ABSTRACT
Acknowledgments .......................................................................................................................... 676 11.A Appendix A ........................................................................................................................... 676 11.B Appendix B ........................................................................................................................... 677 11.C Appendix C ........................................................................................................................... 677 References ...................................................................................................................................... 678
Modern technologies require materials that have the capability to withstand extreme conditions with high reliability. One of the key parameters that has a strong impact on the life expectancy of a material is its microstructure. The acoustic microscope was developed as a tool for studying the internal microstructure of nontransparent solids. In acoustic microscopy, a sample is imaged by ultrasound waves, and the contrast in re¢ection furnishes a map of the spatial distribution of the elastic and acoustic properties. Several books and handbook articles provide detailed historical outlines (Lemons and Quate 1979; Briggs 1992; Gilmore 1999; Zinin 2001; Briggs and Kolosov 2010). Brie¢y, the development of the œrst high-frequency scanning acoustic microscope (SAM) was motivated by the idea of using an acoustic œeld to study the spatial variations of the elastic material properties with nearly optical resolution. The œrst experiments date back to the 1940s when high-frequency acoustic images were obtained by the Leningrad scientist Sokolov (Sokolov 1949). He observed an acoustic image using the tube named after him, in which the acoustic picture was converted into a television display. The œrst SAM was created by Lemons and Quate at Stanford University in 1973 (Lemons and Quate 1974). It was mechanically driven and operated in the transmission mode. Since then, gradual mechanical and electronic circuit improvements have been made, and image recording has been automated. In general, modern acoustic microscopes work in the re¢ection mode (Quate et al. 1979), which will be presented in the next section.
