Seminar Schedule – Spring 2021

Thursday, April 1, 2021
Time: 3:30pm – 5:00pm
This seminar will be held virtually via Zoom in email announcement

Wave-driven inverse problems: from full-waveform imaging to metamaterial design

Dr. Loukas F. Kallivokas, University of Texas at Austin
Professor
Department of Civil, Architectural and Environmental Engineering

Abstract: I discuss recent progress in closely-related inverse problems driven by elastic waves.

First, I address the full-waveform-based imaging of probed solids. The driving problem is similar to geophysical probing –an inverse medium problem– albeit here the focus is in the characterization of the near-surface deposits. I discuss the two key ingredients of the problem: a. modeling of the forward problem, which involves the numerical simulation of wave propagation in PML (perfectly-matched-layer)-truncated domains in the time-domain; and b. the inverse medium problem and the schemes we have implemented in an attempt to lend robustness to the inversion process. I report successful imaging with synthetic and field data in 3D using elastic waves.

Secondly, I discuss a PDE-constrained optimization approach for constructing optimal transient excitations capable of focusing energy to a target underground formation, by steering the wave energy to the formation. The motivation stems from the possibility of “shaking” (via ground, wellbore, or other sources) a target reservoir zone strongly enough to increase oil mobility for Enhanced Oil Recovery (EOR) purposes. The method leads formally to an inverse source problem, where the tempo-spatial characteristics of the excitation are the unknown parameters. I report numerical experiments with elastic and poroelastic targets demonstrating target illumination.

Lastly, I discuss inverse metamaterial design for achieving user-defined band gaps in periodic structures with wave-shielding applications in mind. A systematic procedure based on a (Floquet-Bloch) dispersion-constrained inversion approach is shown to be capable of producing metamaterial designs exhibiting user-defined band gaps, including omni-directional gaps for elastic waves. I report numerical experiments that demonstrate feasibility for constructing omni-wave and omni-directional shields exhibiting sub-wavelength performance.

For further information, please contact Dr. Rui Huang at ruihuang@mail.utexas.edu or (512) 471-7558.