Review of progress and applications in acoustic microscopy

Acoustic microscopy is a relative newcomer to the field of acoustic imaging which will seek to discriminate micron-size structural detail and render visible mechanical microstructure. Although in an early stage of development, wide areas of application are anticipated in both the physical and biological sciences. This paper presents a discussion of recent developments in acoustic microscopy techniques and applications. Due to the resolution requirement, the present efforts to develop experimentally useful systems employ optical methods of sound-amplitude detection through various intermediate methods of coupling. The desired acoustic pattern can be displayed as a hologram or as a conventional image. Phase contrast and dark field techniques are also possible. Resolution better than 10 μm has already been reported and another order of magnitude improvement is only a few years off. Thus, acoustic resolution may soon be demonstrated that is equivalent to that obtained with optical microscopy. During the course of preliminary investigations, various interesting and meaningful contrasts have been demonstrated between acoustic and optical micrographs of the same specimens. These are presented as first examples of applications for acoustic microscopy.