Characterization and Optimization of Acoustic Field for Curved Array Probe
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LASSICAL PROBLEMS OF LINEAR ACOUSTICS AND WAVE THEORY
Characterization and Optimization of Acoustic Field for Curved Array Probe Li Lina, Huan-qing Caoa, and Zhong-bing Luoa, * a
NDT and E Laboratory, Dalian University of Technology, Dalian, 116085 China *e-mail: [email protected] Received September 3, 2019; revised April 23, 2020; accepted April 28, 2020
Abstract—The focusing principle and acoustic field characteristics of curved array probe are studied. Delay laws are first computed in the same way as linear array probe, and its effects on the axial acoustic pressure distributions are quantitatively examined. It is shown that the maximum points of axial acoustic pressure occur at positions deviating from the predefined focal depths. To further analyze the focusing principle of curved array probe, simulations of acoustic field are conducted under different settings of focal depth and active aperture size. It reveals that the circular array profile and the inconsistent electronic delay laws make the pulsed ultrasonic waves unable to constructively interfere at target positions. Subsidiary beams arise and further interfere with the axial acoustic pressure distributions of the main beam. To control the transmitted acoustic field, and thus customize the inspection strategy, an optimized delay law calculation scheme is proposed. The good behavior is well validated both by theoretical calculation and experimental examination. Keywords: curved array probe, acoustic field, focusing principle, delay laws DOI: 10.1134/S1063771020050097
1. INTRODUCTION Components with complex surface are quite common in modern industry, like many welding joints and corner parts [1, 2]. These complex geometries do, however, bring inspection challenges [3, 4]. For conventional ultrasonic testing, inspections of complex parts are performed manually or mechanically with single element transducer to realize full coverage in the form of normal incidence. However, this point to point scanning is inefficient, and the interpretation of single A-scan exhibition is tedious and operatordependant [5]. By contrast, ultrasonic phased array technique is able to customize characteristics of transmitted acoustic beam to improve detection and sizing capabilities for parts with complex geometries [6–8]. Among the recent advances is the arc-shaped curved array probe that ensures a normal incidence transmission of the acoustic field at any point of the surface [9]. It has been applied efficiently during engineering practice. Full coverage of the entire corner of L-shaped CFRP specimen was easily achieved through successive excitation of elements. Furthermore, the C-scan mapping views made the accurate sizing of interlaminar delamination an easy task [10, 11]. The focused acoustic field under this special array profile was investigated theoretically by some researchers. The focus law and acoustic field calculation method were presented using coordinate transformation and an approximation with rectangle
element instead of circular arc element, which were furthe
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