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Broadband impedance matching and zero reflection of acoustic waves at a planar interface between two natural materials is a rare phenomenon, unlike its optical counterpart, frequently observed for polarized light incident at the Brewster angle. In this article, it is shown that, by inserting a metamaterial layer between two acoustic materials with different impedance, it is possible to artificially realize an extremely broadband Brewster-like acoustic intromission angle window, in which energy is totally transmitted from one natural medium to the other. The metamaterial buffer, composed of acoustically hard materials with subwavelength tapered apertures, provides an interesting way to match the impedances of two media in a broadband fashion, different from traditional methods like quarter-wave matching or Fabry-Pérot resonances, inherently narrowband due to their resonant nature. This phenomenon may be interesting for a variety of applications including energy harvesting, acoustic imaging, ultrasonic transducer technology, and noise control. [ABSTRACT FROM AUTHOR]

We explore in detail the concept of mantle cloaking, showing that a single, ultrathin, conformal metasurface may drastically suppress the scattering from planar [one-dimensional (1D)], cylindrical [two-dimensioqal (2D)], and/or spherical [three-dimensional (3D)] objects. We propose realistic designs that may realize this concept at radio (RF) or far-infrared (FIR) frequencies. In addition we discuss properties and physical insights of this cloaking functionality compared to other available techniques involving bulk metamaterials, showing exciting potentials in terms of ultralow-profile, light-weight, and bandwidth of operation. These results may be of great interest for low-observability, camouflaging, noninvasive probing, and low-noise communication applications. [ABSTRACT FROM AUTHOR]

The main objective of this paper is to provide a self-consistent analytical model for the approximate current distribution induced on an arbitrarily loaded wire antenna of moderate length operating in its receiving mode. The results of our analysis shed light on a debated issue regarding the circuit model of a receiving antenna and show that currently available simplified analytical models for receiving dipoles fail to satisfy basic power conservation requirements. These general findings are applied to the proper homogenization of composite materials and surfaces, and to minimum-scattering receivers and absorbers. [ABSTRACT FROM AUTHOR]

The potential use of metamaterial planar bilayers for synthesizing compact subwavelength leaky-wave radiators in the microwave regime is analyzed in detail. In particular, the possibility of pairing "complementary" metamaterials in order to reduce the dimensions of microwave components is explored for the leaky-wave operation of an open waveguide consisting of a grounded pair of planar layers. In connection with our similar findings in other setups employing such complementary pairings, here we show how the compact resonance at the interface between "negative" and "positive" materials may also be properly exploited in this context. Choosing materials with low constitutive parameters, moreover, shows to be effective for enhancing the directivity of these components. We explore in detail the notable guidance and radiation properties of the anomalous natural modes supported by these bilayered structures, giving some physical insights into the anomalous phenomenon and considering the possible limitations in some realistic setups. [ABSTRACT FROM AUTHOR]

This paper develops a quasi-analytical and self-consistent model to compute the polarizabilities of split ring resonators (SRRs). An experimental setup is also proposed for measuring the magnetic polarizability of these structures. Experimental data are provided and compared with theoretical results computed following the proposed model. By using a local field approach, the model is applied to the obtaining of the dispersion characteristics of discrete negative magnetic permeability and left-handed metamaterials. Two types of SRRs, namely, the so-called edge coupled- and broadside Coupled- SRRs, have been considered. A comparative analysis of these two structures has been carried out in connection with their suitability for the design of metamaterials. Advantages and disadvantages of both structures are discussed. [ABSTRACT FROM AUTHOR]

Electromagnetic fields interacting with microscopic structural features in a composite material provide emerging optical properties that surpass those offered by the individual components. However, composite materials can be generally lossy due to the scattering effects induced by inhomogeneities at the interfaces between different compounds. To overcome such problems, complicated and costly manufacturing procedures, such as top‐down approaches, are generally required. In contrast, here ZnO–ZnWO4 eutectic self‐organized composites grown by the micropulling method are considered, displaying sharp and strongly polarized transmission at 397 nm. Such an optical response is notable because it is not observed in either ZnO or ZnWO4 single crystals. The optical response is due to the refractive index matching of the two constituents, which self‐organize into ordered structures via a micropulling down method. The optical behavior reported here can directly lead to applications, such as tunable narrowband filters with bandpass of 3 nm and polarizers, paving the way to a new self‐organization route for manufacturing optical components. [ABSTRACT FROM AUTHOR]

We propose the use of an ultrathin cloak made of an acoustic surface impedance that leads to invisibility for acoustic waves. Unlike current acoustic cloaks that require volumetric metamaterials and a significant shell thickness, the mantle cloak presented here is based on a patterned acoustic metasurface that produces similar effects in a thinner geometry. We show that by covering a cylindrical obstacle by a specific acoustic surface impedance, the total scattering may be significantly reduced in the near- and the far-field, thus suppressing its overall acoustic signature. Potential applications lie in low-detectability, camouflaging, and non-invasive acoustic probing. [ABSTRACT FROM AUTHOR]