Abstract
Artificially created media allow employing material parameters as additional valuable degrees of freedom in tailoring electromagnetic scattering. In particular, metamaterials with either negative permeability or permittivity allow creating deeply subwavelength resonant structures with relatively high scattering cross-sections. However, the equivalence principle allows replacing volumetric structures with properly designed curved impedance surfaces, ensuring the same electromagnetic properties. Here, we examine this statement from a practical standpoint, considering two structures, having a dipolar electric resonance at the same frequency. The first realization is based on arrays of inductively loaded electric dipoles printed on stacked circuit boards (a volumetric metamaterial), while the second structure utilizes a 4-wire spiral on a spherical surface (surface impedance realization). An intermediate conclusion is that the surface implementation tends to outperform the volumetric counterparts in the scenario when a single resonance is involved. However, in the case where multiple resonances are overlapping and lossy materials are involved, volumetric realization can have an advantage. The discussed structures are of significant importance to the field of electrically small antennas, superdirective antennas, and superscatterers, which find use in wireless communications and radar applications, to name just a few.
Highlights
Created media allow employing material parameters as additional valuable degrees of freedom in tailoring electromagnetic scattering
The main drawback of using small structures comes through their reduced scattering efficiencies and operational bandwidths compared to bigger counterparts
Quite a few limiting criteria have been derived over the years, with the Chu-Harrington limit being the most celebrated one
Summary
Created media allow employing material parameters as additional valuable degrees of freedom in tailoring electromagnetic scattering. The equivalence principle allows replacing volumetric structures with properly designed curved impedance surfaces, ensuring the same electromagnetic properties We examine this statement from a practical standpoint, considering two structures, having a dipolar electric resonance at the same frequency. Various approaches have been developed and employed in antenna design, and in certain cases, they are applied to enhance scattering cross-sections and improve d irectivities[1]. Scattering cross-sections of subwavelength structures obey a fundamental singlechannel limit of 2l′ + 1 2/(2π ) , where λ is the free space wavelength, and l′ is related to the orbital angular momentum of a multipolar resonance ( l′ = 1 is the electric or magnetic dipolar case). Metamaterials hold a promise to bring new approaches into the field, as they allow considering material degrees of freedom as additional parameters for electromagnetic design. Assessing the capabilities of metamaterials to improve electromagnetic characteristics in the field of superscattering is the objective here
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