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AGU-Vallen Wavelet is a tool which allows you to calculate and display
the wavelet- and Choi-Williams transformation of individual waveforms.
AGU-Vallen Wavelet has been developed
in collaboration between Vallen Systeme GmbH, Aoyama Gakuin University
(AGU), Tokyo, Japan and University of Denver, US. The AGU group has pioneered in the research of
time-frequency analysis in the field of Acoustic Emission and Vallen has actively
generated software tools.
Click here for details about contributors.
About wavelet transformation
A wavelet transform (WT) of an AE signal provides information which wave modes carry significant energy and where
in a mode the energy as a function of frequency and time is to be found. Thereby a WT
can communicate very useful information. In the following diagram you see an example for a
waveform (top) and the corresponding wavelet transform (below). The
superposed curves show the result of a dispersion curve calculation (by
Vallen Dispersion). The wave modes are identified by arrows.
About Choi-Williams transformation
The time-frequency transformation called Choi-Williams transform as proposed by
Hyung-Ill Choi and William J. Williams and first published in IEEE Transactions
on Acoustic Speech and Signal Processing Vol. 37, No. 6, June 1989. The advantage
of the Choi-Williams transformation is the better resolution of frequency vs. time.
A minor drawback is the less sensitive energy resolution.
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AE signal and its wavelet transform (color contour map, multicolor area,
red strongest) with superimposed modified group-velocity curves
(fundamental modes, solid lines). This diagram has been taken
from a presentation of Prof. Hamstad, which you can download with the link below.
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This figure shows the wavelet transform (colour contour map, multicolor area), the AE-signal (top most diagram),
and 2D Time Projection - (second from top diagram) as well as 2D Frequency Projection (left diagram) diagram.
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Same signal in 3D representation as above. The color coded wavelet
coefficients from the diagram above are shown here as height
(color coding is the same as above). The diagram is turned around,
so the frequency axis increases towards the viewer to show the
lower magnitudes of the high frequencies front of the low
frequencies.
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Vallen Dispersion is a tool allowing you to calculate the dispersion curves of
the wave modes within a plate, based on the velocity of the (bulk) longitudinal
and transversal wave modes and the plate thickness.
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Dispersion curves up to 2nd order
calculated with Vallen Dispersion (Aluminum, cL=6320m/s,
ct=3100m/s, plate thickness 4,7mm).
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AGU-Vallen Wavelet R2010.0202 |
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We at Vallen Systeme view wavelet analysis as having future potential. We wish to share the future
development with as many AE professionals as possible. We launched this free-of-charge wavelet analysis project to
enable any lab in the world to perform research on this issue.
What users say:
»I have already tried the dispersion program and it is an excellent
piece of freeware - well done!
A colleague informed me of the freeware - I expect it to have a
significant impact in NDT ultrasonic circles.«
»I checked most of the features, it looks very nice. You
have done some very nice work!«
»It's a really useful software.«
Download AGU-Vallen Wavelet. It's free!
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AGU-Vallen Wavelet (wvsetup.exe, ca. 3.3 MB)
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