Microwave Interferometry Inspection of Dielectric Materials

The portable microwave interferometry system has been successfully applied to measurement of material properties and detection of defects in a wide range of dielectric materials including: advanced aerospace composite matrix ceramics, composite ceramic armor, fiber reinforced resin components, reinforced rubber components and High Density Poly Ethylene (HDPE) pipe. Performance for field and manufacturing applications has been validated on test specimens, which included: manufacturing and service induced defects in actual samples and engineered features in specially fabricated surrogates. The portable, non-contact NDE system requires access to only one surface, and no coupling medium. Recent developments include: multi-channel instrumentation with frequency modulation and sampling, for 44 layer stack imaging; and phase plane analysis for depth and density measurement. System configuration advances include: hardware evolution to small portable units, development of precision measurement with fixed work stations, and integration in 6 axis fully automated robotic work stations. Related development includes position–self-aware functionality for the hand held probe; permitting direct, handheld examination of components. Metrology and detection capability has been validated using in-process measurement on actual parts; manufacturing and service induced defects in actual parts; specially fabricated surrogates and ballistic impact and non-ballistically damaged specimens. Other NDE methods, including through-transmission X-ray, X-ray computed tomography, destructive examination, and nondestructive measurement are used to verify defects and other detected anomalies. The microwave interference scanning system has been shown to reliably detect cracks, laminar features and material property variations. The development of this portable system will provide a useful tool for nondestructive testing of dielectric materials in the field and in manufacturing environments. This work is supported by, and test samples provided by, US Army Tank- Automotive Research, Development and Engineering Center (TARDEC), US Army Research Laboratory, US Air Force Research Laboratory under Small Business Innovative Research (SBIR) projects.

References
1. High-Resolution, Nondestructive Imaging of Dielectric Materials – U.S. Patent No. 7777499. 2. Apparatus and Method for Nondestructive Testing of Dielectric Materials – U.S. Patent No. 6359446. 3. Interferometric Localization of Irregularities – U.S. Patent No. 6653847. 4. Nondestructive Testing of Dielectric Materials – Australia Patent No. 746997. 5. Nondestructive Testing of Dielectric Materials – Canada Patent No. 2304782. 6. Nondestructive Testing of Dielectric Materials – EPO Patent EP1017996. 7. High-Resolution, Nondestructive Imaging of Dielectric Materials – EPO Patent EP1779123. 8. Schmidt, K., J. Little, W. Ellingson and L. Prokurat-Franks. “Portable Automated Imaging in Complex Ceramics with a Microwave Interference Scanning System,” American Ceramic Society, Proceedings of the 37th International Conference on Advanced Ceramics and Composites, Daytona Beach, FL, (2013). 9. Schmidt, K., J. Little, W. Ellingson and L. Franks. ERC Company, Franks, US Army Tank and Automotive Research and Engineering Center, Green, US Army Research Laboratory, Jefferson, US Air Force Research Laboratory, “Multi-Depth Imaging in Complex Ceramics with a Microwave Interference Scanning System,” Proceedings of the 36th International Conference & Exposition on Advanced Ceramics and Composites (2012). 10. Schmidt, K., R. Goitia, W. Ellingson and W. Green. “Correlation of Scanning Microwave Interferometry and Digital X-Ray Images for Damage Detection in Ceramic Composite Armor,” Review of Progress in Quantitative NDE (2011). 11. Harrison, J. and K. Schmidt. “Technology Transfer for Microwave Interferometry to Nuclear Power Applications,” Electric Power Research Institute, 9th International Conference on NDE, Seattle, WA (2012). 12. Schmidt, K. “Microwave Interferometry Solution to Inspection Challenges in Composites,” 59th Defense Working Group on Nondestructive Testing, Williamsburg, VA (2011). 13. Stakenborghs, R. “New Method to Detect Cold Fusion Joints in High Density Polyethylene Pipe,” ANTEC 2012, Society of Plastics Engineers, Newtown, CT (2012).
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