Acoustic cloaking theory

By Andrew N. Norris. Proceedings of the Royal Society A, 2008

612 citations recorded by the source corpus.

An acoustic cloak is a compact region enclosing an object, such that sound incident from all directions passes through and around the cloak as though the object was not present. A theory of acoustic cloaking is developed using the transformation or change-of-variables method for mapping the cloaked region to a point with vanishing scattering strength. We show that the acoustical parameters in the cloak must be anisotropic: either the mass density or the mechanical stiffness or both. If the stiffness is isotropic, corresponding to a fluid with a single bulk modulus, then the inertial density must be infinite at the inner surface of the cloak. This requires an infinitely massive cloak. We show that perfect cloaking can be achieved with finite mass through the use of anisotropic stiffness. The generic class of anisotropic material required is known as a pentamode material (PM). If the transformation deformation gradient is symmetric then the PM parameters are explicit, otherwise its properties depend on a stress-like tensor that satisfies a static equilibrium equation. For a given transformation mapping, the material composition of the cloak is not uniquely defined, but the phase speed and wave velocity of the pseudo-acoustic waves in the cloak are unique. Examples are given from two and three dimensions.

Subfields: Atomic and Molecular Physics, and Optics, Biomedical Engineering, Electronic, Optical and Magnetic Materials

View Paper: https://www.semanticscholar.org/paper/1fc9e99d442e604741cc806bd62ef83b2b771edb

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Citations in the corpus

Dynamic Mass Density and Acoustic Metamaterials (2007, background): “Acoustic cloaking has attracted theoretical attention in the past few years [55–67].”
Elastic cloaking theory (2011, neutral): “Cloaking with such materials requires very large total mass [9, 20], but the more general class of pentamode materials with anisotropic inertia does not have this constraint.”
Overcoming Mutual Blockage Between Neighboring Dipole Antennas Using a Low-Profile Patterned Metasurface (2012, background): “Several cloaking approaches have been proposed for acoustic [1], [2] and electromagnetic waves [3]–[9].”
Invisibility and Cloaking: Origins, Present, and Future Perspectives (2015, background): “Interestingly, similar considerations apply to acoustic cloaking [177], which is typically noncausal with respect to the background medium [178,179], and can escape the sum rule.”
On the feasibility of pentamode mechanical metamaterials (2012, background): “In three dimensions, one either needs materials with anisotropic mass density tensors [3,7,8,9] or pentamode materials [3,10,11,12] to implement the counterpart of invisibility cloaks or other devices.”