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Ghaffari-Miab M.,University of Tehran | Valdes F.,Nimbic Inc. | Faraji-Dana R.,University of Tehran | Michielssen E.,University of Michigan
IEEE Transactions on Antennas and Propagation | Year: 2014

A simple, highly accurate, and efficient 2D finite-difference technique for computing the direct convolution of time-domain Green's functions (TDGFs) of layered media with temporal interpolators is presented. The proposed TDGFs are incorporated into a recently developed marching-on-in-time (MOT)-based time-domain integral equation (TDIE) solver based on noncausal high-order B-Spline temporal interpolators without requiring the prediction of future unknowns. Numerical results demonstrating the applicability of the technique to the analysis of various microwave structures are presented. © 2014 IEEE.

Valdes F.,University of Michigan | Valdes F.,Nimbic Inc. | Andriulli F.P.,Telecom Bretagne | Bagci H.,King Abdullah University of Science and Technology | Michielssen E.,University of Michigan
IEEE Transactions on Antennas and Propagation | Year: 2013

Single-source time-domain electric-and magnetic-field integral equations for analyzing scattering from homogeneous penetrable objects are presented. Their temporal discretization is effected by using shifted piecewise polynomial temporal basis functions and a collocation testing procedure, thus allowing for a marching-on-in-time (MOT) solution scheme. Unlike dual-source formulations, single-source equations involve space-time domain operator products, for which spatial discretization techniques developed for standalone operators do not apply. Here, the spatial discretization of the single-source time-domain integral equations is achieved by using the high-order divergence-conforming basis functions developed by Graglia alongside the high-order divergence-and quasi curl-conforming (DQCC) basis functions of Valdés The combination of these two sets allows for a well-conditioned mapping from div-to curl-conforming function spaces that fully respects the space-mapping properties of the space-time operators involved. Numerical results corroborate the fact that the proposed procedure guarantees accuracy and stability of the MOT scheme. © 2012 IEEE.

Cui W.,University of Washington | Chakraborty S.,Nimbic Inc. | Jandhyala V.,University of Washington
IEEE Antennas and Propagation Society, AP-S International Symposium (Digest) | Year: 2012

Although electromagnetic (EM) simulators are able to simulate systems and devices with a larger number of design parameters, the next challenge is to use such simulators in order to provide parametric simulation and optimization in a high-dimensional design space, while minimizing the number of calls to the EM simulator. This paper presents an optimization approach which can significantly reduce the number of calls to the EM simulator through a case study of a high-dimensional parametric system which contains 127 design factors. Unlike traditional simulated annealing (SA) and particle swarm optimization (PSO) which randomly select values to create all of the combinations of the variables, the proposed optimization approach uses Taguchi's method which employs large orthogonal arrays (OAs) to create a test set that has an even distribution of all combinations. Therefore, it is more efficient, concise and the global optimum can be guaranteed. To further shorten the simulation time, sensitivity analysis is first conducted and unveils that the top 20 most volatile design factors attribute to 80% of the performance variation. Therefore, the 20 parameters are optimized using a large OA of 361 rows and 20 columns. The results show that the proposed optimization approach is capable of optimizing high-dimensional parametric systems swiftly and may potentially have a wide range of applications. © 2012 IEEE.

Nimbic Inc. | Date: 2013-04-08


Valdes F.,Nimbic Inc. | Ghaffari-Miab M.,University of Tehran | Andriulli F.P.,Telecom Bretagne | Cools K.,University of Nottingham | Michielssen,University of Michigan
IEEE Transactions on Antennas and Propagation | Year: 2013

Two high-order accurate Calderón preconditioned time domain electric field integral equation (TDEFIE) solvers are presented. In contrast to existing Calderón preconditioned time domain solvers, the proposed preconditioner allows for high-order surface representations and current expansions by using a novel set of fully-localized high-order div-and quasi curl-conforming (DQCC) basis functions. Numerical results demonstrate that the linear systems of equations obtained using the proposed basis functions converge rapidly, regardless of the mesh density and of the order of the current expansion. © 1963-2012 IEEE.

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