Ultrasonic, Microwave, and Millimeter Wave Inspection Techniques for Adhesively Bonded Stacked Open Honeycomb Core Composites


Honeycomb sandwich composites are used extensively in the aerospace industry to provide stiffness and thickness to lightweight structures. A common fabrication method for thick, curved sandwich structures is to stack and bond multiple honeycomb layers prior to machining core curvatures. Once bonded, each adhesive layer must be inspected for delaminations and the presence of unwanted foreign materials. From a manufacturing and cost standpoint, it can be advantageous to inspect the open core prior to face sheet closeout in order to reduce end-article scrap rates. However, by nature, these honeycomb sandwich composite structures are primarily manufactured from low permittivity and low loss materials making detection of delamination and some of the foreign materials (which also are low permittivity and low loss) quite challenging in the microwave and millimeter wave regime. Likewise, foreign materials such as release film in adhesive layers can be sufficiently thin as to not cause significant attenuation in through-transmission ultrasonic signals, making them difficult to detect. This paper presents a collaborative effort intended to explore the efficacy of different non-contact NDI techniques for detecting flaws in a stacked open fiberglass honeycomb core panel. These techniques primarily included air-coupled through-transmission ultrasonics, single-sided wideband synthetic aperture microwave and millimeter-wave imaging, and lens-focused technique. The goal of this investigation has been to not only evaluate the efficacy of these techniques, but also to determine their unique advantages and limitations for evaluating parameters such as flaw type, flaw size, and flaw depth.

Meeting Name

41st Annual Review of Progress in Quantitative Nondestructive Evaluation, QNDE 2014 (2014: Jul. 20-25, Boise, Idaho)


Electrical and Computer Engineering

International Standard Book Number (ISBN)


International Standard Serial Number (ISSN)

0094-243X; 1551-7616

Document Type

Article - Conference proceedings

Document Version


File Type





© 2015 American Institute of Physics (AIP), All rights reserved.

Publication Date

01 Mar 2015