Acoustic Pancharatnam-Berry geometric phase for structured sound manipulation

Area of Science:

• Acoustics and Wave Physics
• Metamaterials and Nanophotonics
• Geometric Phase Phenomena

Background:

• Phase control is crucial for manipulating acoustic waves, with propagation and resonant phases commonly utilized.
• The real-space geometric phase, or Pancharatnam-Berry (PB) phase, has been difficult to achieve in acoustics due to the nature of airborne sound waves.

Purpose of the Study:

• To theoretically and experimentally demonstrate the emergence of the PB phase in inhomogeneous sound waves.
• To explore the Janus property of the PB phase and its application in acoustic metasurfaces for wavefront manipulation.
• To extend this mechanism to free-space structured sound for applications like acoustic q-plates.

Main Methods:

• Theoretical modeling of inhomogeneous sound waves with evolving velocity fields.
• Experimental realization using surface sound waves to demonstrate the PB phase and its Janus property.
• Fabrication and testing of acoustic Pancharatnam-Berry metasurfaces and acoustic q-plates.

Main Results:

• Successful demonstration of the PB phase in acoustic systems through polarization evolution of the velocity field.
• Uncovered the Janus property of the acoustic PB phase due to spin-momentum locking.
• Developed acoustic PB metasurfaces for versatile wavefront manipulation and acoustic q-plates for vortex topological charge conversion.

Conclusions:

• This work introduces a novel type of acoustic phase, the geometric phase (PB phase), into acoustics.
• A simple and effective mechanism for structured sound manipulation using acoustic PB metasurfaces and q-plates has been established.
• The findings hold significant promise for advancements in acoustic communications, imaging, and on-chip devices.