Depth Evaluation of Shallow Surface Cracks in Metals using Rectangular Waveguides at Millimeter-Wave Frequencies
This paper presents a resonant technique, which is founded on previous extensive work on millimeter-wave surface crack detection and sizing, for the accurate depth evaluation of long and shallow surface damages (scratches or cracks), which are represented as rectangular slots, in metal plates. A crack in a metal plate may be considered a short-circuited rectangular waveguide, which presents certain resonant characteristics when its electrical depth coincides with a quarter of the operating wavelength. Furthermore, a shallow crack may be filled with a dielectric material to electromagnetically make it appear deeper and hence facilitate its depth evaluation. The resonant properties of a crack depend on the dielectric properties of the material filling the crack and the crack dimensions. It is shown that a slight amount of loss, which is associated with the dielectric material, causes a relatively significant and characteristic change in the reflection coefficient measured using a probing rectangular waveguide aperture. In particular, this change affects the magnitude of the reflection coefficient, which is an easier parameter to measure than the phase. This information, as a function of frequency, may then be used to determine the shallow crack depth. This paper presents the foundation of this technique at millimeter-wave frequencies, along with supporting electromagnetic simulations and experimental results.
A. D. McClanahan et al., "Depth Evaluation of Shallow Surface Cracks in Metals using Rectangular Waveguides at Millimeter-Wave Frequencies," IEEE Transactions on Instrumentation and Measurement, vol. 59, no. 6, pp. 1693-1704, Institute of Electrical and Electronics Engineers (IEEE), Jun 2010.
The definitive version is available at http://dx.doi.org/10.1109/TIM.2009.2027780
Electrical and Computer Engineering
Air Force Research Laboratory (Wright-Patterson Air Force Base, Ohio)
Missouri University of Science and Technology. Center for Aerospace Manufacturing Technologies
Keywords and Phrases
Crack Dimensions; Electromagnetic Simulation; Filled Crack; Function Of Frequency; Metal Plates; Millimeter Wave Frequencies; Non Destructive Testing; Operating Wavelength; Rectangular Slots; Reflection Coefficients; Resonant Characteristics; Shallow Cracks; Surface Cracks; Surface Damages; Damage Detection; Dielectric Materials; Dielectric Properties; Elastic Constants; Millimeter Wave Devices; Millimeter Waves; Nondestructive Examination; Plate Metal; Rectangular Waveguides; Reflection; Surface Defects; Surfaces; Crack Detection; Crack Sizing; Millimeter Wave; Nondestructive Testing; Resonant Technique
International Standard Serial Number (ISSN)
Article - Journal
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