G. Mur

Bio: G. Mur is an academic researcher from Delft University of Technology. The author has contributed to research in topics: Finite element method & Electromagnetic field. The author has an hindex of 14, co-authored 21 publications receiving 3092 citations.

Absorbing Boundary Conditions for the Finite-Difference Approximation of the Time-Domain Electromagnetic-Field Equations

Abstract: When time-domain electromagnetic-field equations are solved using finite-difference techniques in unbounded space, there must be a method limiting the domain in which the field is computed. This is achieved by truncating the mesh and using absorbing boundary conditions at its artificial boundaries to simulate the unbounded surroundings. This paper presents highly absorbing boundary conditions for electromagnetic-field equations that can be used for both two-and three-dimensional configurations. Numerical results are given that clearly exhibit the accuracy and limits of applicability of highly absorbing boundary conditions. A simplified, but equally accurate, absorbing condition is derived for two- dimensional time-domain electromagnetic-field problems.

A finite-element method for computing three-dimensional electromagnetic fields in inhomogeneous media

Abstract: A finite-element method is presented that is particularly suited for the computer modeling of three-dimensional electromagnetic fields in inhomogeneous media. It employs a new type of linear vectorial expansion functions. Across an interface where the constitutive coefficients are discontinuous, they have the following properties: (1) the continuity of the tangential components of the electric and the magnetic field strengths is exactly preserved, (2) the normal component of the electric and the magnetic field strengths are allowed to jump and (3) the electric and the magnetic fluxes are continuous within the pertaining degree of approximation. The system of equations from which the expansion coefficients are obtained is generated by applying a Galerkin-type weighted-residual method. Numerical experiments are described that illustrate the efficiency of our elements, and the computational costs of the method.

Edge elements, their advantages and their disadvantages

Abstract: In finite-element methods for solving electromagnetic field problems, the use of edge elements has become very popular. In fact, edge elements are often said to be a cure for many difficulties that are encountered and they are claimed to yield accurate results. In the present paper we analyse these claims for tetrahedral elements. In particular we compare two different types of "linear" edge elements and the classical linear nodal element. Comparisons for higher-order elements and elements defined on other elementary subdomains, for instance on hexahedra, run along the same lines and yield similar conclusions. >

Computation of the Input Impedances of a Catheter for Cardiac Volumetry

Abstract: Electrical impedances between the electrodes of a catheter in a spheroidal model of the left ventricle are calculated analytically. The fields in the configuration are computed using eigen function expansions of the Laplace equation. For certain realistic combinations of specific conductances of the blood and the myocardium, numerical results are given. These results show the dependence of the impedances on the volume of the ventricle while keeping the length of the major axis of the ventricle constant. Also, the accuracy of the model and the dependence of the total conductance of the ventricle on its shape, and on the conductivity of the tissues surrounding it, are discussed. The theoretical results are compared against the experimental values of conductances, measured post mortem in a canine heart, for different volumes.

Total-field absorbing boundary conditions for the time-domain electromagnetic field equations

Abstract: A method is described for generating absorbing boundary conditions (ABCs) that can be applied to the total fields rather than the usual scattered fields. As compared with the traditional use of ABCs for total-field formulations, this method has the advantages that it does not require the introduction of a mathematical connection surface between the total-field region and the scattered-field region; the total field is computed in the entire domain of computation. The incident field is accounted for by augmenting the ABC used. The resulting code is much simpler than one using ABCs for scattered fields together with a connection surface and the numerical results are much more easily interpreted since they consist of total fields only.

The finite element method in electromagnetics

Abstract: This Key Note presents a summary of the development of the Finite Element Method in the field of Electromagnet ic Engineering, together with a description of several contributions of the authors to the Finite Element Method and its application to the solution of electromagnetic problems. First, a self-adaptive mesh scheme is presented in the context of the quasi-static and full-wave analysis of general anisotropic multiconductor arbitrary shaped waveguiding structures. A comparison between two a posteriori error estimates is done. The first one is based on the complete residual of the differential equations defining the problem. The second one is based on a recovery or smoothing technique of the electromagnetic field. Next, an implementation of the first family of Nedelec's curl-conforming elements done by the authors is outlined. Its features are highlighted and compared with other curl-conforming elements. A presentation of an iterative procedure using a numerically exact radiation condition for the analysis of open (scattering and radiation) problems follows. Other contributions of the authors, like the use of wavelet like basis functions and an implementation of a Time Domain Finite Element Method in the context of two-dimensional scattering problems are only mentioned due to the lack of space.

A 3D perfectly matched medium from modified maxwell's equations with stretched coordinates

Abstract: A modified set of Maxwell's equations is presented that includes complex coordinate stretching along the three Cartesian coordinates. The added degrees of freedom in the modified Maxwell's equations allow the specification of absorbing boundaries with zero reflection at all angles of incidence and all frequencies. The modified equations are also related to the perfectly matched layer that was presented recently for 2D wave propagation. Absorbing-material boundary conditions are of particular interest for finite-difference time-domain (FDTD) computations on a single-instruction multiple-data (SIMD) massively parallel supercomputer. A 3D FDTD algorithm has been developed on a connection machine CM-5 based on the modified Maxwell's equations and simulation results are presented to validate the approach. © 1994 John Wiley & Sons, Inc.

Trapping and emission of photons by a single defect in a photonic bandgap structure

Abstract: By introducing artificial defects and/or light-emitters into photonic bandgap structures1,2, it should be possible to manipulate photons. For example, it has been predicted2 that strong localization (or trapping) of photons should occur in structures with single defects, and that the propagation3,4 of photons should be controllable using arrays of defects. But there has been little experimental progress in this regard, with the exception of a laser5 based on a single-defect photonic crystal. Here we demonstrate photon trapping by a single defect that has been created artificially inside a two-dimensional photonic bandgap structure. Photons propagating through a linear waveguide are trapped by the defect, which then emits them to free space. We envisage that this phenomenon may be used in ultra-small optical devices whose function is to selectively drop (or add) photons with various energies from (or to) optical communication traffic. More generally, our work should facilitate the development of all-optical circuits incorporating photonic bandgap waveguides and resonators.

Continuous measurement of left ventricular volume in animals and humans by conductance catheter.

Abstract: An eight-electrode conductance catheter previously developed by us and used to determine stroke volume in dogs was applied in human beings and dogs to measure absolute left ventricular volume quantitatively. For calibration we developed the formula V(t) = (1/alpha)(L2/sigma b)G(t) - Vc, where V(t) is time-varying left ventricular volume, alpha is a dimensionless constant, L is the electrode separation, sigma b is the conductivity of blood obtained by a sampling cuvette, and G(t) is the measured conductance within the left ventricular cavity. Vc is a correction term caused by the parallel conductance of structures surrounding the cavity and is measured in two ways. The first method, applicable in the anesthetized animal, consists of temporary reduction of volume to zero by suction. The second method uses a transient change in sigma b by injection of a small bolus of hypertonic saline (dogs) or 10 ml of cold glucose (humans) into the pulmonary artery. The validity of the formula was previously established for the isolated postmortem canine heart. The predicted linearity, slope constant alpha, and accuracy of Vc for the left ventricle in vivo were investigated by comparing the conductance volume data with results from independent methods: electromagnetic blood flow measurement for stroke volume and indicator dilution technique for ejection fraction (dogs), thermal dilution for cardiac output (12 patients), and single-plane cineventriculography for V(t) (five patients). In all comparisons, linear regression showed high correlation (from r = .82 [n = 46] to r = .988 [n = 20]) while alpha, with one exception, ranged from 0.75 to 1.07 and the error in Vc ranged from 0.5% to 16.5% (mean 7%). After positioning of the catheter, no arrhythmias were observed. It is concluded that the conductance catheter provides a reliable and simple method to measure left ventricular volume, giving an on-line, time-varying signal that is easily calibrated. Together with left ventricular pressure obtained through the catheter lumen, the instrument may be used for instantaneous display of pressure-volume loops to facilitate assessment of left ventricular pump performance.