Image Processing Reference
In-Depth Information
4
Comparative Analysis of Three Digital Signal
Processing Techniques for 2D Combination of
Echographic Traces Obtained from Ultrasonic
Transducers Located at Perpendicular Planes
Miguel A. Rodríguez-Hernández
1
, Antonio Ramos
2
and J. L. San Emeterio
2
1
ITACA. Universitat Politècnica de Valencia
2
Lab. Ultrasonic Signal, Systems and Technologies, CSIC. Madrid
Spain
1. Introduction
In certain practical cases of quality control in the manufacturing industry, by means of
ultrasonic non-destructive evaluation (NDE), it is very difficult to detect certain types of
internal flaw using conventional instrumentation based in ultrasonic transducers located on
a unique external surface of the piece under inspection. In these cases, the detection
problems are due to the especial flaws orientation or their spatial location, and some
technological solutions for it are still pendent to be proposed.
In addition, it is convenient, in a more general scope, to improve the flaw-location in two
dimensions, by using several ultrasonic transducers emitting beams from distinct places. In
fact, the utilization of more than one detection transducer provides complementary
information in the NDE of many pieces. These transducers can be located at the same or at
different planes depending on the piece shape and the detection necessities. In any case, the
result of such arrangement is a set of ultrasonic traces, which have to be carefully fussed
using digital signal processing techniques in order to extract more accurate and more
complete detection results.
The usual trend for reducing the mentioned limitations in flaw detection is to increase the
number of ultrasonic channels involved in the testing. On the other hand, it is important to
reduce this ultrasonic channels number in order to minimize technological costs. In
addition, it should be noted that the detection capability also depends on other important
factors, because, from a more general point of view, still some physical limitations of the
ultrasonic beams remain for a) certain angles of the scanning (Chang and Hsieh 2002), b) for
certain complex geometries of the industrial components to be tested (Roy et al 1999) or c)
for biological elements in medical diagnosis (Defontaine et al 2004, Reguieg et al 2006).
Schemes have been preliminarily proposed in order to improve flaw detection in difficult
conditions, trying to resolve these type of aspects well with two transducers and additional
digital signal processing of echoes (Chang and Hsieh 2002), or well with several arrays of
few elements (Engl and Meier 2002). Other posterior alternative proposals, based on
perpendicular scanning from two planes with a reduced transducers number and ultrasonic
