Browsing by Subject "Beaming"

Now showing 1 - 3 of 3

Open Access
Connection of collimation, asymmetric beaming, and independent transmission-reflection processes in concentric-groove gratings supporting spoof surface plasmons
(Springer, 2019) Habib, Mohsin; Serebryannikov, A. E.; Çağlayan, H.; Vandenbosch, G. A. E.; Özbay, Ekmel
Transmission through subwavelength apertures enables separation of the incidence half-space and the exit half-space, which leads to that the spatial distribution of the field in the latter is not affected by the distribution in the former. The distribution in the exit half-space is mainly determined by the properties of surface plasmons (SPs) at the exit-side interface. In this paper, for the microwave structures with one-side concentric corrugations around a single annular hole, we demonstrate the possible connections between asymmetric transmission in the beaming regime and collimation of the waves incident at different angles, which can be considered as two sides of the same phenomenon occurring due to the common effect of such a separation and the radiation shaping effect being possible due to the spoof SPs at the corrugated exit interface. Collimation manifests itself in that the waves incident at different angles from a wide range contribute to the single outgoing beam so that a far-zone observer cannot distinguish between the contributions of different angles of arrival. Asymmetry in transmission manifests itself in that the spatial shaping of radiation (beaming) in the exit half-space appears only for one of the two opposite incidence directions. Moreover, even in the structures with the same corrugations on both sides, i.e., without asymmetric transmission, spatial separation of two wave processes, e.g., two symmetric or asymmetric collimation processes, can be obtained for a wide range of nonzero angles of incidence.
Open Access
Enhanced confined microwave transmission by single subwavelength apertures
(2005) Çağlayan, Hümeyra
Grating-coupling phenomena between surface plasmons and electromagnetic waves are studied in the microwave spectrum using metallic circular apertures surrounded by an array of grooves. The measurements are performed in the microwave spectrum of 10-18 GHz, corresponding to a wavelength region of 16.7-30 mm. The metallic samples have a subwavelength hole with a diameter of 8 mm and have concentric grooves with a periodicity of 16 mm. We first present the experimental and theoretical results of enhanced microwave transmission though a subwavelength circular aperture with concentric periodic grooves around the surface plasmon resonance frequency. This is followed by transmission studies through circular annular apertures with and without concentric periodic grooves around the aperture. We demonstrate a 145-fold enhancement factor could be obtained with a subwavelength circular annular aperture surrounded by concentric periodic grooves. Moreover, we study the diffraction of electromagnetic waves from subwavelength metallic circular annular apertures in the microwave spectrum. The theoretical and experimental demonstration of the near- and far-field EM distributions for subwavelength circular apertures and circular annular apertures surrounded by concentric periodic grooves is reported. We present the angular transmission distributions from circular apertures and circular annular apertures surrounded by concentric periodic grooves. At the surface mode resonance frequency the transmitted electromagnetic waves from the subwavelength circular annular aperture surrounded by concentric periodic grooves have a strong angular confinement with an angular divergence of ±3°. This represents a fourfold reduction when compared to the angular divergence of the beam transmitted from a subwavelength aperture. These results show, that not only high transmission but also a confined beam is achieved at the surface plasmon resonance frequency using a circular annular aperture with grooves .
Open Access
Plasmonic structures with extraordinary transmission and highly directional beaming properties
(Wiley Periodicals, 2006) Cağlayan, H.; Bulu, I.; Özbay, Ekmel
We studied the grating-coupling phenomena between surface plasmons and electromagnetic waves in the microwave spectrum. We first present the experimental and theoretical results of an enhanced microwave transmission though a subwavelength circular annular aperture with and without metallic gratings. We demonstrate that a 145-fold enhancement factor could be obtained with a subwavelength circular annular aperture that was surrounded by periodic metallic gratings. This was assisted by the guided mode of the coaxial waveguide and by coupling to the surface plasmons. We present the angular transmission distributions from circular annular apertures, and circular annular apertures surrounded by concentric periodic grooves. At the surface mode resonance frequency, the transmitted electromagnetic waves from the subwavelength circular annular aperture surrounded by concentric periodic grooves have a strong angular confinement with an angular divergence of ±3°. We demonstrate that only the output surface is responsible for the beaming effect. Furthermore, we present the field distributions and showed that there is no beaming effect at the off-resonance frequency. © 2006 Wiley Periodicals, Inc.