TITLE

Image of nonlinear structures of heterogeneous media using the second harmonic in scanning acoustical microscope

AUTHOR(S)
Severin, Fedar M.; O’Neill, Brian; Maev, Roman Gr.
PUB. DATE
May 2000
SOURCE
AIP Conference Proceedings;2000, Vol. 509 Issue 1, p881
SOURCE TYPE
Academic Journal
DOC. TYPE
Article
ABSTRACT
Scanning acoustic microscopy (SAM) images are created on the basis of sound reflection from sharp overfall of acoustical impedance. For that reason any internal structural components and inclusions with similar impedance values will be resolved with certain difficulties. In such particular cases, acoustical nonlinear phenomena could provide very important additional information. Interface between two media at certain conditions can be a very effective source of the second harmonic. It is still correct even in the case of exact equality of acoustical impedance of this media, when regular sound wave “can’t recognize” that interface. The source of such concentrated nonlinearity is either the difference of nonlinear parameters of the heterogeneous media (material nonlinearity) or weak, “breaking” junction inside this structure (contact nonlinearity). The image in second harmonic reproduces the gradient distributions of nonlinearity parameters in the specimen. Such kind of image processing can provide a unique opportunity to detect small (less then wavelength) grains, cracks, inclusions and other inhomogeneous which can’t be resolved using basic frequency. In our experiments, we used the nonlinear mode in the SAM with a basic frequency of 25 MHz. For this reason, the filter-amplifier with a frequency of 50 MHz and bandwidth of 4 MHz was included into the receiving part. As a result of decreasing the receiver bandwidth, brush pulses of second harmonic have a significant duration compared with one of fundamental frequency. It also leads to deterioration of spatial resolution in depth, consequently, this configuration of the device is better for investigations of two-dimensional objects. Based on our experiments and theoretical results, we demonstrate that an acoustical microscope nonlinear regime may be as effective an instrument for detecting various non-full contact in layered structures. © 2000 American Institute ...
ACCESSION #
6029033

 

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