PRINCIPLES OF LOCAL SOUND-VELOCITY AND ATTENUATION MEASUREMENTS USINGTRANSMISSION ACOUSTIC MICROSCOPE

Fundamental of transmission acoustic microscopy as applied to measurem ents of sound velocities and attenuation in thin specimens and films a re discussed. The method is based on measuring the output signal A as a function of a distance z between the radiating and the receiving len ses in the two-lens focusing system of the transmission microscope. It is proposed to measure the A(z)-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 lense s. In the presence of an object, the main peak of the curve is shifted , and its magnitude diminishes. Measuring the changes makes it possibl e to determine local values of sound velocities and attenuation. For d ata interpretation a theory of formation of the output signal in the t wo-lens focusing system was developed. The relationship between the pe ak shift and the ratio of sound velocities in a specimen and a couplan t contains a correction depending on beam angle aperture.