Acoustic Cloaking and Illusion: Passive and Active Mechanisms, Control Architectures, and Evaluation Frameworks

Abstract

Acoustic cloaking has been defined traditionally as the suppression of the acoustic signature of an object, while acoustic illusion consists of creating a real object whose response corresponds to a certain virtual target. Both methods have similar terminology but differ from each other with respect to the reference field, the goal of control, and the verification criterion. The review provides a comprehensive overview of scattering models of acoustic hard objects and transformation-acoustic and metamaterial designs of the passive type, scattered field cancellation of the active type, acoustic illusions and combined passive/active schemes. Comparison is done in relation to the impact of field decomposition, spatial modes, finite observation areas, position of sources and sensors, condition number of the transfer matrix, flow, bandwidth and model mismatch on performance. Specific attention is paid to the difference between total field suppression and scattered field suppression of an object. The global circumferential array, the local and line-array approaches, and different information that can be extracted from analytical, numerical and experimental research are compared on an equal footing. For all approaches considered here, cloaking is understood as conditional field-control statement related to the object, incident excitation, observation area, operating frequencies, and metrics. That is why the results of the different studies cannot be easily compared with each other, and hybrids are promising when passive structures deal with predictable parts and active control works with residual ones.