Finite Integration Algorithm Research Articles

A Fast and Efficient Method for the Composite Scattering of a Coated Object Above 3D Random Rough Surfaces

This paper presents a fast and efficient method that combines physical optics with physical optics to solve the composite scattering problem of a coated object above 3-D random rough surfaces. The object coated with lossy electric or magnetic radar absorbing materials is modeled as a stratified structure, and 3-D random rough surfaces are generated using Monte Carlo method with Gaussian spectrum. The proposed method utilizes fast and efficient physical optics as a solution for the coated object and the underlying random rough surface. Then a reradiation physical optics method based on Huyghens’ principle is used as a solution for coupling scattering between the coated object and the underlying rough surface. The proposed method is numerically validated by comparing it with the commercial software FEKO and a multihybrid Kirchhoff approximation with the hybrid finite element-boundary integral algorithm. Runtime and memory consumption are also compared. Our method is found to reduce considerable time and memory while maintaining sufficient accuracy. The difference scattering radar cross section of a coated sphere above a 3-D perfectly electric conductor rough surface is numerically simulated. Furthermore, the dependence of difference scattering characteristic on the object coating parameters and the underlying rough surface parameters under different polarizations is discussed.

The Protection and Electromagnetic Interference between Tracking Radar and Marine Radar Based on Ship

本文主要针对测量船X频段和S频段测量雷达与导航雷达同频段设备间的电磁干扰问题进行了仿真研究，采用基于时域有限积分的有限元算法和基于MLFMM、高频物理光学和弹跳射线的通用快速电磁计算算法，对测量船X频段和S频段测量雷达的远场辐射方向图、测量雷达与导航雷达耦合度计算等方面进行了仿真计算，并结合设备实测对仿真结果进行了验证。根据仿真结果和实测数据给出了测量雷达的防护措施建议。 In this paper, the electromagnetic interferences between tracking radar and marine radar at X-band and S-band are investigated. Far-field radiation patterns of the tracking radars and the coupling between them and the marine radar are calculated and simulated by adopting time-do- main finite element integration algorithm and a general fast electromagnetics algorithm based on MLFMM (multilevel fast multipole), high-frequency physical optics and shooting-and-bouncing- rays method. The results are verified by test and protection measures are suggested.

Element-wise algorithm for modeling ductile fracture with the Rousselier yield function

Within the theme of ductile fracture in metals, we propose an algorithm for FEM-based computational fracture based on edge rotations and smoothing of complementarity conditions. Rotation axes are the crack front nodes in surface discretizations and each rotated edge affects the position of only one or two nodes. Modified edge positions correspond to the predicted crack path. To represent softening, porous plasticity in the form of the Rousselier yield function is used. The finite strain integration algorithm makes use of a consistent updated Lagrangian formulation which makes use of polar decomposition between each increment. Constitutive updating is based on the implicit integration of a regularized non-smooth problem. The proposed alternative is advantageous when compared with enriched elements that can be significantly different than classical FEM elements and still pose challenges for ductile fracture or large amplitude sliding. For history-dependent materials, there are still some transfer of relevant quantities between meshes. However, diffusion of results is more limited than with tip or full remeshing. To illustrate the advantages of our approach, fracture examples making use of the Rousselier yield function are presented. The Ma-Sutton crack path criterion is employed. Traditional fracture benchmarks and newly proposed verification tests are solved. These were found to be very good in terms of crack path and load/displacement accuracy.

Hybrid finite element-boundary integral algorithm to solve the problem of scattering from a finite array of cavities with multilayer stratified dielectric coating

This work presents a hybrid finite element-boundary integral algorithm to solve the problem of scattering from a finite array of two-dimensional cavities engraved in a perfectly electric conducting screen covered with multilayer stratified dielectric coating. The solution region is divided into interior regions containing the cavities and the region exterior to the cavities. The finite element formulation is applied only inside the interior regions to derive a linear system of equations associated with unknown field values. Using a two-boundary formulation, the surface integral equation employing a closed-form multilayer Green's function in the spatial domain is applied at the opening of the cavities as a boundary constraint to truncate the solution region. The closed-form Green's function in the spatial domain for multilayer planar coating is expressed in terms of complex images using the generalized pencil-of-function method in conjunction with a two-level sampling approach. Placing the truncation boundary at the opening of the cavities and inside the dielectric coating results in a highly efficient solution in terms of computational resources, which makes the algorithm well suited for optimization problems involving scattering from grating surfaces. The near fields are generated for array of cavities with different dimensions and inhomogeneous fillings covered with dielectric layers.

Simulation of high-frequency modes and their effect on insulator breakdown in the pulse line ion accelerator

The pulse line ion accelerator (PLIA) produces a traveling electromagnetic (EM) wave by applying a voltage pulse to one end of a helix that accelerates and axially confines a heavy-ion beam pulse. An anomalous flashover phenomenon has been observed on the vacuum-insulator surface that limits the amplitude of the accelerating field. It has been suspected that a small component of high-frequency modes in the input pulse may be the cause of the breakdown. Simulation using MAFIA (MAxwell's equations by Finite Integration Algorithm) was conducted to investigate the fields on the insulator surface. A scaling law was proposed to reduce substantially the computational time in simulation. It is based on the hypothesis that the pattern of EM field for a given wavelength is independent of the wire spacing as long as the wavelength is much longer than the inter-wire spacing and the termination resistors are adjusted to maintain impedance matching. On the basis of these numerical simulations, we conclude that high-frequency modes, even at very low amplitudes, may indeed lead to the observed insulator flashover.

Analysis of a Multibeam Vircator Configuration for Efficiency Enhancement

A new scheme of efficiency enhancement in virtual cathode oscillator (vircator) is proposed by introducing a multibeam concept. The phenomenon of radiofrequency interaction in both the single and multibeam configurations was analyzed using particle-in-cell modeling in Maxwellpsilas equations by the finite integration algorithm. Appreciable efficiency enhancement was observed for the multibeam configuration due to enhancement in the bunching process attributable to the formation of multiple virtual cathodes and multiple reflexing of electrons. Simulated results of (5 beams, 10 beams) multibeam configurations and single-beam configurations are compared for equal amounts of current, emitting area, and beam voltage in all three configurations.

A massively parallel particle-in-cell code for the simulation of field-emitter based electron sources

For the realistic simulation of electron sources using field emitter arrays, the sub-micron resolution required for the emitters leads to simulation models not suitable for current serial codes. Thus, a parallel high-performance 3D Particle-In-Cell code, called Capone, has been implemented in C++ using the POOMA II framework on the Linux platform. Sophisticated C++ expression templates techniques deliver Fortran performance combined with high-level programming and development comfort. For the computation of external fields, matching parallel field solvers are in development with the electrostatic one being completed. The Maxwell field solver is based on the Finite Integration Algorithm on a non-uniform rectilinear grid. Anisotropic ε and μ constants and perfect electric/magnetic materials stored in triangulated grid cells are supported as well as open, electric and magnetic boundary conditions. Self-consistent macro-particle pushing is accomplished by integrating the classical relativistic equations of motion in combination with charge-conserving current scattering onto the computational grid. Parallelization is performed by partitioning the calculation domain into patches associated to individual processors. Fields are statically distributed while Particles are concurrently distributed to processors according to their position to allow fast local interpolation.

Precise integral algorithm based solution for transient inverse heat conduction problems with multi-variables

By modeling direct transient heat conduction problems via finite element method (FEM) and precise integral algorithm, a new approach is presented to solve transient inverse heat conduction problems with multi-variables. Firstly, the spatial space and temporal domain are discretized by FEM and precise integral algorithm respectively. Then, the high accuracy semi-analytical solution of direct problem can be got. Finally, based on the solution, the computing model of inverse problem and expression of sensitivity analysis are established. Single variable and variables combined identifications including thermal parameters, boundary conditions and source-related termsetc. are given to validate the approach proposed in 1-D and 2-D cases. The effects of noise data and initial guess on the results are investigated. The numerical examples show the effectiveness of this approach.

A Cartesian-Cylindrical Hybrid Fd-Td Analysis of Composite Microwave Applicator Structures

Cylindrical microwave applicators have been proven to be advantageous in industrial microwave heating applications where heating uniformity is highly desired. When the traditional Cartesian Finite Difference Time Domain (FD-TD) approach is used to analyze a cylindrical structure, staircase boundaries are introduced during the discretization of the outer cylindrical boundaries of the applicator. Computational errors, computational time, and computer memory requirements are increased accordingly. In this paper, a new formulation employing a hybrid Cartesian-cylindrical FD-TD scheme is developed to analyze the performance of cylindrical applicators with rectangular waveguide feeding structures. Numerical results show excellent agreement with those calculated by the traditional staircase FD-TD model with very fine meshes and the commercial software package MAFIA (MAxwell equation solution by Finite Integration Algorithm). Compared with the staircase FD-TD model, the hybrid FD-TD model achieved better computational accuracy with much less computational time and computer memory.

Physical–technical basis of invasive microwave hyperthermia—Simulation, construction, and characterization of miniaturized interstitial microwave antennas for the treatment of malignant tumors (in German)

The electromagnetic field of dipole antennas for interstitial microwave hyperthermia was investigated using the field evaluation program MAFIA (MAxwell's equations using the Finite Integration Algorithm). The numerical method was applied to clinically used applicators running at ISM frequencies: 434 MHz and 915 MHz. The method was also used for improvement and optimization of more sophisticated applicators, e.g., those in a triaxial technique having a λ/4 choke section to reduce RF currents on the outer coaxial conductor. Simulations of the frequency dependent impedance match, the electrical field and the specific absorption rate (SAR) distribution of different applicators immersed in a muscle phantom were compared with measurements. Moreover, arrays of two and four applicators, various surrounding tissue properties (bone, fat, tissue), catheter types, and semi‐rigid coaxial cable materials were investigated. Compared with coaxial antennas only triaxial antenna designs produce a homogeneous, symmetric energy deposition pattern below the choke section at all insertion depths. Only triaxial dipole antennas can be designed to run at a specific frequency while the reflection factor ( parameter) does not change with insertion depth. The field simulation allowed studying realistic effects at all discontinuities of the rotational symmetric applicator‐catheter‐tissue system and gave a better understanding of heating phenomena occurring during interstitial hyperthermia treatment.

Computer-Aided Design of Microwave Plasma Sources: Potential and Applications

The electrical behavior of SLAN (slot antenna) plasma sources is analysed with the Maxwell equations finite integration algorithm (MAFIA). The influence of the source components and their dimensions on resonance frequencies and power coupling of all eigenmodes up to 3 GHz is studied. Resonances close to the excitation frequency may adversely influence the power absorption in the source. By shifting the frequencies of these resonances the source performance can be optimized. As an example the azimuthal plasma homogeneity of a SLAN microwave plasma source is improved by a proper design. To be more realistic the plasma has been introduced into the simulation as a lossy dielectric. Although this is a crude approach, the results yield useful insights into the local power absorption.

Field simulation of dipole antennas for interstitial microwave hyperthermia

The electromagnetic field of dipole antennas for interstitial microwave hyperthermia is investigated using a finite integration algorithm program. The numerical method is applied to conventional, clinically used applicators and is also used for the improvement and optimization of sophisticated applicators, e.g., in a triaxial technique. Simulations of the frequency dependent impedance match, the E-field and the specific absorption rate (SAR) distribution of different applicators immersed in a muscle phantom are presented and compared with measurements. Moreover, results for arrays of two and four applicators are given. The field simulation allows one to study the effects at the various discontinuities of the applicator-catheter-tissue system and gives a better understanding of known phenomena.

Comparative Numerical Study of Antennas for Hand Held Mobile Telephones

The Finite Integration Algorithm (FIA) is used for the analysis of monopole and Radiation-Coupled Dual-L (RCDLA) antennas for personal communications at the GSM frequency of 900 MHz. It is found that 44% of the power delivered to the monopole is absorbed by the user, compared to only 20% for the RCDLA. The maximal local Specific Absorbtion Rate SAR inside the head for a transmitted power of 1 W for the monopole and RCDLA is 2 mW/cm 3 and 0.9 mW/cm 3 respectively. It is also found that the RCDLA has a bandwidth of only 30 MHz, and that the user's hand has a strong influence on its resonant frequency. The monopole, on the other hand has a large bandwidth, and its impedance is not so sensitive to the presence of the user.

Status and future of the 3D MAFIA group of codes

An overview is presented of the MAFIA group of fully three-dimensional computer codes for solving Maxwell's equations by the finite integration algorithm. The codes are well established. Extensive comparisons with measurements have demonstrated the accuracy of the computations. The latest additions include a static solver that calculates 3-D magnetostatic and electrostatic field and a self-consistent version of TBCI that solves the field equations and the equations of motion in parallel. Work on new eddy-current modules has started, which will allow treatment of laminated and/or solid iron cores by low-frequency current. Based on experience with the present releases 1 and 2, a complete revision of the whole user interface and data structure has begun that will be included in release 3. >

Use of a multigrid solver in the MAFIA module S3 for electro- and magnetostatic problems

The MAFIA codes are fully 3-D codes for solving Maxwell's equations by the finite integration algorithm. SOR schemes are a well tested standard for finite-difference (FD) methods in electromagnetic calculations. Since for 3-D problems requiring high accuracy, the necessary fine meshes give a large number of unknowns and so SOR becomes very slow, therefore a multigrid (MG) scheme, a technique developed for the solution of problems with many unknowns, has been incorporated into the S3 code. The performance and accuracy of the new scheme has been compared to that of SOR. The tests demonstrated that multigrid is much faster and more accurate than SOR. It also converges for matrices where SOR fails.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>