Liquid‐borne sub‐micron particle detection through acoustic coaxing

Abstract

A novel approach to the detection of liquid‐borne submicron particles in ultraclean liquids (used in semiconductor manufacture) is described. The key concept is to coax the submicron particles to soft cavitate and to detect the ensuing transient bubble activity acoustically rather than the particle itself. The method, therefore, relies on facilitating acoustic microcavitation through acoustic coaxing. Liquid‐borne microparticles do not, ordinarily, cause any cavitation when exposed to strong sound fields (of 1 MHz). If, however, a very weak, high‐frequency auxiliary acoustic field (e.g., 30 MHz) is added to this sound field, cavitation by the microparticles is readily facilitated. This technique of facilitating cavitation is termed ‘‘acoustic coaxing.’’ Results of preliminary experiments indicate that even smooth spherical microparticles can be coaxed to cause cavitation. An explanation of the ‘‘acoustic coaxing effect’’ is offered. This novel method based on the acoustic coaxing of microcavitation promises to be a good basis for an on‐line, real‐time monitor of liquid‐borne submicronic particulate presence. This method is not limited to small sensing volumes, and, unlike optical methods, it has an intrinsic, location‐specific, signal enhancement at the source particle.