Vladimir Okhmatovski

A Three-Dimensional Precorrected FFT Algorithm for Fast Method of Moments Solutions of the Mixed-Potential Integral Equation in Layered Media

A three-dimensional pre-corrected fast Fourier transform (PFFT) algorithm for the rapid solution of the full-dyadic Michalski-Zhengs mixed potential integral equation is presented. The integral equation is discretized with the Rao-Wilton-Glisson (RWG) method of moments. Handling the method of moments interactions with the dyadic kernel is simplified via representation of the RWG functions in terms of barycentric shape functions. The proposed three-dimensional precorrected FFT method distributes two-dimensional FFT grids nonuniformly along the direction of stratification according to conductor locations within the layers. For P two-dimensional FFT grids each with an average of Np associated triangular elements the method exhibits O(P 2 Np logNp) computational complexity and O(P Np) memory usage. The low-frequency breakdown of the integral equation is eliminated via loop-tree decomposition. A unique combination of O(N logN) computational complexity, fully three-dimensional boundary-element modeling in layered substrates, and full-wave modeling from dc to multi-gigahertz frequencies makes the algorithm particularly useful for characterizing large interconnect networks embedded in multilayered substrates. The method is implemented as the electromagnetic solver in Cadences Virtuoso RF Designer software.

Low-Frequency MLFMA on Graphics Processors

A parallelization of the low-frequency multilevel fast multipole algorithm (MLFMA) for graphics processing units (GPUs) is presented. The implementation exhibits speedups between 10 and 30 compared to a serial CPU implementation of the algorithm. The error of the MLFMA on the GPU is controllable down to machine precision. Under the typical method-of-moments (MoM) error requirement of three correct digits, modern GPUs are shown to handle problems with up to 7.5 million degrees of freedom in dense matrix approximation.

New Single-Source Surface Integral Equations for Scattering on Penetrable Cylinders and Current Flow Modeling in 2-D Conductors

The traditional volume electric field integral equation (IE) used for solution of full-wave scattering problems on penetrable scatterers of arbitrary cross section and its magnetostatic counterpart commonly utilized for the resistance and inductance extraction problem are reduced to a novel derivative-free single-source surface IE. The reduction of volume to surface IE is based on representation of the electric field in the cylinder cross section in the form of a single-layer ansatz. Substitution of such surface based electric field representation into the volume IE reduces it to a surface IE with respect to the unknown surface current density. Since the new surface IE enforces exactly the field continuity at the material interfaces, the radiation condition as well as underlying Helmholtz equations both inside and outside the penetrable cylinder, it is rigorously equivalent to the solution of Maxwells equations. The method of moments discretization of the new IE is shown to produce an error-controllable field approximation. Due to the presence of a product of surface-to-volume and volume-to-surface integral operators, the discretization of the novel surface-volume-surface IE requires both surface and volume meshes.

A Novel Skin-Effect Based Surface Impedance Formulation for Broadband Modeling of 3-D Interconnects With Electric Field Integral Equation

The problem of interconnect modeling embedded in multilayered substrate is initially formulated in terms of the volume integral equation (IE) with respect to 3-D conduction current density. One out of three degrees of freedom in volumetric current variation is then eliminated by approximating the current behavior over the coordinate normal to the conductor surface according to the skin-effect. The remaining two degrees of freedom in the volumetric current variation constitute the unknown current distribution on the conductor surface for which a governing surface electric field integral equation is obtained directly from the volume IE via restriction of the volumetric operators range to the conductor surface. The resultant surface IE features a global to the conductor cross section surface impedance operator, which is shown to approximate the relationship between tangential electric and magnetic field components on the conductor surface. The proposed novel surface IE featuring multilayered media dyadic Greens function is amenable to various discretization schemes including the Rao-Wilton-Glisson method of moments. In this paper the latter is implemented by casting the scattered field operator into Michalski-Zhengs mixed-potential form in conjunction with enforcement of global relationships between the basis and testing functions in conductor cross sections according to the surface impedance operator. Numerical comparisons to alternative conductor loss models show that the method achieves volumetric solution accuracy within the framework of a boundary-element formulation.

On the Equivalence of RWG Method of Moments and the Locally Corrected Nyström Method for Solving the Electric Field Integral Equation

The first-order locally corrected Nyström (LCN) method for the electric field integral equation is modified to ensure continuity of the current between triangular elements of the mesh. Rao-Wilton-Glisson (RWG) basis functions are used to create a conversion matrix from the LCN representation of the current to the RWG method-of-moments (MoM) representation of the current in order to enforce continuity of current between adjacent triangular flat patches. Benefits of the method are two fold: first, it provides 4 × reduction in degrees of freedom and removes unacceptable error levels in first-order LCN implementations, second, the method can be viewed as a point-based discretization of the RWG MoM offering improved efficiency in its acceleration with the fast multipole algorithm.

Barnes-Hut Accelerated Capacitance Extraction Via Locally Corrected Nyström Discretization

The Barnes-Hut algorithm is applied to accelerate the locally corrected Nystrom method for implementation of a kernel-independent O(N log N) capacitance extractor

Error Controllable Solutions of Large-Scale Problems in Electromagnetics: MLFMA-Accelerated Locally Corrected Nyström Solutions of CFIE in 3D [Open Problems in CEM]

This work provides an overview of a parallel, high-order, error-controllable framework for solving large-scale scattering problems in electromagnetics, as well as open problems pertinent to such solutions. The method is based on the higher-order locally corrected Nystrom (LCN) discretization of the combined-field integral equation (CFIE), accelerated with the error-controlled Multi-Level Fast Multipole Algorithm (MLFMA). Mechanisms for controlling the accuracy of calculations are discussed, including geometric representation, stages of the locally corrected Nystrom method, and the MLFMA. Also presented are the key attributes of parallelization for the developed numerical framework. Numerical results validate the proposed numerical scheme by demonstrating higher-order error convergence for smooth scatterers. For the problem of scattering from a sphere, the developed numerical solution is shown to have the ability to produce a solution with a maximum relative error of the order 10-9. Open-ended problems, such as treatment of general scatterers with geometric singularities, construction of well-conditioned operators, and current challenges in development of fast iterative and direct algorithms, are also discussed.

The Barnes–Hut Hierarchical Center-of-Charge Approximation for Fast Capacitance Extraction in Multilayered Media

The Barnes-Hut algorithm is widely used in astrophysics for solving large gravitational N -body problems using O(N logN) time and memory. This reduction in computational cost is achieved by a hierarchical application of the classical center-of-mass approximation. As both gravitational and electrostatic potentials are subject to a 1/R dependence, the Barnes-Hut algorithm is also a natural choice for rapidly evaluating interactions between charged particles. The contribution of this paper is an extension of the Barnes-Hut hierarchical clustering to the acceleration of charge interactions in stratified media. We derive and validate a closed-form expression for the shift of the center-of-charge location induced by the physical inhomogeneities and show that proper positioning of the center-of-charge ensures O(1/R 3) error decay in the field approximation. Hierarchical applications of the proposed clustering approximation is demonstrated for the construction of O(N logN) method-of-moment based capacitance extractors.

Full-Periphery Surface Impedance for Skin-Effect Approximation in Electric Field Integral Equation

A new surface impedance model for RL-extraction in lossy two-dimensional (2-D) interconnects of rectangular cross section is presented. The model is derived directly from the volumetric electric field integral equation under the approximation of the unknown volumetric current density as a product of the exponential factor describing the skin-effect and the unknown surface current density on the conductors periphery. By proper accounting for the coupling between the boundary elements situated on the top and bottom surfaces of conductor with the elements located on the side-walls, the model maintains accuracy from dc to multi-GHz frequencies as well as for conductors with both large and small thickness/width ratios.

The Unified-FFT Algorithm for Fast Electromagnetic Analysis of Planar Integrated Circuits Printed on Layered Media Inside a Rectangular Enclosure

The unified fast Fourier transform (UFFT) methodology is proposed for fast method of moments analysis of dense integrated circuits embedded in layered media inside perfectly electric conducting or perfectly magnetic conducting enclosures of rectangular cross section. The pre-corrected fast Fourier transform (FFT) method is modified to handle the dyadic Greens function (DGF) of shielded layered media through factorization of the DGF into four convolution/correlation terms enabling fast matrix solve operations (MSOs). Calculation of the impedance matrix elements in the form of an infinite series of waveguide modes is cast into the form of a 2-D discrete Fourier transform allowing for fast FFT-accelerated matrix fill operations (MFOs). Fast FFT-enhanced MSOs and MFOs used in conjunction form the UFFT method. The computational complexity and memory requirements for the proposed UFFT solver scale as O(NlogN) and O(N), respectively, where N is the number of unknowns in the discrete approximation of the governing integral equation. New criteria specific to shielded circuits for the projection of the current expansion functions on a uniform FFT grid are developed. The accuracy and efficiency of the solver is demonstrated through its application to multiple examples of full-wave analysis of large planar circuits.