Acoustic microscopy with mechanical scanning—A review (original) (raw)

Scanning Acoustic Microscopy: A Physicist’s Tool

Europhysics News Europhysics News(vol. 22, number 9):p. 167-170, 1991

-Principle of the scanning acoustic microscope (SAM ). The spherical interface between the sapphire rod and the coupling fluid (usually water) acts as a lens for pulsed ultrasonic waves travelling down the rod. Spherical ultrasonic waves strike the sam ple and are reflected back into the trans ducer for conversion into a useful signal.

Lens Geometries for Quantitative Acoustic Microscopy

Advances in Acoustic Microscopy, 1995

The purpose of the first Lemons-Quate acoustic microscope(l) was to image the surfaces of materials or biological cells with a high resolution. Unfortunately, competition with the optical microscope was only partially successful due to the high degree of absorption in the liquid-coupling medium at high frequencies. Increasing the resolution beyond optical limits was possible with the use of hot water(2) or cryogenic liquids,tJ) at the cost of operational difficulty and system complexity. Meanwhile it was shown that the acoustic microscope can generate information that has no counterpart in the optical world.(4) The presence of leaky waves resulted in an interference mechanism known as V(z) curves. The V(z) method involves recording the reflected signal amplitude from an acoustic lens as a function of distance between the lens and the object. This recorded signal is shown to depend on elastic parameters of the object material. After underlying processes are well understood, new lens geometries or signal-processing electronics are designed to emphasize the advantage of the acoustic lens. In any case,

A theoretical analysis of acoustic microscopy with converging acoustic beams

Applied Physics B Photophysics and Laser Chemistry, 1988

A theoretical analysis is carried out to synthesize acoustic material signatures (AMS) of solid plates immersed in water. The distinctive feature of this analysis is that it avoids three major simplifying assumptions of the presently available techniques, which are, paraxial approximation, assumption of perfect reflection and Gaussian summation of the incident field. Presently available techniques can avoid some but not all of these simplifying assumptions for computing the AMS. In this paper the analysis is carried out for lowfrequency acoustic waves generated by a cylindrical transducer without a lens rod. Reasons for these changes in the conventional acoustic microscope geometry is given. The AMS is synthesized for an aluminium plate in presence as well as in absence of water on its one side. As expected a significant difference is observed between the signatures generated under these two situations.

A Lamb wave lens for acoustic microscopy

IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, 2000

In a conventional scanning acoustic microscope the excited leaky modes contributes significantly to the high contrast obtained in the images. However, all such modes exist simultaneously, and the interpretation of the images is not straightforward, especially in layered media. A new lens geometry is proposed that can be used with acoustic microscopes to image layered solid structures. This new lens can focus the acoustic waves in only one of the Lamb wave modes of the layered solid with a high efficiency. 1-(Z) curves obtained from this lens are more sensitive to material properties compared to that obtained from conventional lens. Measuring the return signal as a function of frequency results in another characteristic curve, l * (f). The Lamb wave lens and the associated characterization methods for the layered structures are described. The results presented show that the Lamb wave lens is at least an order of magnitude more sensitive than the conventional lens and can differentiate between a good bond and a disbond in a layered structure easily. V (2) effect that is responsible for the high contrast in the acoustic images. When used with a layered structure, the presence of many modes makes the interpretation of V (Z) rather difficult. From such images one hopes to detect flaws Manuscript

Phase imaging in reflection with the acoustic microscope

Applied Physics Letters, 1977

When a polished surface of a single crystal is examined with a converging acoustic beam the reflected signal has a characteristic response that is dependent upon the elastic properties of the reflecting surface. This property can be used in the acoustic microscope to monitor the thickness of layers deposited on these surfaces and the small-scale variations of the elastic parameters in these materials.

A theoretical analysis of acoustic microscopy of spherical cavities

Wave Motion, 1995

In this paper a theoretical analysis of acoustic microscopy of spherical cavities in solids is presented. The incident field of the acoustic microscope is modeled as a converging acoustic beam of nonplanar wave front. This beam goes through reflection and transmission at the liquid-solid interface. The transmitted beam is scattered by the spherical cavity in solid. The scattered waves come back to the receiver after going through another transmission at the liquid-solid interface. Voltage curves generated by this signal for small as well as large cavities in different materials are analytically synthesized for both horizontal and vertical movements of the microscope lens. It is also shown in this paper how one can obtain the size and location of a cavity from the acoustic microscope generated voltage curves. ' On leave from Institute of Chemical Physics, Kosygin str. 4, 117334 Moscow, Russia. 0165-2125/95/$09.50 0 1995 Elsevier Science B.V. All rights reserved SSDIO165-2125(94)00054-9