Difference Time Domain Method Research Articles

Calculation and Conservation of Probability and Energy in the Numerical Solution of the Schrödinger Equation With the Finite- Difference Time-Domain Method

Calculation and Conservation of Probability and Energy in the Numerical Solution of the Schrödinger Equation With the Finite- Difference Time-Domain Method

Analysis of electromagnetic waves reflected by re-entry plasma sheath based on CSO-FDTD

A transmission model of terahertz waves in the plasma sheath is established based on a cascaded finite time domain difference method and analyzed the transmission characteristics of electromagnetic waves under the action of an external magnetic field and collision frequency. The flow field around the hypersonic aircraft is simulated and the characteristics of the flow field as the altitude changes of the aircraft are analyzed based on the flow field distribution of the RAM-C (Rapid Attenuation Measurement) vehicle. The results show the transmission characteristics of terahertz waves in plasma that will be affected by flight height, plasma parameters, external magnetic field, and collision frequency. In addition, under the action of an external magnetic field and the different collision frequency, the transmission characteristics of the left-handed terahertz wave will be improved. The application of the magnetic field will introduce an absorption peak in the right-handed terahertz wave, and it will move to the high frequency direction with the increase of the magnetic induction intensity.

Mechanism of color change of flexible metafilm with structural parameters and stretching methods

Color change metafilm is promising for the color printing of displays and imaging. A metallic array on an elastic film can realize dynamic color change by mechanical extensions, such as uniaxial or biaxial stretching. In this study, an electromagnetic model of a flexible metafilm composed of a microscale Al cylindrical array on a polydimethylsiloxane elastic film was constructed to study the underlying optical mechanism of color change, especially brightness and saturation changes, of the flexible metafilm with structural parameters (diameter and height of the Al cylinders) and stretching methods (uniaxial or biaxial stretching). The 3D finite time domain difference method was used to simulate the propagation behavior of electromagnetic waves through metafilm. With increasing diameter, the lightness increases while the saturation decreases, which is due to the change of surface plasmon resonance from local surface plasmon resonance (LSPR) to propagation surface plasmon (PSP) and Wood Anomaly (WA) and finally to magnetic polariton excitation. With increasing height, lightness first decreases and then increases, while the change in saturation is opposite, which is due to the first increasing and then decreasing of the intensities of PSP and WA. By comparing the dynamic color changes of metafilm under uniaxial stretching and biaxial stretching, it is found that uniaxial stretching achieves lower lightness and saturation under small strain and higher lightness and saturation under large strain, which is caused by the enhanced WA and PSP on the Al-air interface at short wavelengths and the weakened LSPR on the Al-PDMS interface at long wavelengths. This discovery paves the way for practical applications of structural color display with high saturation and brightness.

PS-b-PMMA templated ITO electrodes for improving the performance of non-fullerene organic photovoltaics

We have developed a block copolymer (BCP)-based patterned electrode with a periodic structure of 80 nm and investigated their application in organic photovoltaics. The indium tin oxide (ITO) electrodes with the thicknesses of 30, 50, 70, 90, and 120 nm were sputtered onto BCP-patterned templates and the morphology and optoelectronic properties were investigated. Using the finite difference in time domain method, the effect of different thickness electrodes on the light absorption of the active layer was studied. We found that the ITO thickness of 70 nm has an absorption enhancement effect in the visible wavelength band. Finally, we prepared organic photovoltaic devices based on the non-fullerene PBDB-T:ITIC system, the BCP-patterned templates enhance greatly the light absorption of the active layer through both light diffraction and coupling to surface plasmon polariton modes achieving a 12.9% increase in power conversion efficiency. • ITO electrodes with 80 nm periodic structure were developed by BCP self-assembly. • Patterned ITO greatly enhance the light absorption of the PBDB-T:ITIC active layer. • OPVs with patterned ITO achieve a 12.9% increase in power conversion efficiency.

Remote Measurement of the Lightning Impulse Charge Moment Change Using the Fast Electric Field Antenna

The impulse charge moment change (iCMC) is an important electrical property of cloud-to-ground (CG) lightning. In this paper, a new method of measuring the iCMC at distances of several hundred kilometers is proposed. The method is based on the vertical electric field below 1 kHz measured by the widely used fast electric field antenna with low frequency/very low frequency (LF/VLF) band. The impulse response of Earth-ionosphere waveguide (EIWG) is modeled using a finite difference time domain (FDTD) method considering an anisotropic ionosphere. By comparing the observed waveform with the simulated impulse response, the lightning discharge is classified into the impulsive discharge and the non-impulsive discharge. For the impulsive discharge, its iCMC is obtained directly by comparing the measured ELF waveform to the modeled impulse response at the same distance. For the non-impulsive discharge, its current moment waveform is assumed to be a sum of two Heidler’s functions, and the genetic algorithm is used to search the unknown parameters in the functions. The good agreement between the measured ELF waveform and the simulated waveform implies that the extracted current moments are reasonable. This method can be used to continuously monitor the lightning iCMC in a given time and space.

Design and Photoelectric Performance of Perfect Solar Absorber Based on GaAs Grating

In recent years, solar energy has received extensive attention as a clean and renewable energy. We present a perfect broadband solar absorber based on tungsten and semiconductor GaAs in this paper. The structure of GaAs grating-GaAs film-W substrate has been proposed. And the finite time domain difference method (FDTD) has been used for the numerical simulation of the model. Broadband absorption has been realized in the 500–1,850 nm, by adjusting the parameters of geometry to excite high-efficiency surface plasmon resonance. The absorption spectrum of the structure can be changed by adjusting the geometric parameters to meet different needs. The proposed absorber has incidence insensitive (0–60°) and high short-circuit current characteristics. The structure is simple and easy to manufacture, and has superior photoelectric properties to be application in photothermal conversion, collection and utilization of solar energy.

Plasmonics based refractive index sensor based on square ring resonator

In proposed research, a square ring resonator designed with a straight metal–insulator-metal (MIM) waveguide is investigated for sensing purpose. The interaction between square resonator and waveguide is observed theoretically and calculated numerically using finite difference in time domain method (FDTD). The length of square ring resonator and waveguide width are selected in such a way to transfer maximum power. Different sensing parameters like sensitivity, figure of merit and resolution are calculated to characterize the qualitative analysis of sensor. The proposed refractive index based sensor can be used as different sensing applications like chemical sensing, bio-sensing application etc.

Influence of static strong magnetic field on antenna radiation in hypersonic vehicle

To enhance the radiation performance of the Beidou antenna in the near-space hypersonic vehicle, the static strong magnetic field is used to weaken the electron density in plasma surrounding the antenna. In order to demonstrate the effect of this program, a time-domain multi-physical method is proposed. In the proposed method, what is first analyzed is the reduction of electron concentration in plasma sheath by static strong magnetic field with the spectral element time domain (SETD) method, which has spectral accuracy. Then, the electron density after mitigation is extracted to replace the original electron concentration around the antenna. Hence, the distribution of the manipulated plasma sheath can be obtained. Finally, the radiation characteristics of BeiDou antenna installed in the vehicle are analyzed by the conformal finite difference time domain (CFDTD) method. The simulation results exhibit radiation patterns under different conditions. With the plasma sheath, the radiated electromagnetic waves are greatly attenuated, which will significantly affect the transmission of communication signals. Importantly, the radiation patterns are effectively improved with the external static magnetic field, confirming that it provides an effective tool to mitigate the influence of plasma sheath on the radiation performance of antenna in hypersonic vehicle.

Ultra-Low-Reflective, Self-Cleaning Surface by Fabrication Dual-Scale Hierarchical Optical Structures on Silicon

An integrated functional anti-reflective surface is of great significance for optical and optoelectronic devices. Hence, its preparation has attracted great attention from many researchers. This study combined wet alkaline etching approaches and reactive ion etching (RIE) techniques to create a dual-scale hierarchical anti-reflective surface on silicon substrates. The effect of RIE time on surface morphology and optical performance was investigated using multiple characterization forms. The optimal parameters for the fabrication of dual-scale structures by the composite etching process were explored. The silicon surface with a dual-scale structure indicated excellent anti-reflective properties (minimum reflectivity of 0.9%) in the 300 to 1100 nm wavelength range. In addition, the ultra-low reflection characteristic of the surface remained prominent at incident light angles up to 60°. The simulated spectra using the finite difference time domain (FDTD) method agreed with the experimental results. Superhydrophobicity and self-cleaning were also attractive properties of the surface. The functionally integrated surface enables silicon devices to have broad application prospects in solar cells, light emitting diodes (LEDs), photoelectric detectors, and outdoor equipment.

Antenna Array Based on Fabry–Perot Cavity with Mechanoelectrical Beam Steering

Introduction. Introduction. Low-profile effective antenna systems (AS) with maintained directional characteristics in a wide sector of scanning angles are required for satellite communication at mobile objects. This article investigates the directional characteristics of a subarray based on a Fabry–Perot cavity and an antenna array with mechanoelectrical beam steering.Aim. To investigate a Fabry–Perot based antenna array with mechanoelectrical beam steering and to estimate its gain and directivity at different scanning angles.Materials and methods. Computer simulations were carried out using the finite element method (FEM), finite difference time domain (FDTD) method and template based post-processing.Results. A subarray based on a Fabry–Perot cavity for an antenna array with mechanoelectrical beam steering was simulated. The efficiency of the subarray comprised at least 65 % in the 11.9…12.5 GHz frequency band. An antenna array based on a Fabry–Perot cavity with mechanoelectrical beam steering was developed and investigated. The calculated characteristics of the developed antenna array agreed well with those obtained experimentally. The gain degradation did not exceed 2.5 dB in the 0…70° scanning angle range. The advantages of using antenna elements based on a Fabry–Perot cavity and developing on their basis mobile satellite antenna systems with wide-angle scanning are noted.Conclusion. The use of a radiator based on a Fabry–Perot cavity and the development on it basis an antenna array with mechanoelectrical beam steering provides an antenna efficiency of no less than 0.5 with a gain degradation of no more than 2.5 dB in the scanning angle range 0…70° from 11.9 to 12.5 GHz.

Influence of Intrinsic Impedance on the Phase of Propagation Pulse Through Biologic Tissue

The aim of this study is to examine the influence of the variation of the intrinsic impedance on the phase of a Gaussian pulse during propagation through a biological tissue. This paper describes a method for varying the intrinsic impedance while retaining the characteristics of the propagation medium. The propagation medium is considered as the superposition of four semi-infinite layers each characterized by their thickness, their conductivity, and their dielectric constant. These last parameters, on which the intrinsic impedance depends, are functions of the pulsation of the medium. In this work, we will test the continuity of the phase shift of the signal at the level of interfaces of biological layers with respect to that of the starting point as the function of the excitation pulsation. Next, we are going to vary the intrinsic. Next, we examine the influence of the variation of the intrinsic impedance at the interface on the phase shift of the signal at that level. We will adopt the Finite Difference Time Domain (FDTD) method to simulate the propagation of a Gaussian pulse. This method which is validated in previous work showed robustness to obtained signals very close to the reality at the interfaces. For these two tests, we will notice that the variation of intrinsic impedance has no influence on the variation of the phase at the interfaces.

The Behavior of Electromagnetic Wave Propagation in Photonic Crystals with or without a Defect

In this study, the electromagnetic wave propagation behavior of two-dimensional photonic crystal plates with a defect is investigated. For this purpose, the partial differential equation for the electromagnetic wave propagation in various photonic crystal plates containing a defect or not is obtained by using Maxwell’s equations. The defect is also defined in the electromagnetic wave propagation equation appropriately. In order to solve the electromagnetic wave propagation equation, the finite differences method is used. The material property parameters of the photonic crystal plates are determined with respect to the defects. Accordingly, the effects of material property parameters on electromagnetic wave propagation frequencies, phase velocities, and group velocities are examined. The effects of the size and position of the defects on the electromagnetic wave propagation frequencies are also discussed. The highest electromagnetic wave propagation fundamental frequency value obtained from the analyses performed is 1.198 Hz. This fundamental frequency value is obtained for the electromagnetic wave propagation in the t-shaped photonic crystal plate. Electromagnetic field distribution maps for the fundamental frequencies of the photonic crystal plates whose electromagnetic wave propagation behaviors are examined are obtained with the ANSYS package program based on the finite differences time-domain (FDTD) method.

Controlling the dynamics of the plasmonic field in the nano-femtosecond scale by chirped femtosecond laser pulse

Arbitrary control of the electromagnetic field in femto-nano scale has attracted significant research attention in nano-photonics. Although the electromagnetic field controlled in femto-nano scale could be realized by illuminating metallic nanoparticles with femtosecond chirped laser pulses, the quantitative relation of the laser chirp and the temporal evolution of the plasmonic field hasn’t yet been fully revealed. Here, active control of the localized plasmonic field is demonstrated by a chirped femtosecond laser pulse in an asymmetric Au nano-cross system within nm-fs scale using the finite differential time domain method. The transferring of the plasmonic field between the two poles of the nanocross is determined by the laser chirp and exhibits linear dependence on the time interval between the corresponding plasmonic resonant frequencies dispersed in the chirped laser pulse. The arrival time and amplitude of the peak field from the plasmonic hot spot are determined by the superposition of the induced field excited by the on-resonant and off-resonant frequency components distributed in the chirped laser pulse. The peak field would arrive behind the resonant frequency component for sufficient oscillation of the localized field. This relative delay between the resonant frequency and field peak is influenced by the temporal distribution of the resonant frequency in the chirped pulse and the response of localized field interpreted by the damped harmonic oscillator model. This result demonstrates that larger near-field enhancement is determined by not only the temporal sequence of the frequency component modulated by chirp but also the temporal distribution of the resonant frequency.

Two-dimensional finite difference-time domain analysis of focus boom noise with velocity disturbance in the atmosphere

In this paper, two-dimensional linear sound wave analysis in the stratified atmosphere with temperature gradient and velocity disturbance is numerically applied to the analysis and prediction of focus boom noise. Focus boom occurs when a supersonic transport accelerates or ascent or descent maneuvers at supersonic speed. Its overpressure is typically more than three times greater than that of a cruise sonic boom. As a result, supersonic transports in future commercial operation are likely to face restrictions on their flight conditions. The compact-explicit finite difference-time domain method is applied to the analysis of two-dimensional linear sound wave propagation. Some numerical experiments are carried out for the case of acceleration. As a result, it is shown that the complex wavefront is accurately analyzed by the FDTD method compared with the ray tracing method. It is also shown that a noise disturbed by velocity disturbance in the atmosphere reaches the ground over a wider area than the focus boom in the no disturbance case.

First-order symplectic Euler method for ground penetrating radar forward simulations in dispersive medium

In recent years, the dispersion characteristics of materials are not considered in the numerical simulation of underground structure damages by ground penetrating radar, which leads to errors in the numerical simulation. To solve this proplem, a novel first-order explicit symplectic Euler method with debye model is provided for the electromagnetic simulation of ground penetrating radar (GPR) systems to the road quality detection in two-dimensional pavement structure. The incident wave is considered to be line source. Two numerical examples are bulit to verify the accucracy and efficiency of the symplectic Euler method with debye model. It can be concluded that the first order symplectic Euler method with debye model and the difference time domain method have almost the same precision, however using the proposed method can result in substantial reduction floating point of per second (FLOPS). Finally, the effect of pavement structure content on the performance of GPR trace profile in detecting the road quality by the proposed method with debye model is investigated.

Optimized 3D Finite-Difference-Time-Domain Algorithm to Model the Plasmonic Properties of Metal Nanoparticles with Near-Unity Accuracy

The finite difference time domain (FDTD) method is a grid-based, robust, and straightforward method to model the optical properties of metal nanoparticles (MNPs). Modelling accuracy and optical properties can be enhanced by increasing FDTD grid resolution; however, the resolution of the grid size is limited by the memory and computational requirements. In this paper, a 3D optimized FDTD (OFDTD) was designed and developed, which introduced new FDTD approximation terms based on the physical events occurring during the plasmonic oscillations in MNP. The proposed method not only required ~52% less memory than conventional FDTD, but also reduced the calculation requirements by ~9%. The 3D OFDTD method was used to model and obtain the extinction spectrum, localized surface plasmon resonance (LSPR) frequency, and the electric field enhancement factor (EF) for spherical silver nanoparticles (Ag NPs). The model’s predicted results were compared with traditional FDTD as well as experimental results to validate the model. The OFDTD results were found to be in excellent agreement with the experimental results. The EF accuracy was improved by 74% with respect to FDTD simulation, which helped reaching a near-unity OFDTD accuracy of ~99%. The λLSPR discrepancy reduced from 20 nm to 3 nm. The EF peak position discrepancy improved from ±5.5 nm to only ±0.5 nm.

A Novel Method for Predicting Crosstalk in Lossy Twisted Pair Cable Based on Beetle Antennae Search and Implicit Wendroff FDTD Algorithm

ABSTRACT This paper presents an algorithm for predicting crosstalk in multiconductor transmission lines (MTL). Currently, crosstalk has an increasing impact on signal integrity. In the twisted pair cable (TPC), different rotation degrees correspond to different RLCG parameter matrices, these matrices are predicted by the beetle antennae search-back propagation neural network (BAS-BPNN) algorithm, and use implicit wendroff-finite difference time domain (IWFDTD) method to solve near-end and far-end crosstalk voltages. The CST simulation results show that near end and far end crosstalk can be predicted effectively. This proposed method is expected widely used in electronic applications for fast data transfer.

Analysis of the electromagnetic wave illumination on the transmission lines with nonlinear terminations

AbstractIn this paper, an unconditionally stable time-domain method is proposed to investigate the external electromagnetic (EM) field illumination on the nonlinearly loaded transmission lines. In the proposed algorithm, the field to line coupling equations and linear/nonlinear boundary conditions are incorporated and expressed in a matrix form. The derived differential matrix equations are then discretized and solved using the proposed finite difference time domain (FDTD) method approach. The discretized nonlinear matrix equations are also solved by applying a globally convergent iterative method to ensure the stability of the method. Moreover, the experimental investigations are conducted using a transverse EM (TEM) cell for a single microstrip line and a power detector circuit as a nonlinearly loaded transmission line to confirm the accuracy and stability of the proposed method. With the merit of satisfactory accuracy and unconditional stability for the entire range of time steps, the presented approach would be applicable for analyzing the microwave linear/nonlinear circuits subjected to the external incident EM wave.

Design of Infrared Plasma Absorber with High Refractive Index Sensitivity

Three layers of periodic artificial metamaterial sensing structure (including the upper metal particles, intermediate dielectric layer, and the lower reflective layer) with ultra-narrow band absorption were designed. The resonance characteristics and sensing properties were analyzed by the finite difference time domain (FDTD) method. The effect of localized surface plasmon resonance (LSPR) was obviously observed at the resonance wavelength of 911 nm, and it achieves nearly perfect absorption of exceeding 98% with a full width at half maximum (FWHM) of 3.5 nm. In addition, a wavelength sensitivity of 542 nm/RIU with a figure of merit (FOM) of 155 was obtained in the refractive index (RI) range from 1.00 to 1.35, which has a wide range of applications. The results show that the proposed structure has high absorption and RI sensitivity, which is suitable for bioengineering and medical detection.

Near-field imaging of femtosecond propagating surface plasmon and regulation of excitation efficiency

Near-field imaging and active control of excitation efficiency of femtosecond propagating surface plasmon (fs-PSP) are the prerequisites for its application. Here, we perform near-field imaging of fs-PSP excited at the trench etched on silver nano-film by using photoemission electron microscopy (PEEM). As an excellent near-field microscopy technique of in situ imaging with a high spatial resolution (< 20 nm), it needs neither molecular reporters nor scanning probes as required in nonlinear fluorescence microscopy in nonlinear fluorescence microscopy or scanning near-field optical microscopy, both of which may potentially bias PSP derived from such measurements. The period of the interference patterns induced by the incident femtosecond laser and the laser-induced fs-PSP and the wavelength of fs-PSP in a range of 720–900 nm of the incident laser wavelength are systematically measured. The fringe period of the interference pattern between fs-PSP and the incident laser is a range of 5.9–7.7 µm, and the wavelength of fs-PSP is in a range of 700–879 nm. The experimental results are consistent with the theoretical simulation results. Furthermore, we demonstrate that the excitation efficiency of fs-PSP can be actively controlled by adjusting the polarization direction of the incident laser in the femtosecond pump-probe experiments. Specifically, it is found that when the incident laser is polarized to 0° (p-polarization light), the excitation efficiency of PSP reaches a maximum value, and when the incident light is polarized to 90° (s-polarization light), the excitation efficiency of fs-PSP is the lowest. Unlike the simulation result by the finite difference time domain (FDTD) method, a plateau area of the intensity of the photoemission signal with the polarization direction of the incident laser appears in the femtosecond pump-probe experiment. This phenomenon is attributed to the background noise of the detection laser that masks the change of the fs-PSP excitation efficiency. In a word, this research realizes the experimental measurement of the basic parameters of fs-PSP and the manipulation of fs-PSP excitation efficiency by adjusting the polarization angle of the incident laser. This research lays a foundation for realizing the engineering manipulation of fs-PSP excitation efficiency and optimizing the performance of plasmonic devices.