Illusion for Airborne Sound Source by a Closed Layer with Subwavelength Thickness

Area of Science:

• Acoustics
• Metamaterials
• Wave manipulation

Background:

• Previous acoustic cloaking focused on scattered fields from objects, not sound sources directly.
• Existing methods often result in bulky devices relative to the working wavelength.
• Generating acoustic illusions for sound sources is a largely unexplored area.

Purpose of the Study:

• To propose a new method for creating arbitrary acoustic illusions directly from a sound source.
• To overcome the size limitations of previous transformation acoustics-based designs.
• To demonstrate the manipulation of sound source radiation patterns using acoustic metasurfaces.

Main Methods:

• Utilized acoustic metasurfaces to introduce azimuthally-dependent phase delays to radiated wavefronts.
• Developed a method that avoids the coordinate transformation approach.
• Enclosed the sound source in a thin, single-layer metasurface device.

Main Results:

• Achieved arbitrary acoustic illusions for airborne sound sources.
• Demonstrated the ability to virtually shift a sound source's location.
• Showcased the introduction of angular momentum to the sound field.
• Verified theoretical predictions with numerical simulations confirming pattern manipulation.

Conclusions:

• The proposed acoustic metasurface enables subwavelength device thickness without altering the layer's shape.
• This approach offers unprecedented control over the radiation pattern of simple sound sources.
• Findings open new avenues for acoustic illusion devices with potential applications in architectural acoustics and biomedical engineering.