Suchergebnisse

This is a peer-reviewed, un-copyedited version of an article accepted for publication/published in Journal of Physics D: Applied Physics. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at https://doi.org/10.1088/1361-6463/aae3a5. ; The arbitrary control of surface plasmon (SP) propagation has become an intense research topic for several decades. This is due to the fact that they can be used in a variety of fields such as optical trapping, nanoantennas and medical applications. In this communication, the graded index technique is applied in the design of several steerers able to tailor the direction of propagation of the incident SPs by simply changing the height of a dielectric block on top of a semi?infinite metal slab. The design procedure is shown and the structures are numerically evaluated demonstrating a good agreement with the analytical calculations, with the SPs deflected at the design angles (θ ranging from 10° to 60°) with a wide bandwidth steering of 60 nm around the design value (633 nm) ; V.P.-P. is supported by the Newcastle University (Newcastle University Research Fellow). M. B. acknowledges support by the Spanish Ministerio de Economía y Competitividad with European Union FEDER funds [TEC2014-51902-C2-2-R].

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. ; This work was supported in part by the Spanish Government under Contract TEC2014- 51902-C2-2-R and the Government of the Russian Federation [Grant No. 074-U01]. B. O. is sponsored by the Spanish Ministerio de Economía y Competitividad under grant FPI BES- 2012-054909. M.B. is sponsored by the Spanish Government via RYC-2011-08221. I.K. is sponsored by the Russian Foundation for Basic Research under grant No. 14-07-31272.

The following article appeared in Rodríguez-Ulibarri, P., Beruete, M., & Kuznetsov, S. (2016). Wide angle terahertz sensing with a cross-dipole frequency selective surface. Applied Physics Letters, 108(11), doi:10.1063/1.4944326 and may be found at http://dx.doi.org/doi:10.1063/1.4944326. ; In this work, a terahertz sensor based on a cross dipole frequency selective surface is analyzed and experimentally tested. The sensing structure is optimized for operation at the fundamental band- stop resonance near 0.7THz and characterized under normal and oblique incidence. The sensing performance as a function of the incidence angle and the wave polarization is evaluated with good agreement between simulations and measurements. It is shown that a figure of merit for the pro- posed sensor can be enhanced from 0.2 up to 0.6 due to switching from normal to oblique excita- tion, which yields the maximum performance for TM polarization at the incidence angle of 70º. The presented results demonstrate a wide angle operation regime in THz sensing that opens up an alternative approach in improving capabilities of sensing devices. ; This work was sponsored by the Spanish Government under Contract Nos. TEC2011-28664-C02-01 and TEC2014-51902-C2-2-R. P.R.-U. was sponsored by Public University of Navarra via a predoctoral scholarship. M.B. was sponsored by the Spanish Government via RYC-2011- 08221

UPNa. Departamento de Ingeniería Eléctrica y Electrónica. Laboratorio de Ondas Milimétricas y Terahercios ; By backing or sandwiching a holey metal layer with or between isotropic dielectric slabs, additional peaks of transmission within the long-wavelength regime arise as a result of the induced transverse magnetic (TM) or transverse electric (TE) grounded dielectric modes. A similar control of the complex surface wave modes, and thus of the extraordinary transmission (ET) peaks, is demonstrated here via anisotropic slabs in the form of a fakir's bed of nails. However, it is shown that those ET peaks formed from TE modes are suppressed because of the inherent dispersion characteristics of the free-standing grounded pins. This allows the red-shifting of the ET for the polarization parallel to the larger in-plane period of the hole array, but unlike the dielectric isotropic slab configuration, the orthogonal polarization remains inhibited. ; This work was sponsored by the Spanish Government and European Union funds under contracts Consolider 'Engineering Metamaterials' CSD2008- 00066 and TEC2011-28664-C02-01. MN-C is supported by Imperial College through a Junior Research Fellowship. PR-U is sponsored by the Government of Navarre via the program 'Formación de Tecnólogos' 055/01/11. MB is sponsored by the Spanish Government via RYC- 2011–08221.

This chapter is devoted to polarization effects arisen from perforated metallic plates exhibiting extraordinary transmission (ET). Setting aside the state-of-the-art of perforated metallic plates, we show that by applying Babinet's principle, subwavelength hole arrays (SHAs) arranged in rectangular lattice can further enhance its potential polarization response. Different perspectives are brought about to describe and understand the particular behaviour of self-complementariness-based SHAs: Babinet's principle, equivalent circuit analysis, retrieved constitutive parameters, etc. Afterwards, we embark on the numerical analysis of stacked self-complementariness-based perforated plates. It is shown the potential of having a birefringent artificial medium behaving like negative and positive effective refractive index for the vertical and horizontal polarization, respectively. All these findings are experimentally demonstrated at millimetre-waves. ; Work supported by Spanish Government under contract Consolider "ENGINEERING METAMATERIALS" CSD2008-00066.

Lossy mode resonances (LMRs) and surface plasmon resonaces (SPRs) are obtained experimentally with a Kretschmann configuration using a BK7 glass prism with all sides polished and coated with indium tin oxide (ITO). The properties of ITO allow for obtaining LMRs and SPRs with the same experimental setup. The results are corroborated with a numerical method for calculation of the reflection in the Kretschmann configuration. ; This work was supported in part by the Spanish Ministry of Education and Science under contracts FEDER TEC2013-43679-R, CSD2008-00066 and TEC2011-28664-C02. The FTIR spectrometer was financed by the Spanish Ministry of Economy and Competitiveness in the frame of the project CEI10-2-2005. M. Beruete acknowledges funding by the Spanish Government under the research contract program Ramón y Cajal RYC-2011-08221.

In this paper, we design and numerically demonstrate an ultra-thin super-oscillatory metalens with a resolution below the diffraction limit. The zones of the lens are implemented using metasurface concepts with hexagonal unit cells. This way, the transparency and, hence, efficiency is optimized, compared to the conventional transparent–opaque zoning approach that introduces, inevitably, a high reflection in the opaque regions. Furthermore, a novel two-step optimization technique, based on evolutionary algorithms, is developed to reduce the side lobes and boost the intensity at the focus. After the design process, we demonstrate that the metalens is able to generate a focal spot of 0.46λ0 (1.4 times below the resolution limit) at the design focal length of 10λ0 with reduced side lobes (the side lobe level being approximately −11 dB). The metalens is optimized at 0.327 THz, and has been validated with numerical simulations. ; This research was funded by the Spanish Ministerio de Economía y Competitividad with European Union Fondo Europeo de Desarrollo Regional (FEDER) funds, grant number TEC2014-51902-C2-2-R.

Several converging lenses working in the permittivity near to zero (ENZ) regime at optical frequencies are designed using an array of metal-dielectric-metal plasmonic waveguides. These plasmonic waveguides show a dispersive nature that enable to mimic an effective ENZ medium when using the fast wave transverse electric (TE1) mode near its cut-off wavelength. By arranging multiple plasmonic waveguides with the correct engineered dimensions, several metalenses, including graded index (GRIN) ones, and diffractive optical elements (i.e., zoned metalenses) are proposed. The metalenses are designed at l0 = 474.9nm (f = 631.67THz) with a focal length of 10.75l0. Numerical results demonstrate that the best performance is obtained for the case of the GRIN metalens in terms of the focal position, transversal resolution and thickness, reducing its volume up to ∼52.3% with respect to the smooth-profiled plano-concave metalens. ; This work was supported by the Spanish Ministerio de Economía y Competitividad under contract TEC2014-51902-C2-2-R. V.P.-P. is sponsored by Spanish Ministerio de Educación, Cultura y Deporte under grant FPU AP-2012-3796. M. N.-C. is supported by the Birmingham Fellowship. M.B. is sponsored by the Spanish Government via RYC-2011-08221.

A thorough experimental study of the frequency and beaming angle response of a metallic leaky-wave bull's eye antenna working at 77 GHz with a sinusoidally corrugated profile is presented. The beam scanning property of these antennas as frequency is varied is experimentally demonstrated and corroborated through theoretical and numerical results. From the experimental results the dispersion diagram of the n = −1 and n = −2 space harmonics is extracted, and the operation at different frequency regimes is identified and discussed. In order to show the contribution of each half of the antenna, numerical examples of the nearfield behavior are also displayed. Overall, experimental results are in good qualitative and quantitative agreement with theoretical and numerical calculations. Finally, an analysis of the beamwidth as a function of frequency is performed, showing that it can achieve values below 1.5° in a fractional bandwidth of 4% around the operation frequency, which is an interesting frequency-stable broadside radiation. ; This work was supported by the Spanish Government under contract TEC2014-51902-C2-2-R. MN-C is supported by University of Birmingham (Birmingham Fellowship). MB acknowledges support by the Spanish Government under contract RYC-2011-08221.

UPNa. Departamento de Ingeniería Eléctrica y Electrónica. Laboratorio de Ondas Milimétricas y Terahercios ; In this paper, a deep numerical as well as experimental study of the anisotropy response of extraordinary transmission metamaterials constructed by stacking subwavelength hole arrays is presented. Two-dimensional (2D) dispersion diagrams for S- and P-polarization were obtained from simulation. From them, it was found that negative refraction can be obtained for the latter case for small angles of incidence. Additionally, it was found that double periodic and dielectric loaded hole arrays are optimal to enlarge the numerical aperture that leads to negative refraction. Several experiments are then presented in the V-band of the millimetre-wave range that show excellent agreement with the numerical calculations. Moreover, the richness of the anisotropic characteristic exhibited by the stacked hole array structure allows for designing structures with complex electromagnetic response other than solely negative refraction. Thus, the results presented here could be taken as a novel route to achieve exotic behaviour, such as negative refraction at other frequency ranges, like terahertz or the visible. ; This work was supported by the Spanish Government under the contract Consolider "Engineering Metamaterials" CSD2008-00066.

Scientists and laymen alike have always been fascinated by the ability of lenses and mirrors to control light. Now, with the advent of metamaterials and their two-dimensional counterpart metasurfaces, such components can be miniaturized and designed with additional functionalities, holding promise for system integration. To demonstrate this potential, here ultrathin reflection metasurfaces (also called metamirrors) designed for focusing terahertz radiation into a single spot and four spaced spots are proposed and experimentally investigated at the frequency of 0.35 THz. Each metasurface is designed using a computer-generated spatial distribution of the reflection phase. The phase variation within 360 deg is achieved via a topological morphing of the metasurface pattern from metallic patches to U-shaped and split-ring resonator elements, whose spectral response is derived from full-wave electromagnetic simulations. The proposed approach demonstrates a high-performance solution for creating low-cost and lightweight beam-shaping and beam-focusing devices for the terahertz band. ; This work was supported by the Ministry of Education and Science of the Russian Federation under the State Assignment Contract #3002 (implementation of the Gerchberg-Saxton iterative algorithm and experimental testing), the Russian Science Foundation under the Project 14-12-01037 (full-wave electromagnetic simulations), and the Spanish Government under contracts Consolider "Engineering Metamaterials" CSD2008-00066, and TEC2011-28664-C01. M. Beruete acknowledges funding by the Spanish Government under the research contract program Ramón y Cajal RYC-2011-08221. M. N.-C. was supported by Imperial College London through a Junior Research Fellowship.

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. ; This work was supported in part by the Spanish Government under Contract Consolider Engineering Metamaterials CSD2008-00066 and Contract TEC2011-28664-C02-01. B.O. is sponsored by the Spanish Ministerio de Economía y Competitividad under Grant No. FPI BES-2012-054909. M.B. is sponsored by the Spanish Government via RYC-2011-08221. N.M.E. and A.A. have been supported by the NSF CAREER Award No. ECCS-0953311 and the AFOSR Grant No. FA9550-13-1-0204.

Multiband one-way polarization conversion and strong asymmetry in transmission inspired by it are demonstrated in ultrathin sandwiched structures that comprise two twisted aperture-type arrays of complementary split-ring resonators (CSRRs), metallic mesh, and dielectric layers. The basic features of the resulting mechanism originate from the common effect of chirality and tunneling. The emphasis is put on the (nearly) perfect polarization conversion of linear incident polarization into the orthogonal one and related diodelike asymmetric transmission within multiple narrow bands. Desired polarization conversion can be obtained at several resonances for one of the two opposite incidence directions, whereas transmission is fully blocked for the other one. The resonances, at which the (nearly) perfect conversion takes place, are expected to be inherited from similar structures with parallel, i.e., not rotated CSRR arrays that do not enable chirality and, thus, polarization conversion. It is found that the basic transmission and polarization conversion features and, thus, the dominant physics are rather general, enabling efficient engineering of such structures. The lowest-frequency resonance can be obtained in structures made of conventional materials with total thickness less than λ 50/ and up to ten such resonances can correspond to thickness less than λ 20/ . ; This work is supported by the projects DPT-HAMIT, ESF-EPIGRAT, and NATO-SET-181, by TUBITAK under Project Nos., 107A004, 109A015, 109E301, and 110T306, and by Spanish Government under contract Consolider Engineering Metamaterials CSD2008-00066 and Contract No. TEC2011-28664-C02-01. Contribution of A.E.S. has partially been supported by TUBITAK in the framework of the Visiting Reseracher programme and by ESF in the framework of RNP Newfocus. M.B. acknowledges funding by the Spanish Government under the research contract program Ramón y Cajal RYC-2011-0822. E.O. acknowledges partial support from the Turkish Academy of Sciences.

Reducing the profile, footprint and weight of antennas embarked on aircrafts, drones or satellites has been a long pursued objective. Here we tackle this issue by developing a millimeter-wave 96 GHz elliptical Bull's-Eye antenna with off-axis radiation at 16.5° that has been fabricated by low cost 3-D printing stereolithography, followed by metal coating. The theoretical basis for optimum off-axis operations is explained. Measurement results show an overall good agreement with simulations, displaying a gain of 17 dB and a 3.5° beamwidth (E-plane) at the operational frequency. The off-axis beaming enlarges the potential applicability of this technology with respect to the broadside beam solution. ; This work was supported by the Spanish Government under contract TEC2014-51902-C2-2-R. M. N.-C. is supported by University of Birmingham [Birmingham Fellowship]. M.B. acknowledges support by the Spanish Government under contract RYC-2011-08221

In this letter we present an in-depth circuit analysis of anomalous extraordinary transmission ET through subwavelength slit and hole arrrays loaded by a dielectric slab. We show the key role played by the thickness of the dielectric slab in order to enhance the transmission for TE-polarized waves incident electric field parallel to the slits or to the short in-plane period in hole arrays arranged in rectangular lattice within the cut-off regime of the apertures and to suppress Wood's anomaly. Analytical and numerical results together with experimental data are presented, showing good agreement among them. This work provides physical insight of the underlying mechanism governing anomalous ET and offers further independent control over orthogonal polarized waves impinging into subwavelength aperture arrays. ; This work has been supported by the Spanish Government under contracts Consolider "Engineering Metamaterials" Grant Nos. CSD2008-00066 and TEC2008-06871-C02-01.