Presenter Information

M. Simaan, University of Pittsburgh

Location

La Jolla, CA

Start Date

1-1-1983 12:00 AM

Description

If a nondestructive evaluation system is designed to detect the presence or absence of a flaw in a material, typically one transducer may be sufficient. If, however, a characterization of the flaw is desired, then an array of transducers is in most cases required. Besides the capability of two and three dimensional imaging, array data has the advantages of increased resolution, improved signal-to-noise ratio after preprocessing and sharper focusing.

In any NDE system, the acquisition of data is only one step towards the final objective of flaw characterization. The other step is that of processing the data in order to extract the desired information. In this paper, we consider one signal processing aspect of data obtained by a linear array of transducers. Each element on the array normally operates as transmitter and receiver simultaneously, and the data is collected by exciting one transducer at a time. The measured signals, after suitable time shifting for alignment, are summed in order to focus (or beamsteer) the array at a specific point. The resolution of this summing process depends on the side lobes of the array reject response, and this in turn depends on the number of elements and spacing between elements on the array.

While summing is the simplest signal processing procedure to perform, it is however, as far as beamforming is concerned, not the most effective. The side lobe levels decrease as the number of elements N increases, and this has a lower bound of about -14 dB as N →∞. In this paper, we introduce an additional processing step with specially designed optimum filters before summing. The design methodology for these filters will be discussed in detail, and it will be shown that these filters have a superior frequency reject response which becomes more apparent if the array has a small number of elements.

Book Title

Review of Progress in Quantitative Nondestructive Evaluation

Volume

2B

Chapter

Section 25: Ultrasonic Transducers and Standards

Pages

1783-1795

DOI

10.1007/978-1-4613-3706-5_119

Language

en

File Format

application/pdf

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Jan 1st, 12:00 AM

Nondestructive Evaluation with Beamforming Transducer Arrays

La Jolla, CA

If a nondestructive evaluation system is designed to detect the presence or absence of a flaw in a material, typically one transducer may be sufficient. If, however, a characterization of the flaw is desired, then an array of transducers is in most cases required. Besides the capability of two and three dimensional imaging, array data has the advantages of increased resolution, improved signal-to-noise ratio after preprocessing and sharper focusing.

In any NDE system, the acquisition of data is only one step towards the final objective of flaw characterization. The other step is that of processing the data in order to extract the desired information. In this paper, we consider one signal processing aspect of data obtained by a linear array of transducers. Each element on the array normally operates as transmitter and receiver simultaneously, and the data is collected by exciting one transducer at a time. The measured signals, after suitable time shifting for alignment, are summed in order to focus (or beamsteer) the array at a specific point. The resolution of this summing process depends on the side lobes of the array reject response, and this in turn depends on the number of elements and spacing between elements on the array.

While summing is the simplest signal processing procedure to perform, it is however, as far as beamforming is concerned, not the most effective. The side lobe levels decrease as the number of elements N increases, and this has a lower bound of about -14 dB as N →∞. In this paper, we introduce an additional processing step with specially designed optimum filters before summing. The design methodology for these filters will be discussed in detail, and it will be shown that these filters have a superior frequency reject response which becomes more apparent if the array has a small number of elements.