Key Findings:
Our study presents a promising approach to sound scattering suppression using illusion metamaterials. Through full-wave simulations and experimental measurements, we have confirmed the effectiveness of these metamaterials in guiding acoustic waves around obstacles. The waveguide and phase manipulation capabilities allow our metamaterials to accurately recreate the incoming wavefront on the exit surface, resulting in two remarkable illusionary effects in an ultra-broadband spectrum: disappearing space and time shift.

Here is a visual representation of our strategy, as shown in Fig. 1. In environments filled with randomly dispersed obstacles, sound transmission is often disrupted by multiple scattering phenomena. However, when these obstacles are covered with our designed metamaterials, the incident sound waves are non-destructively guided around the obstacles and recreated to transmit on the exit surface, effectively eliminating overall scattering.

Personal Stories and Experiences:
The inspiration for this research started before my research journey as a visiting PhD student at MIT in 2018. While exploring the concept of transformation optics (TO), I came to realize the bandwidth limit of traditional invisibility cloaks. Under the supervision of Prof. Fang and Prof. Lai, and in collaboration with Dr. Ma, I embarked on the project of overcoming this severe limit. We successfully established this new idea of using illusion acoustics of space and time to solve this long-standing constraint. Prof. Lai and I conducted the analysis, simulations, and sample fabrication. Prof. Fang and Dr. Ma carried out the experiment design and measurements. Finally, after several years, the collective efforts of our team bring this exciting research to fruition.

Broad Implications:
Our research addresses a critical bottleneck in the field of cloaking in transmission—narrow bandwidth limitation. By establishing a metamaterial platform for ultra-broadband sound manipulation, new possibilities are opened for practical applications such as: 
Acoustic camouflage. This technique could revolutionize deep-sea exploration by making ultra-broadband acoustic invisibility camouflages. Such camouflages were previously strongly limited in bandwidth. 
Reverberation control. In architectural acoustics, this technique could tailor the acoustic characteristics within a room, reducing unwanted echoes or reverberation, and thus enhancing sound quality and speech intelligibility. 

External Links and Sources:
For further reading, explore the foundational works that inspired our 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:
Our innovative approach to sound scattering suppression not only overcomes existing limitations but also paves the way for future advancements in acoustic manipulation. We hope to inspire more people to continue the journey towards practical invisibility, and look forward to engaging a diverse readership from experts in the field to curious members of the public. Join us in exploring the fascinating world of illusion acoustics and the endless possibilities it holds.

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