Figure 3-4

 

(a)
(b)
(c)

Figure 3 - Shear wave transducers: (a) in a block diagram; (b) oscillograms at 45 degree intervals - 0 to 180 degrees show that, for an untwisted bar, if the receiving transducer is rotated relative to the transmitting transducer, the received signal magnitude and polarity approximately  follows a cosine functions; (c) expanded view of 0 and 180 degree oscillograms shows polarity difference  corresponding to transducer parallel versus antiparallel.  (Both traces have been multiplied by -1 to compensate for negative spike excitation). Orthogonal transducer yield a small but nonzero amplitude: the expected null is imperfect.  The parallel and antiparallel traces in 3c also shows that the period of the first large received cycle is just under 1 µs.  this means the corresponding frequency is just over 1 MHz, but not 2.25 MHz.  Their spectra in fact pear near 1.1 MHz.

[ Back to January '04 NDT Solution ]

Figure 4 - Shear wave polarization experiments on twisted bars: the angle between transducers compensates for a 5 degree bias.

[ Back to January '04 NDT Solution ]

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