In this project, we apply adaptive wave shaping to acoustic sound. In particular, we aim to achieve active, reconfigurable control of reverberating airborne sound covering a reasonably broad bandwidth in the audible frequency regime. Reverberating cavity is an important class of complex medium. A cavity is in the reverberating regime when frequency is sufficiently high, so that owing to the intrinsic spectral broadening, neighboring eigenmodes can no longer be individually distinguished in measurement. Reverberating sound usually manifests as a disordered wavefield, with a spatial pattern resembling a laser speckle. This characteristic means that despite its commonplace in daily life, its control remains extremely difficult in most situations. A recent breakthrough in optics known as adaptive wave shaping brings new possibility to tackle this challenge. The complexity of reverberating sound is underlain by the richness of eigenmodes, which are in essence standing waves. The interference of these standing waves can be altered to change the spatial pattern of reverberating sound. This can be achieved by altering the phase of a sufficient number of these modes (standing waves) in specific way. To do so, we design and fabricate a device we denote “spatial sound modulator” (SSM), which is now within technological reach, thanks to the recent advance in planar acoustic metamaterials and acoustic metasurfaces. We have exploited the membrane-type acoustic metamaterial to realize an active-controlled reconfigurable acoustic metasurface as a phase-modulating SSM with two switchable states built in to each unit cell. Based on this recent development, we plan to conduct thorough study on the SSM’s capability in controlling reverberating sound, and aim to realize an improved SSM for the effective reshaping of a broadband sound field.
|Effective start/end date||1/10/18 → 31/03/21|
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