January 29, 2014

Some Applications of Vector Fitting in the Solution of Electromagnetic Fields and Interactions

Bio

Abstract

A common engineering task is deducing an equivalent circuit that has electrical characteristics that match those of a system being analyzed. In some cases, the system may only be known through a series of hardware tests or simulations, limiting knowledge to the discretely sampled data points that have been measured. In other scenarios, there may already exist a numerical recipe for predicting the behavior of the system under analysis, but the process would be much faster if there were a theoretical equation that could be evaluated directly. In these situations, the equivalent electrical circuit, and thus circuit theory provide an efficient means for numerically analyzing the system. The key objective is then to estimate the circuit parameters that form the deterministic model of the system.

Vector Fitting (VF) is a suitable method for obtaining a circuit-based model (or macromodel) for a system. Specifically for material measurement applications, VF is shown to estimate either the permittivity or permeability of a multi-Debye material accurately, even when measured in the presence of noise and interferences caused by test setup imperfections.

A brief history and survey of methods utilizing VF for material measurement will be introduced in this work. It is shown how VF is useful for macromodeling dielectric materials after being measured with standard transmission line and freespace methods. The sources of error in both an admittance tunnel test device and stripline resonant cavity test device are identified and VF is employed for correcting these errors. Fullwave simulations are performed to model the test setup imperfections and the sources of interference they cause are further verified in actual hardware measurements. An accurate macromodel is attained as long as the signal-to-interference-ratio (SIR) in the measurement is sufficiently high such that the Debye relaxations are observable in the data.

Bio
Aditya Kalavagunta is a Technical Sales Engineer with COMSOL. He received his Ph.D. (Electrical engineering) in Semiconductor and Optical Physics from Vanderbilt University in 2009. He has over 10 years  experience in the simulation of semiconductor and optoelectronics devices. At COMSOL he has helped a variety of customers with applications including heat transfer, electromagnetics and semiconductor physics. He has been an avid COMSOL user since 2003.

Abstract
COMSOL will present a workshop on modeling Optical Nanoantennas and RF devices using their general-purpose software platform that is based on advanced numerical methods for modeling and simulating physics-based problems.

Bio 

Levent Gürel (S'87-M'92-SM'97-F'09) received the B.Sc. degree from the Middle East Technical University (METU), Ankara, Turkey, in 1986, and the M.S. and Ph.D. degrees from the University of Illinois at Urbana-Champaign (UIUC) in 1988 and 1991, respectively, all in electrical engineering.
He joined the Thomas J. Watson Research Center of the International Business Machines Corporation, Yorktown Heights, New York, in 1991, where he worked as a Research Staff Member on the electromagnetic compatibility (EMC) problems related to electronic packaging, on the use of microwave processes in the manufacturing and testing of electronic circuits, and on the development of fast solvers for interconnect modeling. Since 1994, he has been a faculty member in the Department of Electrical and Electronics Engineering of the Bilkent University, Ankara, where he is currently a Professor. He was a Visiting Associate Professor at the Center for Computational Electromagnetics (CCEM) of the UIUC for one semester in 1997. He returned to the UIUC as a Visiting Professor in 2003-2005, and as an Adjunct Professor after 2005. He founded the Computational Electromagnetics Research Center (BiLCEM) at Bilkent University in 2005, where he is serving as the Director.
Prof. Gürel's research interests include the development of fast algorithms for computational electromagnetics (CEM) and the application thereof to scattering and radiation problems involving large and complicated scatterers, antennas and radars, frequency-selective surfaces, high-speed electronic circuits, optical and imaging systems, nanostructures, and metamaterials. He is also interested in the theoretical and computational aspects of electromagnetic compatibility and interference analyses. Ground penetrating radars and other subsurface scattering applications are also among his research interests. Since 2006, his research group has been breaking several world records by solving extremely large integral-equation problems, most recently the largest involving as many as 540 million unknowns.
Among the recognitions of Prof. Gürel's accomplishments, the two prestigious awards from the Turkish Academy of Sciences (TUBA) in 2002 and the Scientific and Technical Research Council of Turkey (TUBITAK) in 2003 are the most notable.
He is a member of the USNC of the International Union of Radio Science (URSI) and the Chairman of Commission E (Electromagnetic Noise and Interference) of URSI Turkey National Committee. He served as a member of the General Assembly of the European Microwave Association (EuMA) during 2006-2008.
He is currently serving as an associate editor for Radio Science, IEEE Antennas and Wireless Propagation Letters, Journal of Electromagnetic Waves and Applications (JEMWA), and Progress in Electromagnetics Research (PIER).
Prof. Gürel served as the Chairman of the AP/MTT/ED/EMC Chapter of the IEEE Turkey Section in 2000-2003. He founded the IEEE EMC Chapter in Turkey in 2000. He served as the Cochairman of the 2003 IEEE International Symposium on Electromagnetic Compatibility. He is the organizer and General Chair of the CEM’07 and CEM’09 Computational Electromagnetics International Workshops held in 2007 and 2009, technically sponsored by IEEE AP-S.

Abstract
Solutions of extremely large matrix equations require iterative solvers. MLFMA accelerates the matrix-vector multiplications performed with every iteration. Despite the acceleration provided by MLFMA, the number of iterations should also be kept at a minimum, especially if the dimension of the matrix is in the order of millions. This is exactly where the preconditioners are needed. We have developed several novel preconditioners that can be used to accelerate the solution of various problems formulated with different types of integral equations. For example, it is well known that the electric-field integral equation (EFIE) is worse conditioned than the magnetic-field integral equation (MFIE) for conductor problems. Therefore, the preconditioners that we develop for EFIE are crucial for the solution of extremely large EFIE problems. For dielectric problems, we formulate several different types of integral equations to investigate which ones have better conditioning properties. Furthermore, we develop effective preconditioners specifically for dielectric problems. In this talk, we will review three classes of preconditioners:
1. Sparse near-field preconditioners
2. Approximate full-matrix preconditioners
3. Schur complement preconditioning for dielectric problems
We will present our efforts to devise effective preconditioners for MLFMA solutions of difficult electromagnetics problems involving both conductors and dielectrics, such as the block-diagonal preconditioner (BDP), incomplete LU (ILU) preconditioners, sparse approximate inverse (SAI) preconditioners, iterative near-field (INF) preconditioner, approximate MLFMA (AMLFMA) preconditioner, the approximate Schur preconditioner (ASP), and the iterative Schur preconditioner (ISP).