Time-domain Transmission Line Research Articles

Sound propagation modeling in forests using the transmission line matrix method: Comparison with experimental in situ measurements

We present efforts to adapt the time-domain Transmission Line Matrix (TLM) method for modeling sound propagation in forests. It is relevant to professionals and researchers in environmental acoustics and to those interested in studying sound propagation in outdoor environments using numerical modeling techniques. The study aims to demonstrate the applicability of the method in complex media where sound waves undergo multiple reflections combined with ground effects during their propagation from a sound source to a receiver point. The TLM method is used to numerically model sound propagation in a 3D forest geometry generated based on a real tree distribution case. Data from an experimental campaign conducted in the rainforest of French Guyana are used as a reference. The results show an encouraging comparison between them and the in situ measurements, even if the hypotheses made to adapt the input data in the model were strong. We find that more measurement points and more specifications (ground impedance measurements, canopy density, etc.) about the experimental site are needed for further simulations, even if obtaining them presents technical difficulties.

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.

Improvement on stability of direct modulation laser with integrated active feedback by partial corrugated gratings.

Researchers have developed a uniform grating DFB with an integrated active optical feedback waveguide (UG-AFDFB) to enhance the modulation speed of direct modulation lasers (DMLs) while reducing costs based on identical active layer designations. However, this design has difficulties in obtaining high single mode yield (SMY) and low relative intensity noise (RIN) as a result of the strong optical feedback caused by the integrated active feedback waveguide (AFW) and the random phase of the facet phase. In this paper, a partial corrugated grating DFB with an integrated active optical feedback waveguide (PG-AFDFB) is proposed to address this issue. Comparison of SMY, S21, RIN, modulation eye pattern, and frequency chirp parameters between UG-AFDFB and PG-AFDFB based on time-domain transmission line laser mode reveals that PG-AFDFB with an optimized grating couple parameter κ performs significantly better than UG-AFDFB under the same conditions. Furthermore, the performance of PG-AFDFB is not sensitive to the random phase of the rear facet phase. Even when κ ranges from 6000 /m to 12000 /m, the current in the AFW is between 0 mA and 20 mA, and the length of the AFW ranges from 50 µm to 100 µm; the SMY of PG-AFDFB remains above 80%.

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.

Time-Domain Transmission Line Fault Location Method With Full Consideration of Distributed Parameters and Line Asymmetry

Accurate fault location reduces operating cost and outage time. This paper proposes a time-domain method to accurately locate faults in transmission lines, which only requires a very short data window (several milli-seconds) during faults. First, the voltage distribution through the line during faults is accurately obtained by solving the matrix form partial differential equations using the proposed numerical scheme. The proposed numerical scheme is mathematically validated for the transmission line fault location problem, with the optimal selection of time and distance intervals to ensure stability and minimum solution error. Afterwards, the fault location is obtained via the extremum value of the voltage distribution. The method fully considers distributed parameters as well as asymmetry of the line. Extensive numerical experiments validated that (a) the proposed numerical scheme demonstrates advantages towards other numerical schemes; (b) the proposed method presents higher fault location accuracy compared to the existing method, independent of fault types, locations and impedances; and (c) the fault location accuracy is not sensitive towards fault inception angles, loading conditions, measurement errors and parameter errors. The proposed method works with relatively low sampling rates (80 samples per cycle) and is compatible with IEC 61850 standard in present digital substations.

Hybrid method for transient responses of transmission line in an apertured enclosure based on FETD method and transmission line equations

A hybrid method combining the finite-element time-domain (FETD) method and transmission line (TL) equations (FETD-TL) is presented for evaluating the transient responses of a lossy TL in an apertured rectangular enclosure excited by electromagnetic pulses. First, the electric fields in the enclosure without the TL are calculated based on the Bethe's small holes theory and the mirror procedure. Then, the enclosure's electric fields are introduced into the second-order TL equation for current as the equivalent distributed sources. The transient currents induced on the TL are obtained by solving the second-order TL equation for current based on the FETD method with a single iteration variable. Finally, the transient voltages induced on the TL are computed by discretising the first-order TL equation. Compared with the method based on finite-difference time-domain (FDTD) method and TL (FDTD-TL) via several examples, the proposed hybrid method is proved to be correct and effective, which possesses much higher convenience and efficiency than FDTD-TL method in dealing with TL model terminated by complex lumped parametric networks.

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.

Modelling of composite right/left‐handed active multiconductor transmission lines (AMCTL) in time domain

AbstractAn explicit finite difference time domain method is proposed for modelling of composite right‐/left‐handed active multiconductor transmission lines in time domain. For the first time, the concept of active composite right‐/left‐handed transmission lines is considered in field effect transistor (FET) modelling. In this work, based on the distributed model, the FET is considered as an active multiconductor transmission line in the mm/wave frequency range. In this modelling technique, the FET is divided into 2 different parts, the active part, represents the intrinsic equivalent circuit of the transistor, while the passive part symbolizes the device electrodes. The finite‐difference time‐domain scheme is proposed for the analysis, and the results of this technique are compared with the ones obtained from simulations. Furthermore, the stability issue is investigated and the sufficient condition for stability is derived.

Local Time-Step TLM Unstructured Block Meshing for Electromagnetic and Bio-Thermal Applications

Many practical problems are of multiscale nature. This issue appears when relatively small regions inside the computational domain have a large impact on the overall behavior of the structure. This requires using small mesh size in these regions of interest for adequately representing their geometrical details. Using uniform fine grid everywhere is computationally very exhaustive. The use of irregular structured grids may lead to some memory cost reduction as compared to uniform fine mesh. However, it imposes a smaller time step and yields higher dispersion as cell aspect ratio deviates from unity. The alternate approach is to use block meshing which allows fine discretization in regions with fine details and larger mesh size in quasi homogenous regions. The main disadvantage of this technique is that a global time step corresponding to the Courant–Friedrichs–Lewy (CFL) limit in the smallest cells should be used to avoid long-term instability. In this paper, we present a time-domain transmission-line matrix (TLM) algorithm for interfacing block regions that allows the use of local time steps. Hence, cubic cells can be optimally used in all regions with substantial coarseness error reduction. Applied to both electromagnetic and heat transfer TLM models, simulation experiments are presented to show the behavior and performances of the algorithm.

Modifications to Improve the Time-Domain Performance of the Van Veen Loop

The Van Veen loop is intrinsically well adapted to time-domain measurements of net magnetic dipole moment. That is, the system comes very close to preserving the shape of the time-domain waveform of the net or residual magnetic dipole moment produced by the device under test. This property makes the Van Veen Loop very useful in the characterization of magnetic field wireless power transfer systems in which short-time-scale features such as ringing in inverter and rectifier circuits are present in the extraneous magnetic field. We present a unified derivation of the frequency response of the internal coaxial structure of the Van Veen loop showing explicitly why the system intrinsically provides nearly flat frequency response and hence distortionless time response. Additionally, we present two simple modifications to the internal circuitry, which further improve the time- and frequency-domain performance of the system to the extent that it approaches having a distortionless transfer function. A physical explanation for the mechanism by which the time-domain performance is improved is provided. This argument is based on the source termination in a time-domain transmission line analysis. Finally, an alternative frequency-domain analysis based on the high-pass Kuroda transform is given, which provides significant insight into the operation of the distortionless system.

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.

A HYBRID METHOD FOR ELECTROMAGNETIC COUPLING PROBLEMS OF TRANSMISSION LINES IN CAVITY BASED ON FDTD METHOD AND TRANSMISSION LINE EQUATION

A time domain hybrid method is presented for efficiently solving the electromagnetic coupling problems of transmission lines in cavity. The proposed method is based on the finite-difference time-domain (FDTD) method and transmission line (TL) equations (FDTD-TL), which can achieve a strong synergism on the computations of field and circuit. The FDTD method with an auto mesh generation technique is employed to obtain the electric fields of transmission lines excited by an incident wave from the outside of the cavity. The electric fields are introduced into the TL equations as additional voltage sources at each time step of FDTD method. The current and voltage responses of terminal loads can be obtained by the TL equations. Two examples are presented to demonstrate the correctness of this method. The high efficiency of this hybrid method is verified by comparing the computation time with the traditional method.

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.

Modeling of electromagnetic waves propagation in four-level two-electron atomic systems governed by Pauli Exclusion Principle using the TLM method

This paper presents a computational model of electrons dynamics and gain in four-level two-electron atomic systems. These systems, submitted to an electromagnetic wave, are governed by Pauli Exclusion Principle and they are modeled using the Time-Domain Transmission Line Matrix (TLM) method with the symmetrical condensed node (SCN) with novel voltage sources. The development of the proposed model is based on the incorporation, in Maxwell's equations, of the coupled rate equations with Pauli Exclusion Principle, taking into account the dynamic pumping in the TLM formulation. The scattering matrix characterizing the SCN with the new voltage sources is provided and the numerical results are compared with those of the literature or with the theoretical ones.

Waveform Relaxation-Based Large-Scale Circuit Simulation for MOSFET and Lossy Coupled Transmission Line Circuits

In this paper, we propose a modified Waveform Relaxation algorithm to perform large-scale circuit simulation for MOSFET circuits containing lossy coupled transmission lines that have been encountered in modern circuit design community, in which a full time-domain transmission line calculation algorithm based on the Method of Characteristic is adopted. New software techniques are proposed to enhance the robustness as well as efficiency of the simulation process. All proposed methods have been implemented and executed to justify the claimed advantages.