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Reflection and Transmission Behaviors of Ultrasonic Wave at Nano-Air Gap Examined Using Newton's Ring Specimen

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Published 20 July 2012 Copyright (c) 2012 The Japan Society of Applied Physics
, , Citation Masaki Inoue et al 2012 Jpn. J. Appl. Phys. 51 07GB12 DOI 10.1143/JJAP.51.07GB12

1347-4065/51/7S/07GB12

Abstract

Although in previous studies were examined the ultrasonic reflection behaviors at a nano-air gap using a relatively small optical Newton's ring specimen and a commercial acoustic lens, the details of the quantitative ultrasonic behaviors at a nano-air gap have remained unqualified until now. Since the accuracy of estimating these behaviors is directly related to the accuracy of industrial ultrasonic crack sizing, we tried to measure more accurately quantitative ultrasonic behaviors at a nano-air gap in this study. For this purpose, a special highly focused acoustic lens was designed and fabricated and applied to a large optical Newton's ring specimen to obtain accurate and reliable experimental results. Comparisons between the experimental and the conventional small gap theoretical results for a nano-air gap were also carried out. As a result, ultrasonic transmission was found to begin to occur from 60–70 nm air gaps in all the measurements. This finding was largely different from that based on the gap theory. Regarding the cause of this large difference between the experimental and theoretical results, we also examined the influence of the surface roughness of contact plates.

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10.1143/JJAP.51.07GB12