Abstract
We propose a tunable acoustic metasurface using a nested structure as the microunit, which is constituted by two distinct resonators. Thanks to the coupling resonance for the microunit and by simply adjusting the rotation angle of the inner split cavity, this nested structure provides nearly 2π phase shift. The full-wave simulations demonstrate that the constructed metasurface can be tuned to reflect incident sound waves to different directions in the operation frequency region with a very narrow bandwidth, which is a key functionality for many applications such as filtering and imaging. Meanwhile, the reflected sound waves out of the operation frequency region always remain unchanged. As a result, a high Q-factor spectrum splitting can be realised. The presented metasurface is of importance to develop many metamaterial-based devices, such as tunable acoustic cloaks and acoustic switching devices.
Highlights
It is always the main theme in the field of acoustics to control and mould the propagation of sound waves
Many works about acoustic metasurfaces have been devoted to investigating new possibilities to manipulate sound waves, such as abnormal reflection [13,14,15], abnormal transmission [16,17,18,19], ultra-thin slab focusing [20], non-diffracting Airy beam [21,22], and ultra-thin cloaking [23]
The key to design the structural unit of a metasurface is to realise a phase shift covering 2π
Summary
It is always the main theme in the field of acoustics to control and mould the propagation of sound waves. Acoustic metasurfaces, metamaterials of reduced dimension, have attracted much research efforts owing to their ultra-thin thickness Such metasurfaces are constructed with space variant acoustic resonators with a subwavelength size, whose acoustic response is designed to exhibit desired phase shift by adjusting their geometry. Spectrum splitting is enabled by either geometrical optics or diffractive optics. Owing to the strong coupling resonance for the nested structure, the operation bandwidth of this metasurface is quite narrow, and a high-Q (~102 ) spectrum splitting is realised. Such metasurface designs could find applications for wavelength-selective filters, directional emitters, and focusing lenses
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