Abstrakt
We study how the perturbations of a generally heterogeneous bianisotropic structure manifest themselves in the wave field, and which perturbations can be detected within a limited aperture and a limited frequency band. A short-duration broad-band incident wave field with a smooth frequency spectrum is considered.
Infinitesimally small perturbations of the constitutive tensor are decomposed into Gabor functions. The wave field scattered by the perturbations is then composed of waves scattered by the individual Gabor functions.
The scattered waves are estimated using the first-order Born approximation with the paraxial ray approximation. For each incident wave, each Gabor function acts like a 3-D Bragg grating and generates at the most 3 scattered Gaussian packets propagating in specific directions.