Propagation of Electromagnetic Waves Through Composite Media

Open Access
Author:
Rajab, Khalid Z
Graduate Program:
Electrical Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
February 13, 2008
Committee Members:
  • Michael T Lanagan, Committee Chair
  • Raj Mittra, Committee Chair
  • Wenwu Cao, Committee Member
  • Elena Semouchkina, Committee Member
  • Randy Haupt, Committee Member
  • Douglas Henry Werner, Committee Member
Keywords:
  • terahertz
  • metamaterials
  • effective media
  • anisotropic
  • material characterization
  • multiple scattering
  • characteristic basis function method
Abstract:
The propagation of electromagnetic waves through ceramics and composite materials is investigated in this work. The design of complex artificial materials has potential as a valuable tool for application to many new devices, such as high-resolution lenses and electromagnetic imaging devices, as well as for the improvement of currently existing ones. A technique is demonstrated for the characterization of ceramics and other dielectrics, at terahertz frequencies, with the use of terahertz time-domain spectroscopy (THz TDS). Composite materials comprised of complex scatterers, and in particular spherical resonators, are studied using the same system. In order to calculate the scattered fields from a large number of resonant spheres, a new technique is developed, based on the characteristic basis function method (CBFM). This technique improves the computational speed of the calculation, as well as allowing the solution of bigger scattering problems, with a larger number of larger sized spheres. Finally, a technique is developed that allows the characterization of an anisotropic material, at any angle of incidence, to provide all the material tensor coefficients of the material of interest. The material tensors of effective media are related to the structure of the medium's lattice, and the importance of symmetry in the structure is demonstrated. A procedure is demonstrated that allows one to verify that the retrieved parameters are indeed those of the bulk material, by comparing eigenvectors of the extracted extit{T}-matrices. The procedure reveals that for many complex materials, such as dielectric resonators arrays, effective medium approximations do not apply, and so calculation techniques such as the CBFM, or the finite-difference time-domain method must be used to correctly determine the behavior of a composite.