Self-calibrating Terahertz Technique for Measuring Coating Thickness
Publication: Publication Date: 1 September 2015
This study investigates the applicability of a novel noncontact single-sided terahertz electromagnetic measurement technique for measuring thickness in dielectric coating systems on simulated and realworld coating/substrate systems. The technique does not require knowledge of the velocity of terahertz waves in the coating material. The dielectric coatings ranged from approximately 200 to 1400 μm in thickness. The simulated coating consisted of layered thin paper samples of varying thicknesses on a superalloy substrate and the realworld system consisted of an actual thermal barrier coating on the superalloy substrate. The unique aspects and limitations of this technique for thickness measurements are discussed.
- Chen, C.C., D.J. Lee, T. Pollock, and J.F. Whitaker, “Pulsed-terahertz Reflectometry for Health Monitoring of Ceramic Thermal Barrier Coatings,” Optics Express, Vol. 19, No. 4, 2010, pp. 3477–3486.
- Cheville, R.A., M.T. Reiten, J. O’Hara, and D.R. Grischkowsky, “THz Time Domain Sensing and Imaging,” Proceedings of SPIE, Vol. 5411, September 2004, pp. 196–206.
- Clipper, “Dielectric Constants of Materials,” Clipper Controls, Inc., San Francisco, California, 2007.
- Duvillaret, L., F. Garet, and J.-L. Coutaz, “Highly Precise Determination of Optical Constants and Sample Thickness in Terahertz Time-domain Spectroscopy,” Applied Optics, Vol. 38, No. 2, 1999, pp. 409–415.
- Generazio, E.R., D.J. Roth, and D.B. Stang, “Ultrasonic Imaging of Porosity Variations Produced During Sintering,” Journal of the American Ceramic Society, Vol. 72, No. 7, 1989.
- Ghosn, L., and D. Zhu, “Thermal Barrier and Protective Coatings to Improve the Durability of a Combustor under a Pulse Detonation Engine Environment,” 48TH AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, Honolulu, Hawaii, 23–26 April 2007.
- Jeong, S.H., I.S. Bae, Y.S. Shin, S.-B. Lee, H.-T. Kwak, and J.-H. Boo, “Physical and Electrical Properties of ZrO2 and YSZ High-k Gate Dielectric Thin Films Grown by RF Magnetron Sputtering,” Thin Solid Films, Vol. 475, Nos. 1–2, 2005, pp. 354–358.
- Lide, D.R., ed., CRC Handbook of Chemistry and Physics, 81st ed., CRC Press, Boca Raton, Florida, 2000.
- Mittleman, D.M., R.H. Jacobsen, and M.C. Nuss, “T-ray Imaging,” IEEE Journal of Selected Topics in Quantum Electronics, Vol. 2, No. 3, 1996, pp. 679–692.
- Roth, D.J., “Demonstration of an NDE Post-processing Software Tool Developed at NASA Glenn Research Center,” Proceedings of 2007 ASNT Fall Conference, Las Vegas, Nevada, 12–16 November 2007.
- Roth, D.J., US 7876423 B1, Simultaneous Noncontact Precision Imaging of Microstructural and Thickness Variation in Dielectric Materials using Terahertz Energy, January 2011.
- Roth, D.J., D.B. Stang, S.M. Swickard, M.R. DeGurire, and L.E. Dolhert, “Review, Modeling, and Statistical Analysis of Ultrasonic Velocity—Pore Fraction Relations in Polycrystalline Materials,” Materials Evaluation, Vol. 49, No. 7, 1991, pp. 883–888.
- Roth, D.J., J.D. Kiser, S.M. Swickard, S. Szatmary, and D. Kerwin, “Quantitative Mapping of Pore Fraction Variations in Silicon Nitride using an Ultrasonic Contact Scan Technique,” Research in Nondestructive Evaluation, Vol. 16, No. 3, 1995.
- Roth, D.J., J.P. Seebo, and W.P. Winfree, “Simultaneous Noncontact Precision Imaging of Microstructural and Thickness Variation in Dielectric Materials using Terahertz Energy,” Materials Evaluation, Vol. 66, No. 3, 2008a, pp. 325–331.
- Roth, D.J., J.P. Seebo, and W.P. Winfree, “Simultaneous Noncontact Precision Imaging of Microstructural and Thickness Variation in Dielectric Materials using Terahertz Energy,” NASA/TM -2008-214997, 2008b.
- Roth, D.J., L.M. Cosgriff, B. Harder, D. Zhu, and R.E. Martin, “Absolute Thickness Measurements on Coatings Without Prior Knowledge of Material Properties using Terahertz Energy,” NASA/TM-2013-216603, December 2013.
- Vassen, R., Y. Kagawa, R. Subramanian, P. Zombo, and D. Zhu, “Testing and Evaluation of Thermal-barrier Coatings,” MRS Bulletin, Vol. 37, No. 10, 2012, pp. 911–916.
- Yasui, T., T. Yasuda, K. Sawanaka, and T. Araki, “Terahertz Paintmeter for Noncontact Monitoring of Thickness and Drying Progress in Paint Film,” Applied Optics, Vol. 44, No. 32, 2005, pp. 6849–6856.
- Zhu, D., and R. Miller, “Development of Advanced Low Conductivity Thermal Barrier Coatings,” International Journal of Applied Ceramic Technology, Vol. 1, No. 1, 2004, pp. 86–94.
184 Page Views
0 PDF Downloads
0 Facebook Shares