Three-Dimensional Axisymmetric Cloak Based on the Cancellation of Acoustic Scattering from a Sphere

Abstract

This Letter presents the design, fabrication, and experimental characterization of a directional three-dimensional acoustic cloak for airborne sound. The cloak consists of 60 concentric acoustically rigid tori surrounding the cloaked object, a sphere of radius 4 cm. The major radii and positions of the tori along the symmetry axis are determined using the condition of complete cancellation of the acoustic field scattered from the sphere. They are obtained through an optimization technique that combines genetic algorithm and simulated annealing. The scattering cross section of the sphere with the cloak, which is the magnitude that is minimized, is calculated using the method of fundamental solutions. The low-loss fabricated cloak shows a reduction of the 90% of the sphere scattering cross section at the frequency of 8.55 kHz.

A transient thermal cloak experimentally realized through a rescaled diffusion equation with anisotropic thermal diffusivity

“…[1][2][3][4][5][6][7][8] The TO technique has also led to the creation of many other important EM devices with functionalities previously deemed impossible or unconceivable. [9][10][11] In general, this coordinate operation can be applied to different partial differential equations governing the behaviors of other physical phenomena such as thermal flux, [12][13][14][15][16][17][18][19][20][21][22][23] acoustic wave, [24][25][26][27] and matter or quantum [28][29][30] waves, demonstrating important scientific and application potentials.…”

An elasto-mechanical unfeelability cloak made of pentamode metamaterials

“…Invisibility cloaks [4][5][6][7] and counterparts thereof are demonstrations of this progress. Cloaks have been demonstrated experimentally in electromagnetism at microwave 8 and at optical frequencies [9][10][11] , in airborne 12,13 and fluid-borne acoustics 14 , for fluid surface waves 15 , for electrical 16 and heat conduction [17][18][19] , as well as for flexural waves 20 in thin (quasi two-dimensional) elastic membranes. In three-dimensional (3D) solid mechanics, only unidirectional cloaking of stress waves in fibrous materials has been achieved 21 .…”

“…The theory underlying cloaking has either been based on analytical coordinate transformations [3][4][5][6] or on numerical topology optimization 13,[23][24][25] . The analytical theory for mere invisibility and analogues thereof based on simple spherical or cylindrical core-shell geometries has been worked out a long time ago [26][27][28] .…”

Active control of membrane-type acoustic metamaterial by electric field

“…Functionalities such as phase modulation and acoustic switch with on/off ratio up to 21.3 The development of acoustic metamaterials has significantly enhanced our ability in sound wave manipulation. Their unusual constitutive effective parameters, [1][2][3][4][5][6][7][8][9] which are not found in nature, have led to numerous remarkable phenomena, such as acoustic cloaking, [10][11][12][13][14] acoustic focusing and imaging, [15][16][17][18] nonreciprocal transmission, [19][20][21] wave propagation and wave front engineering, [22][23][24] and super absorption. 25,26 To date, most metamaterials are passive and hardly adjustable once fabricated.…”