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TECHNICAL PAPERS

Beam Forming of Lamb Waves for Structural Health Monitoring

[+] Author and Article Information
Steven E. Olson

 University of Dayton Research Institute, Dayton, OH 45469

Martin P. DeSimio

 ATK Space Systems and Sensors, Dayton, OH 45430

Mark M. Derriso

Air Vehicles Directorate, Air Force Research Laboratory, WPAFB, OH 45433

J. Vib. Acoust 129(6), 730-738 (Jan 05, 2007) (9 pages) doi:10.1115/1.2731404 History: Received May 08, 2006; Revised January 05, 2007

Structural health monitoring techniques are being developed to reduce operations and support costs, increase availability, and maintain safety of current and future air vehicle systems. The use of Lamb waves, guided elastic waves in a plate, has shown promise in detecting localized damage, such as cracking or corrosion, due to the short wavelengths of the propagating waves. Lamb wave techniques have been utilized for structural health monitoring of simple plate and shell structures. However, most aerospace structures are significantly more complex and advanced techniques may be required. One advanced technique involves using an array of piezoelectric transducers to generate or sense elastic waves in the structure under inspection. By adjusting the spacing and/or phasing between the piezoelectric transducers, transmitted or received waves can be focused in a specific direction. This paper presents beam forming details based on analytical modeling, using the finite element method, and experimental testing, using an array of piezoelectric transducers on an aluminum panel. Results are shown to compare well to theoretical predictions.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 6

Functional diagram of a receiving array

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Figure 7

Look angle versus normalized delay

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Figure 8

Theoretical gain patterns using eight-element receiving array for look angles of (a)63deg, (b)91deg, (c)100deg, and (d)110deg

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Figure 1

Aluminum plate test article showing locations of piezoelectric transducers (drawing not to scale)

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Figure 2

Five-cycle Hanning-windowed sine burst: (a) time signal and (b) frequency content of the signal

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Figure 3

Five-cycle square wave burst: (a) time signal and (b) frequency content of the signal

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Figure 4

Array of two identical omnidirectional elements

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Figure 5

Theoretical gain patterns for (a) two- and (b) eight-element arrays

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Figure 9

Measured gain patterns using eight-element receiving array for transmitting piezoelectrics at angles of (a)63deg, (b)91deg, (c)100deg, and (d)110deg

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Figure 10

Simulated gain patterns using eight-element receiving array for transmitting piezoelectrics at angles of (a)63deg, (b)91deg, (c)100deg, and (d)110deg

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Figure 11

Functional diagram of a transmitting array

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Figure 12

Measured gain patterns of eight-element transmitting array for sensors at angles of (a)63deg, (b)91deg, (c)100deg, and (d)110deg as transmitting look angle varies from 0deg to 180deg

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Figure 13

Functional diagram of an adaptive array

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Figure 14

Gain patterns for seven-element, uniformly spaced collinear arrays, with (heavy line) and without (thin line) weights corresponding to a noise canceling notch at 45deg

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