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Metamaterials with carefully chosen negative permittivity and permeability can guide electromagnetic wave to bypass a target without any scattering theoretically. This paper uses the basic theory of coordinate transformation to generate such permittivity and permeability which can result in such a perfectly cloak effect. The invisibility of the cloak is demonstrated by a cylinder and a sphere wrapped with metamaterial. COMSOL Multiphysics software is utilized to simulate the interaction between incident electromagnetic wave and the cloaks. Monostatic and bistatic radar cross section (RCS) is calculated to show the scattering suppression effect. The results show that metamaterials have an excellent performance in reduction of the scattering. Backscattering RCS can be reduced about 20 dB relative to the non-cloak target. [ABSTRACT FROM AUTHOR]

In this paper, we apply the mantle cloaking method to reduce the mutual coupling between two closely spaced wideband antennas operating at microwave frequencies. We show that by introducing two dielectric elliptical shells around the antennas and covering them with two strongly coupled elliptically shaped metasurfaces comprised of I-shaped printed unit cells, it is possible to significantly increase the original bandwidth of the antennas and, at the same time, reduce the mutual electromagnetic interaction. This effect is observed both in a reduction of mutual S-parameters between the antennas and in the restoration of the original radiation patterns, as if the antennas were almost completely isolated from each other. Broadband metasurface/cloak designs are proposed for two geometries, with the free-standing strip monopole antennas placed over a ground plane and with the metasurface cloaks integrated with microstrip antennas. [ABSTRACT FROM AUTHOR]

The radar cross section (RCS) reduction of hypersonic targets by radar absorbing materials (RAM) coating under different reentry cases is analyzed in the C and X bands frequency range normally used for radar detection. The physical optics method is extended to both the inhomogeneous plasma sheath and RAM layer present simultaneously. The simulation results show that the absorbing coating can reduce the RCS of the plasma cloaking system and its effectiveness is related to the maximum plasma frequency. Moreover, the amount of the RCS decrease, its maxima, and the corresponding optimal RAM thickness depend on the non-uniformity and parameters of the plasma sheath. In addition, the backward RCS of the flight vehicle shrouded by plasma shielding and man-made absorber is calculated and compared to the bare cone. [ABSTRACT FROM AUTHOR]

Metasurfaces are optically thin layers of subwavelength resonators that locally tailor the electromagnetic response at the nanoscale. Our metasurface research aims at developing novel designs and applications of metasurfaces that go beyond the classical regimes. In contrast to conventional phase gradient metasurfaces where each meta-atom responds individually, we are interested in developing metasurfaces where neighboring meta-atoms are strongly coupled. By engineering a non-Hermitian coupling between the meta-atoms, new degrees of freedom are introduced and novel functionalities can be achieved. We are also interested in combining classical metasurface with quantum emitters, which may offer opportunities for on-chip quantum technologies. Additionally, we have been designing metasurfaces to realize exciting phenomena and applications, such as ultrathin metasurface cloak and strong photonic spin-Hall effect. In this paper, we review our research efforts in optical metasurfaces in the past few years, which ranges from conventional to novel type of metasurface and from classical to quantum regime. [ABSTRACT FROM AUTHOR]

Locally resonant acoustic metamaterials have recently attracted a great interest due to their dynamic behaviour, characterized by a band gap at relatively low frequencies. This paper provides a numerical study, by means of finite element modal analyses, of the dynamic properties of 1D mass-inmass and 2D cellular locally resonant metamaterials. The 2D metamaterial is constituted by a cellular metallic lattice, filled by a soft light material with heavy inclusions or resonators. The influence of material parameters and cell geometry on the band gap width and frequency level are explored. In addition to the usual square lattice we also consider a hexagonal one, which proves to be more efficient for wave filtering. [ABSTRACT FROM AUTHOR]

This paper is concerned with the invisibility cloaking in acoustic wave scattering from a new perspective. We are especially interested in achieving the invisibility cloaking by completely regular and isotropic mediums. It is shown that an interior transmission eigenvalue problem arises in our study, which is the one considered theoretically in Cakoni et al. (Transmission eigenvalues for inhomogeneous media containing obstacles, Inverse Problems and Imaging, 6 (2012), 373–398). Based on such an observation, we propose a cloaking scheme that takes a three-layer structure including a cloaked region, a lossy layer and a cloaking shell. The target medium in the cloaked region can be arbitrary but regular, whereas the mediums in the lossy layer and the cloaking shell are both regular and isotropic. We establish that if a certain non-transparency condition is satisfied, then there exists an infinite set of incident waves such that the cloaking device is nearly invisible under the corresponding wave interrogation. The set of waves is generated from the Herglotz approximation of the associated interior transmission eigenfunctions. We provide both theoretical and numerical justifications. [ABSTRACT FROM PUBLISHER]

For a two-dimensional model of thermal scattering, inverse problems arising in the development of tools for cloaking material bodies on the basis of a mixed thermal cloaking strategy are considered. By applying the optimization approach, these problems are reduced to optimization ones in which the role of controls is played by variable parameters of the medium occupying the cloaking shell and by the heat flux through a boundary segment of the basic domain. The solvability of the direct and optimization problems is proved, and an optimality system is derived. Based on its analysis, sufficient conditions on the input data are established that ensure the uniqueness and stability of optimal solutions. [ABSTRACT FROM AUTHOR]

The present analysis shows that two conducting cylindrical particles illuminated by an axially-polarized electric field of plane progressive waves at arbitrary incidence will attract, repel or become totally cloaked (i.e., invisible to the transfer of linear momentum carried by the incident waves), depending on their sizes, the interparticle distance as well as the angle of incidence of the incident field. Based on the rigorous multipole expansion method and the translational addition theorem of cylindrical wave functions, the electromagnetic (EM) radiation forces arising from multiple scattering effects between a pair of perfectly conducting cylindrical particles of circular cross-sections are derived and computed. An effective incident field on a particular particle is determined first, and used subsequently with its corresponding scattered field to derive the closed-form analytical expressions for the radiation force vector components. The mathematical expressions for the EM radiation force components (i.e. longitudinal and transverse) are exact, and have been formulated in partial-wave series expansions in cylindrical coordinates involving the angle of incidence, the interparticle distance and the expansion coefficients. Numerical examples illustrate the analysis for two perfectly conducting circular cylinders in a homogeneous nonmagnetic medium of wave propagation. The computations for the dimensionless radiation force functions are performed with particular emphasis on varying the angle of incidence, the interparticle distance, and the sizes of the particles. Depending on the interparticle distance and angle of incidence, the cylinders yield total neutrality (or invisibility); they experience no force and become unresponsive to the transfer of the EM linear momentum due to multiple scattering cancellation effects. Moreover, pushing or pulling EM forces between the two cylinders arise depending on the interparticle distance, the angle of incidence and their size parameters. This study provides a complete analytical method and computations for the longitudinal and transverse radiation force components in the multiple scattering of EM plane progressive waves with potential applications in particle manipulation, optically-engineered metamaterials with reconfigurable periodicities and cloaking devices to name a few examples. [ABSTRACT FROM AUTHOR]

In this article, we describe the notion of a cloak achieved by employing the usual composite dielectrics surrounding a metal cube, a concept that was first presented by Hwang and Chin [1]. Here, we use an optimization procedure to improve on their results and obtain a three-dimensional composite dielectric structure that can achieve a better broadband match than that of [1]. The two structures of interest are an empty metallic waveguide and a metal cube placed inside the same waveguide but surrounded by different-sized dielectric slabs so that the effect of the metal cube in the transmitted fields inside the waveguide will not be much different from the fields that would exist in an empty waveguide. The dimensions and properties of the simple dielectrics making up the different slabs inside the waveguide are optimized using an electromagnetic simulator called Higher Order Basis Based Integral Equation Solver (HOBBIES) [2] so that the waveguide will appear empty by looking at the nature of the transmitted fields from the waveguide loaded with a metallic cube but surrounded by some dielectrics. [ABSTRACT FROM PUBLISHER]

This letter demonstrates the design of continuously graded elastic cylinders to achieve passive cloaking from harmonic acoustic excitation, both at single frequencies and over extended bandwidths. The constitutive parameters in a multilayered, constant-density cylinder are selected in a partial differential equation-constrained optimization problem, such that the residual between the pressure field from an unobstructed spreading wave in a fluid and the pressure field produced by the cylindrical inclusion is minimized. The radial variation in bulk modulus appears fundamental to the cloaking behavior, while the shear modulus distribution plays a secondary role. Such structures could be realized with functionally-graded elastic materials. [ABSTRACT FROM AUTHOR]

A lot of researchers utilize side-information, such as the map which is likely to be exploited by some attackers, to protect users' location privacy in location-based service (LBS). However, current technologies universally model the side-information for all users and don't distinguish different users. We argue that the side-information is personal for every user. In this paper, we propose an efficient method, namely EPLA, to protect the users' privacy using visit probability. We select the dummy locations to achieve k-anonymity according to personal visit probability for users' queries. In EPLA, we use AKDE(Approximate Kernel Density Estimate), which greatly reduces the computational complexity compared with KDE approach. We conduct the comprehensive experimental study on the two real Gowalla and Foursqure data sets and the experimental results show that EPLA obtains fine privacy performance and low computation complexity. [ABSTRACT FROM AUTHOR]

Abstract: The aim of this study is to propose guidelines for the systems engineering of future stealth combat vehicles using Low Observable Technology (LOT). A case study approach, based on interviews and document reviews, was used to analyze the systems engineering processes of the SEP multirole armored vehicle and the Visby class corvette respectively. The result is a thorough investigation of what worked in the cases studied, but with lessons extrapolated into recommendations for future development programs. These will have to deal with an increasingly complex sensor threat and a transformed, multilateral, European procurement environment. The main conclusion is that coherence and traceability between military needs on the battlefield and signature requirements is expected to be particularly challenging. A workflow tailored for requirements analysis in LO combat vehicle programs has, therefore, been derived and is presented here. In addition, the most important enablers for future multilateral development programs involving LOT have been identified as: establishing common best practices, demonstrator programs, an integrated product team approach, and, in line with similar work on combat aircraft, establishing stealth as a key architectural principle. [ABSTRACT FROM AUTHOR]

Shielding charged particle beams from transverse magnetic fields is a common challenge for particle accelerators and experiments. We demonstrate that a magnetic field cloak is a viable solution. It allows for the use of dipole magnets in the forward regions of experiments at an Electron Ion Collider (EIC) and other facilities without interfering with the incoming beams. The dipoles can improve the momentum measurements of charged final state particles at angles close to the beam line and therefore increase the physics reach of these experiments. In contrast to other magnetic shielding options (such as active coils), a cloak requires no external powering. We discuss the design parameters, fabrication, and limitations of a magnetic field cloak and demonstrate that cylinders made from 45 layers of YBCO high-temperature superconductor, combined with a ferromagnetic shell made from epoxy and stainless steel powder, shield more than 99% of a transverse magnetic field of up to 0.45 T (95% shielding at 0.5 T) at liquid nitrogen temperature. The ferromagnetic shell reduces field distortions caused by the superconductor alone by 90% at 0.45 T. [ABSTRACT FROM AUTHOR]

In this paper we establish the explicit expression for two-dimensional (2D) electro-magnetic cloaks of arbitrary star shapes without explicit contour expressions of the objects. Furthermore, 2D arbitrary star-shaped time domain cloak models are developed. A new finite element time domain (FETD) scheme is developed to solve the governing equations, and its stability is also proved. Numerical results are presented to confirm our theoretical analysis of the cloak models and the effectiveness of our FETD method. To our best knowledge, this is the first time domain finite element simulation of arbitrary star-shaped cloaks. [ABSTRACT FROM AUTHOR]

• An adaptive strategy for active thermal convective cloak via heat gain and loss is proposed. • Adaptive heat sources have been demonstrated to be feasible for heat convection. • An inverse process is built to calculate the heat source via conjugate gradient method. • Thermal cloak is experimentally validated using a heat source matrix. Thermal metamaterials, known for their effective and directional heat control and management strategy, have garnered significant attention leading to the investigation of various functional thermal conductive metadevices. Nevertheless, conventional thermal convective metadevices resort to artificial structures in the flow field, which face the challenge of the coupling of heat and mass transfer and unstable flow field. Herein, we report an adaptive strategy for fabricating an active thermal convective cloak via tunable heat gain and loss. Adaptive body and surface heat sources, rather than graded structures inside functional regions, have been demonstrated to be feasible for heat convection. Accompanied by the active manipulation scheme, an inverse design process was constructed to calculate the heat source distributions based on the knowledge of the target temperature fields. The proof-of-concept heat source matrix, using well-laid out resistance heaters and thermoelectric components, experimentally validated the thermal cloaking pattern in the flow field. The active scheme overcomes the limitations of the complex engineered structures required for conventional thermal convective metadevices. Thus, in this study, we establish a new paradigm for thermal convective camouflage and pave the way for active thermal management in heat convection. [ABSTRACT FROM AUTHOR]

[Display omitted] • An acoustic metafluid made of hollow regular polygons immersed in water is proposed, which can realize independent manipulation of mass density and bulk modulus. • A theory model is established to accurately calculate the effective acoustic parameters of the proposed metafluid. • The underwater impedance-matched gradient index lens and carpet cloak have been designed and experimentally demonstrated based on the proposed metafluid. Tuning the mass density and bulk modulus independently is the key to manipulate the propagation of sound wave. Acoustic metamaterials provide a feasible method to realize various acoustic parameters. However, the relevant studies are mainly concentrated in air, and the huge impedance difference makes it difficult to directly extend these airborne structures to underwater application. Here, we propose a metafluid to realize independent manipulation of the mass density and bulk modulus underwater. The metafluid is composed of hollow regular polygons immersed in the water. By adjusting the side number of the hollow regular polygons and choosing proper materials, the effective mass density and bulk modulus of the metafluid could be modulated independently. Based on the flexible adjustment method, metafluids with same impedance but different sound velocities are designed and used to realize an underwater impedance-matched gradient index lens. In addition, by combining the proposed metafluid with other artificial structures, acoustic parameters with great anisotropy can be achieved, which is exemplified by the design and demonstration of an impedance-matched underwater acoustic carpet cloak. This work can expand the practicability of underwater metamaterials and pave the way for future potential engineering applications in the practical underwater devices. [ABSTRACT FROM AUTHOR]

The thermocapillary motion of both cloaked and non-cloaked droplets on slippery liquid-infused porous surface were investigated experimentally. The effect of droplet radius, temperature gradient and oil viscosity on the migration velocity of droplet were considered. We found that the migration velocity of cloaked droplet was larger than that of non-cloaked droplet, which was attributed to the larger apparent radius. Through nondimensional analysis, the migration velocity of both cloaked and non-cloaked droplet followed the same linear relation with Marangoni number with slope of k = 22, which indicated that the cloaking effect actually promoted the thermocapillary motion of droplet on SLIPS with an external temperature gradient. In addition, the motion of oil layer underneath droplet was observed, which was responsible for the positive intercept of migration velocity. [ABSTRACT FROM AUTHOR]

The phase pattern tailoring and finite/nonzero wave impedance properties of double-near-zero materials, which have both the permittivity and permeability close to zero, are utilized to reduce the size of certain electromagnetic devices. As a proof of concept, it is applied to internal and external cloaks and field concentrators. The proposed technique enables reducing the size of the investigated devices by 50% by changing their structure from a full cylinder to half cylinder. The half-sized devices can still perform the functions of their full-size counterparts. To understand the phenomenon and validate the numerical results, the method is proven analytically for the internal cloak. The same analysis can also be applied for the external cloak and concentrator. For the included analysis, the transverse electric Z-polarization is used. For the transverse magnetic Z-polarization, the duality principal can be applied. [ABSTRACT FROM PUBLISHER]

A topology optimization technique based on the topological derivative and the level set function is utilized to design/synthesize the microstructure of a pentamode material for an acoustic cloaking device. The technique provides a microstructure consisting of a honeycomb lattice composed of needle-like and joint members. The resulting metamaterial shows a highly anisotropic elastic response with effective properties displaying a ratio between bulk and shear moduli of almost three orders of magnitude. Furthermore, in accordance with previous works in the literature, it can be asserted that this kind of microstructure can be realistically fabricated. The adoption of a topology optimization technique as a tool for the inverse design of metamaterials with applications to acoustic cloaking problems is one contribution of this paper. However, the most important achievement refers to the analysis and discussion revealing the key role of the external shape of the prescribed domain where the optimization problem is posed. The efficiency of the designed microstructure is measured by comparing the scattering wave fields generated by acoustic plane waves impinging on bare and cloaked bodies. Copyright © 2017 The Authors. International Journal for Numerical Methods in Engineering Published by John Wiley & Sons Ltd. [ABSTRACT FROM AUTHOR]

Transient thermal cloak has been attracting considerable attention due to the excellent performance in terms of heat-front maintenance and stable heat protection. However, their inhomogeneous and extreme parameters usually require challenging realization with metamaterials, thus leading to time-consuming and complicated fabrication even after some simplifications. In this paper, we propose a novel method to design an arbitrarily N-sided polygonal transient thermal cloak with nonsingular and homogenous material parameters. We further demonstrate that such cloak can be realized with only four kinds of natural bulk materials in bilayer configuration throughout. The multilayered materials can be easily arranged in a planarly stratified configuration due to all the flat boundaries, which makes the proposed cloaks much easier in fabrication and application. Simulation results validate the proposed scheme applicable to both steady-state and time-dependent cases with excellent performance. Based on the fact that an arbitrary shape can be approached by a polygon, our work actually opens up an avenue to arbitrarily shaped transient thermal cloaks made with natural bulk materials in bilayer configurations. [ABSTRACT FROM AUTHOR]

With the development of sensor technology and the popularization of the data-driven service paradigm, spatial crowdsourcing systems have become an important way of collecting map-based location data. However, large-scale task management and location privacy are important factors for participants in spatial crowdsourcing. In this paper, we propose the use of an R-tree spatial cloaking-based task-assignment method for large-scale spatial crowdsourcing. We use an estimated R-tree based on the requested crowdsourcing tasks to reduce the crowdsourcing server-side inserting cost and enable the scalability. By using Minimum Bounding Rectangle (MBR)-based spatial anonymous data without exact position data, this method preserves the location privacy of participants in a simple way. In our experiment, we showed that our proposed method is faster than the current method, and is very efficient when the scale is increased. [ABSTRACT FROM AUTHOR]

In many applications, a cloaked resonator is highly desired, which can harvest and maximize the energy within the resonator without being detected. This paper presents the resonator cloaking achieved by topology optimization-based inverse design methodology. The resonator cloaking is inversely designed by solving the topology optimization problem with minimizing the ratio of the scattering field energy outside the cloak and the cloaked resonating field energy. By inversely designing the resonator cloaking with relative permittivity 2 for both the resonator and cloak, the topology optimization-based inverse design methodology is demonstrated, where the incident angle sensitivity is considered to derive incident angle insensitive design. Then, the proposed methodology is applied for the cases with resonator and cloak materials chosen from dielectrics with low, moderate and high permittivity, respectively. The derived results demonstrate that the resonator cloaking can be categorized into three types, which are the Fabry-Pérot resonance cloaking, Mie resonance cloaking and hybrid resonance cloaking. [ABSTRACT FROM AUTHOR]

This paper demonstrates the design of ultra-transparent anisotropic media for broadband acoustic invisibility. The required parameter distributions of the proposed invisibility cloak are derived by coordinate transformation, and its practical implementation simply consists of two-dimensional solid arrays in fluids. By studying the acoustic properties of the structures in the quasi-static limit, it is found that similar anisotropic features and transparent effects can be achieved with two kinds of structures, i.e., anisotropic solid cells arranged in the square lattice and cylindrical cells arranged in the highly anisotropic lattice. The acoustic impedance of the anisotropic cloaking media can be perfectly matched to the background fluid. The performances of the designs are quantitatively evaluated and compared in broadband by the averaged invisibility parameter. The full threedimensional structure is also analyzed for demonstrating the practical feasibility of the scheme. The results show that the anisotropic structures are effective for manipulating the acoustic field and suppressing the wave scattering. [ABSTRACT FROM AUTHOR]

The inverse problem of designing multilayered spherical shells, intended for thermal cloaking a spherical body or concentrating heat in it, has been analyzed. The stationary heat conduction equation for an anisotropic medium is applied as an original mathematical model. The optimization method is used to reduce this inverse problem to an extreme problem, where the role of controls is played by the thermal conductivities of shell layers. A numerical algorithm for solving the problem is proposed, and the results of computational experiments are discussed. [ABSTRACT FROM AUTHOR]

We design an acoustic metamaterial by coiling up space, namely the spiral-labyrinthine acoustic metamaterial (SLAM). The transmission coefficient illustrates that the SLAM exhibits extraordinary abilities for sound absorption at the two dips with a subwavelength scale. Even at the extremely small filling ratio, the corresponding transmission loss at the two dip frequencies are also up to 99%. The reason is that the monopolar resonance and the dipolar resonance can remarkably concentrate the energy of sound wave. A much wider frequency range between the monopolar resonant frequency and the dipolar resonant frequency can be obtained by the SLAMs for sound blocking. The SLAM has many other interesting applications, such as the acoustic cloaking and the sound supertunneling. [ABSTRACT FROM AUTHOR]

Declaration of 2015 as theInternational Year of Light and Light-based Technologiesinspired many workers who are involved in some way in the development of new applications of light. This article attempts to spread the awareness about the challenges for electrical engineers in the field of nanophotonics, currently at the center of intense activities. We have chosen four areas of nanophotonics, which can be explored using electromagnetic principles and methods: Plasmonics, Superlens, Optical Antenna and Transformation Optics. No attempt is made to review the work done in these areas and the emphasis is on the concepts that can be appreciated and absorbed by the electrical engineers. [ABSTRACT FROM PUBLISHER]

In this paper, we present various schemes of cloaking an arbitrary object via anomalous localized resonance and provide their analysis in two and three dimensions. This is a way to cloak an object using negative index materials in which the cloaking device is independent of the object. As a result, we show that in the two dimensional quasi-static regime an annular plasmonic structure of coefficient -1 cloaks small but finite size objects nearby. We also discuss its connections with superlensing and cloaking using complementary media. In particular, we confirm the possibility that a lens can act like a cloak and conversely. This possibility was raised about a decade ago in the literature. [ABSTRACT FROM AUTHOR]

Optimization problems for a three-dimensional model of acoustic scattering are formulated and studied. These problems arise in designing tools for cloaking material bodies by applying the wave flow method. The cloaking effect is achieved due to an optimal choice of variable parameters of the inhomogeneous isotropic medium occupying the sought shell. The solvability of direct and optimization problems for the acoustic scattering model is proved, and sufficient conditions ensuring the uniqueness and stability of optimal solutions are established. [ABSTRACT FROM AUTHOR]

A great deal of interest has reemerged recently in the study of surface waves. The possibility to control and manipulate electromagnetic wave propagations at will opens many new research areas and leads to lots of novel applications in engineering. In this paper, we will present a comprehensive modeling and design approach for surface wave cloaks, based on graded-refractive-index materials and the theory of transformation optics. It can be also applied to any other forms of surface wave manipulation, in terms of amplitude and phase. In this paper, we will present a general method to illustrate how this can be achieved from modeling to the final design. The proposed approach is validated to be versatile and allows ease in manufacturing, thereby demonstrating great potential for practical applications. [ABSTRACT FROM AUTHOR]

An efficient iterative analytical-numerical method is proposed for three-dimensional (3D) electromagnetic scattering from an inhomogeneous object buried beneath a two-dimensional (2D) randomly dielectric rough surface. In the hybrid method, the electric and magnetic currents on the dielectric rough surface are obtained by current-based Kirchhoff approximation (KA), while the scattering from the inhomogeneous object is rigorously studied by finite element method (FEM) combined with the boundary integral method (BIM). The multiple interactions between the buried object and rough surface are taken into account by updating the electric and magnetic current densities on them. Several numerical simulations are considered to demonstrate the algorithm’s ability to deal with the scattering from the inhomogeneous target buried beneath a dielectric rough surface, and the effectiveness of our proposed method is also illustrated. [ABSTRACT FROM AUTHOR]

Recent advances in the design of metamaterials that control diffusive transport processes have enabled efficient devices to manipulate heat conduction. In contrast, control of mass diffusion with metamaterial devices has been largely unexplored. Mass diffusion is critically important in multiple research areas ranging from electronic and energy materials to chemical and biological systems. In this work, we introduce a physical approach to design mass diffusion metamaterial devices that take into account the fundamental physical mechanisms behind mass transport. We demonstrate that mass concentration discontinuities arising from different material solubilities are critical physical factors that need to be incorporated for the accurate design and characterization of mass diffusion metamaterial devices. We employ our approach to devise and analyze cloaking and focusing of molecules and show how the difference in solubilities is critically important for the efficiency of the metamaterials. This work provides physical insights and guidelines to understand and design mass diffusion in metamaterial devices. [ABSTRACT FROM AUTHOR]

Using a sum rule, we derive new bounds on Herglotz functions that generalize those given in Bernland et al. [J. Phys. A: Math. Theor. 44(14), 145205 (2011)] and Gustafsson and Sjöberg [New J. Phys. 12(4), 043046 (2010)]. These bounds apply to a wide class of linear passive systems such as electromagnetic passive materials. Among these bounds, we describe the optimal ones and also discuss their meaning in various physical situations like in the case of a transparency window, where we exhibit sharp bounds. Then, we apply these bounds in the context of broadband passive cloaking in the quasistatic regime to refute the following challenging question: is it possible to construct a passive cloaking device that cloaks an object over a whole frequency band? Our rigorous approach, although limited to quasistatics, gives quantitative limitations on the cloaking effect over a finite frequency range by providing inequalities on the polarizability tensor associated with the cloaking device. We emphasize that our results hold for a cloak or object of any geometrical shape. [ABSTRACT FROM AUTHOR]

The inception of transformation optics has led to the realisation of the invisibility devices for various applications, one of which is spherical cloaking. In this paper, a formulation for a higher-order spherical cloak has been proposed to reduce its physical thickness significantly by introducing a nonlinear relation between the original and transformed coordinate systems and it has been verified using the ray tracing approach. Analysis has been carried out to observe the anomalies in the variation of refractive index for higher order cloaks indicating the presence of poles in the relevant equations. Furthermore, a higher-order spherical cloak with predefined values of the material characteristics on its inner and outer surfaces has been designed for practical application. [ABSTRACT FROM AUTHOR]

Protein corona formation was regulated on the surface in vivo by molecular imprinting to enable polymeric nanogels to acquire stealth upon intravenous administration. Albumin, the most abundant protein in blood, was selected as a distinct protein component of protein corona for preparing molecularly imprinted nanogels (MIP-NGs) to form an albumin-rich protein corona. Intravital fluorescence resonance energy transfer imaging of rhodamine-labeled albumin and fluorescein-conjugated MIP-NGs showed that albumin was captured by MIP-NGs immediately after injection, forming an albumin-rich protein corona. MIP-NGs circulated in the blood longer than those of non-albumin-imprinted nanogels, with almost no retention in liver tissue. MIP-NGs also passively accumulated in tumor tissue. These data suggest that this strategy, based on regulation of the protein corona in vivo, may significantly influence the development of drug nanocarriers for cancer therapy. [ABSTRACT FROM AUTHOR]

Non-linear shape external cloak using a parabolic transformation function is proposed with finite material properties. A simple one directional folding operation is utilised that provides homogeneous material properties in the complementary region, and also eases the creation of anti-object in the complementary region from an object present in the cloaked region. In the core region, the axial material parameter is spatially invariant and other parameters are spatially varying but possess finite value. Due to finite small material range and its one directional spatial variation, the proposed cloak even with discrete material properties in core region shows nearly zero scattering in contrast to earlier reported cloak. Further, off-diagonal elements of the core constitutive tensors in the Cartesian coordinate system are removed by converting them to diagonal elements in the principal coordinate system. Thus, only three diagonal elements are needed in the principal coordinate system to create the core medium, which are finite and realisable using two-dimensional metamaterials. [ABSTRACT FROM AUTHOR]

An epsilon-near-zero graphene--silica metamaterial-based structure is proposed and numerically investigated to realize super-reflection and cloaking. The advantage of this structure is that the operating bandwidth can be actively controlled by varying the chemical potential of graphene. By applying different electromagnetic boundary conditions, super-reflection and cloaking can be realized no matter what shape and size the object is inside this device. The ultracompact structure has potential applications in microcosmic science and military detection. [ABSTRACT FROM AUTHOR]

Thermal cloaks have been widely studied and experimented with. However, discussions on cloaking performance based on different design parameters effects are lacking. In this paper, we focus on predicting the cloaking performances of 2D thermal cloak schemes with different design parameters such as layer number, thickness, temperature difference, and relative thermal conductivity. The concept of response entropy, which is based on entropy generation analysis and is used to characterize the cloaking performance, is proposed. A regression model is established to predict the response entropy of the variational design parameters using response surface method (RSM). Five confirmation tests are conducted to verify the accuracy of the prediction. The relationship between the response entropy and the interaction effects of the design parameters are described with the help of 3D response surfaces using analysis of variance (ANOVA). In conclusion, we propose that a core-shell cloaking scheme with modest parametric values of 1–18 layers, a thickness of 1–5 mm, a small relative thermal conductivity, and large temperature difference can provide a better cloaking performance. This paper presents a theoretical prediction of the cloaking performance and provides suggestions on fabricating better thermal cloaks under different parameters. [ABSTRACT FROM AUTHOR]

A singular coordinate transformation leads to extreme materials in a transformation-based cloak. If a non-singular transformation is used, the perfect invisibility is lost. The invisibility is also influenced by the homogenization process. In this paper, we investigate these two influences in 2-D circular cylindrical cloaks, obtained from different non-singular mappings. Considering a further deterministic optimization, we also conclude that it is better to use a non-singular cloak based on a mapping scale up to 20%, since it has lower scattering and simpler materials when compared with cloaks based on other mappings. [ABSTRACT FROM AUTHOR]

We predict scattering cancellation in diffusive transport of acoustics waves propagating through multiple scattering media in the stationary limit. This would enable sensing of diffusive sound without disrupting the exterior acoustic field. We present design schemes for making spherical or cylindrical core-shell structures with multiple layers, characterized by homogenous and isotropic diffusion coefficients, neutral to an arbitrary applied multipole field. The double-layered sphere is found to support transparency to two concurrent multipole fields and unique cloaking solutions of arbitrary multipole order. One extra degree of freedom is provided by every layer added to the core-shell structure which may be exploited with our iterative formula for effective diffusivity for cloaking of additional field terms. From this we pass over to the long wavelength limit of ballistic sound and provide formulas for effective mass densities of multi-layered structures in spherical and cylindrical geometries with respect to multipole pressure fields. [ABSTRACT FROM AUTHOR]

We show that a stacking defect or a shift has a striking effect on transport properties of bilayer graphene. The tunneling through a ballistic n-neutral-n junction of shifted bilayer graphene may result at normal incidence in a zero-energy cloaking effect. States normally incident on the barrier are confined under it, depending on their pseudospin orientation. These confined states are perfectly decoupled from continuum states having the opposite pseudospin orientation. The barrier at normal incidence acts as a cloak for confined states. We also show a shift-dependent asymmetric zero-energy Fano resonance at near normal incidence arising from the interference between continuum and confined states. These zero-energy cloaking effect and Fano resonance are unique since they are achieved due to the stacking defect. They do not exist in the same setup of perfectly Bernal-stacked bilayer graphene. [ABSTRACT FROM AUTHOR]

We propose in this work a novel optimizationbased wideband invisibility cloaking approach at optical frequencies. We exploit the memory efficient anisotropic adjoint variable method (AVM) to significantly accelerate the sensitivity analysis with respect to the large number of parameters. Minimizing the cloaking objective function involves the gradients estimation with respect to a massive number of parameters at every iteration for time-intensive electromagnetic simulations. The AVM evaluates the required gradients over one thousand time faster than conventional methods. The significant reduction in the computational cost enables wideband optimization-based cloak design at optical region. [ABSTRACT FROM AUTHOR]