Open Access
Experimental demonstration of metasurface-based ultrathin carpet cloaks for millimetre waves
(Wiley, 2016) Orazbayev, Bakhtiyar; Mohammadi Estakhri, Nasim; Alù, Andrea; Beruete Díaz, Miguel; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
A metasurface carpet cloak for millimeter-wave range with polarization-independent performance is experimentally demonstrated. It is shown that the cloak is able to mimic the ground plane by fully restoring the amplitude and phase distributions for both transverse electric and transverse magnetic polarizations, with a relatively wide frequency and angular widths response.
Open Access
Zoned fishnet lens antenna with reference phase for side lobe reduction
(IEEE, 2015) Pacheco-Peña, Víctor; Navarro Cía, Miguel; Orazbayev, Bakhtiyar; Minin, Igor V.; Minin, Oleg V.; Beruete Díaz, Miguel; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
Reduction of first side lobe level and nulls in artificial fishnet metalenses is accomplished here by applying the reference phase concept along with the zoning technique. Higher focusing efficiency is achieved for a specific reference phase when comparing numerically and experimentally four different designs. For such best design, an improvement of the first side lobe level (2.4 dB), first null (13 dB) and gain (1.77dB) is achieved experimentally compared to the design without reference phase.
Open Access
Terahertz carpet cloak based on a ring resonator metasurface
(American Physical Society, 2015) Orazbayev, Bakhtiyar; Mohammadi Estakhri, Nasim; Beruete Díaz, Miguel; Alù, Andrea; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
In this work we present the concept and design of an ultrathin (λ/22) terahertz (THz) unidirectional carpet cloak based on the local phase compensation approach enabled by gradient metasurfaces. A triangular surface bump with center height of 4.1 mm (1.1λ) and tilt angle of 20° is covered with a metasurface composed of an array of suitably designed closed ring resonators with a transverse gradient of surface impedance. The ring resonators provide a wide range of control for the reflection phase with small absorption losses, enabling efficient phase manipulation along the edge of the bump. Our numerical results demonstrate a good performance of the designed cloak in both near field and far field, and the cloaked object mimics a flat ground plane within a broad range of incidence angles, over 35° angular spectrum centered at 45°. The presented cloak design can be applied in radar and antenna systems as a thin, lightweight, and easy to fabricate solution for radio and THz frequencies.
Open Access
Diffusive-light invisibility cloak for transient illumination
(American Physical Society, 2016) Orazbayev, Bakhtiyar; Beruete Díaz, Miguel; Martínez, Alejandro; García Meca, Carlos; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
Invisibility in a diffusive-light-scattering medium has been recently demonstrated by employing a scattering-cancellation core-shell cloak. Unlike nondiffusive cloaks, such a device can be simultaneously macroscopic, broadband, passive, polarization independent, and omnidirectional. Unfortunately, it has been verified that this cloak, as well as more sophisticated ones based on transformation optics, fail under pulsed illumination, invalidating their use for a variety of applications. Here, we introduce a different approach based on unimodular transformations that enables the construction of unidirectional diffusive-light cloaks exhibiting a perfect invisibility effect, even under transient conditions. Moreover, we demonstrate that a polygonal cloak can extend this functionality to multiple directions with a nearly ideal behavior, while preserving all other features. We propose and numerically verify a simple cloak realization based on a layered stack of two isotropic materials. The studied devices have several applications not addressable by any of the other cloaks proposed to date, including shielding from pulse-based detection techniques, cloaking undesired scattering elements in time-of-flight imaging or high-speed communication systems for diffusive environments, and building extreme optical security features. The discussed cloaking strategy could also be applied to simplify the implementation of thermal cloaks.
Open Access
Exploiting the dispersion of the double-negative-index fishnet metamaterial to create a broadband low-profile metallic lens
(Optical Society of America, 2015) Orazbayev, Bakhtiyar; Pacheco-Peña, Víctor; Beruete Díaz, Miguel; Navarro Cía, Miguel; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
Metamaterial lenses with close values of permittivity and permeability usually display low reflection losses at the expense of narrow single frequency operation. Here, a broadband low-profile lens is designed by exploiting the dispersion of a fishnet metamaterial together with the zoning technique. The lens operates in a broadband regime from 54 GHz to 58 GHz, representing a fractional bandwidth ~7%, and outperforms Silicon lenses between 54 and 55.5 GHz. This broadband operation is demonstrated by a systematic analysis comprising Huygens-Fresnel analytical method, full-wave numerical simulations and experimental measurements at millimeter waves. For demonstrative purposes, a detailed study of the lens operation at two frequencies is done for the most important lens parameters (focal length, depth of focus, resolution, radiation diagram). Experimental results demonstrate diffraction-limited ~0.5λ transverse resolution, in agreement with analytical and numerical calculations. In a lens antenna configuration, a directivity as high as 16.6 dBi is achieved. The different focal lengths implemented into a single lens could be potentially used for realizing the front end of a non-mechanical zoom millimeter-wave imaging system.
Open Access
Metamaterials for enhanced light control: from high resolution focusing to invisibity
(2015) Orazbayev, Bakhtiyar; Beruete Díaz, Miguel; Escuela Técnica Superior de Ingenieros Industriales y de Telecomunicación; Telekomunikazio eta Industria Ingeniarien Goi Mailako Eskola Teknikoa
Artificial dielectrics and their descendants – metamaterials, have unusual electromagnetic parameters and provide more abilities than naturally available dielectrics for control of the light. The first experimental realization of a double negative medium gave an enormous impulse for research in the field of electromagnetism. As result, a lot of fascinating electromagnetic devices have been developed since then, including metamaterial lenses, beam steerers and even invisibility cloaks. The aim of this master thesis is to contribute to the development of such devices, especially metamaterial lenses and invisibility cloaks. First, a background of metamaterial and metasurfaces is introduced. The main aspects of metamaterials and their characteristics are reviewed, so that the working principles of metamaterials can be acquired with minimal prerequisite mathematics. Then we review the design process of several metamaterial lenses, including a zoned fishnet metamaterial lens and a Soret lens, a member of Fresnel zone plate lenses. Finally we design a carpet cloak, using a metasurface with double ring resonators. In the first application, the time-honored zoning technique is used to reduce the volume, and therefore weight, of a fishnet metamaterial lens. By properly optimizing a profile of the zoned lens we are able to reduce a volume of the lens up to 60% and broaden the fractional bandwidth up to 3 times. With this optimization technique the bandwidth of the zoned lens, which usually is narrow band, increases without causing any deterioration in its performance. The second metamaterial lens is a member of the well-known Fresnel zone plate’s family and consists of alternating and opaque concentric rings. Since half of the power is blocked by opaque rings the efficiency of such lenses is low. In order to improve the coupling and illumination efficiency we propose using an array of subwavelength holes instead of the transparent ring. Also by supporting the lens with a block of fishnet metamaterial working in near-zero index regime it is possible to improve radiation characteristics of a metalens antenna, such as directivity and side lobe level. Finally, in the third application a ground cloak design is described as simulation results. The presented ground cloak is based on a metasurface, an array of closed ring resonators, and, therefore, has an ultrathin design and relatively simple in fabrication. The proposed cloak has been successfully employed to conceal an electrically large object (1.1λ0) for wide range of incident angles and relatively wide frequency range.
Open Access
Soret fishnet metalens antenna
(Springer Nature, 2015) Orazbayev, Bakhtiyar; Beruete Díaz, Miguel; Pacheco-Peña, Víctor; Crespo López, Gonzalo; Teniente Vallinas, Jorge; Navarro Cía, Miguel; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
At the expense of frequency narrowing, binary amplitude-only diffractive optical elements emulate refractive lenses without the need of large profiles. Unfortunately, they also present larger Fresnel reflection loss than conventional lenses. This is usually tackled by implementing unattractive cumbersome designs. Here we demonstrate that simplicity is not at odds with performance and we show how the fishnet metamaterial can improve the radiation pattern of a Soret lens. The building block of this advanced Soret lens is the fishnet metamaterial operating in the near-zero refractive index regime with one of the edge layers designed with alternating opaque and transparent concentric rings made of subwavelength holes. The hybrid Soret fishnet metalens retains all themeritsof classicalSoret lenses suchas lowprofile, lowcost andeaseofmanufacturing. It is designed for the W-band of themillimeter-waves range with a subwavelength focal lengthFL51.58 mm(0.5l0) aiming at a compact antenna or radar systems. The focal properties of the lens along with its radiation characteristics in a lens antenna configuration have been studied numerically and confirmed experimentally, showing a gain improvement of ,2 dB with respect to a fishnet Soret lens without the fishnet metamaterial.
Open Access
THz tripod metasurfaces for sensing applications: from the basic, to more elaborated designs
(IEEE, 2021) Jáuregui López, Irati; Orazbayev, Bakhtiyar; Pacheco-Peña, Víctor; Beruete Díaz, Miguel; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren
In this work, we propose, design, and evaluate three types of : three types of metasurfaces using tripod-shaped unit cells when working as thin-film sensing devices. The three meta-atoms of the proposed metasensors area simple solid tripod, a hollow tripod, and a hollow tripod structure with arms.The best design showed a mean numerical sensitivity of 1.42 × 10−4nm for extremely thin samples, meaning an improvement of 381% with respect to the initial designs. These results highlight the importance of using metastructures with complex geometries that enable high-intensity electric field distributions over the whole metasurface.
Open Access
Experimental demonstration of a millimeter-wave metallic ENZ lens based on the energy squeezing principle
(IEEE, 2015) Torres Landívar, Víctor; Orazbayev, Bakhtiyar; Pacheco-Peña, Víctor; Teniente Vallinas, Jorge; Beruete Díaz, Miguel; Navarro Cía, Miguel; Sorolla Ayza, Mario; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
The performance of an epsilon-near zero (ENZ) plano-concave lens is experimentally demonstrated and verified at the D-band of the millimeter-waves. The lens is comprised of an array of narrow metallic waveguides near cut-off frequency, which effectively behaves as an epsilon-near-zero medium at 144 GHz. A good matching with free space is achieved by exploiting the phenomenon of energy squeezing and a clear focus with a transmission enhancement of 15.9 dB is measured. The lens shows good radiation properties with a directivity of 17.6 dBi and low cross-polar components of -34 dB. All results are supported by numerical simulations.
Open Access
Tunable beam steering enabled by graphene metamaterials
(Optical Society of America, 2016) Orazbayev, Bakhtiyar; Beruete Díaz, Miguel; Khromova, Irina; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
We demonstrate tunable mid-infrared (MIR) beam steering devices based on multilayer graphene-dielectric metamaterials. The effective refractive index of such metamaterials can be manipulated by changing the chemical potential of each graphene layer. This can arbitrarily tailor the spatial distribution of the phase of the transmitted beam, providing mechanisms for active beam steering. Three different beam steerer (BS) designs are discussed: a graded-index (GRIN) graphene-based metamaterial block, an array of metallic waveguides filled with graphene-dielectric metamaterial and an array of planar waveguides created in a graphene-dielectric metamaterial block with a specific spatial profile of graphene sheets doping. The performances of the BSs are numerically analyzed, showing the tunability of the proposed designs for a wide range of output angles (up to approximately 70°). The proposed graphene-based tunable beam steering can be used in tunable transmitter/receiver modules for infrared imaging and sensing.