Acoustic Microscopy of Curved Surfaces

The Metrology and Imaging modes of the acoustic reflection microscope are applied to spherically shaped specimens. Metrology is usually practiced by translating the specimen along the acoustic beam axis. This operation yields a measurement of the local Rayleigh velocity at a single location in the specimen plane. Imaging is accomplished through raster-scanning in the plane transverse to the beam axis. The two modes are, in effect, simultaneously employed when a nonplanar surface of\u27 known curvature is scanned. The resulting image reveals nearly concentric rings with radial, periodic brightness variation, if the surface is spherical in shape. Stainless steel bearing balls of the type used in gyros are used to demonstrate the technique. It is suggested that the obtained images represent a two-dimensional map of elastic properties applicable to convex (bearing ball) and concave (bearing raceway) surfaces

Nondestructive Subsurface Imaging with the Reflection Acoustic Microscope

The Reflection Acoustic Microscope, operating at a microwave frequency near 400 MHz, has been used to image and examine subsurface detail in a multilayer ceramic chip capacitor (MCCC). Bulk examination of the 0.9 mm thick MCCC is at present not possible with this high resolution acoustic microscope because of the short depth of focus of the particular lens designed for the system and because of the short wavelength ( w 4 m)

Ultrasonic Evaluation of Titanium Alloy Diffusion Bonding

During the diffusion bond process, parts are heated to about one half the absolute melting point, pressed together at a stress below the macroscopic yield stress, and conditions maintained for a specified time. Bonding proceeds through three steps: local yielding of contact points upon initial application of stress; creep deformation on the bonding plane to yield discontinuous voids; and closure of voids by vacancy diffusion. Presently, nondestructive evaluation emphasizes detection of residual unbonds and voids, from incomplete void isolation or closure

Line-Focus Acoustic Mcroscopy Measurements of Thin-Film Elastic Constants

Thin film materials are widely used as hard, protective coatings for softer surfaces. It is known that fracture strength and hardness are related to the elastic and plastic properties [1]. The elastic constants of the film deposited on a substrate are, however, difficult to measure. By a technique which was recently discussed [2] the elastic constants of amorphous (isotropic) films and single-crystal (anisotropic) films can be obtained by measuring the velocities of surface acoustic waves (SAWs) propagating over a thin-film/ substrate specimen by the use of a line-focus acoustic microscope

Convergence and Stability of the Inverse Scattering Series for Diffuse Waves

We analyze the inverse scattering series for diffuse waves in random media. In previous work the inverse series was used to develop fast, direct image reconstruction algorithms in optical tomography. Here we characterize the convergence, stability and approximation error of the serie

Detection of Delaminations Located at Ceramic/Metal Jointed Interface by Scanning Acoustic Microscopy

Since ceramic/metal joints currently play an important role of the structural parts for applications in electrical, electronic or aerospace industries, techniques must be developed for evaluating the integrity of these joints. Such techniques as collimated X-ray beam radiography [1], indentation fracture, and laser speckle imaging have been developed with limited success. No truly nondestructive techniques for evaluating joint strength have been established to date. If a conventional C-scan mode apparatus could be applied directly for detecting a defect such as a delamination on a joint interface, it might be an attractive solution in terms of visualizing the defect as a first step in the evaluation. The shape of the standard specimen of the ceramic/metal joint is essentially a rectangular bar. When the C-scan mode apparatus is used to visualize the jointed interface, an acoustic wave is required to be incident from the ceramic side of the specimen. When considering the attenuation of an ultrasonic wave in the frequency range from 10 to 100 MHz and the thickness of the ceramic portion of the specimen, the wave may not reach the interface, or the wave reflected from the interface may not be detected. When using frequencies lower than 10 MHz, the interface may be imaged, but with limited resolution. Moreover, the contrast may be poor because of water diffusing into the crack in the surface of the specimen. When a conventional A-mode apparatus such as a digital oscilloscope is used to obtain quantitative data, reflected waveforms might be collected. However, the data might not be good enough to analyze details of a defect, such as caused by a fracturing process. Recent studies have shown that delaminations at a ceramic/metal joint, such as a Si3N4/Cu/Steel joint, originate along the periphery of the interface [2]

On the Convergence of the Born Series in Optical Tomography with Diffuse Light

We provide a simple sufficient condition for convergence of Born series in the forward problem of optical diffusion tomography. The condition does not depend on the shape or spatial extent of the inhomogeneity but only on its amplitude.Comment: 23 pages, 7 figures, submitted to Inverse Problem

Determination of Elastic Constants by Line-Focus V(Z) Measurements of Multiple Saw Modes

Line focus acoustic microscopy (LFAM) provides a method to determine the elastic constants of homogeneous materials and thin-film/substrate configurations, see Refs. [1–5]. The elastic constants are determined from the velocities of surface acoustic waves, which are obtained from measurement of the V(z) curve. Generally more than one elastic constant has to be determined. It is interesting to note that the procurement of sufficient data is sometimes more complicated for isotropic materials. For anisotropic solids the velocity can be measured as a function of the angle defining the propagation direction in the surface to yield a sufficiently large data set. For thin-film/substrate configurations measurements at various frequencies or for different film thickness may be carried out to obtain sufficient data. There are, however, obvious advantages to work with a single specimen and at a single frequency. This can be done by considering the contributions of more than one leaky SAW mode to the V(z) curve