Viscoelastic structural damping enables broadband low-frequency sound absorption

Area of Science:

• Acoustics
• Materials Science
• Metamaterials

Background:

• Traditional low-frequency sound absorbers, like Helmholtz resonators, use stiff materials and are narrowband and bulky.
• Energy dissipation in these systems relies on air resonance and thermal-viscous effects, limiting performance.
• Achieving broadband absorption typically requires complex and large designs.

Purpose of the Study:

• To present a composite acoustic metamaterial that overcomes limitations of traditional sound absorbers.
• To enable broadband low-frequency sound control using a materials-centered design approach.
• To shift the primary energy dissipation mechanism from air resonance to intrinsic viscoelastic damping.

Main Methods:

• Replaced the stiff neck of a Helmholtz resonator with a soft, viscoelastic cylindrical shell.
• Investigated the acoustic performance of the composite metamaterial.
• Developed a discretized impedance model to correlate material properties and geometry with absorption.

Main Results:

• Achieved over 97% sound absorption across a broad low-frequency range (227–329 Hz).
• Demonstrated deep-subwavelength thickness (λ/15 at 227 Hz) for a single absorption unit.
• Established a quantitative link between material properties, geometry, and absorption behavior.

Conclusions:

• The developed composite metamaterial offers compact and broadband low-frequency sound control.
• Material deformation and viscoelastic damping are key to enhanced absorption performance.
• A materials-centered design paradigm allows tunable parameters for optimized sound absorption.