser processing of materials and surface structuring. [ABSTRACT FROM AUTHOR]

Ground-penetrating radar (GPR) has been widely used for subsurface detection and testing. Numerical simulations of GPR signal are commonly performed to aid the interpretation of subsurface structures and targets in complex environments. To enhance the accuracy of GPR simulations on heterogeneous medium, this paper proposes a hybrid modeling method that combines the discrete element method with a component fusion strategy (DEM–CFS). Taking the asphalt pavement as an example, three 3D stochastic models with distinctly different porosities are constructed by the DEM–CFS method. Firstly, the DEM is utilized to establish the spatial distribution of random coarse aggregates. Then, the component fusion strategy is employed to integrate other components into the coarse aggregate skeleton. Finally, the GPR response of the constructed asphalt models is simulated using the finite-difference time-domain method. The proposed modeling method is validated through both numerical and laboratory experiments and demonstrates high precision. The results indicate that the proposed modeling method has high accuracy in predicting the dielectric constant of heterogeneous media, as generated models are closely aligned with real-world conditions. [ABSTRACT FROM AUTHOR]

In this paper, a broadband solar absorber is constructed and simulated based on the finite difference time domain method (FDTD). The modeled structure of the absorber consists of cyclic stacking of five absorber cells with different periods on refractory metal W, where a single absorber cell is composed of a three-layer SiO2-InAs-TiN square film. Due to the Fabry–Perot resonance and the surface plasmon resonance (SPR), an absorptivity greater than 90% within a bandwidth of 2599.5 nm was achieved for the absorber. Notably, one of these bands, 2001 nm, is a high-efficiency absorption with an absorption rate greater than 99%. The average absorption efficiency reaches 99.31% at an air mass of 1.5 (AM 1.5), and the thermal radiation efficiencies are 97.35% and 97.83% at 1000 K and 1200 K, respectively. At the same time, the structure of the absorber is also polarization-independent, and when the solar incidence angle is increased to 60°, it still achieves an average absorption of 90.83% over the entire wavelength band (280 nm to 3000 nm). The novelty of our work is to provide a design idea based on a unit structure with multiple cycles, which can effectively expand the absorption bandwidth of the absorber in the visible-near-infrared wavelengths. The excellent performances make the structure widely used in the field of solar energy absorption. [ABSTRACT FROM AUTHOR]

With the development of wireless communication, satellite, and radar technologies operated at millimeter wave (MMW) frequency range, it is essential to consider the adverse health effects of the radiated electromagnetic (EM) fields at MMW frequency. In most EM dosimetry analyses for the human body models, bare human models have been considered. However, the presence of fabrics such as cotton and wool on the human body can affect the accuracy of the EM dosimetry analysis. At the MMW frequency range, the effect of fabrics on EM dosimetry analysis in a human body model has not been extensively investigated using the finite-difference time-domain (FDTD) method. In this study, the effects of fabrics on the human body on the power transmission coefficient, specific absorption rate, absorbed power density, and heating factor due to EM MMW exposure are investigated using the FDTD method. Numerical results show that the thickness of the fabrics and air gap introduced between the fabrics and the skin surface significantly affects the accuracy of EM dosimetry analysis at the frequency range 1-100 GHz. [ABSTRACT FROM AUTHOR]

Femtosecond lasers have garnered widespread attention owing to their subdiffraction processing capabilities. However, their intricate natures, involving intrapulse feedbacks between transient material excitation and laser propagation, often present significant challenges for near-field ablation predictions and simulations. To address these challenges, the current study introduces an improved finite-difference time-domain method (FDTD)–plasma model (plasma)–two-temperature model (TTM) framework for simulating the ablation processes of various nanospheres on diverse substrates, particularly in scenarios wherein dynamic and heterogeneous excitations significantly influence optical-field distributions. Initially, FDTD simulations of a single Au nanosphere on a Si substrate reveal that, with transitions in the excitation states of the substrate, the field-intensity distribution transforms from a profile with a single central peak to a bimodal structure, consistent with experimental reports. Subsequently, simulations of a polystyrene nanosphere array on a SiO2 substrate reveal that different excitation states of the nanospheres yield two distinct modes, namely near-field enhancement and masking. These modes cannot be adequately modeled in the FDTD simulations. Our combined model also considers the intrapulse feedback between the electromagnetic-field distribution resulting from near-field effects and material excitations. Furthermore, the model can quantitatively analyze subsequent electron–phonon coupling and material removal processes resulting from thermal-phase transitions. Consequently, our model facilitates predictions of the femtosecond-laser ablation of single nanospheres or nanosphere arrays with varying sizes and materials placed on substrates subjected to near-field effects. [ABSTRACT FROM AUTHOR]

Achieving high-speed and efficient data processing in optical processors is a key goal for researchers in integrated photonics. Photonic crystals, with their ability to control light propagation through periodic variations in refractive index, offer a promising platform for realizing compact and high-performance optical components. This work presents a novel low-power 4 × 2 all-optical encoder design based on a two-dimensional photonic crystal structure. The proposed encoder makes use of waveguides and ring resonators inside the photonic crystal to create AND, OR, and NOT gates in combination. The design incorporates four input ports, two output ports, two ring resonators, five optical waveguides, and two power dividers. By strategically introducing defects and optimizing the coupling between waveguides and resonators, the desired logical operations are achieved. The encoder exhibits a low input power requirement of 15 mW and a maximum delay time of 1.33 ps. Additionally, the compact footprint of 522 μm2 makes the design well-suited for integration into photonic integrated circuits. Simulation results, obtained through plane-wave expansion and finite-difference time-domain methods, validate the functionality of the proposed encoder, with output powers of 55% and 10% for logic 1 and logic 0, respectively. This work demonstrates the potential of photonic crystal-based architectures for realizing efficient, high-speed, and compact optical signal processing components with applications in data communication and optical computing. [ABSTRACT FROM AUTHOR]

In this paper, we have investigated a tunable and high transmission efficiency plasmonic power splitter and also a wavelength demultiplexer based on metal–insulator-metal surface. By using Finite Difference Time Domain method, the power splitter exhibits high transmission peaks of about 45% in each output port. Additionally, the simulation results demonstrate that the equal transmitted wavelengths of the two output ports can be easily tuned by changing the geometric parameters of the waveguide. Subsequently, the structure was amended to become a demultiplexer with selecting wavelengths of 1272 and 912 nm, and transmission efficiencies of 76.44 and 88.03%, respectively. Following that, the dependence of demultiplexing wavelengths on geometrical parameters of the structure is investigated. Besides being highly compact and efficient, having narrow-band spectra and low reflectance coefficient are the other main advantages of these devices. The compact power splitter presented in this study is one of the critical components of an integrated processor and hence can be of great interest in a wide range of applications, from highly integrated photonic circuits to on-chip optoelectronic modules and other optical devices such as erbium-doped fiber amplifiers. [ABSTRACT FROM AUTHOR]

Diseases such as voids behind the initial support of the tunnel will lead to problems such as lining rupture and concrete damage in the tunnel structure, which seriously affects the driving safety in the tunnel. In tunnel construction, ground penetrating radar is frequently employed as a method for detecting hidden defects. However, when the cavity size is small, there will be a large error when the original radar data is directly interpreted, which cannot meet the needs of practical engineering. To enhance the precision in tunnel detection, the Finite-Difference Time-Domain method is used to simulate various small cavities of different shapes located behind the primary support lining of the tunnel, and the study involves examining the electromagnetic response characteristics of different kinds of holes. The migration techniques of KIRCHHOFF, F-K, and reverse time are employed to reconstruct the hole target. Furthermore, digital morphology is employed to enhance the clarity of the image. Finally, the edge detection technology is used to further extract the hole features. After that, small cavities of different shapes are buried in the established outdoor concrete model box and radar detection is carried out. The detection position of the reconstructed radar image and the actual position of the cavity in the model box are verified. The results show that compared with KIRCHHOFF migration and F-K migration, the image processed by reverse time migration is clearer and more intuitive, and can restore the contour of small holes well. The research findings can serve as a reference for the interpretation of radar data of the cavity behind the initial support of the tunnel. [ABSTRACT FROM AUTHOR]