Time, Wavelet and Hilbert-Huang Domain Analysis of Signals from Ultrasonic Based Equipment for the Non Destructive Evaluation of Concrete and Brick Masonry Walls.
ABSTRACT In this paper we compare the effectiveness of the time, wavelet and Hilbert-Huang domain analysis of waveforms from a Non
Destructive Test (NDT) equipment. The analysis of the signals from NDT systems is one of the most important activities in
the recognition of the presence of possible defects that are usually associated with the presence of echoes from the defects
themselves. Very often the echoes traveling back to the sensors are superimposed with the signal from the transducer. We analyze
the waveforms obtained by couples of sensors in order to extract the echoes and to recognize the points were they originate.
Data are obtained by a measurement campaign on a concrete wall and on masonry specimens of different texture and thickness.
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ABSTRACT: A time-frequency analysis method based on Hilbert-Huang transform (HHT) was employed to character ultrasonic flaw echo signals. In this method, time and frequency characteristics of ultrasonic transducers used in inspection were considered to eliminate noises and identify the flaws. First, the flaw echo signals were decomposed into a series of mono-components called intrinsic mode functions (IMF) using the theories of EMD. Secondly, the best IMF was identified and represented in time-frequency domain using Hilbert transform, time and frequency characteristics were used to determine the flaw. Finally, the addition of the best IMF and the hypo-best IMF comes close to approximating the original flaw signal. The results of experiments with three transducers validate the effectiveness of the method in ultrasonic echo signal analysis.01/2010;