We propose a practical realization of electromagnetic spherical cloaking by layered structure of homogeneous isotropic materials. By mimicking the classic anisotropic cloak by many alternating thin layers of isotropic dielectrics, the permittivity and permeability in each isotropic layer can be properly determined by effective medium theory in order to achieve invisibility. The model greatly facilitates modeling by Mie theory and realization by multilayer coating of dielectrics. Eigenmode analysis is also presented to provide insights of the discretization in multilayers. DOI: 10.1103/PhysRevE.79.047602 PACS number͑s͒: 41.20.Jb, 42.25.Fx, 41.20.Ϫq Recently, invisibility cloaks ͓1-4͔ have received great attention since Pendry et al. ͓5͔ suggested that an object coated by an inhomogeneous anisotropic shell becomes invisible to electromagnetic waves. The electromagnetic wave interaction with such a cloak was analyzed ͓6͔. In addition to the common method of geometric transformation, various approaches have been proposed to create invisibility cloaks, such as plasmonic resonances ͓7͔, scattering cancellation ͓8͔, negative index material ͓9͔, and stationary Schrödinger equation ͓10͔. Attempts to realize the cloaking idea have been initiated with encouraging results ͓11͔.Conventional cloaks need to be anisotropic and their parameters are functions of position. Although this restriction can be bypassed with the simplified material parameters ͓11͔, later it was found that the coating established by simplified parameters cannot perfectly shield the targeted object inside without electromagnetic perturbation to external EM fields ͓12͔. However, the cylindrical invisibility cloak is still difficult to realize due to the limited resource of natural materials exhibiting radial anisotropy ͓13͔, not to mention that those tensorial parameters are spatially varying. In this connection, Cai et al. ͓14͔ investigated a multilayered cylindrical cloak by discretizing the conventional position-dependent cloak into many layered coatings, and the material in each layer is position independent but still anisotropic. Huang et al. ͓15͔ proposed a cylindrical cloak by replacing one anisotropic coating with a multilayered structure in which each layer is constructed with a certain homogeneous isotropic medium. Some recent works on cylindrical acoustic cloaks were also reported ͓16,17͔. When each layer is thin enough, the effective medium theory can be employed to find out the required permittivity for each layer ͓18͔. More recently, this idea was further applied to three-dimensional acoustic cloak by multilayered isotropic materials ͓19͔.As for electromagnetic spherical invisibility cloaks, material parameters for the perfect cloak are suggested ͓5͔:where the cloak occupies the spherical region ͑a Ͻ r Ͻ b͒ and its constitutive material parameters are given bywhere the unit dyad is I = rr + + and the subscripts r and t denote the parameters along radial ͑r͒ and tangential direction ͑ or ͒, respectively. The anisotropic cloaking proposed b...

A new and simple method is proposed for the miniaturisation design of patch antenna utilising a low‐profile mushroom type meta‐substrate. The functional mushroom element is analytically studied. A simple designing rule is obtained to tailor the effective high permittivity for the element as one desires. In validation, one proof of the conceptual patch antenna is presented experimentally loaded with the mushroom meta‐substrate. The antenna size is 0.18λ0 × 0.18λ0 × 0.029λ0. Numerical and measured antenna characteristics are in good agreement. The impedance is well matched in bandwidth of 2.1%. The measured cross‐polar levels are all below −23 dB. The measured antenna gain is 5.7 dBi and the radiation efficiency is 85%. The authors remark that the meta‐substrate is intrinsically compatible with printed planar fabrication technology and can be easily made using common dielectrics and metals of low cost. The designing method in this work is simple and yet promising. With the intuitive analytical rule, any other desirable high index permittivity can be further obtained for future potential compact patch antenna designs.

We present optimized design of cylindrical invisibility cloak with minimum layers of non-magnetic isotropic materials. Through an optimization procedure based on genetic algorithm, simpler cloak structure and more realizable material parameters can be achieved with better cloak performance than that of an ideal non-magnetic cloak with a reduced set of parameters. We demonstrate that a cloak shell with only five layers of two normal materials can result in an average 20 dB reduction in the scattering width for all directions when covering the inner conducting cylinder with the cloak. The optimized design can substantially simplify the realization of the invisibility cloak, especially in the optical range.

Through a particularly chosen coordinate transformation, we propose an optical carpet cloak that only requires homogeneous anisotropic dielectric material. The proposed cloak could be easily imitated and realized by alternative layers of isotropic dielectrics. To demonstrate the cloaking performance, we have designed a two-dimensional version that a uniform silicon grating structure fabricated on a silicon-on-insulator wafer could work as an infrared carpet cloak. The cloak has been validated through full wave electromagnetic simulations, and the non-resonance feature also enables a broadband cloaking for wavelengths ranging from 1372 to 2000 nm.

We present the design, fabrication and performance test of a quasi three-dimensional carpet cloak made of normal dielectric in the microwave regime. Taking advantage of a simple linear coordinate transformation we design a carpet cloak with homogeneous anisotropic medium and then practically realize the device with multilayer of alternating normal dielectric slabs based on the effective medium theory. As a proof-of-concept example, we fabricate the carpet cloak with multilayer of FR4 dielectric slabs with air spacing. The performance of the fabricated design is verified through full-wave numerical simulation and measurement of the far-field scattering electromagnetic waves in a microwave anechoic chamber. Experimental results have demonstrated pronounced cloaking effect in a very broad band from 8 GHz to 18 GHz (whole X and Ku band) due to the low loss, non-dispersive feature of the multilayer dielectric structure.Comment: 10 pages, 4 figures. Accepted in Appl. Phys. Let