Cancellation of air-borne acoustic plane waves obliquely incident upon a planar phased array of active surface elements.

Abstract

The control of sound inside and outside an enclosure has recently been of much interest to researchers in acoustics. The approach most often used has been to control the sound in a given region (due to a known distribution of point sources) with destructive interference from a set of point sources whose strengths, phases, and locations can be adjusted. However, the work of the active surfaces research group at the National Center for Physical Acoustics has been to design surfaces that react to an incident wave in a manner defined by the operator. If this reaction is such that the surface moves with and at the same amplitude as the incoming wave, reflections will be controlled. Such surfaces have been built by this group for the control of normally incident plane waves. This paper reports on the extension of this work to oblique incidence. Since the phase of the incident wave varies over the surface of the transducer, a phased array is required for acceptable performance.