Science & Technology

Ultra-broadband Invisibility Enabled by Illusion Acoustics: A Breakthrough in Sound Manipulation

Scientists from Nanjing University, University of Hong Kong and University of Wisconsin-Madison, have developed an innovative way to manipulate sound waves using illusion acoustics, enabling ultra-broadband sound invisibility. This breakthrough has significant implications for fields ranging from deep-sea exploration to architectural acoustics.       

                     Image: Illustration of the illusion.

The collaborative research team has achieved a significant achievement in sound manipulation through the use of illusion metamaterials. This novel approach successfully suppresses sound scattering over a broad spectrum, making obstacles effectively undetectable by sound waves of arbitrary frequencies. Such technology could enable a range of applications, including acoustic camouflage and reverberation control.

Using full-wave simulations and experimental measurements, the research demonstrates how to design illusion metamaterials to guide sound waves around objects without distortion. This results in two key illusionary effects: disappearing space and time shift. Both effects are achieved across an ultra-broadband spectrum, overcoming the traditional limitations of narrowband acoustic cloaking.

Key Findings:

l Illusion metamaterials enable ultra-broadband sound scattering suppression.

l Two illusionary effects—disappearing space and time shift—are observed across a broad spectrum.

l The technique can guide sound waves around obstacles without significant loss or scattering.

Research Background:

The project began in 2018 and was inspired by earlier works in transformation optics. Despite great achievements in invisibility cloaks via transformation optics, they all suffer from the narrow bandwidths due to the need for resonant metamaterials as well as the causal limitation of the speed of light. The team, consisting of Prof. Yun Lai and Dr. Chenkai Liu in Nanjing University, Prof. Nicholas Fang in University of Hong Kong and Dr. Chu Ma in University of Wisconsin-Madison, aimed to overcome this narrow bandwidth limitation of traditional invisibility cloaks. After years of analyses, simulations, and experiments, they have finally achieved this goal by showing an illusionary device that allows ultra-broadband acoustic invisibility, and thus developed a new metamaterial platform for sound manipulation.

Implications:

This breakthrough opens doors for practical applications, including:

l Acoustic camouflage: The technology could revolutionize deep-sea exploration, providing ultra-broadband sound invisibility camouflages.

l Architectural acoustics: It could enable fine-tuning of acoustic environments, reducing reverberation and improving sound quality in spaces like concert halls and auditoriums.

Further Reading:

Explore foundational works that inspired this research:

Invisibility Cloaks:

Leonhardt, U. Science 312, 1777–1781 (2006)

Pendry, J. B. et al. Science 312, 1780–1782 (2006).

Schurig, D. et al. Science 314, 977–980 (2006).

Zhang, S. et al. Phys. Rev. Lett. 106, 024301 (2011).

Cummer, S. A. et al. New J. Phys. 9, 45 (2007).

Chen, H. et al. Appl. Phys. Lett. 91, 183518 (2007).

Chen, H. S. et al. Nat. Commun. 4, 2652 (2013).

Illusion Optics (Acoustics):

Lai, Y. et al. Phys. Rev. Lett. 102, 253902 (2009).

Scattering Cancellation:

Lai, Y. et al. Phys. Rev. Lett. 102, 093901 (2009).

Sanchis, L. et al. Phys. Rev. Lett. 110, 124301 (2013).

Conclusion:

This research represents a critical advancement in the field of sound manipulation, overcoming longstanding limitations and offering new possibilities for the future. The potential for acoustic invisibility across diverse fields is now within reach.


Link to Full Study: DOI Foundation-024-49856-z



Source: School of Physics

Correspondent: Lai Yun