Non-closed acoustic cloaking devices enabled by sequential-step linear coordinate transformations

Zahra Basiri,Chen Shen,Mohammad Hosein Fakheri,Ali Abdolali

doi:10.1038/s41598-021-81331-3

Zahra Basiri, Chen Shen + Show 2 more

Open Access

https://doi.org/10.1038/s41598-021-81331-3

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Abstract

Hitherto acoustic cloaking devices, which conceal objects externally, depend on objects' characteristics. Despite previous works, we design cloaking devices placed adjacent to an arbitrary object and make it invisible without the need to make it enclosed. Applying sequential linear coordinate transformations leads to a non-closed acoustic cloak with homogeneous materials, creating an open invisible region. Firstly, we propose to design a non-closed carpet cloak to conceal objects on a reflecting plane. Numerical simulations verify the cloaking effect, which is completely independent of the geometry and material properties of the hidden object. Moreover, we extend this idea to achieve a directional acoustic cloak with homogeneous materials that can render arbitrary objects in free space invisible to incident radiation. To demonstrate the feasibility of the realization, a non-resonant meta-atom is utilized which dramatically facilitated the physical realization of our design. Due to the simple acoustic constitutive parameters of the presented structures, this work paves the way toward realization of non-closed acoustic devices, which could find applications in airborne sound manipulation and underwater demands.

Highlights

Hitherto acoustic cloaking devices, which conceal objects externally, depend on objects’ characteristics
Cloaks based on linear coordinate transformation have homogeneous constitutive parameters with finite anisotropy, which obviates the need for space dependent materials
The cloaking effect of the proposed non-closed devices is independent of the shape and constitutive material of the target

Summary

Introduction

Hitherto acoustic cloaking devices, which conceal objects externally, depend on objects’ characteristics. Applying sequential linear coordinate transformations leads to a non-closed acoustic cloak with homogeneous materials, creating an open invisible region. We propose to design a non-closed carpet cloak to conceal objects on a reflecting plane. Numerical simulations verify the cloaking effect, which is completely independent of the geometry and material properties of the hidden object We extend this idea to achieve a directional acoustic cloak with homogeneous materials that can render arbitrary objects in free space invisible to incident radiation. The inhomogeneous structure of quasi-conformal cloaks leads to a difficult fabrication process and neglecting the weak anisotropy causes a lateral shift in the reflected w ave[16] Another disadvantage is the size of this type of cloaks, which is bulky compared to that of the target. The dependence of the cloaking device on target and inevitable inhomogeneity of obtained materials are the remaining challenges that make the implementation of conventional external cloaks practically nonrealistic

Methods

Conclusion