Acoustic forces, fluid manipulation

Another method recently developed for manipulating small particles uses the forces created by a two- or three-dimensional sound field that is excited by a vibrating plate, the surfaces of which move sinusoidally and emit an acoustic wave into a layer of fluid. Such a wave is reflected by a rigid surface and generates a standing sound field in the fluid, the forces of which act on particles by displacing them in one, two or three dimensions. In this way, particles of sizes between one and several hundred microns can be simultaneously manipulated in a contactless manner. Equations describing this behaviour have been reported [63]. 

In addition to the typical thermal and pressure forces exerted on fluids in microchannels, acoustic/ultrasonic and electric held forces have also been applied to manipulate huids as a body - referred to as body force driven processes. 

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