Analysis of Acousto-Electromagnetic Wave Interaction Using the Finite-Difference Time-Domain Method

We model electromagnetic scattering from two-dimensional objects under seismic or acoustic illumination. The vibration of the object gives rise to a frequency modulated, or Doppler, component in the scattered electromagnetic field. The Doppler component is primarily produced by two mechanisms, the boundary perturbation on the surface of the object and the density modulation within the object. The contributions from the boundary perturbation, which are analyzed in a previous publication, are reviewed and expanded upon herein; the contributions from density modulation are also presented. The wave interaction is analyzed with a unique, two-step approach. First, a finite element acoustic simulation is used to obtain the displacements within the acoustically excited object. This information is then input to a specialized formulation of the finite-difference time-domain method to simulate electromagnetic scattering. Analytical solutions for a cylinder are used to verify the computational modeling approach. Results for a more complex geometry are also presented.