Three-Dimensional Acoustic Double-Zero-Index Medium with a Fourfold Degenerate Dirac-like Point

Area of Science:

• Acoustics
• Materials Science
• Condensed Matter Physics

Background:

• The realization of 2D acoustic double-zero-index media (DZIM) has been achieved over the past decade.
• Achieving a 3D acoustic DZIM has remained a significant challenge in the field.

Purpose of the Study:

• To report the first experimental realization of a 3D acoustic double-zero-index medium (DZIM).
• To demonstrate the unique wave manipulation capabilities of this novel 3D acoustic material.

Main Methods:

• Fabrication of a 3D acoustic DZIM using a cubic lattice of metal rods.
• Induction of a fourfold degenerate point with conical dispersion at the Brillouin zone center.
• Construction of a 3D acoustic waveguide in the form of a "periscope" with two 90° turns.

Main Results:

• The material was confirmed to be a 3D DZIM with near-zero effective mass density and compressibility.
• A normally incident planar wave was observed to tunnel through the 3D DZIM waveguide.
• An undistorted planar wave front was achieved at the waveguide exit, demonstrating wave control.

Conclusions:

• This work presents a practical method for realizing 3D acoustic DZIM.
• The developed 3D DZIM acts as an effective acoustic "void space" offering unprecedented control over acoustic wave propagation.