Switching on and off acoustic waves through metamaterials has potential in noise canceling, underwater detection, and communication. However, traditional acoustic designs are challenging in manipulating underwater acoustic waves when the device thickness is less than wavelength. Here we report an alternative design of an underwater metasurface-based acoustic switcher to achieve this goal. The switching mechanism is revealed by combing acoustic diffraction of grating with mode conversion of double-layer PMMA plates. The device is tuned to control wave transmission by changing grating angle. Furthermore, we experimentally fabricate the metasurface acoustic switcher. The broadband-switching performance is realized to control underwater target detection and to produce binary digital encoding for acoustic waves. The proposed metasurface acoustic switcher offers the advantages of broadband performance and thin structure, which promises the opportunity for designing next-generation broadband-switching devices in underwater acoustic detection and communication.
No abstract
The sound-transmission, beam-formation, and sound-reception processes of a short-finned pilot whale (Globicephala macrorhynchus) were investigated using computed tomography (CT) scanning and numerical simulation. The results showed that sound propagations in the forehead were modulated by the upper jaw, air components, and soft tissues, which attributed to the beam formation in the external acoustic field. These structures owned different acoustic impedance and formed a multiphasic sound transmission system that can modulate sounds into a beam. The reception pathways composed of the solid mandible and acoustic fats in the lower head conducted sounds into the tympano-periotic complex. In the simulations, sounds were emitted in the forehead transmission system and propagated into water to interrogate a steel cylinder. The resulting echoes can be interpreted from multiple perspectives, including amplitude, waveform, and spectrum, to obtain the acoustic cues of the steel cylinder. By taking the shortfinned pilot whale as an example, this study provides meaningful information to further deepen our understanding of biosonar system operations, and may expand sound-reception theory in odontocetes.
Finless porpoises have evolved to equip a unique sound reception system composed of acoustic structures with gradient sound speed and density to achieve sound reception. Through numerical simulations and experiments, we demonstrated that this reception feat can be accomplished through physical implementation. Using the effective medium theory, we built respective composites to form an artificial bioinspired receptor to mimic the sound reception system of porpoise. This paper introduces an alternate aspect to bridge the gap between natural biosonar and artificial construction, shedding lights on inspiring additional advanced sound reception designs and systems.
We demonstrated that the feats of the dolphin biosonar system can be achieved through physical implementation. Numerical and experimental results suggested that dolphins have evolved to intelligently manipulate physical laws. Gradient distributions of sound speed and density in the forehead counterpart can enhance the main beam by gathering more sound energy to reinforce the main beam and lowering side lobes. As dolphins prove to accomplish efficient control on their biosonar capabilities in multiple ways, this paper provides an additional aspect to enrich our understanding of how one of the best natural biosonar systems works and build a step to inspire additional advanced sound control systems.
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