Active acoustic cloaking and illusions of sound-hard bodies using the boundary element method

Abstract

Acoustic cloaking has received significant interest due to the appealing ability to render an object acoustically invisible. In a similar concept to acoustic cloaking, acoustic illusions provide the capability to misrepresent the acoustic field of an object. Combining acoustic cloaking and illusions with numerical discretization methods allow objects of greater complexity to be considered. This work presents active acoustic cloaking and illusions of three-dimensional rigid objects. The boundary element method is utilized to efficiently predict the exterior acoustic domain. A multi-input/multi-output control system comprising monopole control sources, error sensors, and a controller based on a feedforward linear-quadratic regulator algorithm is employed. Active acoustic cloaking of a simple object corresponding to a sphere is demonstrated for both non-decaying and decaying incident fields. For the same control configuration but minimizing a cost function based on different error signals, acoustic illusions are generated to mimic the presence of a sphere within a free field. Illusional fields are also generated for a cube and a bird to misrepresent their size or orientation.

Fast active thermal cloaking through PDE-constrained optimization and reduced-order modelling

“…Among alternative methods, another possible option is represented by the so-called ‘active’ cloaking: firstly developed in the context of the Helmholtz equation [23–26], where sensors and sources are used in a similar fashion as in classical noise cancellation [27], it has become an attractive solution for the thermal case as well [28–30]. Indeed, thermoelectric materials can be used to design heat sources and sinks that exert a suitable manipulation of the thermal field in a localized region of the domain (usually around the target to cloak) to achieve the cloaking objective.…”

Multilayer acoustic invisibility cloak based on composite lattice

“…Kim et al investigated the use of an optimized structure as a double split hollow sphere acoustic cloaking structure for irregular surfaces 26 . Using acoustic illusions, Lin et al provide the ability to misrepresent the sound field of an object 27 . Ahmed et al present the notion of a machine learning driven acoustic cloak.…”

Two-Dimensional Distributed Transmission-Line Models for Broadband Full-Tensor Anisotropic Acoustic Metamaterials Based on Transformation Acoustics

“…Recently, the theory of the 2-D equivalent circuit models for full-tensor anisotropic electromagnetic metamaterials has been extended to acoustic metamaterials [33,34] in order to realize acoustic invisible cloaks [21,[35][36][37][38][39][40][41][42][43][44][45][46][47], acoustic carpet cloaks [33,[48][49][50][51][52][53][54][55][56], or acoustic illusion media [34,[57][58][59][60] based on the concept of transformation acoustics [35]. As is the same in the case of the electromagnetic metamaterials, the conventional design methods have issues like many calculations for designing the unit cell structures or narrowband characteristics, but the models introduced from the electromagnetic metamaterials can solve these simultaneously.…”