Elliptical Metasurface Research Articles

Investigating the effect of surface protrusions on galloping energy harvesting

This Letter explores the potential effect of implementing different surface protrusions on galloping energy harvesters. Three types of protruded bluff bodies with rectangular, triangular, and elliptical metasurfaces are proposed, and four kinds of surface treatments are deployed to vary their protruded shape. Wind tunnel experiments reveal that adding the protrusions can obviously change the mode of oscillations, and only the backward protrusions can enhance the galloping response. Both the experiments and simulations show that elliptical surface protrusions have the greatest potential to enhance the galloping energy harvesting performance. Specifically, with a backward protruded length of 15 mm, the maximum output power in the experiments is measured to be 0.757 mW, which occurs at 5.1 m/s, and an optimal load resistance of 300 kΩ. In this case, the energy harvester outperforms its counterpart carrying a simple square prism by 157.48%.

Cloaking of Slot Antennas at C-Band Frequencies Using Elliptical Metasurface Cloaks

In this letter, we endeavor to curb the adverse effects of mutual coupling between two-slot antennas (operating at C-band frequencies), situated at a subwavelength separation. The effects of mutual coupling become extremely apparent at such close proximity and leads to the deterioration of the radiation aspects of each antenna. To mitigate these detrimental effects, we exploit the concept of mantle cloaking for the design of specialized cloaks, consisting of elliptical dielectric regions integrated with capacitive metallic strips. It is demonstrated through simulation results that by enclosing each radiating edge of the individual slots with these uniquely designed metasurfaces, the slot antennas are decoupled in the near field. Moreover, the metasurface cloaks also facilitate restoration of the far field radiation properties of the slots. In this regard, our cloak design ensures that the slot antennas do not sense the presence of each other, enabling each slot antenna to operate individually, as if they were isolated.

Ultra-broadband metamaterial absorber based on cross-shaped TiN resonators.

In this paper, a novel broadband plasmonic absorber based on cross-shaped titanium nitride (TiN) resonators in the ultraviolet, visible, and near-infrared regions is presented. The proposed perfect solar absorber consists of periodic arrays of cross-shaped TiN resonators located on a stack of ${{\rm SiO}_2}/{\rm TiN}$SiO2/TiN layers. By using the finite-difference time-domain method, the effects of variations of the thickness and radius of the elliptical metasurface resonators on the absorption are comprehensively investigated. The cross-shaped metamaterial absorber exhibits an averaged absorption of 90%, ranging from 200 to 3000 nm, and shows over 90% absorption from 200 to 2500 nm. Furthermore, the proposed absorber indicates absorption efficiency over 80% for an oblique incidence up to 50 deg for both TE- and TM-polarized light. These features make the proposed solar absorber usable in many solar-based applications, imaging, and thermal emitting.

Decoupling and Cloaking of Interleaved Phased Antenna Arrays Using Elliptical Metasurfaces

We apply the concept of electromagnetic invisibility/cloaking to improve the radiation properties and decouple two tightly spaced and interleaved phased linear antenna arrays of strip monopoles operating at close frequencies, in order to restore their isolated radiation patterns and eliminate the undesired cross-coupling between their elements. We realize this effect using elliptically shaped cloaking metasurfaces designed for mutually cross-coupled elements of the distinct arrays. We analyze and investigate the cloaking and decoupling effects in improving the functionality of the coupled arrays in terms of their radiation patterns and realized gain, respectively. As a result, the antenna arrays placed in close proximity of each other can radiate independently for a wide range of beam scanning angles, restoring the properties they would have when isolated from each other.

Wideband Elliptical Metasurface Cloaks in Printed Antenna Technology

In this paper, we apply the mantle cloaking method to reduce the mutual coupling between two closely spaced wideband antennas operating at microwave frequencies. We show that by introducing two dielectric elliptical shells around the antennas and covering them with two strongly coupled elliptically shaped metasurfaces comprised of I-shaped printed unit cells, it is possible to significantly increase the original bandwidth of the antennas and, at the same time, reduce the mutual electromagnetic interaction. This effect is observed both in a reduction of mutual S-parameters between the antennas and in the restoration of the original radiation patterns, as if the antennas were almost completely isolated from each other. Broadband metasurface/cloak designs are proposed for two geometries, with the free-standing strip monopole antennas placed over a ground plane and with the metasurface cloaks integrated with microstrip antennas.

Decoupling antennas in printed technology using elliptical metasurface cloaks

In this paper, we extend the idea of reducing the electromagnetic interactions between transmitting radiators to the case of widely used planar antennas in printed technology based on the concept of mantle cloaking. Here, we show that how lightweight elliptical metasurface cloaks can be engineered to restore the intrinsic properties of printed antennas with strip inclusions. In order to present the novel approach, we consider two microstrip-fed monopole antennas resonating at slightly different frequencies cloaked by confocal elliptical metasurfaces formed by arrays of sub-wavelength periodic elements, partially embedded in the substrate. The presence of the metasurfaces leads to the drastic suppression of mutual near-field and far-field couplings between the antennas, and thus, their radiation patterns are restored as if they were isolated. Moreover, it is worth noting that this approach is not limited to printed radiators and can be applied to other planar structures as well.

Reduction of Mutual Coupling Between Neighboring Strip Dipole Antennas Using Confocal Elliptical Metasurface Cloaks

In this paper, we propose a novel approach to reduce the mutual coupling between two closely spaced strip dipole antennas with the elliptical metasurfaces formed by conformal and confocal printed arrays of subwavelength periodic elements. We show that by covering each strip with the metasurface cloak, the antennas become invisible to each other and their radiation patterns are restored as if they were isolated. The electromagnetic scattering analysis pertained to the case of antennas with frequencies far from each other is shown to be as a good approximation of a 2-D metallic strip scattering cancellation problem solved by expressing the incident and scattered fields in terms of radial and angular Mathieu functions, with the use of sheet impedance boundary conditions at the metasurface. The results obtained by our analytical method are confirmed by full-wave numerical simulations.