Michael Mattes

Effect of Model Accuracy on the Result of Computed Current Densities in the Simulation of Transcranial Magnetic Stimulation

In this paper, we study the effects of model complexity on the accuracy of the results in the computer simulation of transcranial magnetic stimulation (TMS). The method has been extensively used in the last decade as a noninvasive technique to excite neurons in the brain by inducing weak electric currents in the tissue and proved to be a very promising alternative for currently invasive treatments in Parkinsons and Alzheimers diseases. A detailed 3-D model of a human head has been developed by combining individual patient-based brain images and the public domain Visible Human data consisting of brain white/gray matter, CSF, skull, and muscles. The finite-element method (low-frequency Ansoft Maxwell 3D package) is used to simulate the interaction of time-varying magnetic fields with brain tissues and to compute the densities of induced currents in different areas. Models with different levels of tissue separation have been developed and tested under the same condition to investigate the effects of model complexity on the distribution of fields and induced currents inside different tissues.

Prediction of Multipactor Breakdown for Multicarrier Applications: The Quasi-Stationary Method

A new prediction algorithm for multipactor breakdown determination in multicarrier signals is presented. This new algorithm assumes a quasi-stationary (QS) model based on the nonstationary theory for single-carrier signals. It determines the worst case, i.e., the combination of signal phases that yields the lowest breakdown level per carrier, using multipactor electron growth models. It considers the secondary emission yield properties of the material and the time-varying value of the multicarrier signal envelope.

Considerations on Double Exponential-Based Cubatures for the Computation of Weakly Singular Galerkin Inner Products

Highly accurate and efficient cubatures based on the double exponential quadrature rules are presented for the computation of weakly singular integrals arising in Galerkin mixed potential integral equation formulations. Due to their unique ability to handle non-smooth kernels, the proposed integration schemes can safely replace (in a “plug-n-play” sense) the traditional Gauss-Legendre rules in the existing singularity cancellation and singularity subtraction methods. Numerical examples using RWG basis functions confirm the excellent performance of the proposed method.

Improved Computation of Propagation Losses in Waveguide Structures Using Perturbation of Boundary Conditions

In this letter, a method for the improved consideration of propagation losses in metallic waveguide structures is presented. The method relies on the perturbation of the boundary conditions on the metallic walls of the waveguides. Following this advanced technique, we are able to compute a complex modal propagation constant, thus avoiding the drawbacks of the classical power-loss method where losses associated to evanescent modes were not taken into account. A Computer Aided Design (CAD) software package based on such a modal analysis tool has been applied to predict the propagation loss effects in a Ka-Band rectangular waveguide filter.

Analysis of Multilayer Boxed Printed Circuits

This paper presents an efficient integral equation (IE) formulation based on the method of moments (MoM) for analysis of packaged printed circuits embedded within a multilayered medium. The approach uses a robust algorithm for computing the parameters of equivalent transmission lines, the analytic integration of MoM reaction terms, and the acceleration technique based on the extraction of quasi-static part. The algorithms are implemented in the simulation tool MAMBO (simulation of arbitrary multilayer boxed printed circuits). The simulation results of several packaged multilayered circuits show good agreement with the results obtained using commercial simulation tools, outperforming them in terms of computational time

Microwave Corona Breakdown Prediction in Arbitrarily-Shaped Waveguide Based Filters

This letter describes an efficient algorithm to predict the RF gas breakdown power threshold in microwave devices with complex geometries. The two necessary calculations when investigating such a phenomenon have been performed: on the one hand, the computation of the electromagnetic fields inside the structure and, on the other hand, the determination of the breakdown onset itself. The electromagnetic fields are solved by means of modal techniques and coupled to the free electron continuity equation, which is solved by the Finite Element Method. Proceeding in this way, a very simple criterion to find out whether microwave corona breakdown will take place is derived. This numerical implementation of the developed algorithms has been tested with other theoretical approaches and with experimental measurements, showing very good agreement.

A numerically stable transmission line model for multilayered Green's functions

The evaluation of a multilayered media Greens function (GF) in the spectral domain can be reduced to the analysis of a uniform transmission line (TL) circuit along the normal component (Michalski, K. and Mosig, J., IEEE Trans. Antennas and Propag., vol.45, p.508-19, 1997). In a practical situation, the computation of the GF requires many evaluations of this circuit by a transmission line model (TLM) (Michalski and Mosig, 1997; Chow, Y.L. et al., IEE Proc. Microwaves, Antennas and Propag., vol.145, p.85-91, 1998) which combines very different TL states (under cutoff, resonance, etc.). In addition, modern manufacturing techniques include components made of new materials and dimensions which commonly produces instabilities in a classical TLM analysis. The paper proposes a fast and accurate TLM algorithm to overcome this problem.

Integral Equation Modeling of Waveguide-Fed Planar Antennas

This paper presents a method for the analysis of planar multilayered waveguide-fed antennas. The method combines mixed-potential integral equations (for laterally open regions) and modal-field integral equations (for laterally closed regions) with a seamless transition between the two domains. The method has been implemented in a numerical tool, and the simulation results of two waveguide-fed planar structures are presented. The results are in good agreement with both measurements and simulations obtained with other commercial electromagnetic tools. Comparisons in terms of memory utilization and simulation time have also been performed.

Dyadic Green's Functions of a graphene layer and their efficient calculation

The development of Greens Functions (GF) for structures including graphene layers is a keypoint for the design and analysis of future graphene-based antenna components. Their properties and computational challenges are presented and discussed within this contribution. Additionally, a novel computational technique that offers high evaluation speed and good accuracy for calculating such GFs is proposed and compared to reference methods.

An Efficient Truncation Criteria for Computation of Modal Series Appearing in the Green's Function of Shielded Media

For the problem of boxed printed circuits embedded within a stratified media, efficient formulations based on the Method of Moments have been suggested which involve the computation of modal series appearing in the representation of Greens functions in this context. This paper suggests an efficient truncation criterion in computing these modal series which guarantees attaining an acceptable accuracy in final results while avoiding unnecessary computational effort. Different structures are examined in the framework of printed circuits packaged in rectangular shields to verify the validity of the suggested criterion using rectangular and triangular mesh schemes.