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Reduction of Material Noise in Ultrasonic Nondestructive Evaluation
Using Synthetic Frequency Diversity Algorithms
Lars Ericsson
Licentiate Thesis, Report UPTEC 94108R, October 1994.
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Abstract:
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Ultrasonic nodestructive evaluation of coarse materials, such as
stainless steel, is often complicated by the backscattering from the
material microstructure. This material noise can, however, be
substantially reduced by making use of either spatial diversity or
frequency diversity methods.
The thesis concerns signal processing
techniques for implementing the latter approach using a single received
ultrasonic response signal. The investigated class of Synthetic
Frequency Diversity Algorithms process the signal in the time-frequency
domain, using a filter bank followed by a statistical processor. The
Split Spectrum Processing (SSP) technique, belonging to this category of
algorithms, is elaborated and novel filter banks and statistical
processors are developed and compared to the original SSP
implementation.
The algorithms are evaluated using real ultrasonic
signals, originating from test blocks with structures similar to those
found in nuclear reactor vessels.
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Related publications:
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[Eric95] L.Ericsson, T. Stepinski,
Ultrasonic Pulse Detection with Split Spectrum
Processing and Consecutive Polarity Coincidence,
Proc. of the 13th Int. Conf. on
NDE in the Nuclear and Pressure Vessel Industries,
May 1995, pp. 201-208
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