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RESEARCH PAPERS

Design of Two-Dimensional Ultrasonic Phased Array Transducers

[+] Author and Article Information
Shyamal C. Mondal, Paul D. Wilcox, Bruce W. Drinkwater

 University of Bristol, Department of Mechanical Engineering, Bristol BS8 1TR, UK

J. Pressure Vessel Technol 127(3), 336-344 (Mar 02, 2005) (9 pages) doi:10.1115/1.1991873 History: Received February 24, 2005; Revised March 02, 2005

Two-dimensional (2D) phased arrays have the potential to significantly change the way in which engineering components in safety critical industries are inspected. In addition to enabling a three-dimensional (3D) volume of a component to be inspected from a single location, they could also be used in a C-scan configuration. The latter would enable any point in a component to be interrogated over a range of solid angles, allowing more accurate defect characterization and sizing. This paper describes the simulation and evaluation of grid, cross and circular 2D phased array element configurations. The aim of the cross and circle configurations is to increase the effective aperture for a given number of elements. Due to the multitude of possible array element configurations a model, based on Huygens’ principle, has been developed to allow analysis and comparison of candidate array designs. In addition to the element configuration, key issues such as element size, spacing, and frequency are discussed and quantitatively compared using the volume of the 3D point spread function (PSF) as a measurand. The results of this modeling indicate that, for a given number of elements, a circular array performs best and that the element spacing should be less than half a wavelength to avoid grating lobes. A prototype circular array has been built and initial results are presented. These show that a flat bottomed hole, half a wavelength in diameter, can be imaged. Furthermore, it is shown that the volume of the 3D reflection obtained experimentally from the end of the hole compares well with the volume of the 3D PSF predicted for the array at that point.

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Copyright © 2005 by American Society of Mechanical Engineers
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Figures

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Figure 1

The geometry of (a) grid, (b) cross, and (c) circular arrays. The coordinate system used to define the array, image planes and reflector locations is shown in (d).

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Figure 2

B scan images from three geometries when the point reflector at x=0, y=0, and z=8.33λ: (a) grid; (b) cross; (c) circular. The scale shown to right of each image is in dB.

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Figure 3

Images from three geometries when the point reflector is at x=3.3λ, y=0, and z=8.33λ: (a) grid; (b) cross; (c) circular. The scale shown to right of each image is in dB.

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Figure 4

Graph showing the effect of voxel length on API value

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Figure 5

(a) API value vs reflector z position; (b) API value vs reflector x position at z=8.33λ; (c) API value vs reflector x position at z=16.6λ

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Figure 6

Effect of ring size on side lobes and main beam width for an 8 element circular array transducer: (a) ring size 1.67λ; (b) ring size 3.33λ; (c) ring size 5λ. The scales shown to right of each image are in dB.

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Figure 12

Testing of aluminium block containing a 100 mm deep ϕ3mm FBH: (a) geometry; (b) image obtained in x-z plane

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Figure 11

Testing of aluminium block containing a 50 mm deep ϕ3mm FBH: (a) geometry; (b) image obtained in x-z plane

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Figure 10

Testing of defect free aluminium cylinder: (a) geometry; (b) image obtained in x-z plane

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Figure 9

Schematic of experimental setup

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Figure 8

(a) Layout of array; (b) detail of elements

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Figure 7

Effect of number of elements on side lobes when the diameter of the circular array is 5λ: (a) 4 elements; (b) 8 elements; (c) 32 elements. The scales shown to right of each image are in dB.

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