S-Parameter Macromodels Incorporated into FDTD Simulation of Transmission Line Networks

New version of FDTD with GFM program in Schwarzschild space–time

The numerical dispersion is one of the main factors to affect the accuracy of the finite-difference time-domain (FDTD) method. It can be easy to be taken for granted that a smaller time step leads to smaller simulation errors. This paper reveals that smaller time steps do not always make more accurate results in FDTD simulations. We analytically investigated how time steps affect the numerical dispersion of two FDTD methods: the leapfrog FDTD(2,2) method and the FDTD(2,4) method. The investigations in this paper show that in the FDTD(2,2) method, a larger time step limited by the Courant-Friedrichs-Lewy (CFL) condition is more helpful to reduce the numerical dispersion error. However, in the FDTD(2,4) method, as the time step grows, the numerical dispersion error decreases at the beginning and then increases. Several numerical examples are carried out to verify our analysis.

The Finite-Difference Time-Domain (FDTD) method is used to study the scattering effects of extreme ultraviolet (EUV) mask. It requires significant amounts of memory and computation time as the fine grid size is needed for simulation. Theoretically, the accuracy can be increased as the mesh size is decreased in FDTD simulation. However, it is not easy to get the accurate simulation results for the multilayer (ML) structures by FDTD method. The transmission line theory is used to calculate the equivalent refractive index for EUV mask ML to simulate the ML as one layer of bulk artificial material. The reflectivities for EUV light with the normal incidence and small-angle oblique incidence in the bulk artificial material and EUV mask ML are simulated by FDTD method. The Fresnel's equation is used to evaluate the numerical errors for these FDTD simulations, and the results show good agreement between them. Using the equivalent refractive index material for EUV multilayer mask can reduce the computation time and have the accuracy with tolerable numerical errors. The ML structure with periodic surface roughness is also studied by this method, and it shows that only half of computation time is needed to substitute ML to a bulk equivalent refractive index material in FDTD simulations. This proposed method can accelerate the simulations of EUV mask designs.

ABSTRACTWe have numerically investigated the tunable surface plasmon in graphene square-nanoring structure. Due to an enhancement of the local field, graphene surface plasmons (GSPs) can be strongly confined in the graphene grating region. The expressions of the lifetime for resonant modes have been investigated with the the finite difference time domain (FDTD) simulations and the coupled mode theory (CMT). Altering the Fermi energy and varying the carrier mobility have an important influence in optimizing the light absorption and the lifetime of GSPs. The CMT theoretical results agree well with FDTD simulations. Besides, by utilizing the different inner length and the different refractive index of substrate material, we find that the absorption peak of the GSPs structure can be tuned in a wide wavelength range. Our proposed graphene gratings structure shows good prospects in the mid-infrared region, such as ultracompact tunable integrated modulators and absorbers.

It is very useful to know the soil capabilities on different external impacts acting on it, especially for electromagnetic waves from Ground Penetrating Radar. In the underground detection domain actually, dealing with soil permittivity is one of the challenging research problems nowadays. In this paper, we study tropical soil constitution, taking in account the tropical climate region and we took Rwanda as a case study. Rwanda's elevation ranges from 1,000m (south and east) to 4,500m above sea level. The "thousand hills" terrain is dominated from north to south by a watershed (2.500m high) that separates the basin of the Congo River from that of the Nile and by the Ibirunga volcano chain. In spite of its proximity (2 degrees south) to the equator, the country enjoys a fine spring climate (due to its altitude), with two rainy seasons and two dry seasons. In fact, when considering the tropical climate region with his considerable rainfall period, it is better to collect information regarding the zone in consideration. Using Finite Difference Time Domain(FDTD) simulation with GPRMax simulator, and varying the permittivity, the aim of this paper is to have a benchmark of dry and rainfall season; this will help when doing measurements with the GPR instruments and others non destructive tools. In this paper, we analysed the clay soil (one of the component of Rwandan pedology) and from the variation of dry clay to wet clay associated with different fixed frequencies (300MHz, 600MHz, 900MHz, 1200MHz and 1500MHz). For each fixed frequency, we vary the clay permittivity from dry to wet clay and analysed data after simulation. From this benchmark, and in the near future work, we will use the GPR instrument and the Time Division Reflectometry(TDR) to verify the simulation results.

In this paper, we describe a hybrid circuit and electromagnetic simulation technique for electrostatic discharge (ESD) events. First, we perform the transient simulation of an equivalent circuit of an ESD generator. At the same time, a computational domain without the ESD generator is analyzed by means of the finite-difference time-domain (FDTD) method. The results from the SPICE-like and FDTD simulations are exchanged for each other by using analogy between the circuit theory and electromagnetics. The proposed method can reduce the computational cost significantly because we perform the FDTD simulation only for the reduced domain, which is much smaller than the whole domain. The adequacy of the proposed method is verified by comparing simulation results with measurement results.

ABSTRACTMicrowave sintering of ceramics in multimode cavities, particularly the use of picket-fence arrangements, has recently received considerable attention. Various types of ceramics have been successfully sintered and, in some cases, a desirable and unique “microwave effect” has been observed.At present, various aspects of the sintering process such as sample sizes and shapes, types of insulations, and the desirability of including a process stimulus such as SiC rods are considered forms of art and highly dependent on human expertise. The simulation of realistic sintering experiments in a multimode cavity may provide a better understanding of critical parameters involved and allow for the development of guidelines towards the optimization of the sintering process.In this paper, we utilize the FDTD technique to model various geometrical arrangements and material compatibility aspects in multimode microwave cavities and to simulate realistic sintering experiments. The FDTD procedure starts with the simulation of a field distribution in multimode microwave cavities that resembles a set of measured data using liquid crystal sheets. Also included in the simulation is the waveguide feed as well as a dielectric loading plate placed at the base of the cavity. The FDTD simulation thus provides realistic representation of a typical sintering experiment. Aspects that have been successfully simulated include types of insulation, role of SiC rods on the uniformity of the resulting fields, problems that may result from presence of thermocouples, and the possible shielding effects that may result from excessive use of SiC. These results as well as others showing the electromagnetic fields and power-deposition patterns in multiple ceramic samples are presented.

In this paper, we present finite difference time domain (FDTD) simulations of millimetre-wave propagation through the near-field plasma plume of low power Hall thrusters. The simulations are intended to address potential issues (collisions, magnetic fields) that may affect the validity of simple theory used for phase shift determination in the recent measurements of plasma density using microwave interferometry (Cappelli et al 2006 J. Phys. D: Appl. Phys. 39 4582). One-dimensional plane wave FDTD simulations indicate that plasma non-uniformities along the direction of wave propagation have only a minor effect on the phase shifts estimated from collisionless, non-magnetized wave propagation through a path-length averaged plasma slab. Three-dimensional FDTD simulations that also account for electron collisions and magnetic fields indicate that the departure from the use of usual simple models is no more than about 15%, well within the limits of uncertainty in the experimental measurements taken within the near field of these plasma sources.

The finite difference time domain (FDTD) method has been proposed and used for sound field simulation. To reproduce actual sound wave propagation in sound field simulations, it is necessary to apply the radiation characteristics. With the FDTD method, radiation characteristics can be applied by setting sound pressure in a dense grid arrangement. However, conventional techniques for capturing radiation characteristics use a sparse array of microphones and are considered insufficient for the FDTD simulation. Furthermore, the technique required to apply captured acoustic signals in a dense grid arrangement with the FDTD method has not been considered. In this paper, we propose a novel hardware and software system that captures the radiation characteristics for a dense grid arrangement and applies them to the FDTD method, while controlling the sound wave propagation with the non-propagation region. The proposed system produces the average differences from measured values of sound pressure, propagation time, center frequency, and log-spectral distortion of 1.8 dB, 0.04 ms, 700 Hz, and 3.5 dB, respectively, which is more accurate than the conventional techniques. The result shows that this system is useful for improving the accuracy of sound wave propagation reproduction with the sound field simulation.

Metal probe-based near-field tweezers can provide optical trapping and alignment of dielectric particles at nanometer scale. A finite difference time domain (FDTD) numerical method of solution is applied to optimize the metal probe geometry for better nano-manipulation. Calculations for copper probes of truncated, infinite and finite rectangular pyramid are considered. The calculations show that sharper probes would generate stronger fields, and probes whose geometry size matched to the excitation frequency could lead to higher field enhancement, in addition, finite probes might generate strong field enhancement due to resonance with the excitation source. Consequently, FDTD calculations were made to optimize metal probes in the near-infrared regime, the enhancements for cone probes are found to be higher than for similar length pyramidal probes. The cone probes designed with FDTD are particularly well suited for use in metal probe-based near-field tweezers.

The importance of dielectric losses in planar microstrip structures is evaluated with the finite-difference time-domain (FDTD) method. This analysis was previously not possible in many FDTD simulators due to a lack of absorbing boundary conditions (ABCs), which appropriately terminate air/dielectric interfaces for which the dielectric is lossy. The newly proposed lossy two-time derivative Lorentzian material (L2TDLM) model ABC allows for these terminations and is presented and implemented here for three-dimensional FDTD simulations. The effect of dielectric losses on several well-known planar microstrip structures is evaluated. It is shown that the inclusion of these losses in FDTD simulations, which is facilitated by the L2TDLM ABC, is, in fact, important to predict the performance of resonant structure on lossy dielectric substrates.

Plasmonics is a new and exciting field that has the potential to advance many different types of technology, from information processing and energy harvesting to sensing and imaging. The broad field of plasmonic materials and their potential to improve the functionality of cutting-edge technologies are examined in this thesis. The thesis explores the synthesis, characterization, and manipulation of plasmonic materials after providing an overview of the basic ideas behind plasmonics. Their distinct plasmonic properties and possible uses are clarified by a thorough investigation of a variety of materials, including noble metals, two-dimensional materials, metal oxides and hybrid structures. A thorough analysis of the Finite-Difference Time-Domain (FDTD) simulations used with different plasmonic materials is presented in this thesis. The theoretical foundation for FDTD simulations and their use in the investigation of plasmonic phenomena is established at the onset of the study. It then goes on to examine the properties of various plasmonic materials, such as noble metals, 2D materials and hybrid structures. The optical response, near-field enhancements, and dispersion properties of these materials are examined and contrasted using thorough simulations. This understanding of these plasmonic behaviors is utilized to control and manipulate a material’s performance and functionality in a particular technology. Using FDTD simulations, the thesis explores how material parameters, including size, shape, and dielectric constant, affect the plasmonic properties. Through the systematic variation of these parameters, valuable insights can be obtained regarding the optimization of plasmonic devices and systems' performance. The thesis also discusses new developments and avenues for future research in plasmonics, including the creation of novel materials, the investigation of hybrid plasmonic systems. It also addresses the difficulties and restrictions associated with using FDTD simulations to model plasmonic materials, including issues with accuracy and computational complexity. All things considered; this thesis offers an in-depth overview of how FDTD simulations are used to study different plasmonic materials. Through clarifying the optical characteristics, investigating dependence between parameters, and assessing new materials, it advances the field of plasmonics research and makes the creation of creative plasmonic systems and devices easier.

The light extraction efficiency of OLEDs with a nano-sized random scattering layer (RSL-OLEDs) was analyzed using the Finite Difference Time Domain (FDTD) method. In contrast to periodic diffraction patterns, the presence of an RSL suppresses the spectral shift with respect to the viewing angle. For FDTD simulation of RSL-OLEDs, a planar light source with a certain spatial and temporal coherence was incorporated, and the light extraction efficiency with respect to the fill factor of the RSL and the absorption coefficient of the material was investigated. The design results were compared to the experimental results of the RSL-OLEDs in order to confirm the usefulness of FDTD in predicting experimental results. According to our FDTD simulations, the light confined within the ITO-organic waveguide was quickly absorbed, and the absorption coefficients of ITO and RSL materials should be reduced in order to obtain significant improvement in the external quantum efficiency (EQE). When the extinction coefficient of ITO was 0.01, the EQE in the RSL-OLED was simulated to be enhanced by a factor of 1.8.

For physical modelling sound synthesis, many techniques are available; time-stepping methods (e.g., finite-difference time-domain (FDTD) methods) have an advantage of flexibility and generality in terms of the type of systems they can model. These methods do, however, lack the capability of easily handling smooth parameter changes while retaining optimal simulation quality and stability, something other techniques are better suited for. In this paper, we propose an efficient method to smoothly add and remove grid points from a FDTD simulation under sub-audio rate parameter variations. This allows for dynamic parameter changes in physical models of musical instruments. An instrument such as the trombone can now be modelled using FDTD methods, as well as physically impossible instruments where parameters such as e.g. material density or its geometry can be made time-varying. Results show that the method does not produce (visible) artifacts and stability analysis is ongoing.

Light-emitting diodes (LEDs) are becoming increasingly important across various sectors of the lighting industry and are being used more frequently. In the field of symbolic projection, research is increasingly focusing on implementing light modulation using energy-efficient, incoherent LEDs rather than lasers. Since light modulation in micro- and nano-optics is typically achieved through phase modulation, Finite-Difference Time-Domain (FDTD) simulations are employed for analysis. The objective of this article is to investigate different approaches for approximating incoherent monochromatic light sources within FDTD simulations. To this end, two approaches based on dipole sources are considered, as well as a method involving plane waves with modulated wavefronts based on Cosine–Fourier functions and a method based on the superposition of Gaussian beams. These methods are evaluated in terms of their accuracy using a two-dimensional double-slit configuration and are compared against a fully incoherent analytical reference.