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Air Coupled Acoustic Thermography

NASA's Langley Research Center researchers have developed a novel noncontact method to identify internal damage inside structures. Air Coupled Acoustic Thermography (ACAT) was originally developed for damage identification in honeycomb sandwich structures but can also be applied to other...
Abstract: 
ACAT consists of an infrared camera, an image data capture system, an acoustic excitation source, and a chamber. The structure of interest is placed in a chamber to contain the sound and create a stable thermal environment. A loudspeaker is placed near to, but not in contact with, the structure, and it is then pulsed with acoustic energy for approximately 4080 cycles. The majority of the acoustic excitation is reflected off the structure, and very little energy absorption is observed. However, weak or damaged areas vibrate and act like heat sources. These heat sources can then be visualized using an infrared camera. A typical inspection time takes 23 minutes. The data is processed pixel by pixel in the time domain using a fast Fourier transform algorithm to produce a magnitude of images as a function of frequency. ACAT can visualize core and near skin structure damage over wide areas without the need for a couplant. This permits ACAT to identify damage in curved and linear structures.
Benefits: 
Noncontact technique -damage in curved and linear surfaces -Defect or damage visible as heat -Identification of defects not found via conventional flash thermography -Inexpensive system requiring thermal imager and audio equipment -Able to do large area inspections -Ability to detect core and peripheral damage
applications: 
Agency
NASA
State: 
Virginia
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