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Technical Discussions
Rolf Diederichs
Director,
NDT.net, Germany, Joined Nov 1998, 604

Rolf Diederichs

Director,
NDT.net,
Germany,
Joined Nov 1998
604
00:44 May-12-1997
Model generated by an inverse Fast Fourier Transformation

Concerning the article "Approximative Modeling for the Practical Ultrasonic Inspections" by H.Wüstenberg, A.Erhard.
The A-Scans are in the model generated by an inverse Fast Fourier Transformation.
What are the advantages and drawbacks of this approach?

Rolf Diederichs



    
 
 
Hermann Wuestenberg
R & D
BAM Berlin, Germany, Joined Nov 1998, 26

Hermann Wuestenberg

R & D
BAM Berlin,
Germany,
Joined Nov 1998
26
06:37 May-16-1997
Re: Model generated by an inverse Fast Fourier Transformation
: Concerning the article "Approximative Modeling for the Practical Ultrasonic Inspections" by H.Wüstenberg, A.Erhard.
: The A-Scans are in the model generated by an inverse Fast Fourier Transformation.
: What are the advantages and drawbacks of this approach?

: Rolf Diederichs


Pleas find here an first attempt of answering the following question:

1. The model can be linked to well known pulse spectra of UT-probes,
which commonly are available as data measured and also - depending
from the manufacturer - calculated by a KLM-quadrupol model or
similar equivalent circuits for the probe. The influence of the
bandpass filter characteristic of the receiving amplifier within the
UT-equipment can easely be studied.

2. The phase behaviour of reflection or mode conversion factors and of
the point source directivities for the different wave modes and its
influence can be considered without any difficulty

3. This enables us to cut the totality of the process into different
parts and to multiply or add them in order to get the transfer
function of the whole system.

4. The necessary number of frequency samples to be calculated can be
adapted to the extension of the time domain to be considered for the
A-Scan. E.g. many of the examples in the above mentioned contribution
are using 64 samples in the frequeny domain and 128 in the time
domain, which corresponds e.g. to 16 mm sound path length. That means
that the use of the inverse FFT enables us to reach very short
computational times.


The drawbacks have to listed by someone else favorising a time domain
approach.

greetings

and Frohe Pfingsten

Hermann Wuestenberg



    
 
 

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