1,720,962 research outputs found
Mantle cloaking due to ideal magnetic dipole scattering
Get PDFOne of the most exciting applications of metaparticles and metasurfaces consists in the magnetic light excitation. However, the principal limitation is due to parasitic extra multipoles of electric family excited in magnetic dipole meta-particles characterized by a radiating nature and corresponding radiating losses. In this paper, we propose the “ideal magnetic dipole” with suppressed additional multipoles except of magnetic dipole moment in the scattered field from a cylindrical object by using mantle cloaking based on metasurface and on anapole concept. The considered metasurface consists of a periodic width modulated microstrip line, with a sinusoidally shaped profile unit cell printed on a dielectric substrate
All-dielectric nanoantenna for efficient reflectors irradiation
Get PDFIn this paper, we propose a new kind of nanoantenna for effective illumination of parabolic surfaces, constituting of a silicon cylinder acting as a reflector and dipole source as an emitter. Tailored parameters of the nanoantenna ensure specific radiation pattern with broad main lobe and strongly suppressed side lobes that in the E-plane of the dipole is quite similar to the ideal “П” configuration, necessary for an as uniform as possible illumination of parabolic surfaces. This above radiation pattern is mostly due to the properly designed dielectric inclusion in the reflector that, therefore, is free of any losses. Consequently, we study how varying the antenna parameters affects the radiation pattern.Results of our numerical simulations are compared with already existing ones and highlight the principal features that provide the desired effect. Furthermore, due to the simple geometry of the inclusions, the considered nanoantenna, required in application such as nanoreflector antennas and/or nanophotonic devices, exhibits advantages in manufacturing processes with respect to already proposed solutions
Nonradiating Sources, Cloaking Devices and Related Anapole Modes
No full textIn this work, theoretical findings on the common feature describing nonradiating sources is reported, based on equivalent sources from which it is possible to derive cloaking devices and anapole mode conditions. Starting from the differential form of Maxwell's Equations expressed in terms of equivalent electromagnetic sources, we derive two unique compact conditions. By specifing the nature of these passively induced or actively impressed current density sources in certain volumes and/or predefined surfaces, we derive theoretical results consistently with the literature about nonradiating particles, cloaking devices and anapole mode structures through peculiar destructive interactions between volumetric-volumetric, volumetric-surface and surface-surface equivalent sources
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
High-Q Factor Dual-Layer Anapole Metamaterial
No full textSimulation results and an experimental study are presented for a dual-layer metamaterial exhibiting a resonance with Q-factor of 4000 in the mm-wave frequency range, achieved by combining resonances from two complementary planar metamaterials. The initial layer, which is the original metamaterial, is composed of metallic unit-cells shaped like epsilon letters and is based on a high Q-factor planar toroidal metamaterial [1]. This metamaterial shows significant localization of electromagnetic energy in the near field region rather than in the radiation zone due to the destructive interference of toroidal and electric dipole moments with identical radiation patterns in the far zone. The second layer, which complements the first one, consists of a metallic layer with cutouts in the epsilon letter shape. Individually, the original metamaterial demonstrates a high Q-factor resonance and confines the electric field of the incident wave. Conversely, the inverted structure does not respond to the incident wave but is instead stimulated by near-field interaction with the original metamaterial. The low losses observed can be attributed to the interaction between the two most significant multipoles excited within the metamaterials. In the case of the original metamaterial, this interaction involves destructive interference between toroidal and electric dipole moments, leading to the formation of an anapole. On the other hand, the properties of the inverted metamaterial stem from the interaction between toroidal dipole and magnetic quadrupole moments. Both metamaterials are fabricated as free-standing to avoid dielectric losses from the substrate, which can significantly diminish the resonance’s Q-factor. The simulated metamaterial (Fig.1a) is excited with the wave polarized along the wires of the metamolecules of the original type, allowing for the support of dual loops of currents along the voids, leading to toroidal excitation
Broadband transparency of Babinet complementary metamaterials
Get PDFAccording to the Babinet principle, the diffraction pattern from an opaque body is identical to that from a hole of the same shape and size. Intuitively, placing two complementary structures such as an opaque metal body and its transparent counterpart one by one may result in destructive or constructive interference leading to unexpected electromagnetic response. We propose a Babinet principle-based metamaterial made of two complementary metal/hole checkerboards. The unit cell of each layer is either a metal square with 1/4 of 8 neighboring squares, four of which are made of metal, whereas the other four are square holes, or vice versa. Being placed complementary at optimal distance equal to three-unit cell length, the compound bi-layered Babinet structure demonstrates absolute transparency in a very broad frequency range. The observed absolute transparency of the bi-layered Babinet metasurface is the result of the modified multipole interaction of layers with shifted centers of radiation. We demonstrate both theoretically and experimentally absolute transmission of 0 dB for the Babinet metamaterial made of 3 cm sized Cu squares and complementary holes in the broad frequency range from 4.5 to 6.62 GHz in simulations and from 4.6 to 6.4 GHz in the experiment when the distance between two layers is 1.2 cm. Moving layers toward each other leads to blurring of the resonances. The proven concept of simple, reproducible, and scalable design of the Babinet metamaterial paves the way for the fabrication of broadband transparent devices at any frequency, including THz and optical ranges. The main advantage of broadband Babine metamaterials is applications in optical switching, sensing, filtering, and slow light devices
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Free-standing sub-THz metamaterial with the high Q-factor isolated electric dipole response
Get PDFAchieving high-Q resonances in the terahertz frequency range is crucial for applications such as sensors, filters, and emitters. One effective strategy for achieving such resonances involves the use of metamaterials. However, the performance of terahertz (THz) metamaterials is often limited by radiation losses in their meta-atoms and in substrates. In this paper, we present both simulation and experimental results of a dual-layer free-standing metamaterial, exhibiting Q-factor of 3570 in the sub-terahertz range, achieved by integrating two complementary planar metamaterial layers that induce an isolated dominant electric dipole moment. This unique metamaterial displays the potential for advances in antennas, quantum computing, THz sensors, offering efficient energy confinement and low losses
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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