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A metamaterial cloak, however, causes the light bouncing off it to perfectly cancel the light reflected from the object underneath it, producing undisturbed light waves that conceal the object's presence (right). Several research teams around the world, including mine, have de sign ed and produced metamaterial coatings that can redirect light waves that hit them, effectively preventing light from bouncing off the object and reaching our eyes and even from leaving shadows. The emerging light-matter interactions are controlled by the twisted symmetry of the crystal lattice, en ab ling a large rotation of the incoming light polarization over a broad range of wavelengths. [Extracted from the article]

Purpose – The purpose of this paper is to present an analytical expression for the characteristic impedance of a microstrip line in presence of a dielectric cover. Design/methodology/approach – Assuming a quasi-TEM propagation mode, a rigorous conformal mapping based on the Schwarz-Christoffel transformation is employed to derive the equivalent capacitance model, which can then be applied to derive a closed analytical expression for the effective permittivity and the characteristic impedance of the line. Findings – Such a formulation is not limited to the case of a single cover layer, but an arbitrary number of electric overlays can be considered as well. Comparisons with published numerical results and full-wave simulations in the case of a single cover layer have been also performed to test the validity of the proposed approach. Originality/value – The new analytical formula for the characteristic impedance of a microstrip line with a single dielectric cover shows better performances compared to the one of closed formulas already presented in the literature. [ABSTRACT FROM AUTHOR]

In this paper, we address nonradiating and cloaking problems exploiting the surface equivalence principle, by imposing at any arbitrary boundary the control of the admittance discontinuity between the overall object (with or without cloak) and the background. After a rigorous demonstration, we apply this model to a nonradiating problem, appealing for anapole modes and metamolecules modeling, and to a cloaking problem, appealing for non-Foster metasurface design. A straightforward analytical condition is obtained for controlling the scattering of a dielectric object over a surface boundary of interest. Previous quasistatic results are confirmed and a general closed-form solution beyond the subwavelength regime is provided. In addition, this formulation can be extended to other wave phenomena once the proper admittance function is defined (thermal, acoustics, elastomechanics, etc.). [ABSTRACT FROM AUTHOR]

The cross-coupling between strain and velocity in acoustic materials, known as Willis coupling, has recently been receiving increasing attention within the broad acoustics community. Willis coupling can provide a new degree of freedom to control sound propagation, which has been enabling several novel applications. In this work, based on the general constitutive relations of Willis media and the acoustic Poynting theorem, we study the constraints stemming from fundamental symmetries – parity, time-reversal, reciprocity and energy conservation – in these media. The wave features, such as wave-vectors, wave impedance and orthogonality are also generally investigated. In addition, we put forward a nonlocal model that unveils the relation between Willis media and nonlocal materials, and how Willis phenomena stem from weak forms of nonlocality. • We relate wave properties in Willis media to physical symmeties: parity, time-reversal, reciprocity and energy conservation. • We generally prove orthogonality relations, wave numbers and impedance for eigen-waves in Willis media. • We highlight the exotic responses emerging in purely nonreciprocal Willis media. • We derive an equivalent description of Willis media in terms of weak nonlocality. [ABSTRACT FROM AUTHOR]

Purpose – The work is aimed at studying the electromagnetic interaction between a homogeneous, isotropic single-negative (SNG) slab and an inhomogeneous, anisotropic double-positive (DPS) slab. Design/methodology/approach – The approach is based on the transformation optics framework, which allows systematic design and modelling of anisotropic, inhomogeneous metamaterials with inherent field-manipulation capabilities. Findings – The paper finds that a transformation-optics-based DPS slab can compensate the inherent opaqueness to the electromagnetic radiation of a SNG slab. Here, "compensation" means that the resulting bi-layer may give rise to zero-reflection for a normally-incident plane wave at a given frequency. Such phenomenon is inherently accompanied by (de)funneling effects for collimated-beam illumination, and it turns out to be quite robust to material losses as well as geometrical and constitutive-parameter truncation. Originality/value – The results provide further evidence and insight in how SNG-like responses may be emulated (within narrow parametric ranges) by suitably-engineered spatial inhomogeneity and anisotropy in DPS media. Moreover, they also show that resonant transmission phenomena through SNG materials may be engineered via the powerful framework of transformation optics. [ABSTRACT FROM AUTHOR]

Abstract: One popular approach to cloaking objects from electromagnetic waves at moderately long wavelengths is the scattering cancelation technique. This mechanism is based on the use of a single homogeneous thin layer to cover an object of interest in order to provide scattering suppression in a given frequency band. This approach has also been recently extended to acoustic waves. This paper provides an investigation of the physical nature of scattering cancelation by a uniform thin layer for both electromagnetic and acoustic waves in inviscid fluids. Two distinct scattering cancelation regions are obtained within the available parameter space: a non-resonant plasmonic cloaking region and an anti-resonant cloaking region, which are identified and compared in both the electromagnetic and acoustic domains. Although both types of operations allow for the suppression of the dominant scattering orders, the resulting internal fields and physical functionality of the cloaks present distinct differences between the two domains. We discuss analogies and differences between these functionalities and their implications in electromagnetic and acoustic cloaking problems, with an insight into their practical implementation. [Copyright &y& Elsevier]

We explore the dynamics of spontaneous breakdown of mirror symmetry in a pair of identical optomechanical cavities symmetrically coupled to a waveguide. Large optical intensities enable optomechanically induced nonlinear detuning of the optical resonators, resulting in a pitchfork bifurcation. We investigate the stability of this regime and explore the possibility of inducing multistability. By injecting proper trigger pulses, the proposed structure can toggle between two asymmetric stable states, thus serving as a low-noise nanophotonic all-optical switch or memory element. [ABSTRACT FROM AUTHOR]

Abstract: The intriguing concept of “anti-cloaking” has been recently introduced within the framework of transformation optics (TO), first as a “countermeasure” to invisibility-cloaking (i.e., to restore the scattering response of a cloaked target), and more recently in connection with “sensor invisibility” (i.e., to strongly reduce the scattering response while maintaining the field-sensing capabilities). In this paper, we extend our previous studies, which were limited to a two-dimensional cylindrical scenario, to the three-dimensional spherical case. More specifically, via a generalized (coordinate-mapped) Mie-series approach, we derive a general analytical full-wave solution pertaining to plane-wave-excited configurations featuring a spherical object surrounded by a TO-based invisibility cloak coupled via a vacuum layer to an anti-cloak, and explore the various interactions of interest. With a number of selected examples, we illustrate the cloaking and field-restoring capabilities of various configurations, highlighting similarities and differences with respect to the cylindrical case, with special emphasis on sensor-cloaking scenarios and ideas for approximate implementations that require the use of double-positive media only. [Copyright &y& Elsevier]