Moreover, tunability mechanisms can be implemented using varactor-diode-loading 68 or advanced materials like graphene (in the form of monolayers 69 or nanostructured metasurfaces 70, 71, 72). By comparison with the plasmonic implementation 10, 11, 12, mantle cloaks tend to be particularly suited for microwave and terahertz frequencies, providing low-profile, conformal, easy-to-fabricate configurations that are especially attractive for applications to reduction of antenna coupling 56, 66, 67.
13 as a possible implementation of the scattering-cancellation strategy, and experimentally validated at microwave frequencies 61, 62, 63, this approach conceptually relies on the design 64, 65 of a reactive metasurface whose response, at a given design frequency, can cancel out the lowest-order multipolar contribution to the scattering signature. In this paper, we focus on the mantle-cloak approach. The reader is referred to refs 59, 60 for recent comprehensive reviews. Overall, cloaking has rapidly become a fast-pacing multidisciplinary research topic, with a wealth of potentially disruptive practical applications, besides the more or less obvious invisibility and camouflaging, ranging from the reduction of antenna interference 55, 56 to noninvasive sensing 57, 58 and thermal management 48, 49, 50. Moreover, applications to multiphysics scenarios (e.g., thermal/electric 51, 52, also in conjunction with other functionalities 53, 54) seem also very promising. More recently, a growing interest has been elicited by applications to dc (electrostatic and magnetostatic) scenarios 35, 36, 37, 38 and diffuse light 39, as well as to other physical domains including acoustics 40, 41, 42, 43, elastodynamics 21, 44, 45, liquid surface waves 46, quantum matter waves 47, and thermodynamics 48, 49, 50. 34) and/or to achieve otherwise unattainable effects (e.g., unidirectionality). Also, strategies based on ray optics (for incoherent natural light) 27, 28, active sources 29, 30, non-Foster elements 31, and parity-time-symmetric configurations 32, 33 have been explored in order to overcome certain inherent limitations of passive, material-based schemes (see, e.g., ref. Alternative approaches also worth of mention are those based on anomalous localized resonances 21, transmission-line networks 22, parallel-plate structures 23, and topology optimization 24, 25, 26. In electromagnetic (EM) scenarios, of specific interest for this study, concepts such as “neutral” inclusions as well as “invisible” sources, scatterers, and antennas have been investigated since the 1960s (see, e.g., refs 2, 3, 4, 5, 6, 7, 8), but a major revamp has taken place during the last decade, associated with the suggestive term of “cloaking” and catalyzed by the advances in the field of artificial materials and “metamaterials.” Within this framework, prominent approaches are based on the scattering cancellation concept 9 (and its possible plasmonic– 10, 11, 12 and mantle-based 13 implementations) and the transformation-optics paradigm 14, 15, 16 (and its possible non-Euclidean 17 and carpet-type 18, 19, 20 variants). In a broad sense, the problem can be posed as the suppression of the scattering signature due to an interrogating wave signal impinging on a given object. The quest for “invisibility” is a longstanding research topic which has always fascinated researches in various fields of physics (see, e.g., ref.
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