Numerical computation of acoustic radiation force in two and three dimensional resonators

Abstract

Large scale acoustophoretic separation of particles in a flow field can be accomplished by trapping the particles, i.e., remain in a stationary position, in ultrasonic standing waves. The particles are collected in a column pattern, separated by half a wavelength. Within each nodal plane, the particles are trapped in the minima of the acoustic radiation potential. The axial component of the acoustic radiation force drives the particles to their stable axial position. The radial or lateral component of the acoustic radiation force is the force that traps the particle. It must be larger than the combined effect of fluid drag force, i.e., Stokes drag, and gravitational force. There is a need for a better understanding of the lateral acoustic radiation force in realistic acoustophoretic separation devices. COMSOL Multiphysics® software was used to predict the acoustic field in two and three dimensional models of acoustophoretic separation devices driven by piezoelectric transducers. The resulting acoustic field was then used to calculate the acoustic radiation force acting on a suspended particle in two and three dimensions by applying Gor’kov’s equation. Measurements of trapped particles in standing waves indicate accurate calculations of acoustic field and radiation force. [Work supported by NSF PFI:BIC 1237723.]