Simplified models for ultrasonic cleaning: wave incidence angle effects

Abstract

We have previously studied simple axisymmetric finite element models for ultrasonic cleaning. In these models, we sought the magnitude of the particle removal force for a 1 GHz acoustic plane wave incident on a rigid 1 micron diameter sphere lying on a rigid plane. Now we wish to extend this work and determine the effect of the wave incidence angle on the horizontal and vertical sphere forces. By employing a Fourier decomposition of the ambient plane wave we reduce the three-dimensional problem to two two-dimensional problems. Calculation of the sphere forces for various wave incidence angles reveals that the magnitude of the vertical force is not significantly affected by scattering for angles below about 60 degrees. However, the horizontal force is a complicated function of the scattered and ambient wave solutions. In addition, we find that the horizontal force magnitude at 30 degrees incidence is almost as large as that at 60 degrees.