NDTnet 1998 Aug, Vol.3 No.8

Abstract

For most applications in ultrasonic testing two features of the ultrasonic probe are of special importance. First, a high pulse amplitude is needed for effective transmission through a test object and good signal to noise ratio of the detected signal. This is especially important when large parts or very attenuative or scattering materials have to be tested (austenitic steel, cast iron, composite materials, plastics etc.) where we are often at the limits of flaw detectability.

Second, a short pulse duration is necessary for good axial resolution, i.e. two signals in a short distance should be detected without interference. The task is e.g. to detect a small reflector near to the surface or backwall of the test object, as the inspection should scan the whole volume including the near surface regions.

The transducer materials presently used for the probe design are limited concerning these demands. Indeed, there are high resolution probes on the market which are built by using lead metaniobate piezoceramic or piezoelectric polymers. However, these probes have low sensitivity as most of the acoustic energy is absorbed in the backing and the transducer materials efficiency is low. There are also probes of high sensitivity which are built by using standard PZT piezoceramic. However, these probes have minor resolution according to their design principles. In summary, the needs of high resolution and high sensitivity are antipodes for traditional probes, which often results in acompromise for the probe construction.

Fig. 1: Sketch of 1-3 piezocomposite

By using piezocomposite transducer material we can meet both requirements at the same time. Piezocomposite material is an important update ofexisting piezoceramic. A mixture of polymermaterial and piezoceramic is used to modifyspecific features of the ceramic. Several types of piezocomposites have been investigated but today the 1-3 type piezocomposite is mostly used to build ultrasonic probes. Parallel orientated piezoceramic rods are embedded in a polymermatrix as shown in figure 1. As demonstrated by the examples, we can take profit of the high acoustic efficiency, low crosstalk, low mechanical Q, low acoustic impedance and mechanical flexibility to improve the overall probe performance. Especially, with this new transducer material we gain high sensitivity in combination with high resolution signals.

Abstract Source:
Book of Abstracts, 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN: 87-986898-0-00

Full-Text Source:
Proceedings of the 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN:

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