Using liner surface modes in acoustic ducts to make obstacles reflectionless

Area of Science:

• Acoustics
• Wave Phenomena
• Materials Science

Background:

• Backscattering of sound waves within ducts poses challenges for acoustic management.
• Existing methods for sound suppression often lack broadband effectiveness or introduce unwanted reflections.

Purpose of the Study:

• To propose and numerically demonstrate acoustic cloaking for suppressing backscattering inside ducts in the audible frequency range.
• To investigate the use of resonant liners to create a zone of silence for acoustic hiding.

Main Methods:

• Utilizing surface modes of a slowly varying resonant liner (e.g., an array of tubes) to curve plane waves around an object.
• Numerical simulations to analyze the cloaking performance for objects of arbitrary shape within a conduit.

Main Results:

• A resonant liner creates a zone of silence, enabling acoustic hiding of objects across a wide frequency band.
• The resonant liner exhibits deflecting properties, approaching ideal invisibility cloak characteristics without wavefront reflection.
• Cloaking bandwidth is dependent on the impedance and height of the obstacle relative to the conduit; smooth obstacles can enhance cloaking (self-cloaking).

Conclusions:

• Acoustic cloaking using resonant liners is a viable strategy for broadband sound suppression and acoustic invisibility in ducts.
• The proposed method offers near-ideal cloaking performance, with potential for self-cloaking enhancement.
• Dispersion effects introduce considerations of slow sound and wave phase distortion.