Acoustic Metamaterials for Sound Absorption

Acoustic metamaterials are artificially structured media engineered to control, direct and manipulate sound waves in ways not possible with natural materials. By arranging subwavelength resonant elements within a host, these structures can exhibit extreme effective properties—such as negative density or compressibility—and induce strong localisation of acoustic energy. Such localisation enables exceptionally high absorption of incident sound in panels or coatings whose thickness is orders of magnitude smaller than the wavelength. Innovations in metamaterial design have exploited cascaded resonators, critical coupling and gradient impedance profiles to achieve near-perfect absorption over broad frequency bands, while maintaining compact form factors. Applications range from compact noise-control liners in aeronautics and automotive industries to ultrathin acoustic liners for architectural acoustics and advanced biomedical ultrasound shielding. The global significance of this field lies in its potential to reduce environmental noise pollution, enhance energy efficiency in buildings and improve the performance of acoustic sensors and actuators.

Research from Nature Portfolio

Recent studies have developed subwavelength panels composed of graded arrays of Helmholtz resonators, achieving asymmetric and broadband absorption by cascading resonance frequencies from low to high. These panels demonstrate near-perfect absorption across multiple octaves while maintaining thicknesses 10–40 times smaller than the lowest operating wavelength. Another approach employs critically coupled multi-resonant scatterers in which overlapping resonant peaks and controlled energy leakage balance intrinsic losses to yield absorption exceeding 93% over a frequency span of a factor of two, all within a λ/12 thick structure. These works provide design guidelines for tailoring absorber bandwidth and peak performance via resonator geometry and coupling strength.

Acoustic Metamaterials for Sound Absorption publication trend

The graph below shows the total number of articles in acoustic metamaterials for sound absorption across all publications each year (not limited to Nature Index journals).

Technical terms

Metamaterial: An engineered composite whose effective acoustic properties arise from its subwavelength structure rather than its chemical composition.

Subwavelength: Describes structural features much smaller than the wavelength of interest, enabling homogenised effective behaviour.

Helmholtz resonator: A cavity-neck system that resonates at a characteristic frequency, used to trap and dissipate acoustic energy.

Critical coupling: A condition where resonator leakage and intrinsic losses are balanced, maximising energy absorption.

Cascaded resonance: Sequential arrangement of resonators with graded frequencies to broaden the overall absorption bandwidth.

Intrinsic loss: Inherent energy dissipation within a resonant element, due to viscosity or material damping.

References

1. Rainbow-trapping absorbers: Broadband, perfect and asymmetric sound absorption by subwavelength panels for transmission problems. Scientific Reports (2017).
2. Perfect and broadband acoustic absorption by critically coupled sub-wavelength resonators. Scientific Reports (2016).
3. Sound‐Speed Modifying Acoustic Metasurfaces for Acoustic Holography. Advanced Materials (2023).
4. Meta-silencer with designable timbre. International Journal of Extreme Manufacturing (2023).