Time-domain Transmission Line Model Research Articles

Polynomial chaos expansion for sensitivity analysis of two types of transmission line models

This paper presents two sensitivity analyses, one of which is for the time-domain transmission line (TL) model using the latest weight-based algorithm that is a combination of the coherence-optimal sampling (COS) and the l1-minimum problem (l1-M) and the other is for the high-frequency field line coupling model based on the algorithm that combines the Latin hypercube sampling (LHS) with the l1-M for the first time, where the COS and the LHS are employed to draw samples and the polynomial chaos expansion (PCE) coefficients are obtained by solving the l1-M. Both algorithms are within the PCE framework. The results show that for the time-domain TL model, the capacitance has the greatest impact on the voltage response, followed by the resistance. The height and the radius have the least impact, while there is little difference between them. For the high-frequency field line coupling model, the azimuth angle has the greatest impact on the current in the TL, followed by the elevation angle. The terminal load, the conductivity, the field amplitude, the relative permittivity, and the TL radius have the least effect, and there is little difference among them. Additionally, both algorithms only require no more than 0.60% of the total Monte Carlo (MC) computation time when yielding solutions with almost identical accuracy. Compared to performing a sensitivity analysis using the MC method, the use of two algorithms significantly improves efficiency.

Transient Response of Twisted Wire Pairs Illuminated by HEMP

In this paper, the time domain characters of the response of twisted wire pairs (TWPs) excited by the high-altitude electromagnetic pulse (HEMP) have been proposed. The finite different time domain transmission line model (FDTD-TLM) method, which we have proposed previously, is used to calculate the terminal response of TWP. It shows that the time domain response includes two stages: The transient stage and damped stage. The transient stage is the key point of the coupling and protecting research. The influence factors of the transient stage have been analyzed. In the end, we obtain the changes of the induced voltage when the incident wave parameters and TWP parameters change.

Wideband Modeling of Power SiC mosfet Module and Conducted EMI Prediction of MVDC Railway Electrification System

The SiC mosfet in the medium-voltage direct-current (MVdc) transportation electrification system features faster switching performance, while simultaneously binging more significant electromagnetic interference (EMI) issues within the rolling stocks, substations, and radiated disturbance into space along the catenaries and tracks. Due to the necessity to involve both the transient characteristics of power semiconductor devices and the stray parameters of all the equipment in the analysis of EMI, it is considerably challenging to perform wideband device-level simulation on traditional commercial software for such a complex system with numerous trains and stations. A computationally efficient method for wideband modeling and simulation of the MVdc high-speed railway system for the assessment of conducted EMI during the project design stage is proposed in this article. Physical characteristics of the semiconductor devices, parasitic parameters of the mosfet package, and converter topology are all taken into consideration to provide not only accurate system-level performance of the system but also an insight into high-frequency characteristics under different operation conditions. The calculation burden is alleviated by a hierarchical circuit partitioning architecture based on the frequency-dependent time-domain transmission line model and the Norton equivalent parameter extraction of each mosfet module to split the whole system into several smaller subcircuits in terms of matrix size, and a fully parallel implementation of the MVdc system is carried out on the graphics processor. The developed program is used to study the case of Jing–Zhang high-speed railway system topology, which is compatible to be modified to the MVdc project. Simulation results show that it is essential to estimate the EMI level comprehensively considering the alternative of speed and dc voltage.

Mutual conversion between B-mode image and acoustic impedance image

To study the acoustic properties of a B-mode image, two ways of analysis methods were proposed in this report. The first method is the conversion of an acoustic impedance image into a B-mode image (Z to B). The time domain reflectometry theory and transmission line model were used as reference in the calculation. The second method is the direct a conversion of B-mode image into an acoustic impedance image (B to Z). The theoretical background of the second method is similar to that of the first method; however, the calculation is in the opposite direction. Significant scatter, refraction, and attenuation were assumed not to take place during the propagation of an ultrasonic wave. Hence, they were ignored in both calculations. In this study, rat cerebellar tissue and human cheek skin were used to determine the feasibility of the first and second methods respectively. Some good results are obtained and hence both methods showed their possible applications in the study of acoustic properties of B-mode images.

Some developments on phase coordinates line modeling based on Idempotent decomposition

Abstract Time-domain transmission line models remains a topic of ongoing research. The state of the art consists in using the Method of Characteristics (MoC) with a rational approximation of the characteristic admittance and propagation function matrices. The so-called universal line model (ULM) stands as among the most accurate phase-domain line models using MoC. However, it might present unstable responses due to large residue-pole ratios which amplifies the error associated with the interpolation scheme of the reflected current wave. In this work we investigate the possibility of using Idempotent Decomposition as an alternative for a full-frequency-dependent transmission line model suitable for the analysis of underground cables and overhead lines. An overview of the basic structure of time-domain transmission line modeling is presented. Results indicate that the separation of the propagation function into the sum of products of an Idempotent matrix with the corresponding exponential time-delay function avoids the stability problems related to large residue-pole ratios. A proposition to group Idempotent matrices with similar time-delays to reduce the order of the rational approximation of the propagation function matrix is also analyzed. Four test cases were considered including two previously reported cases where unstable simulation responses were found using ULM with a simple interpolation scheme. A Numerical Laplace Transform (NLT) approach was used to compare the time-domain responses. While results indicate that the Idempotent decomposition can be used to model underground cables, there is some accuracy loss in the rational approximation of the propagation function in the case of overhead transmission lines when a large number of phases is involved.

Time domain adjoint sensitivity analysis of electromagnetic problems with nonlinear media.

In this paper, we propose a theory for wideband adjoint sensitivity analysis of problems with nonlinear media. We show that the sensitivities of the desired response with respect to all shape and material parameters are obtained through one extra adjoint simulation. Unlike linear problems, the system matrices of this adjoint simulation are time varying. Their values are determined during the original simulation. The proposed theory exploits the time-domain transmission line modeling (TLM) and provides an efficient AVM approach for sensitivity analysis of general time domain objective functions. The theory has been illustrated through a number of examples.

Wideband Second-Order Adjoint Sensitivity Analysis Exploiting TLM

We present, for the first time, an efficient adjoint variable method (AVM) for estimating second-order sensitivities exploiting time-domain transmission-line modeling. For a structure with n designable parameters, the complete Hessian matrix of any desired objective function is estimated using n extra simulations as compared to O(n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) using the traditional finite-difference approaches. Our approach is illustrated through estimating the second-order sensitivities for energy functions and scattering parameter with respect to dimensions and material properties of metallic and dielectric discontinuities. The results achieved using our AVM approach are verified using the expensive finite-difference approaches.

Ultrafast optical switching using parity–time symmetric Bragg gratings

This paper reports on time-domain modeling of an optical switch based on the parity–time (PT) symmetric Bragg grating. The switching response is triggered by suddenly switching on the gain in the Bragg grating to create a PT-symmetric Bragg grating. Transient and dynamic behaviors of the PT Bragg gratings are analyzed using the time-domain numerical transmission line modeling method including a simple gain saturation model. The on/off ratio and the switching time of the PT Bragg grating optical switch are analyzed in terms of the level of gain introduced in the system and the operating frequency. The paper also discusses the effect the gain saturation has on the operation of the PT-symmetric Bragg gratings.

TIME-DOMAIN DISTRIBUTED PARAMETERS TRANSMISSION LINE MODEL FOR TRANSIENT ANALYSIS

This article describes a time-domain transmission line model based on distributed parameters for transient analysis. This model is based directly on the difierential equations for the basic transmission line without any previous simpliflcation. The solution presented here for these difierential equations results in a more detailed time-domain model than others models currently in use, and with certain structural similarities with the distributed parameter frequency-domain model for long transmission lines. The deduction of a general time-domain transmission line model for fundamental frequencies parameters and single-phase line are presented in this article, but the model can also be extended to cases with multiconductor and frequency-depended parameters. In order to validate the model, a comparative test is presented to facilitate the analysis about the main similarities and difierences between this and other models.

Adjoint variable method for two-dimensional plasmonic structures

We present, for the first time, an adjoint variable method (AVM) for wideband sensitivity analysis of dispersive materials. The time domain transmission line modeling technique is exploited to calculate the response and its sensitivities with respect to all the designable parameters using at most one extra simulation. A z-domain representation of dispersive materials is utilized in the derivation of this technique. Our approach is illustrated through sensitivity analysis of a two-dimensional teeth-shaped plasmonic resonator. The AVM sensitivities are compared with the accurate and expensive finite difference approach and good agreement is achieved. This theory can be extended to other dispersive materials and dispersive metamaterials as well.

Quality factor assessment of subwavelength resonant cavities at FIR frequencies

Subwavelength resonators at FIR are presented and studied. The structures consist of 1D cavities formed between a metallized (silver) surface and a metamaterial surface comprising a periodic array of silver patches on a silver-backed silicon substrate. The concept derives from recent discoveries of artificial magnetic conductors (AMC). By studying the currents excited on the metamaterial surface by a normally incident plane wave, the nature of the emerging resonant phenomena and the physical mechanism underlying the AMC operation are investigated. Full wave simulations, based on finite element method and time-domain transmission line modelling technique, have been carried out to demonstrate the effective AMC boundary condition and prove the possibilities for subwavelength cavities. The quality factor of the resonant cavities is assessed as a function of the cavity profile. It is demonstrated that the quality factor drops to about 1/8 of the half-wavelength value for a λ/8 resonant cavity.

A Complete Model for Simulating Magnitude and Phase of Emissions from a DUT Placed Inside a GTEM Cell

Since the publication of IEC 61000-4-20, the gigahertz transverse electromagnetic (GTEM) cell has gained popularity in radiated emission and immunity electromagnetic compatibility tests. Various numerical methods such as finite-difference time-domain, finite element method, and method of moments have been used to model the GTEM cell in the pursuit of getting to know the characteristic of the GTEM cell with varying degrees of verification. In this paper, the time-domain transmission line model will be used to model the GTEM cell. The advantages of this method include high accuracy and the ability to model different materials. Thus, the GTEM is realistically modeled including radio absorbing material (RAM) and lumped terminations. In addition, the model of a realistic device under test (DUT) was also included in the GTEM model. The DUT consists of a standard sized box with an aperture, placed in different orientations inside the GTEM for power and phase measurements. The particular features of this paper are: 1) the inclusion of a realistic numerical model of RAM, 2) the inclusion of a realistic DUT model, 3) systematic verification of the model against measurements, and 4) the method of phase measurement in a GTEM cell. Good agreement between the experimental results and simulations is obtained.

An AVM technique for 3-D TLM with symmetric condensed nodes

We demonstrate, for the first time, the feasibility of the adjoint variable method (AVM) in three-dimensional (3-D) time-domain transmission-line modeling (TLM). Using only two 3-D simulations of the original and adjoint problems, the sensitivities of the objective function with respect to all design parameters are estimated. The AVM approach is applied to both perfectly conducting and dielectric discontinuities. Analytical derivatives of the symmetric condensed node (SCN) scattering matrix are utilized in the case of dielectric discontinuities to derive a semi-analytical adjoint system. Our approach is illustrated with waveguide discontinuities.

Efficient estimation of sensitivities in TLM with dielectric discontinuities

We present two novel approaches for efficient estimation of objective function sensitivities related to dielectric discontinuities with time-domain transmission line modelling. Using only two simulations, of the original and adjoint structures, the sensitivities with respect to all parameters are obtained. The first approach utilizes an approximation of the adjoint problem. It adapts a recent approach that handles perfectly conducting discontinuities. The second approach exploits the analytic dependence of the nodal scattering matrix on the material properties. The adjoint problem is exact for this case. Our approaches are illustrated through examples involving waveguide dielectric discontinuities.

Efficient estimation of adjoint-variableS-parameter sensitivities with time domain TLM

We present a novel algorithm for efficient estimation of S-parameter sensitivities with the time-domain transmission line modelling (TLM) method. The original electromagnetic structure is simulated using TLM to obtain the S-parameters in the desired frequency band. For each port, an adjoint TLM simulation that runs backward in time is derived and solved. The sensitivities of the S-parameters in the desired frequency band are estimated using only the original and adjoint simulations. For a structure with Np ports and n designable parameters, our approach requires only Np additional simulations regardless of n. This can be easily contrasted with the 2nNp additional simulations required by the central difference approximation. Our algorithm is illustrated through the estimation of S-parameter sensitivities with respect to the dimensions of waveguide discontinuities. Very good match is obtained between our sensitivity estimates and those obtained using central difference approximation. Copyright © 2005 John Wiley & Sons, Ltd.

Time domain simulation in photonics: A comparison of nonlinear dispersive polarisation models

The paper investigates and compares a range of different models currently used for modelling nonlinear optical phenomena. The models are implemented in the numerical time domain Transmission Line Modelling (TLM) method and include a Kerr model and different formulations of the Duffing model. The models are used to simulate an all-optical limiter for a CW input and results compared with ones available in the literature. This enables a comparison to be made between the different models, from which it is concluded that the Duffing model has some advantages, when modelling materials and phenomena involving more than one frequency, arising from its ability to describe dispersive effects. These conclusions are further supported by the simulation results obtained for a pulse input.

An Adjoint Variable Method for Time-Domain TLM With Wide-Band Johns Matrix Boundaries

We present a novel algorithm for efficient estimation of objective function sensitivities for time-domain transmission-line modeling (TLM) with dispersive Johns matrix boundaries. The original electromagnetic structure is simulated using TLM. An adjoint TLM simulation that runs backward in time is derived and solved. The sensitivities of the objective function with respect to all designable parameters are estimated using only the original and adjoint simulations. We show that the Johns matrix of the adjoint problem at each time step is the transpose of the corresponding matrix for the original structure. Our approach is illustrated through the estimation of the sensitivities of objective functions with respect to the dimensions of waveguide discontinuities. A very good match is obtained between our sensitivity estimates and those obtained using central difference approximation.

An Adjoint Variable Method for Time-Domain Transmission-Line Modeling With Fixed Structured Grids

We present a novel algorithm for efficient estimation of objective function sensitivities for time-domain transmission-line modeling (TLM) with nondispersive boundaries. The original electromagnetic structure is simulated using TLM. An adjoint TLM simulation that runs backward in time is derived and solved. The sensitivities of the objective function with respect to all designable parameters are estimated using only the original and adjoint simulations. Our approach is illustrated through the estimation of the sensitivities of objective functions with respect to the dimensions of waveguide discontinuities. A very good match is obtained between our sensitivity estimates and those obtained through the accurate and time-intensive central difference approximation.

Efficient description of fine features using digital filters in time-domain computational electromagnetics

The use of digital filters for the description of perforated metal plates in the time-domain transmission-line modelling (TLM) method is presented. The frequency-domain Prony method is used to approximate the analytic scattering coefficients of perforated plates using Laplace-domain functions. These functions are transformed into the -domain and the resulting digital filters are embedded into the TLM mesh. Three types of perforated plates are studied and the results obtained for the shielding effectiveness of equipment enclosures having perforated plates are shown.

An improved transmission-line model of grounding system

This paper presents a time-domain transmission line model of grounding system, which includes the mutual electromagnetic coupling between the parts of the grounding structure and the influence of air-earth interface. The model can be used to simulate the transient behavior of the grounding system under lightning strike. The simulation results are in good agreement with that of the model based on the solution of full Maxwell's equations. The influence of different parameters, such as the soil relative permittivity /spl epsi//sub /spl tau//, the soil resistivity /spl rho/, and the conductivity and diameter of the conductor, on the transient voltage distribution of the grounding system is investigated. It shows that, among the parameters investigated here, the soil resistivity is the most important parameter that affects the transient response of bare buried conductors. The soil permittivity has very little influence on the transient response of the grounding system when the grounding system is buried in the soil with low resistivity, but have moderate influence in the soil with extremely high resistivity. The conductivity of the conductor and skin effect have practically no influence on the peak transient voltage of the grounding system. Increase in conductor diameter tends to decrease the peak transient voltage. The model presented in this paper is simple, but sufficiently accurate and can be used easily in engineering practice. Since the model is in the time domain, it could be easily coupled to the other time-domain models of nonlinear surge-protection components.