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Graduate Exam Abstract


Nada Sekeljic

Ph.D. Final

March 27, 2015, 9:00 am - 11:00 am

ECE Conference room, C101B

TRANSIENT ANALYSIS OF CLOSED- AND OPEN-REGION ELECTROMAGNETIC PROBLEMS USING HIGHER ORDER FINITE ELEMENT METHOD AND METHOD OF MOMENTS IN THE TIME DOMAIN


Abstract: The principal objective of this dissertation is to develop computational electromagnetic (CEM) methodology and tools for modeling of closed (waveguide and cavity based) and open (radiation and scattering) electromagnetic structures in the time domain (TD), employing two CEM approaches. The first method is a novel higher order and large-domain Galerkin finite element method (FEM) for transient analysis of multiport microwave waveguide devices with arbitrary metallic and dielectric discontinuities. It is based on geometrical modeling using Lagrange interpolation generalized hexahedral elements, spatial field expansion in terms of hierarchical curl-conforming polynomial vector basis functions, time-stepping with an implicit unconditionally stable finite difference scheme using the Newmark-beta method, and mesh truncation introducing the waveguide port boundary condition. The second method is a novel spatially large- domain and temporally entire-domain method of moments (MoM) proposed for surface integral equation (SIE) modeling of 3-D conducting scatterers in the TD. The method uses higher order curved Lagrange interpolation generalized quadrilateral geometrical elements, higher order spatial current expansions based on hierarchical divergence-conforming polynomial vector basis functions, and temporal current modeling by means of orthogonal weighted associated Laguerre basis functions. It implements full temporal and spatial Galerkin testing and marching-on-in- degree (MOD) scheme for an iterative solution of the final system of spatially and temporally discretized MoM-TD equations. Numerical examples of waveguides and scatterers, modeled using flat and curved large elements in conjunction with field/current expansions of orders from 2 to 9, demonstrate excellent accuracy, efficiency, convergence, and versatility of the proposed methodologies. The results obtained by higher order TD-FEM and TD- MoM are in an excellent agreement with indirect solutions obtained from FEM and MoM analyses in the frequency domain (FD) in conjunction with discrete Fourier transform and its inverse, as well as with measurements and alternative full- wave numerical solutions in both TD and FD.

Adviser: Prof. Branislav Notaros
Co-Adviser: N/A
Non-ECE Member: Prof. Jennifer Mueller, MATH
Member 3: Prof. Steven Reising, Prof. V. Chandrasekar
Addional Members: Prof. Milan Ilic

Publications:
1. N. J. Sekeljic, M. M. Ilic, and B. M. Notaros, "Spatially Large-Domain and Temporally Entire-Domain Electric-Field Integral Equation Method of Moments for 3-D Scattering Analysis in Time Domain," IEEE Transactions on Antennas and Propagation, under review.

2. E. Chobanyan, N. J. Sekeljic, A. B. Manic, M. M. Ilic, V. N. Bringi, and B. M. Notaros, "Efficient and Accurate Computational Electromagnetics Approach to Precipitation Particle Scattering Analysis Based on Higher Order Method of Moments Integral Equation Modeling," Journal of Atmospheric and Oceanic Technology, under review.

3. M. Thurai, V. N. Bringi, A. B. Manic, N. J. Sekeljic, and B. M. Notaros, "Investigating rain drop shapes, oscillation modes, and implications for radiowave propagation," Radio Science, Vol. 49, Issue 10, October 2014, pp. 921-932.

4. N. J. Sekeljic, M. M. Ilic, and B. M. Notaros, "Higher Order Time-Domain Finite Element Method for Microwave Device Modeling with Generalized Hexahedral Elements," IEEE Transactions on Microwave Theory and Techniques, Vol. 61, No. 4, April 2013, pp. 1425-1434.

5. E. M. Klopf, N. J. Šekeljić, M. M. Ilić, and B. M. Notaroš, "Optimal Modeling Parameters for Higher Order MoM-SIE and FEM-MoM Electromagnetic Simulations", IEEE Transactions on Antennas and Propagation, vol.60, no.6, pp.2790-2801, June 2012.

6. M. M. Ilic, I. Perovic, P. Athalye, N. Sekeljic, A. A. Tonyushkin, B. M. Notaros, "Full-Wave Frequency-Domain Electromagnetic Modelling of RF Fields in MRI Applications," Proceedings of 2015 IEEE AP-S/URSI International Symposium, accepted.

7. M. M. Ilic, N. Sekeljic, P. Athalye, A. A. Tonyushkin, B. M. Notaros, "RF Excitation in 7 Tesla MRI Systems Using Monofilar Axial-Mode Helical Antenna," Proceedings of 2015 IEEE AP-S/URSI International Symposium, accepted.

8. P. Athalye, N. Sekeljic, M. M. Ilic, A. A. Tonyushkin, B. M. Notaros, "Improving Traveling-Wave RF Fields inside Magnetic Resonance Imaging Bores by Incorporating Dielectric Loadings," Proceedings of 2015 IEEE AP-S/URSI International Symposium, accepted.

9. Branislav M. Notaros, Milan M. Ilic, Alexey A. Tonyushkin, Nada J. Sekeljic, and Pranav Athalye, "Quadrifilar Helical Antenna as a Whole-Body Traveling-Wave RF Coil for 3T and 7T MRI", Proceedings of 23th International Society for Magnetic Resonance Imaging (ISMRM) 2015, accepted.

10. N. J. Sekeljic, A. B. Manic, E. Chobanyan, M. Thurai, V. N. Bringi, and B. M. Notaros, "Electromagnetic scattering by oscillating rain drops of asymmetric shapes," Proceedings of 2014 IEEE Antennas and Propagation Society International Symposium, July 6-12, 2014, Memphis, Tennessee, pp. 1572-1573.

11. N. J. Sekeljic, S. B. Manic, M. M. Ilic, and B. M. Notaros, "Efficient Models for Transient Analysis of Passive Microwave Devices Using FEM-TD with Time-Marching and FEM-FD with Discrete Fourier Transform,” invited paper, Special Session “Time-Domain FEM," 12th International Workshop on Finite Elements for Microwave Engineering – FEM2014, May 14-17, 2014, Chengdu, China.

12. N. J. Sekeljic, M. M. Ilic, and B. M. Notaros, "p-Refined Large-Domain 3-D Curvilinear FEM Solutions of Arbitrarily Loaded and Shaped Waveguide Sections and Bends in the Time Domain," Proc. 2014 USNC-URSI National Radio Science Meeting, January 8-11, 2014, Boulder, Colorado.

13. N. J. Sekeljic, A. Manic, M. M. Ilic, and B. M. Notaros, "Transient Analysis of 3D Waveguides Using Double- Higher-Order Time-Domain Finite Element Method," Proceedings of 2013 IEEE Antennas and Propagation Society International Symposium, July 7-12, 2013, Orlando, Florida.

14. E. Chobanyan, N. J. Sekeljic, A. B. Manic, M. M. Ilic, and B. M. Notaros, "Atmospheric Particle Scattering Computation Using Higher Order MoM-SIE Method," Proceedings of 2013 IEEE Antennas and Propagation Society International Symposium, July 7-12, 2013, Orlando, Florida.

15. N. J. Sekeljic, S. B. Manic, M. M. Ilic, and B. M. Notaros, "Direct and Indirect Time-Domain FEM Higher Order Solutions to 3-D Closed-Region Problems," Proc. 2013 USNC-URSI National Radio Science Meeting, January 9-12, 2013, Boulder, Colorado.

16. N. J. Sekeljic, S. V. Savic, M. M. Ilic, and B. M. Notaros, "Rules for Adoption of Expansion and Integration Orders in FEM Analysis Using Higher Order Hierarchical Bases on Generalized Hexahedral Elements," invited paper, Special Session "Adaptive FEM, Higher Order Bases, and Advanced FEM Formulations," 11th International Workshop on Finite Elements for Microwave Engineering – FEM2012, June 4-6, 2012, Estes Park, Colorado.

17. B. M. Notaros, M. M. Ilic, S. V. Savic, N. J. Sekeljic, and A. Z. Ilic, "Accurate and Efficient Curvilinear Geometrical Modeling Using Interpolation Parametric Elements in Higher Order CEM Techniques," invited paper, Special Session "Higher Order Numerical Methods", Proceedings of the 28th International Review of Progress in Applied Computational Electromagnetics - ACES 2012, April 10-14, 2012, Columbus, Ohio, pp. 602-607.

18. N. J. Sekeljic, E. Chobanyan, M. M. Ilic, and B. M. Notaros, "Rules for Adoption of Expansion and Integration Orders in Moment-Method Computation of Electromagnetic Scattering and Radiation," Proc. 2012 USNC-URSI National Radio Science Meeting, January 4-7, 2012, Boulder, Colorado.

19. E. M. Klopf, N. J. Sekeljic, M. M. Ilic, and B. M. Notaros, "Investigations of Optimal Geometrical and Field/Current Modeling Parameters for Higher Order FEM, MoM, and Hybrid CEM Techniques," Proc. 2011 USNC-URSI National Radio Science Meeting, January 5-8, 2011, Boulder, Colorado.


Program of Study:
ECE 548
ECE 512
ECE 540
ECE 641
ECE 642
ECE 742
MATH 545
MATH 676