Use of a slightly curved reflector to enhance an airborne ultrasonic standing wave in a semi-infinite rectangular channel

One way to separate small particles from a moving air stream is to pass the stream through an intense ultrasonic standing wave. If the standing wave propagates perpendicular to the fluid flow direction, acoustic radiation pressure will move the particles to specific locations in the stream, where they can be collected at the stream outlet. Of primary importance is to achieve very high pressure amplitude in the standing wave, in spite of the presence of openings for fluid flow. In this presentation, the use of a slightly curved reflector within a flow channel to increase the amplitude of an ultrasonic standing wave is discussed. A finite element analysis was used to predict the amplitude of the standing wave that would be excited in a semi-infinite channel. A perfectly matched layer was used to account for the semi-infinite geometry. The finite element analysis showed that a significant gain in amplification within the channel could be achieved with a surprisingly small amount of reflector curvature. Experiments show that much of this gain can be obtained in practice.