Nondestructive Testing Method in Artificial Intelligence Real Time Systems

Modern sonar and radar measurement systems are widely used in the field of nondestructive testing for a long time. Usually reference signal is emitted towards the object to be investigated and we get a signal, which is the sum of reference signal reflected from different plies. The task of signal processing is to determine time instances corresponding positions of certain ply, which allow analyzing structure of object. Usually the cross correlation function (CCF) of transmitted sequence and received sequence is calculated. If peaks were clearly identified in the cross correlation function (CCF), it would be easy to determine time instances. Due to the noise some coherent peaks, additive to the expected peaks, appear on the CCF, which are confusing in regard to the clear distinction of target. In order to cancel effects of noise as much as possible some measures have to be taken for data manipulation noise cancellation, such as averaging, inverse filtering and so on. These signal-processing methods need a lot of floating point floating point operations and are time consuming. That is why the usage of such ultrasonic systems is limited in real time systems, which are the base for self-organizing systems. Amount of calculations depends on the length of reference signal, the length of reflected signal to be processed and the noise reduction method used in such system. A new system with reduced amount of calculations is considered in this article. In this system only parts of reflected signal corresponding peaks of CCF are processed. These parts are defined in acquisition mode and afterwards system enters measurement mode. New noise reduction method based on wavelet transforms coefficients thresholding is applied in this system. The length of reference signal impacts system noise immunity and amount of calculations. The main problem in ultrasonic non-destructive testing systems is to cancel out effects of the noise. The optimal length of reference signal for wavelet based signalprocessing method is defined. All these measures allowed significantly reduce amount of calculations in the self-organizing systems. Introduction Ultrasonic pulse echo flaw detection systems are widely used in the field of non-destructive testing. The limitations of currently ultrasonic instruments hardly lies on the property of hardware, but it may lie on the lack sufficient signal processing techniques. It is believed that that the received Ascan signal may carry a lot of information on material properties and defects but information appears in various guises of noise, which is to be deciphered completely. Further research in ultrasonic signal processing techniques is essential to enhance the testing ability of ultrasonic instruments. Generally the flaw signals measured in ultrasonic non-destructive testing (NDT) include the effects of measurement system and are corrupted by different kind of noise. So the signal processing techniques, which require a priori knowledge of noise statistics are subject to fail in many situations [1,6]. Therefore the approach of signal processing should be involving the noisy signal itself in signal processing method [2]. The main drawback of such systems is amount of calculations [7], and it is important to reduce amount of calculations in real time NDT systems. Solid State Phenomena Vols. 97-98 (2004) pp 71-76 online at http://www.scientific.net © (2004) Trans Tech Publications, Switzerland All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of the publisher: Trans Tech Publications Ltd, Switzerland, www.ttp.net. (ID: 130.203.133.34-17/04/08,09:48:35) 2 Title of Publication (to be inserted by the publisher) Signal Processing in Ultrasonic NDT Systems Let us analyze a real time system in which a transmitter and a receiver are located at predetermined points. Several M-sequences (usually the Barker code), modulated by ultrasonic wave are used as the transmitting signal and receiver receives signals reflected from the target. Such a system is depicted in Fig. 1.