ABSTRACT Fundamentals of transmission acoustic microscopy as applied to measurements of sound velocities and attenuation in thin specimens and films are discussed. The method is based on measuring the output signal A as a function of a distance z between the radiating and the receiving lenses in the two-lens focusing system of the transmission microscope. It is proposed to measure the A(z)M-dependence twice: initially without a specimen, and then in the presence of it. When a specimen is absent, maximum of the A(z)-curve arises in the confocal position of the lenses. In the presence of an object, the main peak of the curve is shifted, and its magnitude diminishes. Measuring the changes makes it possible to determine local values of sound velocities and attenuation. For data interpretation a theory of formation of the output signal in the two-lens focusing system was developed. The relationship between the peak shift and the ratio of sound velocities in a specimen and a couplant contains a correction depending on beam angle aperture.
1997 IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 44:1224-1231
© 1997 by The Institute of Electrical and Electronics Engineers, Inc. All rights reserved.