A terahertz (THz) axial computed tomography
system has been developed that uses time-domain
measurements in order to form cross-sectional
image slices and 3D volume renderings of THztransparent
materials. The system can test
samples as large as 0.0283 m3 with no safety
concerns. In this study, the system was evaluated
for its ability to detect and characterize drilled
holes and embedded voids in foam materials that
were utilized as thermal protection on the external
fuel tanks of space shuttles. X-ray micro-computed
tomography was also performed on the samples to
compare against the THz computed tomography
results and better define embedded voids. Limits
of detectability are loosely defined, based on
depth and size for the samples used in this study.
Image sharpness and morphology characterization
ability for THz computed tomography are qualitatively
Arnone, D. D., C. M. Ciesla, A. Corchia, S. Egusa, M. Pepper, J. M. Chamberlain,
C. Bezant, E. H. Linfield, R. Clothier and N. Khammo, “Application
of Terahertz (THz) Technology to Medical Imaging,” Proceedings of
Terahertz Spectroscopy Applications II, International Society for Optical
Engineering, Bellingham, Washington, 1999, pp. 209–219.
Dorney, T., W. Symes, R. G. Baraniuk and D. Mittleman, “Terahertz Multistatic
Reflection Imaging,” Journal of the Optical Society of America, Vol. 19,
No. 7, 2002, pp. 1432–1442.
Herman, G. T., Fundamentals of Computerized Tomography: Image Reconstruction
from Projections, 2nd Edition, Springer, New York, New York,
IMTEC, “FlashCT Data File Format Specification Manual, Version 3.1,”
Industrial Measurement Technology Engineering Consultants Corporation,
IMTEC, “ILUMAVision Industrial Getting Started Guide,” Document
1.0.1, Industrial Measurement Technology Engineering Consultants Corporation,
Mittleman, D. M., Sensing with Terahertz Radiation, Springer-Verlag, Berlin,
Mittleman, D. M., R. H. Jacobsen and M. C. Nuss, “T-Ray Imaging,”
Journal of the IEEE Selected Topics in Quantum Electronics, Vol. 2, No. 3,
1996, pp. 679–692.
Mittleman, D. M., M. Gupta, R. Neelamani, R. G. Baraniuk, J. V. Rudd and
M. Koch, “Recent Advances in Terahertz Imaging,” Applied Physics B-lasers
and Optics, Vol. 68, No. 6, 1999, pp. 1085–1094.
Mittleman, D. M., S. Hunsche, L. Boivan and M. C. Nuss, “T-Ray Tomography,”
Optical Society of America Trends in Optics and Photonics Series,
17 March 1997.
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,
2008, pp. 325–331.
Roth, D. J., “Demonstration of an NDE Post-Processing Software Tool
Developed at NASA Glenn Research Center,” Presentation at ASNT Fall
Conference and Quality Testing Show, 12 – 16 November 2007, Las Vegas,
Roth, D. J., NDE Wave & Image Processor Software User Manual, version
Roth, D. J., S. Reyes-Rodriguez, D. A. Zimdars, R. W. Rauser and W. W.
Ussery, “Terahertz Computed Tomography Of NASA Thermal Protection
System Materials,” Review of Progress in Quantitative NDE, 17 – 22 July
2011, University of Vermont, Burlington, Vermont.
Siegman, A. E., Lasers, University Science Books, Sausalito, California,
1986, pp. 663–672.
Wang, S. and X. C. Zhang, “Pulsed Terahertz Tomography,” Journal of
Physics D: Applied Physics, Vol. 37, 2004.
Zimdars, D., J. A. Valdmanis, J. S. White, G. Stuk, S. Williamson, W. P.
Winfree and E. I. Madaras, “Technology and Applications of Terahertz
Imaging Non Destructive Examination: Inspection of Space Shuttle
Sprayed on Foam Insulation,” Review of Progress in Quantitative Nondestructive
Evaluation, Vol. 24, 25 – 30 July 2004, Golden Colorado.
Zimdars, D., I. Duling, G. Fichter and J. White, “Production Process Monitoring
of Multilayered Materials Using Time-Domain Terahertz Gauges,”
Review of Progress in Quantitative Nondestructive Evaluation, Vol. 29A, 2009,