FDTD Method Research Articles

Time-dependent Schrödinger Equation based on HO-FDTD Schemes

A high order finite-different time-domain methods using Taylor series expansion for solving time-dependent Schrodinger equation has been systematically discussed in this paper. Numerical characteristics have been investigated of the schemes for the Schrodinger equation. Compared with the standard Yee FDTD scheme, the numerical dispersion has been decreased and the convergence has been improved. The general update equations of the methods have been presented for wave function. Numerical results of potential well in one-dimension show that the application of the schemes is more effective than the Yee’s FDTD method and the higher order has the better numerical dispersion characteristics.

Research on analogue of electromagnetically induced transparency effect based on asymmetric structure all-dielectric metamaterial

The electromagnetically induced transparency (EIT), which is a result of destructive interference between different excitation paths in a three-energy-level atomic medium, makes opaque probe light transparent over a range of frequencies. As this EIT effect is usually accompanied with strong dispersion, it has potential applications such as slow light propagation, optical buffering, nonlinear optics, optical sensing, etc. However, for conventional quantum EIT effect which requires stable gas lasers and low temperature environment, the implementation of EIT in chip-scale applications is severely hampered by the scathing experimental requirements. Recently, the EIT-like effect in metamaterials, which are constructed by designing the artificial subwavelength functional elements and arranging the spatial sequences, attracts tremendous attention because of its advantages, such as room temperature manipulability, large bandwidth, and small sizes. In addition, the high-quality factor(<i>Q</i>) value obtained by EIT-like effect has great significance in designing the metamaterial-based devices. In this paper, we design an EIT-like metamaterial with such a structure. The unit cell of the proposed metamaterial is constructed by two asymmetric silicon blocks embedded on a silicon dioxide substrate. Meanwhile, we analyze its optical properties and EIT-like effects by using three-dimension (3D) FDTD method. Based on the coupled Lorentz model, the EIT-like effect of the designed metamaterial is investigated. Then, by employing the electric field distribution on the surface of the metamaterial, and combining with the three-level atomic system, the mechanism of the EIT-like effect is analyzed in detail. We find that the EIT-like effect in the proposed metamaterial has high <i>Q</i> value (<i>Q</i> ≈ 8616) and the high transmission (<i>T</i> = 96%). By changing the length of the silicon block to destroy the asymmetry of the metamaterial structure, an active tuning EIT-like effect is realized. Furthermore, the metamaterial structure has the advantages of low loss, easy preparation, and active-controllability. This study represents an innovative approach to designing the EIT-like metamaterial, which is expected to be useful for designing active tunable slow-light devices and highly sensitive optical sensors.

Development of the Electromagnetic Calculation Software Package for a Synchronous Motor Based on the Field‐Circuit Combination Algorithm

Nowadays, domestic motor manufacturers often use high‐speed circuit and magnetic circuit parameters in engine models. In addition, the calculation accuracy is low and cannot fully meet the requirements of a modern engine design. The field‐circuit combination algorithm is based on electric field analysis, which avoids many rough assumptions and empirical formulas; its calculations are more accurate and reliable than traditional algorithms. It is used to analyze and calculate the steady‐state operating conditions and characteristics of motors, which can effectively improve the design level of China’s boss synchronous motors. This article mainly introduces software algorithms and auxiliary FDTD methods. In this article, we use the field‐circuit coupling algorithm to develop an electromagnetic calculation software package for synchronous motors and establish a mathematical model for the potential field‐circuit coupling algorithm. We use the cassette electromagnetic calculation program to solve the model, evaluate the synchronous motor, and use historical data to modify the model and improve the accuracy of the development‐state evaluation of the electromagnetic calculation software package for the synchronous motor based on the motor electromagnetic circuit coupling algorithm. The experimental results of this article show that the field circuit combination algorithm increases the development of the electromagnetic calculation software package for synchronous motors by 55% and reduces the false alarm rate and false alarm rate. Finally, by comparing the phases of traditional algorithms, we analyzed the excitation circuit combination algorithm to calculate the parameters and performance of the synchronous motor.

Wavelength-Selective Transmittance in Nano Structure

Purpose : In order to investigate the cause of the change in light transmittance according to the diameter, the optical properties of incident light and transmitted light were analyzed. The change in transmittance of the central wavelength according to the collagen fiber diameter was analyzed. Methods : In order to analyze the characteristics of transmitted light, a 3D simulator of the FDTD method was used. The incident light was set to a Gaussian Modulated Continuous Wave with the center wavelength of 589 nm and the wavelength range of 300 to 900 nm.Results : Even when the radius of the collagen fiber was changed, there was no significant difference in the ratio of the area occupied by the collagen fiber to the simulation space. However, as the diameter of collagen fibers increased, the sum of the transmittance intensity decreased. It increased at 20 to 30 nm of the diameter and rapidly decreased at 30 nm again. Analyzing the optical characteristics according to the change of the central wavelength, it was found that the wavelength at which the transmittance became lowered was not constant depending on the collagen fiber diameter.Conclusion : In the simulation of a real collagen-like structure, selective transmission or absorption occurs at a specific wavelength regardless of the range of central wavelength. It is expected that there will be applied to the selective light beam that runs high-efficiency optical devices.

Giant responsivity of a new InGaZnO ultraviolet thin-film phototransistor based on combined dual gate engineering and surface decorated Ag nanoparticles aspects

In this paper, a new InGaZnO (IGZO) thin-film UV Phototransistor (Photo-TFT) based on both dual material gate (DM) and plasmonic Ag nanoparticles (NPs) is proposed, in hope of combining the beauties of both aspects to achieve enhanced photogeneration/collection efficiency. An accurate drain-current model for the investigated device is developed, where a good agreement with the experimental data is achieved. The optical behavior of IGZO thin-film decorated with Ag NPs is analyzed using 3-D FDTD method. Interestingly, a strategic combination between the developed model and Particle Swarm Optimization (PSO) technique is conducted to find out the appropriate DM gate configuration and the best Ag NPs spatial arrangement offering the highest device Figure of Merits (FoMs). It is revealed that the optimized design showcases giant responsivity exceeding 103 A/W and superb detectivity of 6.8 × 1014 Jones, which are far beyond conventional IGZO Photo-TFTs. These improvements are attributed to localized surface plasmon resonance effects (LSPR), leading to enhance the UV-absorbance capability. Moreover, the optimized DM gate generates intense electric-field in the IGZO channel, allowing the efficient separation and transfer of photo-induced carriers. Therefore, promoting enhanced photogeneration/collection efficiency, this innovative strategy based on decorated Ag NPs combined with DM gate engineering provide a sound pathway for designing potential alternative IGZO Photo-TFT for the future optoelectronic technology.

Numerical and Experimental Analysis of On-Chip Optical Wireless Links in Presence of Obstacles

In this work, we analyze the effects of the presence of waveguides in a wireless on-chip optical channel, which act as obstacles for the rays composing the propagating signal. The analysis has been performed numerically by using the FDTD method, and the simulation results have been validated by the experimental characterization. This work focuses on the relationship between the received signal and the position of the obstacles on the circuit plane in a multilayered channel made of heterogeneous dielectric cladding. We show how the crossing waveguide perturbates the received power and we provide ad hoc guidelines for the best topological choices allowing to mitigate losses. Moreover, with a good agreement between numerical and experimental results, amounting to a variation of less than 1 dB, we have demonstrated that the effects of this perturbation in real chips can be predicted. The results of this analysis, as well as increasing the level of knowledge of on-chip optical wireless links, allow a better comprehension and control of unbound optical signals within the optical chip environment.

FDTD-Based Diffuse Scattering and Transmission Models for Ray Tracing of Millimeter-Wave Communication Systems

At millimeter-wave frequencies, diffuse scattering from rough surfaces is an important propagation mechanism. Including this mechanism in radio propagation modeling tools,such as ray-tracing, is a key step towards realizing accurate propagation models for 5G and beyond systems. We propose a two-stage solution to this problem. First, we model reflection and transmission through rough slabs, such as doors, walls and windows with the FDTD method. Our results indicate the influence of roughness and whether this influence is measurable, either reducing the magnitude of the reflected and transmitted waves, or (most importantly) generating diffuse scattering components. In the latter case, the surface effectively acts as a secondary source, whose pattern is computed by full-wave analysis. Then, this pattern is embedded in a ray-tracer, enabling the computation and tracing of diffuse scattering field components. We demonstrate this approach in the ray-tracing analysis of a 28 GHz indoor environment.

Multilayer Structure Technique for Improving Determination of Electromagnetic Properties of Radar Absorbers Based on Two-Layer Method and Flanged Rectangular Waveguide Probe

This paper presents further development of utilization of two-layer method to perform nondestructive electromagnetic properties determination of planar radar absorbers using flanged open-ended rectangular waveguide probe. A multilayer structure of three layers was proposed to improve the measured results of these parameters obtained using two-layer method. These layers were arranged such that the test material is sandwiched between two known low loss materials to provide the needed two independent reflection coefficients necessary to extract them at different conditions of testing. The proposed structure was aimed to decrease the effect of direct backing of test material by metal plate, which influences measurement accuracy if two-layer method is used. The structure permits a suitable electric field interrogation in test material and decreases the influences of both radial and surface waves. FDTD method was adapted for modeling the problem geometry to calculate the reflection coefficients since a probe with finite flange size is used. Measurements were carried out using the proposed technique to determine complex permittivity and complex permeability of several radar absorbers over X-band applications of microwaves. In comparison with both single-layer and two-layer methods results, the measured results of these parameters agreed well with the published data. by companies and literatures.

Multilayer Structure Technique for Improving Determination of Electromagnetic Properties of Radar Absorbers Based on Two-Layer Method and Flanged Rectangular Waveguide Probe

This paper presents further development of utilization of two-layer method to perform nondestructive electromagnetic properties determination of planar radar absorbers using flanged open-ended rectangular waveguide probe. A multilayer structure of three layers was proposed to improve the measured results of these parameters obtained using two-layer method. These layers were arranged such that the test material is sandwiched between two known low loss materials to provide the needed two independent reflection coefficients necessary to extract them at different conditions of testing. The proposed structure was aimed to decrease the effect of direct backing of test material by metal plate, which influences measurement accuracy if two-layer method is used. The structure permits a suitable electric field interrogation in test material and decreases the influences of both radial and surface waves. FDTD method was adapted for modeling the problem geometry to calculate the reflection coefficients since a probe with finite flange size is used. Measurements were carried out using the proposed technique to determine complex permittivity and complex permeability of several radar absorbers over X-band applications of microwaves. In comparison with both single-layer and two-layer methods results, the measured results of these parameters agreed well with the published data. by companies and literatures.

Solution of the Helmholtz equation within volumes bounded by convex polygonal surfaces

We present a surface integral algorithm, utilizing Fourier integrals to solve optical fields within a volume bounded by a complicated polygonal surface. The method enables the full electric field to be solved from electric field values on the bounding surface at any point within the volume. As opposed to FDTD and FEM methods, volume discretization and the need to iteratively solve the E-field at every discrete volume element is not needed with this method. Our new surface integral algorithm circumvents the limitations that exist in current surface methods. Namely, in present methods, the need to determine a Green’s function only allows for simple bounding surfaces, and these methods generally use integrals that cannot utilize computationally fast Fourier integrals. Here, we prove the algorithm mathematically, show it with a numerical example, and outline important cases where the algorithm can be used. These cases include the design of free-form reflectors and near field optical scanning microscopy (SNOM). We then briefly analyze the algorithm's computational scaling.

Assessing the Efficacy of a GPU-Based MW-FDTD Method for Calculating Lightning Electromagnetic Fields Over Large-Scale Terrains

This article presents for the first time an OpenACC (Open accelerators)-aided Graphics Processing Unit (GPU)-based approach adopting a 3D moving window finite difference time domain (MW-FDTD) method for calculating lightning electromagnetic fields over large-scale terrains. The efficacy and accuracy of the proposed method are evaluated by comparing its results with the results obtained from a conventional FDTD method. The results show that the GPU-based MW-FDTD method is capable of providing highly accurate results 42 times faster than the conventional CPU-based FDTD method. Moreover, the proposed method required only (2M/N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> ) × 100 = 40%. of the memory needed for carrying out the calculation compared to a conventional FDTD method, where M and N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> are the size of the entire domain in the conventional FDTD method and size of the divided blocks in the MW-FDTD method domain, respectively. The results show the applicability of the MW-FDTD-GPU method for dealing with lightning electromagnetic problems as well as large-scale electromagnetic compatibility (EMC) applications where the efficiency and minimization of the computational time and memory requirements are of great importance.

Stable thin‐wire model of buried pipe‐type power distribution cables for 3D FDTD transient simulation

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.

A Compact 2-D Stochastic FDTD Method for Uncertainty Analysis in Superconducting Transmission Lines

In this article, a stochastic finite-difference time-domain (S-FDTD) method is proposed for analyzing the influence of physical size uncertainty on the time-domain response of superconducting transmission lines. The formulations of the proposed method are, in detail, derived with the two-fluid model and London equation. A typical superconducting microstrip line is simulated to verify the effectiveness of the proposed algorithm. Compared with the Monte Carlo simulation, the proposed method has the same accuracy but much higher efficiency. The computation time of the proposed S-FDTD method is only about 3% of that of the Monte Carlo simulation. Therefore, the proposed method shows a promising prospect on predicting the variability in transmission line's performance caused by variation in superconducting manufacturing.

Study of the Super Directive THz Photoconductivity Antenna

The photoconductivity antenna is a promising technology to generate THz wave. However, the technology is problematic in THz low antenna gain. The improvement of efficiency and directive is very important to the photoconductivity antenna. Here, a super directivity THz photoconductivity antenna (PCA) is proposed. The antenna uses the dielectric resonator to enhance the directivity which yields the super directivity in radiation. The eigen mode analysis is performed to the super directivity antenna, which is used to help design the antenna and understand the mechanism for the super directivity. The spherical cap is used as the dielectric resonate antenna (DRA), and the relationship between the radius of sphere and the height of cap and super directivity is surveyed. The dielectric cap height and sphere radius are found both playing an important role in enhancing the directivity of the antenna. To validate the proposed design, a THz photoconductivity antenna is designed. The simulations are performed using FDTD and FEM method. Both results show that the designed THz antenna has the super directivity value above 9.0 at 2.0 THz.

Decomposition of LF Resultant Waves With Multipropagation Modes in the Earth-Ionosphere Waveguide

Decomposition work of Loran-C resultant waves propagating in the Earth-ionosphere waveguide is concentrated on in this article. Resultant waves of different Earth-ionosphere models are predicted by the FDTD method first. The inverse fast Fourier transform (IFFT) spectral-division technique combined with a filtering process is employed to estimate the delays of different wave-propagation modes in the resultant waves, whereas the amplitudes are solved with the least-square method. Finally, accurate field strengths and delays of different modes (ground waves and skywaves of diverse hops) are obtained, which are important for Loran-C receivers to optimize their performances.

Structurally tunable gear-shaped plasmonic sensor.

We present a gear-shaped plasmonic nano-structure with structural tunability and high RI sensitivity. New tunable geometric parameters of the gear-tooth give further flexibility for design. By using FDTD method, the reflection spectrum of the structure is theoretically analyzed with analyte RI in the range of 1.0 to 1.44. The best achieved sensitivity is- 1044 nm/RIU for our proposed structure. The resonance wavelength of the structure is independent of the polarization angle for large number of teeth. The structure can be used to design tunable sensors for biomedical and chemical applications.

Numerical Stability and Accuracy of CCPR-FDTD for Dispersive Medi

The complex-conjugate pole-residue (CCPR) model has been popularly adopted because CCPR-finite-difference time domain (FDTD) can reduce the memory requirement with the help of complex conjugate property of auxiliary variables. To fully utilize CCPR-FDTD, it is of great necessity to investigate its numerical stability since the FDTD method is conditionally stable. Nonetheless, the numerical stability conditions of CCPR-FDTD have not been studied because its derivation is not straightforward. In this communication, the numerical stability conditions of CCPR-FDTD are systematically derived by combining the von Neumann method with Routh–Hurwitz criterion. It is found that the numerical stability conditions of CCPR-FDTD are the same as those of the modified Lorentz-FDTD with bilinear transform. Moreover, the numerical accuracy of CCPR-FDTD is studied, and numerical examples are employed to validate this work.

High numerical aperture metalens to generate an energy backflow

Using electronic beam lithography and reactive ion beam etching, a metalens is manufactured in a thin layer of amorphous silicon of a 130-nm depth, a 30-µm diameter, and a 633-nm focal length (equal to the illumination wavelength). The metalens is composed of 16 sectored subwavelength binary gratings with a 220-nm period. The uniqueness of this metalens is that when illuminated by left-handed circularly polarized light, it is capable of generating a left-handed circularly polarized vortex beam with a topological charge of 2, generating a second-order cylindrical vector beam when illuminated by linearly polarized light. Both for linear and circular incident polarization, an energy backflow is found to be generated in the vicinity of the tight focus. Transverse intensity distributions measured with a scanning near-field optical microscope near the focus of the metalens are in qualitative agreement with the intensity distributions calculated by the FDTD method. This confirms that a backward energy flow takes place at the focus of the metalens. A metalens generating an energy backflow near its focus is fabricated and characterized for the first time.

Using constructed impulse responses to study the influence of sound speed profiles on outdoor acoustic propagation

Time-domain predictions can be accomplished by either explicitly calculating within the time domain, such as with the Finite-Difference, Time-Domain method, or by processing frequency-domain calculations into impulse responses. While the FDTD method has been used extensively in outdoor sound propagation studies, the requirement for extensive computational resources greatly limits the computational domain. The impulse response method, while well-utilized in underwater sound propagation has seen limited use in outdoor sound studies. For a given environmental scenario, the impulse response may be obtained from the inverse Fourier transform of transmission loss simulations in the frequency-domain. When it is convolved with the time variation of the source, the receiver signal may be readily predicted. One may re-use the impulse response for any new source, so long as the sampling criteria are met, and the source and receiver positions and environment match those of the modeled situation. A discussion of the implications of frequency resolution and example comparisons to measurements are presented. [This work was funded by the Assistant Secretary of the Army (Acquisition, Logistics, and Technology) [ASA(ALT)] with portions funded under 0602784/T40/24 and 0602146/AR9/01. Distribution Statement A: Approved for public release; Distribution is unlimited.]

Pr–Co co-doped BFO multiferroics nanomaterials for absorber applications

Pr and Co co-doped BiFeO3 multiferroics of the following composition BiCoxPrxFe1-2xO3, where (x = 0.00, 0.05, 0.10, 0.15, 0.20 and 0.25) were prepared via sol-gel route. XRD, FTIR, SEM, VSM and VNA were used to evaluate the structural, phase, morphological and electromagnetic properties of Pr and Co co-doped multiferroics. All the undoped and Pr–Co co-doped multiferroics were of single rhombohedral phased whereas at higher concentration the orthorhombic structure was present. FTIR analysis exhibited the presence of orthorhombic phase. SEM images revealed that the grains of Pr and Co doped multiferroics are circular and elliptical in shape. Dielectric and electromagnetic properties were analysed using VNA from 1 to 6 GHz. Dielectric constant, dielectric loss factor, electric modulus, relative permeability, loss tangent, ac conductivity, and Q factor were determined from the toroidal shaped multiferroics. The double doping of Pr and Co multiferroics at x = 0.15 unveiled higher dielectric constant, ac conductivity and other related electromagnetic properties as compared to doped and undoped multiferroics. Pr and Co doped multiferroics also disclosed higher Q factor values at 2.65 GHz. Thin substrate as absorber and square shape resonator of Pr–Co co-doped BiFeO3 multiferroics at x = 0.15 were simulated using FDTD method. The first resonance absorption peak with a very high Q-factor was achieved at ~ 1.2 GHz whereas the second absorption peak was attained at ~ 2.4 GHz respectively. The absorptivity was also analysed corresponding to the different angles of incident for both TE- and TM-modes. Therefore, Pr–Co co-doped multiferroics have potential applications in the absorption and resonator devices in GHz regime.