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1.
Daniel Torrent José Sánchez-Dehesa 《Wave Motion》2011,48(6):497-504
We present an analysis of acoustic cloaks based on the homogenization of two fluidlike materials, with an emphasis on periodically layered imperfect cloaks, by removing the singularities of the acoustic parameters required for ideal cloaks. The conditions that material layers should satisfy are systematically analyzed and critically discussed according to their feasibility. 相似文献
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We simplify the material parameter equation for elliptical cylinder
cloaks under transverse-electric and transverse-magnetic models,
respectively, and confirm these simplified equations by numerical
simulations. As a result, the number of the component parameters is
reduced from three to two, which simplifies the design of
meta-materials and thus opens up the possibility of achieving elliptical
cylinder cloaks in an easy way. 相似文献
4.
We start by a review of the chronology of mathematical results on the Dirichlet-to-Neumann map which paved the way toward the physics of transformational acoustics. We then rederive the expression for the (anisotropic) density and bulk modulus appearing in the pressure wave equation written in the transformed coordinates. A spherical acoustic cloak consisting of an alternation of homogeneous isotropic concentric layers is further proposed based on the effective medium theory. This cloak is characterized by a low reflection and good efficiency over a large bandwidth for both near and far fields, which approximates the ideal cloak with an inhomogeneous and anisotropic distribution of material parameters. The latter suffers from singular material parameters on its inner surface. This singularity depends upon the sharpness of corners, if the cloak has an irregular boundary, e.g. a polyhedron cloak becomes more and more singular when the number of vertices increases if it is star shaped. We thus analyze the acoustic response of a non-singular spherical cloak designed by blowing up a small ball instead of a point, as proposed in [Kohn, Shen, Vogelius, Weinstein, Inverse Problems 24, 015016, 2008]. The multilayered approximation of this cloak requires less extreme densities (especially for the lowest bound). Finally, we investigate another type of non-singular cloaks, known as invisibility carpets [Li and Pendry, Phys. Rev. Lett. 101, 203901, 2008], which mimic the reflection by a flat ground. 相似文献
5.
By using coordinate transformation method, this paper obtains an
useful equation of designing meta-material cloaks embedded in
anisotropic medium. This equation is the generalization of what was
introduced early by Pendry et al (2006 \textit{Science}
{312 1780) and can be more widely used. As an example of its
applications, this paper deduces the material parameter equation for
cylinder cloaks embedded in anisotropic medium, and then offers the
numerical simulation. The results show that such a cylinder cloak
has perfect cloaking performance and therefore verifies the method
proposed in this paper. 相似文献
6.
By using the coordinate transformation method, we have deduced the
material parameter equation for rotating elliptical spherical cloaks
and carried out simulation as well. The results indicate that the
rotating elliptical spherical cloaking shell, which is made of
meta-materials whose permittivity and permeability are governed by
the equation deduced in this paper, can achieve perfect invisibility
by excluding electromagnetic fields from the internal region without
disturbing any external field. 相似文献
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Two-dimensional(2D) elliptically cylindrical invisible cloaks with multiple regions are designed based on the transformation optics and the complementary media theory. Multiple invisible cloak regions can be obtained by properly using the compressed or folded transformation in each space layer. The constitutive parameter tensor expressions for each region have been obtained. The results of full wave simulations by using finite element software confirm the validity of the constitutive parameter tensor expressions. In addition, the parameters are relatively easier to realize. 相似文献
9.
This paper reports that a general method of designing
invisible cloaks is using variant constitutive material
parameters to realize the space transformation. A hollow region can
be hidden after this transformation. It was recently shown (Ma H, Qu
S B, Xu Z and Wang J F 2009 \wx{Appl. Phys. Lett.}{94} 103501) that
when the original point moves to the boundary of a cloak, the cloak
can be designed to be open. Based on this theory, we propose
multi-window invisible cloaks which can conceal a group of objects.
Full wave simulations for invisible cloaks with regular and
irregular shapes verified this method. 相似文献
10.
By making a comparison between the acoustic equations and the
2-dimensional (2D) Maxwell equations, we obtain the material
parameter equations (MPE) for acoustic elliptical cylindrical
cloaks. Both the theoretical results and the numerical results
indicate that an elliptical cylindrical cloak can realize perfect
acoustic invisibility when the spatial distributions of mass density
and bulk modulus are exactly configured according to the proposed
equations. The present work is the meaningful exploration of
designing acoustic cloaks that are neither sphere nor circular
cylinder in shape, and opens up possibilities for making complex and
multiplex acoustic cloaks with simple models such as spheres,
circular or elliptic cylinders. 相似文献