Aircraft structural components such as wings and fuselages are constantly exposed to harsh environments, which make them susceptible to corrosion initiation and growth. To complicate matters, corrosion is normally hidden under paint and primer and cannot be visually detected until significant corrosion has occurred, causing the paint to blister. Corrosion of this type is usually preceded by the presence of corrosion precursor pitting. Hence, early detection of pitting is a critical issue in the maintenance of an aircraft and its structural components. Near-field microwave nondestructive testing techniques have been successfully used for detection of corrosion under paint, including very small laser machined pits. However, it is desirable to improve the spatial resolution associated with these techniques so that pits with dimensions in the range of a few hundreds of micrometers can be effectively detected. In this paper, a comparison between several different millimeter-wave open-ended rectangular waveguide-based probes is made for the detection and evaluation of corrosion precursor pitting at Ka-band (26.5-40 GHz) and V-band (50-75 GHz). A number of laser machined pits with dimensions varying between 150 to 500 μm were produced for this investigation. Using these probes, millimeter-wave images of these pits were produced, indicating that the modified open-ended rectangular waveguide probes, namely, single and double tapered and dielectric slab-loaded waveguide probes, were successful in detecting small pits. The results of this investigation, along with a complete discussion of the results, are presented.


Electrical and Computer Engineering

Keywords and Phrases

Corrosion; Microwave imaging; Nondestructive testing; Pitting; Dielectric waveguides; Electric fields; Nondestructive examination; Rectangular waveguides; Millimeter wave probes

International Standard Serial Number (ISSN)


Document Type

Article - Journal

Document Version

Final Version

File Type





© 2005 Institute of Electrical and Electronics Engineers (IEEE), All rights reserved.

Publication Date

01 Aug 2005