Acoustic Microscope operating at 100 MHz

Abstract

THE concept of acoustic microscopy is not new¹, but the means for constructing a working device are only now becoming available^2,3. As acoustic microscopy relies on mechanical vibration, rather than electromagnetic radiation, it may be possible to visualize features of a specimen which go undetected by conventional methods. The lower propagation velocity of sound compared with that of light, in all known materials, results in a corresponding reduction in wavelength for a given frequency of excitation. The theoretically attainable resolution with acoustic microscopy is limited by the angular aperture and the wavelength in a manner entirely analogous to the optical situation. Present ultrasonic technology limits the upper frequency attainable to about 10 GHz which corresponds to a wavelength of 3000–6000 Å in most solids and 1000–2000 Å in most liquids.