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Advanced Imaging Magazine

Updated: July 8th, 2008 05:26 PM CDT

Ultrasound Excited Thermography

Fig. 1: The principle of ultrasound excited thermography.
Fig. 2: Crack detection in a steel gear.
Fig. 3: Missing adhesive resulting in bad bonding on an automobile door.
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By Emilie Cornee, Cedip Infrared Systems

Ultrasound excited thermography is a new non-destructive testing (NDT) / non-destructive examination (NDE) technology that provides defect selective recognition of material failure. The technology was developed and patented in a cooperative venture between the German based IKP GmbH, the University of Stuttgart and Enhanced Defect Visualization GmbH.

Based upon the interaction of elastic and thermal waves, Ultrasound excited thermography provides a new method of detection of mechanical hysteresis in material caused by cracks, delaminations, poor bonding, or other material weakness.

In ultrasound excited thermography an ultrasound converter is used to produce the elastic wave stimulation in samples (Fig. 1). The acoustic waves are launched into the whole volume of the test specimen, where they are reflected until they disappear, preferentially in defects, and generate heat. These defects can now be visualized using an infrared camera that provides an image of heat flow caused by these hot spots inside the test specimen. This kind of high frequency sonic excitation is very efficient in heating since many hysteresis cycles are performed per second providing a dissipation image in very short time and with an excellent signal-to-noise ratio. Consequently measurements can be performed within only a few seconds.

Using this new technique inspection areas as large as 0.5 m by 0.5 m or more have been efficiently examined for defects. In addition, the technique has shown excellent inspection results with many kind of materials including metals, ceramics, fiber-reinforced compounds, fiber-ceramics and other solids with low mechanical damping in the ultrasound regime.

In the following paragraphs two of the many possible applications of Ultrasound Excited Thermography are presented.

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