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Crack Imaging with Time Reversal - Experimental Results


The videos below demonstrate the focusing of elastic energy onto a crack as a result of using the TR NEWS process. (Ulrich et al, 2007). Both movies show the elastic energy as measured by the laser vibrometer. The movies begin at the time of termination of the rebroadcast signals.

These photos show the arch used in these experiments. The photo on the right displays the area which was scanned by the laser vibrometer and corresponds to the same area displayed in the movies below.
(Click the thumbnails below to view a larger image or movie.)

 

Difference Frequency -> Focusing

The energy coalesces first at the crack opening (i.e., at the arched boundary) and then the crack tip. The focusing is complex, moving from crack opening to crack tip as well as back and forth across the crack opening.

 

Arbitrary Frequency -> No Focusing

An arbitrary frequency is rebroadcasted that does not stem from wave mixing at the crack. Throughout this video there is no focusing in the region of the nonlinear scatterer. Furthermore, the elastic energy contained in the scan area is greatly reduced from what appears in the difference frequency movie (above), despite identical experimental settings (i.e., rebroadcast signal amplification, same sample, same transducer array). The energy feature along the sample arch appears in other movies as well which may imply a geometric focusing.

Arch - No Focusing

For more information, contact TJ Ulrich.

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