Prof. Qing Huo Liu
Department of Electrical and Computer Engineering
Duke University
Durham, NC 27708, USA
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Multiscale Computational Electromagnetics and Applications
Abstract

Electromagnetic sensing and system-level design problems are often multiscale and very challenging to solve. They remain a significant barrier to system-level sensing and design optimization for a foreseeable future.  Such multiscale problems often contain three electrical scales, i.e., the fine scale (geometrical feature size much smaller than a wavelength), the coarse scale (geometrical feature size greater than a wavelength), and the intermediate scale between the two extremes.  Most existing commercial solvers are based on single methodologies (such as finite element method or finite-difference time-domain method), and are unable to solve large multiscale problems. We will present our recent work in solving realistic multiscale system-level EM design simulation problems in time domain. The discontinuous Galerkin method is used as the fundamental framework for interfacing multiple scales with finite-element method, spectral element method, and finite difference method. Numerical results show significant advantages of the multiscale method.

Subsurface Sensing and Super-Resolution Imaging: Application of Computational Acoustics and Electromagnetics

Abstract
Acoustic/seismic and electromagnetic waves have widespread applications in geophysical subsurface sensing and imaging. In these applications, often the problems of understanding the underlying wave phenomena, designing the sensing and imaging measurement systems, and performing data processing and image reconstruction require large-scale computation in acoustics and electromagnetics. It is very challenging to solve such problems with the traditional finite difference and finite element methods. In this presentation, several high-performance computational methods and super-resolution imaging in acoustics and electromagnetics will be discussed along with their applications in oil exploration and subsurface imaging.

Progress and Challenges in Microwave Imaging and Microwave Induced Thermoacoustic Tomography

Abstract
Breast cancer imaging by microwaves bas been investigated intensively over the past two decades due to the potentially high contrasts in permittivity and conductivity between malignant tumors and normal breast tissue. In comparison with the conventional ultrasound imaging where the acoustic impedance contrast between malignant tumors and normal breast tissue is low (typically a few percent), the dielectric contrast is indeed one to two orders of magnitude higher. Nevertheless, progress toward a clinically mature system for microwave breast imaging is painfully slow, primarily due to the low resolution of microwaves that can provide adequate penetration only at a relatively low frequency. We will describe challenges in achieving such a system, and ways to improve the resolution of microwave imaging. In the meantime, recent progress in microwave induced thermoacoustic tomography (MITAT) provides a new impetus for combining microwave and ultrasound modalities.  In MITAT, we use millisecond-pulsed microwaves to produce ultrasound through thermal expansion, thus the induced ultrasound source represents the high contrast in electrical conductivity, while the collected ultrasound signals provide the high resolution corresponding to a short wavelength of ultrasound. We will describe our recent progress in both microwave imaging and MITAT, in both computational methods and system development.

Spectral Element Method for Nanophotonics

Abstract
Nanophotonics is a major technological frontier with numerous new applications.  However, a significant challenge in design optimization of nanophotonic devices is the huge computational costs in large-scale simulations. Advances in high-precision, high-efficiency computational methods will have significant impact on this emerging area. In this presentation, we will discuss our recent efforts to improve the methods for computational electromagnetics in nanophotonics. Particular topics will include the spectral-element method and spectral integral method in frequency domain for Maxwell's equations with applications in photonic crystals and plasmonics, and for nonlinear effects such as second harmonic generation. We use the spectral element method in the frequency domain for the simulation of nonlinear optical effects and the associated second harmonic generation (SHG). In most materials the SHG effect is weak in general because their nonlinear optical coefficients are usually small. Moreover, as optical materials are usually dispersive, there is a phase mismatch between the fundamental frequency and second harmonic fields, further weakening the SHG effect.  With our accurate and efficient computational method, we design an air-bridge multiple layer photonic crystal slab based on the structure of GaAs/AlAs distributed Bragg reflector. We show that the SHG effect can be enhanced by ten orders of magnitude.

Biography
Qing Huo Liu (S’88-M’89-SM’94-F’05) received his B.S. and M.S. degrees in physics from Xiamen University in 1983 and 1986, respectively, and Ph.D. degree in electrical engineering from the University of Illinois at Urbana-Champaign in 1989. His research interests include computational electromagnetics and acoustics, and their applications in inverse problems, geophysics, nanophotonics, and biomedical imaging. He has published over 230 refereed journal papers and 300 conference papers in conference proceedings. His H index is 42 and has been cited over 7000 times (Google Scholar). He was with the Electromagnetics Laboratory at the University of Illinois at Urbana-Champaign as a Research Assistant from September 1986 to December 1988, and as a Postdoctoral Research Associate from January 1989 to February 1990. He was a Research Scientist and Program Leader with Schlumberger-Doll Research, Ridgefield, CT from 1990 to 1995. From 1996 to May 1999 he was an Associate Professor with New Mexico State University. Since June 1999 he has been with Duke University where he is now a Professor of Electrical and Computer Engineering.

Dr. Liu is a Fellow of the IEEE, a Fellow of the Acoustical Society of America. Currently he serves as the Deputy Editor in Chief of Progress in Electromagnetics Research, an Associate Editor for IEEE Transactions on Geoscience and Remote Sensing, and an Editor for the Journal of Computational Acoustics. He was recently a Guest Editor in Chief of the Proceedings of the IEEE for a 2013 special issue on large-scale electromagnetics computation and applications. He received the 1996 Presidential Early Career Award for Scientists and Engineers (PECASE) from the White House, the 1996 Early Career Research Award from the Environmental Protection Agency, and the 1997 CAREER Award from the National Science Foundation.