NDTnet - August 1997, Vol.2 No.08

Improved Sound Field Penetration Using Piezocomposite Transducers

by Paul A. Meyer, Ph.D. *

Abstract

Ultrasonics has found widespread use in industrial and medical applications. Flaw detection, thickness measurement, and diagnostic imaging are just a few of the tools utilizing this technology. All information acquired by the ultrasound system passes through the transducer before being processed and presented to the operator. Therefore, the performance characteristics of the transducer can significantly influence system performance. In most situations, system performance will improve with increased signal amplitude (provided system noise does not increase) permitting detection of smaller reflectors. Decreased pulse length will improve axial resolution. In a previous presentation I demonstrated that the incorporation of piezocomposites into transducer design yields a theoretical improvement of 4 to 10 dB in many applications. Prototype transducers constructed exemplified the expected improvements when used on low loss test materials. However, when these same transducers were evaluated on lossy materials, performance improvements greater than 30 dB were recorded as shown in Figures below.

This presentation explains a major reason for this performance improvement. A mathematical model is used to predict the received waveform for both a monolithic PZT transducer and a piezocomposite design. Frequency spectra are recorded for each model transdueer and used as input to the model. We then increase the test material attenuation to determine the effeet on the eeho responses. The results demonstrate that the broader bandwidth of the piezoeomposite transdueer aecounts for the improved penetration. Are piezocomposite transducers necessary to achieve broad bandwidth? No, but most monolithic designs rely on heavy backing to increase bandwidth. This causes signifieant reduction in signal amplitude. Piezoeomposite designs provide both broad bandwidth and high signal amplitudes making them more suitable for use on lossy test materials.

Desirable Characteristics of UT Transducers

Piezocomposite Material

Why is the Performance Better than Expected?

Summary


Author:

Paul A. Meyer, Ph.D.
Krautkramer Branson
Lewistown, PA USA

This paper was presented at the ASNT Fall Conference Seattle, Washington October 17, 1996. See our Report.
Refer to another article:
Guided Wave Applications of Piezocomposite Transducers By Paul A. Meyer, Ph.D. and Joseph L. Rose |Top |
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