Transmission Line Matrix Method 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.

Quasi-3D Model for Lateral Resonances on Homogeneous BAW Resonators.

Lateral modes are responsible for the in-band spurious resonances that appear on BAW resonators, degrading the in-band filter response. In this work, a fast computational method based on the transmission line matrix (TLM) method is employed to model the lateral resonances of BAW resonators. Using the precomputed dispersion curves of Lamb waves and an equivalent characteristic impedance for the TE1 mode, a network of transmission lines is used to calculate the magnitude of field distributions on the electrodes. These characteristics are specific to the stack layer configuration. The model's implementation is based on nodal Y matrices, from which particle displacement profiles are coupled to the electric domain via piezoelectric constitutive relations. Consequently, the input impedance of the resonator is obtained. The model exhibits strong agreement with FEM simulations of FBARs and SMRs, and with measurements of several SMRs. The proposed model can provide accurate predictions of resonator input impedance, which is around 200 times faster than conventional FEM.

A New Method for Twisted Wire Crosstalk Estimation Based on GA-BP Neural Network Algorithm

Based on the research of genetic algorithm (GA) to optimize the BP neural network algorithm, this paper proposes a method for predicting twisted wire crosstalk based on the algorithm. Firstly, the equivalent circuit model of a multi-conductor transmission line is established, combined with the method of similarity transformation, the second-order differential transmission line equations are decoupled into n groups of independent two-conductor transmission line equations, and the crosstalk is finally solved. Then the mathematical model of the twisted wire is established and its structural characteristics are analyzed, and the GA-BP neural network algorithm is used to realize the mapping of the electromagnetic parameter matrix of the twisted wire and the position of the twisted wire. Finally, the mapping relationship is substituted into the transmission line equation, and the near-end crosstalk (NEXT) and the far-end crosstalk (FEXT) of an example three-core twisted wire are predicted based on the idea of cascade combined. By comparing with the transmission line matrix method (TLM), it can be seen that the method proposed in this paper is in good agreement with the crosstalk results obtained by the electromagnetic field numerical method, which verifies the effectiveness of the algorithm proposed in this paper.

A model for the prediction of the shielding effectiveness of cylindrical enclosure

This paper presents a model to predict the shielding effectiveness (SE) and resonant modes of cylindrical enclosure with apertures or dielectric substrate. In this model, the Robinson equivalent circuit model (RECM) is introduced to deal with aperture impedance, and the extended form of the Baum–Liu–Tesche equation is deduced to calculate the induced voltage in the enclosure. The electromagnetic topology (EMT) model is established to analyze the process of energy transmission inside the enclosure. The energy propagation coefficient matrix and the scattering coefficient matrix are calculated to deal with the SE results of the observation point. To quantify the efficiency of the proposed model, the calculation results are compared with the full-wave transmission line matrix method (TLM) and RECM through the Fréchet distance. The comparison results show that the accuracy of the proposed model is better over a wide frequency range compared with RECM, and meanwhile, it consumes less run time and fewer CPU resources than traditional numerical methods. The validity of the presented model is verified by TLM.

On-Line Partial Discharge Localization in Power Cables Based on Electromagnetic Time Reversal Theory - Numerical Validation

This paper presents the numerical validation of a new on-line location method of partial discharge (PD) in cables of Medium Voltage (MV) power networks based on the electromagnetic time reversal (EMTR) theory. Because PD events are a symptom of cable insulation degradation, PDs localization is a key topic for fault prevention on power networks, increasing their reliability and resilience and to guaranteeing electricity security. A description of the proposed EMTR PD location method is given and its effectiveness and accuracy are analyzed in lines with both homogeneous and inhomogeneous power cables. The accuracy of PD location methods is strongly affected by the distortion of the PD pulses during their propagation on power lines, caused mainly by the skin effect. For this reason, the accuracy of the proposed location method is analyzed using a lossy model of power networks that is able to reproduce PD signals distortion. The model used, realized using the transmission line matrix (TLM) method, is also presented here and theoretically validated.

Lightning the Electromagnetic Pulse Coupling of Airborne Secondary Radar Electronic Equipment Using Intelligent Computing

In order to analyze the lightning coupling of the airborne secondary radar electronic equipment, this study analyzes the transient electromagnetic field strength of the airborne secondary radar electronic equipment and the current density distribution on the aircraft surface when the lightning directly hits the aircraft based on the simulation technology of the transmission-line matrix method. On this basis, the simulation research of field distribution and cable coupling is further carried out. Through the simulation calculation, it can be seen that when the lightning strikes the aircraft, the current density is relatively small in the continuous parts of the upper and lower surfaces of the fuselage and the middle of the wing. In addition to the areas where the lightning current is easily attached, structural irregularities such as windows, engines, front and rear edges of wings, and outboard antennas are often affected by edge effects, and the current density is often concentrated, requiring key protection. For more sensitive electronic equipment, the cable connected to it can be considered to use an appropriate type of shielded cable to achieve the shielding effect on the electromagnetic environment.

Study of the substrate surface treatment of flexible polypyrrole-silver composite films on EMI shielding effectiveness: theoretical and experimental investigation

Abstract Conductive flexible polypyrrole-silver (PPy-Ag) composite films were prepared on Biaxial Oriented Polyethylene Terephthalate (BOPET) substrate with surfaces treated by (3-aminopropyl) trimethoxysilane (APTMS). The surface treatment was carried out to improve the adhesion, morphology, and electrical properties of the deposited film to enhance the Electromagnetic Interference Shielding Effectiveness (EMI-SE). APTMS grafting on the BOPET substrate was confirmed by X-ray Photoelectron Spectroscopy (XPS) and Atomic Force Microscopy (AFM) analyses. All structural, morphological, and electrical features of PPy-Ag raised from different AgNO3 molar ratio were investigated. The shielding effectiveness properties, experimentally determined for the synthesized PPy-Ag films were compared to those simulated analytically and numerically based on the transmission line matrix method (TLM). Both analytical and numerical models showed a good agreement with experimental measurements. The obtained results confirmed that the PPy-Ag films of 0.5 M/1 M molar ratio exhibits high EMI shielding performance of about 21 dB along with an electrical conductivity of 47 S/cm. Therefore, the treated surface flexible PPy-Ag films can be considered as potential candidate for high frequency electromagnetic interference shielding applications.

The Effect of the Ring Mains Units for On-Line Partial Discharge Location With Time Reversal in Medium Voltage Networks

The performance of a new on-line partial discharge (PD) location method based on the Electromagnetic Time Reversal (EMTR) theory and the Transmission Line Matrix (TLM) method are investigated for characterization of Medium-Voltage (MV) networks. The distortion of the PD signal during its propagation along a cable connection including network components modelled based on experimental data is reproduced in simulation and the effectiveness of the EMTR-based method to localize the PD source is analyzed. In particular, the effects of the ring main units (RMUs), that behave as a complex impedance, the variation with frequency of the MV cable impedance and the reflection patterns, due to impedance mismatches, are considered and investigated. Simulation results are given showing the performance of the EMTR method in two different networks configurations: the former one with a RMU at the end of a MV cable and the latter one with a second MV cable connected to the RMU of the first configuration having a distribution transformer at its far end. The results show that the EMTR method is able, with only a single observation point, to localize PDs also in the presence of RMU with a relative error, with respect to the line length, of approximately 1%.

Dispersion and Stability Analysis for TLM Unstructured Block Meshing

The insatiable demand to optimize and engineer new functionalities in electromagnetic devices has risen their geometrical complexity to unprecedented levels. This usually results in computationally multiscale problems with some tiny components of great importance to the overall behavior of these devices. Block meshing is a powerful technique for treating such problems. The usage of variable mesh size is adaptable for adequately representing the geometrical details without exhausting the computational resources with a uniform fine grid in the entire computational domain. In addition, block meshing allows the use of cubic cells only for which time step in maximum and velocity error is minimal in each subregion. In this article, we present a mathematical formulation for stability and dispersion analysis when using block meshing in the transmission-line matrix (TLM) method. These relations permit us to compute the maximum mesh size and time step that guarantee a tolerable level of numerical dispersion, hence minimizing the computational expenditures. Moreover, we study the case of adopting the local time step and demonstrate the origins of the instability that may appear in this case. Finally, some numerical experiments are presented to show the advantages of the proposed approach when using TLM block meshing. A similar procedure can be used for FDTD or FIT with block meshing.

A New Approach to the Modeling of Anisotropic Media with the Transmission Line Matrix Method

A reformulation of the Transmission Line Matrix (TLM) method is presented to model non-dispersive anisotropic media. Two TLM-based solutions to solve this problem can already be found in the literature, each one with an interesting feature. One can be considered a more conceptual approach, close to the TLM fundamentals, which identifies each TLM in Maxwell’s equations with a specific line. But this simplicity is achieved at the expense of an increase in the memory storage requirements of a general situation. The second existing solution is a more powerful and general formulation that avoids this increase in memory storage. However, it is based on signal processing techniques and considerably deviates from the original TLM method, which may complicate its dissemination in the scientific community. The reformulation presented in this work exploits the benefits of both methods. On the one hand, it maintains the direct and conceptual approach of the original TLM, which may help to better understand it, allowing for its future use and improvement by other authors. On the other hand, the proposal includes an optimized treatment of the signals stored at the stub lines in order to limit the requirement of memory storage to only one accumulative term per field component, as in the original TLM versions used for isotropic media. The good behavior of the proposed algorithm when applied to anisotropic media is shown by its application to different situations involving diagonal and off-diagonal tensor properties.

Simulation of pulsed ultrasonic diffraction in viscous fluids using transmission line matrix method.

Ultrasonic fields propagating in viscous media undergo changes in shape due to diffraction, attenuation, and dispersion. Until now, some implementations in the transmission line matrix (TLM) method has been developed to simulate either diffraction or attenuation but never both. In this work, the quadratic frequency dependence of the absorption coefficient as well as the dispersive effect of a viscous fluid are introduced in the TLM method. The idea is to decompose the emitted wave into its components at different frequencies using Fourier transform. Then, dispersion and attenuation effects are considered for each wave component separately before superposing them to get the required acoustic response. This is possible because each one of them is characterized by a constant absorption coefficient and propagates at a single speed. This TLM model has been applied to the diffracted ultrasonic field by a circular transducer radiating a short pulse in a viscous fluid. The obtained waveforms are interpreted in terms of plane and edge waves. A study of the influence of the most important parameters on the waveform of the detected ultrasonic pulses is performed. The numerical results obtained highlight the attenuation effect on the waves' shapes and the influence of the dispersion on their arrival times.

Electromagnetic Time Reversal Method to Locate Partial Discharges in Power Networks Using 1D TLM Modelling

This letter sets out to describe the first results of the design process that will lead to a new on-line partial discharge location method based on Electromagnetic Time Reversal theory and using the Transmission Line-Matrix method. A description of the basic steps of the method under design is given together with the modeling procedure used to describe time inverted signal propagation. Finally, the ability of the method to locate partial discharges on power cables both using two observation points and a single observation point is proved in simulation.

Hybrid model for estimating the shielding effectiveness of metallic enclosures with arbitrary apertures

Electronic enclosures often require ventilation and electromagnetic shielding, which have conflicting design requirements. This study proposes a hybrid model, based on circuit model and full-wave method, for estimating the shielding effectiveness of empty metallic enclosures with ventilation apertures of arbitrary shape or aperture arrays of arbitrary distribution on one side of the enclosures. Such perforated enclosures are split into a perforated plate and semi-enclosed waveguide that is shorted at the end. The S parameters of the perforated plate are calculated by a full-wave method and used to estimate the aperture impedance. An equivalent circuit model of a perforated enclosure is established, considering arbitrarily-positioned apertures, arbitrarily-chosen observation points, and higher-order modes. A modified plane wave decomposition technique is adopted to solve the problem of plane waves with arbitrary incident and polarisation directions. In particular, the effects of the electric field components perpendicular to the perforated plate are considered. The efficiency and accuracy of the hybrid model are evaluated by the transmission line matrix method, finite integration technique, experimental observations and existing circuit models. The hybrid model requires much less simulation time than pure full-wave methods such as the transmission line matrix method.

Impact of Modeling Simplifications on Lightning Strike Simulation for Aeroengine

With the development of electromagnetic simulation software and affordable hardware, it is allowed for us to complete simulations for EMC purposes. However, simulation demands will be immense when simulations for models with complex structures, especially aircraft components, have to be solved. Hence, it is meaningful to investigate how to minimize the computational demands. One of the solutions to reduce the simulation expense is the simplification for the simulated model. But the simplified model should be guaranteed to provide credible simulation results which do not deviate from the original model apparently. Generally, the difference between the simulation results and experimental data is estimated, or if the experimental conditions are not achieved, the comparison between the simplified model and the original one has to be analyzed, at least. This paper explores the electromagnetic simulation of a turbofan engine encountering lightning strike. With the simplifications of different components on the turbofan engine, the influences on induced currents of engine controller cables are simulated and analyzed based on the transmission-line matrix method. A combining method of components removal and geometric structure simplification is proposed to simplify the whole engine model. Simplified components include compressor, combustion chamber, turbine, and nozzle. The effects of different simplification methods are quantified, and the rationality of the simplified model is verified by simulation analysis.

Simulation and Protection of Lightning Electromagnetic Pulse in Non-Metallic Nacelle of Wind Turbine

When the nacelle of a wind turbine is struck by lightning, lightning electromagnetic pulse (LEMP) is generated inside the nacelle and consequently impacts inside electronic devices or even seriously destroys them. In order to study the LEMP inside the nacelle, this paper firstly built a full-scale model of a non-metallic nacelle. The lightning electromagnetic environment in the nacelle was simulated and analyzed by the transmission-line matrix method. Then the protective measures of applying metallic shielding mesh on the nacelle were studied, including the mesh size and material of the shielding mesh on the protective effect. The results show that LEMP in the nacelle can be effectively attenuated by metallic shielding meshes. The shielding effect is highly dependent on the conductivity of the shielding mesh material and the mesh size.

A hybrid method for shielding effectiveness estimation of a perforated enclosure against planewave excitation

ABSTRACTThis paper develops a hybrid model based on the combination of full-wave simulation method and circuit model analytic algorithm, which can predict the shielding effectiveness of a perforated rectangular enclosure irradiated by a planewave with arbitrary incident and polarization direction. In order to take the effect of the electromagnetic losses of the aperture into account, the full-wave simulation method is adopted to calculate the coupling voltage of the aperture. The circular aperture or rectangular aperture with arbitrary length–width ratio can be positioned anywhere in the front panel of the enclosure. Taking the effect of the thickness into account, we establish the equivalent circuit model of the perforated enclosure with aperture coupling voltage as an equivalent voltage source. Then, the TEmn and TMmn modes of the coupling electric field at arbitrary observation point within the enclosure are calculated based on waveguide theory. Simulation results of the hybrid model are in good agreement with those of transmission line matrix method within the frequency range of 0–3 GHz. Solution times using the hybrid model are far less than those required by pure numerical methods.

Modeling and Analysis of TSV Noise Coupling Effects on RF LC-VCO and Shielding Structures in 3D IC

In this paper, we proposed through silicon via (TSV) to active circuit noise coupling model based on 3-dimensional transmission line matrix method and analyzed the noise coupling paths. When a TSV is located near the active circuit, the noise can easily travel through various coupling paths. With the proposed model, the noise coupling coefficient between TSV and the active circuit in a 3D IC can be estimated precisely. The cross-coupled differential LC-VCO was analyzed as the target active circuit because it is one of the main components in RF applications. With the suggested model, the noise coupling effects from the various coupling paths were compared, and the most critical noise coupling path was determined. We verified the accuracy of the proposed model with full 3D EM simulation results. Additionally, we proposed shielding structures using a guard ring and the ground TSVs for suppression of the noise coupling in 3D IC. The proposed noise suppression methods can reduce the TSV noise by blocking the noise paths to the active circuit. Various shielding structures were evaluated by comparing the different phase noise of LC-VCO to analyze the shielding effectiveness.

A TLM study of bioheat transfer during freeze-thaw cryosurgery

The transmission line matrix (TLM) method is developed to efficiently solve the bioheat transfer with phase change in freeze-thaw cryoablation. This new design of three dimensional TLM model with an automatic time stepping is based on hyperbolic heat transfer model. It is able to consider many factors such as temperature-dependant thermophysical properties during phase change, blood perfusion and latent heat release/absorption. Thermal analysis of heat transfer in the cryotreated tissue is detailed; with special emphases on lethal temperature isotherms with respect to the cooling rates and duration of freeze-thaw cycle. The basic numerical model is validated through available experimental data on skeletal muscle of rabbit hind-limbs.

Transmission line matrix (TLM) modeling of self-heating in power PIN diodes

Design of high-performance electronic components with stable static and dynamic characteristics requires a study of self-heating on electrical properties. TLM method is used to model electrothermal behavior of PIN diodes. Simulation results show a non-uniform temperature distribution in the device. TLM simulation results are in good agreement with those obtained by DESSIS-ISE commercial simulator. TLM computational effort is only a fraction of that required by finite element methods. TLM method is useful in dealing with nonlinear problems since it is unconditionally stable. Modeling and analysis results show that device self heating depends very much on material physical parameters and its geometry. In addition, it has been observed that blocking and conduction times influence heat dissipation.

Efficient 3D-TLM Modeling and Simulation for the Thermal Management of Microwave AlGaN/GaN HEMT Used in High Power Amplifiers SSPA

A three-dimensional thermal simulation investigation for the thermal management of GaN-on-SiC monolithic microwave integrated circuits (MMICs) of consisting multi-fingers (HEMTs) is presented. The purpose of this work is to demonstrate the utility and efficiency of the three-dimensional Transmission Line Matrix method (3D-TLM) in a thermal analysis of high power AlGaN/GaN heterostructures single gate and multi-fingers HEMT SSPA (solid state power amplifiers). The self-heating effects induce thermal cross-talk between individual fingers in multi-finger AlGaN/GaN that affect device performance and reliability. Gate-finger temperature differences only arise after a transient state, due to the beginning of thermal crosstalk which is attributed to the finite rate of heat diffusion between gate fingers. The TLM method accounts for the real geometrical structure and the non-linear thermal conductivities of GaN and SiC in order to improve the realistic calculations accuracy heat dissipation and thermal behavior of the device. In addition, two types of heat sources located on the top of GaN layer are considered in thermal simulations: Nano-scale hotspot as a pulsed wave heat source under gate and micro-scale hotspot as a continuous wave heat source, between gate and drain. Heat diffusion however, occurs not only between individual gate fingers (inter-finger) in a multi-finger HEMT, but also within each gate finger (intra-finger). To compare results, a Micro-Raman Spectroscopy experience is conducted to obtain a detailed and accurate temperature distribution. Good agreement between the microscopic spectral measurement and TLM simulation results is observed by accepting an error less than 2.2% relative to a maximum temperature. Results show that the 3D-TLM method is suitable for understanding heat management in particular for microwave devices AlGaN/GaN HEMTs SSPA amplifier. TLM method helps to select and locates the expected hot spots and to highlight the need of thermal study pre-design in order to minimize the system-level thermal dissipation and lead therefore to higher reliability.