Chapter 53. 3-D Localization of Flaws in Structural Ceramics by Use of Scanning Laser Acoustic Microscopy
- John B. Wachtman Jr.
Published Online: 26 MAR 2008
Copyright © 1989 The American Ceramic Society, Inc.
A Collection of Papers Presented at the 13th Annual Conference on Composites and Advanced Ceramic Materials, Part 1 of 2: Ceramic Engineering and Science Proceedings, Volume 10, Issue 7/8
How to Cite
Wey, A. C. and Kessler, L. W. (1989) 3-D Localization of Flaws in Structural Ceramics by Use of Scanning Laser Acoustic Microscopy, in A Collection of Papers Presented at the 13th Annual Conference on Composites and Advanced Ceramic Materials, Part 1 of 2: Ceramic Engineering and Science Proceedings, Volume 10, Issue 7/8 (ed J. B. Wachtman), John Wiley & Sons, Inc., Hoboken, NJ, USA. doi: 10.1002/9780470310557.ch53
- Published Online: 26 MAR 2008
- Published Print: 1 JAN 1989
Print ISBN: 9780470374863
Online ISBN: 9780470310557
- chemical vapor infiltration;
- thermal expansion;
- scanning laser acoustic microscopy;
- holographic image reconstruction
Scanning laser acoustic microscopy (SLAM) is an important nondestructive testing (NDT) tool which provides not only real-time inspection of samples, but high resolution for imaging the detailed structure of a small object. The SLAM operates in a transmission mode. The micrograph produced by SLAM is, however, a two dimensional (2-D) shadowgraphic view of 3-D object. Because of diffraction, the resultant images are often unfocused and ambiguous. Inaccuracies in identifying the actual position, size, shape, and depth of flaws arise when those flaws are far below the surface. To overcome this problem we have developed a digital image processing technique for SLAM. We used the principles of acoustical holography with the calculation of wavefield propagation so that the wavefield could be digitally backpropagated to any plane of specified depth. This new holographic SLAM can reconstruct an entire object field in depth from one hologram and provides 3-D information about the object. In this paper, we review the SLAM technology and describe the holographic reconstruction process. The required modification of conventional SLAM to acquire both amplitude and phase information necessary for image reconstruction is also described. We demonstrate the power of this technique by providing 3-D localization of flaws in structural ceramics. High resolution images of subsurface defects at various depths within a silicone nitride sample were reconstructed from experimentally acquired data and the results will be presented.