Figure 9(a) shows the freeze frame at 29.4 [micro]s of the UWPI video result, which is the moment when the propagating wave interacts with the crack as presented in Figure 4(b).
A multiple-damage visualization platform consisting of the four algorithms, UWPI, USI, WUPI, and DAWS, was equipped in the proposed system.
The filtered UWPI data is inversely transformed from wavenumber and frequency domain to spatial and time domain.
First, an intact aluminum plate was scanned to verify the feasibility of the UWPI system.
Using the UWPI system, the snapshot of the UWPI at 20 [micro]s is depicted in Figure 4.
The UWPI image is complex before wavenumber filtering due to incident waves, reflections from side boundaries, and the notch as shown in Figure 8(a).
Scan area was same as in Figure 3 and UWPI snapshots at 55 [micro]s are plotted as in Figure 10 so that reflected waves from boundaries cannot be observed.
Then, RMS values were calculated at 48 y.s using the UWPI images before and after the wavenumber filtering.
Figure 8 shows the spatial domain freeze-frames of the UWPI videos, while Figure 11 shows the time domain signals extracted at the impinging point of the center of the crack.
Since the UWPI freeze-frames of Figures 5-7 show the moments of the maximum ultrasonic amplitudes at the crack location, the freezing times also imply the relative ultrasonic time-of-flights in the free plate and water- and glycerin-immersed plates, respectively.