Ultrasonic activation of stabilized gas bodies at frequencies in the lower megahertz range

Abstract

A microscopic gas body is stabilized against diffusion if it exists in a hole at the surface of a solid. Certain membranes sold commercially for filters (e.g., polycarbonate membranes prepared by Nuclepore Corp.) provide holes of micron dimensions, and under suitable conditions air remains trapped in these holes when they are immersed. The gas bodies so formed are suitable for strong activation at frequencies of 1–10 MHz. Experiments have been done in which suspensions of small particles are subjected to ultrasound in the presence of various membrane configurations. When the suspension can be viewed through a microscope during irradiation it is found that movements of suspended particles are visible near the gas‐filled pores even at pressure amplitudes as low as 0.1 bar. The movements are apparently a result of radiation force and acoustic microstreaming, such as are expected near a pulsating gas bubble. In experiments with biological suspensions it is found that significant changes are produced at relatively low intensity levels. A film will be shown. [Work supported by the NIH through grant GM08209.]