| ABSTRACT: | NON LINEAR FILTERING OF ULTRASONIC SIGNAL USING TIME SCALE DEBAUCHEE
DECOMPOSITION
F. Bettayeb1, S. Haciane2, and S. Aoudia
2
1 Scientific Research Center On Welding And Control - C.s.c -, Algiers, Algeria; 2 University Of Science
And Technology -Usthb-, Algiers, Algeria
Nowadays, ultrasonic flaw detection is an important research topic. To enhance the flaw detection, methods
based on thresholding have given good results, only when the signal to noise ratio is high. Since bandwidth
of the reflected signals as well as its principal frequency is subject to wide variation, it is impossible to
create an appropriate band pass filter for de-noising, so linear filtering does not provide good results,
because both the structure noise and flaw signal concentrate energy in the same frequency band. Non linear
filtering can be used to reduce or suppress the noise from ultrasonic signals. One way out is to use the time
scale filtration. The method is based on the Wavelet packet decomposition. The "Debauchee 8" procedure
has been chosen after successive tests on the analyzing Wavelet function for ultrasonic data. So each
measured ultrasonic signal is analyzed by a filter bank through only a 3 level Wavelet packet decomposition.
This work demonstrates that the multi-resolution analysis is very efficient with respect to signal recovery
from noisy data. The experimental results have shown that the proposed method has excellent performances
on SNR enhancements.
|