Recent advances in acoustical microscopy.

Abstract

One cannot be involved in research in universities, government establishments and industry for 35 years without becoming aware of a number of misconceptions about pure science, applied science, engineering and technology in the mind of the public and also in the very places where research is carried out. There is confusion about the aims of research and development. There is uncertainty about the proper roles of universities, research establishments and industry. There is the question whether science is intrinsically good or not. The author illuminates some of these issues by relating milestones in the development of microscopy--optical as well as electron--and gives a snapshot picture of the recent work at Stanford University on the acoustic microscope as a felicitous instance of physics applied to the ever-present desire of mankind: to explore the unknown and to understand nature. Experiments with a mechanically scanning type of acoustic microscope have shown that a resolution limited only by diffraction can be attained and using a sonic frequency of 1-2 GHz, objects of less than 1 mum diameter can in principle be resolved. Various biological tissues have been explored and it appears that the acoustical images contain information substantially different from that obtained optically or electron-optically. Images have also been obtained using the harmonic radiation generated within the object and this mode of operation promises to open up yet another dimension of information. When, in due course, the full power, and the limitations, of the acoustic microscope are appreciated, its use may well lead to advances in science and technology comparable to those brought about by the introduction of the electron microscope.