Modeling of surface hairline-crack detection in metals under coatings using an open-ended rectangular waveguide
- Colorado State Univ., Ft. Collins, CO (United States). Applied Microwave Nondestructive Testing Lab.
A surface-breaking hairline crack or a narrow slot in a metallic specimen when scanned by an open-ended rectangular waveguide probe influences the reflection-coefficient properties of the incident dominant mode. Subsequent recording of a change in the standing-wave pattern while scanning such a surface results in what is known as the crack characteristic signal. Since microwave signals penetrate inside dielectric materials, this methodology is capable of detecting cracks under dielectric coatings of various electrical thicknesses as well. To electromagnetically model the interaction of an open-ended rectangular waveguide with a surface-breaking hairline crack under a dielectric coating, the dielectric-coating layer is modeled as a waveguide with a large cross section. Thus, the problem is reduced to a system of three waveguides interacting with each other while the location of the crack is continuously changing relative to the probing waveguide aperture. An analysis of modeling the dielectric-coating layer as a dielectric-filled waveguide with a large cross section is given, and its comparison with radiation into an unbounded medium is presented.
- Sponsoring Organization:
- Federal Highway Administration, Washington, DC (United States)
- OSTI ID:
- 566544
- Journal Information:
- IEEE Transactions on Microwave Theory and Techniques, Vol. 45, Issue 11; Other Information: PBD: Nov 1997
- Country of Publication:
- United States
- Language:
- English
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