Application of hilbert-huang transform for improved defect detection in terahertz nde of shuttle tiles.

Content Provider	CiteSeerX
Author	Anastasi, Robert F. Madaras, Eric I.
Abstract	Terahertz NDE is being examined as a method to inspect the adhesive bond-line of Space Shuttle tiles for defects. Terahertz signals are generated and detected, using optical excitation of biased semiconductors with femtosecond laser pulses. Shuttle tile samples were manufactured with defects that included repair regions unbond regions, and other conditions that occur in Shuttle structures. These samples were inspected with a commercial terahertz NDE system that scanned a tile and generated a data set of RF signals. The signals were post processed to generate C-scan type images that are typically seen in ultrasonic NDE. To improve defect visualization the Hilbert-Huang Transform, a transform that decomposes a signal into oscillating components called intrinsic mode functions, was applied to test signals identified as being in and out of the defect regions and then on a complete data set. As expected with this transform, the results showed that the decomposed low-order modes correspond to signal noise while the high-order modes correspond to low frequency oscillations in the signal and mid-order modes correspond to local signal oscillations. The local oscillations compare well with various reflection interfaces and the defect locations in the original signal.
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Subject Keyword	Terahertz Nde Hilbert-huang Transform Shuttle Tile Improved Defect Detection Original Signal Complete Data Set Space Shuttle Tile Mid-order Mode Correspond Intrinsic Mode Function Optical Excitation Decomposed Low-order Mode Correspond Ultrasonic Nde Rf Signal C-scan Type Image Local Oscillation Terahertz Signal Shuttle Tile Sample High-order Mode Defect Visualization Shuttle Structure Low Frequency Oscillation Defect Location Adhesive Bond-line Repair Region Unbond Region Data Set Defect Region Biased Semiconductor Various Reflection Interface Commercial Terahertz Nde System Local Signal Oscillation Femtosecond Laser Pulse
Content Type	Text