A dual frequency, ultrasonic, microengineered particle manipulator

Ultrasonic standing waves can be used to generate forces on particles within a fluid. Recent work has concentrated on developing devices that manipulate the particles so that they are concentrated near the centre of the cavity. It is also possible to design a device that concentrates the particles at the wall of a cavity. This paper describes a device that has the capability of operating in several modes to allow concentration of particles at either the cavity wall or the centre of the cavity, depending on the driving frequency.