ANALYSIS OF THE CRACK CHARACTERISTIC SIGNAL USING A GENERALIZED SCATTERING MATRIX REPRESENTATION

Electromagnetic properties of a system formed by an open-ended rectang ular waveguide and a surface crack/slot in a metallic specimen are des cribed in this paper, Scanning a crack on a metal surface changes the reflection coefficient of the incident dominant mode, A model as a fun ction of relative crack location within the waveguide aperture (i,e,, crack moving with respect to the waveguide aperture) is desired to des cribe and optimize practical crack detection applications, Hence, the change in the reflection coefficient for a generalized system encompas sing empty, filled, and finite cracks located at an arbitrary position inside the waveguide aperture, is evaluated, A moment solution approa ch is employed, and a magnetic current density M is introduced over th e common aperture formed by the waveguide and the crack, Subsequently, the junction formed by the waveguide and the cracked metallic surface is separated into two systems. A numerical solution employing the met hod of moments is obtained, and the reflection coefficient at the wave guide aperture is expressed in terms of the generalized scattering mat rix, The convergence behavior is studied to determine an optimized set of basis functions and the optimal number of higher order modes for a fast and accurate solution, Numerical results presented in this paper include the evaluation of the field distribution over the waveguide a perture, Finally, the theoretical and measured crack characteristic si gnals are compared.