Superscattering from Subwavelength Corrugated Cylinders

Abstract

Wave scattering from a cylinder with a tensor impedance surface is investigated on the basis of the Lorentz-Mie theory. A practical example of such a cylinder is a subwavelength metallic rod with helical dielectric-filled corrugations. The investigation is performed with the aim to maximize the scattering cross section by tailoring the surface impedance of cylindrical scatterers. For normally incident ${\mathrm{TE}}_{z}$ and ${\mathrm{TM}}_{z}$ waves, the required surface impedance of a subwavelength cylinder can be produced by longitudinal (axial) and transverse (circumferential) corrugations, respectively. It is shown that such corrugations induce superscattering at multiple frequencies, which can be widely tuned with either the size or the permittivity of dielectric-filled corrugations or both. In the microwave band, this effect is demonstrated to be robust to material losses and is validated against full-wave simulations and experimental results. For ${\mathrm{TE}}_{z}$ waves the enhanced scattering from the cylinder is found to have a broad frequency bandwidth, provided that the relative permittivity of corrugations is low or equal to unity. In the latter case, the corrugated cylinder acts as an all-metal superscatterer. For such cylinders, near-field measurements are performed and provide experimental evidence of the superscattering phenomenon for all-metal objects. In addition to multifrequency superscattering, the dielectric-filled corrugations are shown to provide multifrequency cloaking of the cylinder for incident ${\mathrm{TM}}_{z}$ waves. Simultaneous superscattering and cloaking at multiple frequencies distinguishe corrugated cylinders from other known practicable scatterers for potential applications in antenna designing, sensing, and energy harvesting.