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Time domain wave form (A scan) showing modulation due to interference between the two orthogonal shear wave polarizations for the through thickness shear wave modes of a thick aluminum sheet. The inset shows that individual shear wave pulses are not distinguishable.
FFT of the A scan in Fig. 1 showing what is actually a double peak structure centered around . Only one double peak is visible in this case as the wave form does not contain sufficient ultrasonic signals at the next resonant frequency at approximately .
“Zoomed in” FFTs of the A scans for an uncoated thick aluminum sheet (black and on right) and a thick aluminum sheet from the same strip with a nominal thick polymer coating (gray and on left). Note that the double peak structure is due to acoustic birefringence in the aluminum.
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