BUSCADOR RECOLECTA

UPNa. Departamento de Ingeniería Eléctrica y Electrónica. Laboratorio de fotónica TERALAB, Fresnel-zone plate lenses provide focusing performance while having low profile. Unfortunately, they usually display higher reflection losses than conventional dielectric lenses. Here, we demonstrate a low-profile Wood zone plate metalens based on the fishnet metamaterial working in a near-zero regime with an equivalent refractive index less than unity (nf = 0.51). The metalens is made of alternating dielectric and fishnet metamaterial concentric rings. The use of fishnet metamaterial allows reducing the reflections from the lens, while maintaining low profile, low cost and ease of manufacturing. The lens is designed towork at theW-band of the millimeter-waves range with a focal length FL = 22.8 mm (7.5 λ0) aiming at antenna or radar system applications. The focusing per- formance 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 ~2.5 dB with respect to a fishnet Soret metalens., This work was sponsored by Spanish Government under contract TEC2014-51902-C2-2-R. B. O. is sponsored by Spanish Ministerio de Economía y Competitividad under grant FPI BES-2012-054909. M. B. is sponsored by the Spanish Government via RYC-2011-08221.

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.

The following article appeared Pacheco-Pena, V., Beruete, M., Minin, I., & Minin, O. (n.d). Terajets produced by dielectric cuboids. Applied Physics Letters, 105(8), doi: 10.1063/1.4894243, and may be found at http://dx.doi.org/10.1063/1.4894243, The capability of generating terajets using three-dimensional (3D) dielectric cuboids working at terahertz (THZ) frequencies (as analogues of nanojets in the infrared band) is introduced and studied numerically. The focusing performance of the terajets is evaluated in terms of the transversal full width at half maximum (FWHM) along x- and y-directions using different refractive indices for a 3D dielectric cuboid with a fixed geometry, obtaining a quasi-symmetric terajet with a subwavelength resolution of 0.46 wavelengths when the refractive index is n=1.41. Moreover, the backscattering enhancement produced when metal particles are introduced in the terajet region is demonstrated for a 3D dielectric cuboid and compared with its two-dimensional (2D) counterpart. The results of the jet generated for the 3D case are experimentally validated at sub-THZ waves, demonstrating the ability to produce terajets using 3D cuboids., This work was supported in part by the Spanish Government
under Contract Consolider Engineering Metamaterials
CSD2008-00066 and Contract TEC2011-28664-C02-01.
V.P.-P. is sponsored by Spanish Ministerio de Educacion,
Cultura y Deporte under Grant FPU AP-2012-3796. M.B. is
sponsored by the Spanish Government via RYC-2011-08221.

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., This work was supported in part by the Spanish
Government under contract Consolider Engineering Metamaterials CDS2008-00066 and
contract TEC2011-28664-C02-01. B. O. is sponsored by Spanish Ministerio de Economía y
Competitividad under grant FPI BES-2012-054909. V.P.-P. is sponsored by Spanish
Ministerio de Educación, Cultura y Deporte under grant FPU AP-2012-3796. M. B. is
sponsored by the Spanish Government via RYC-2011-08221. M. N.-C. is supported by the
Imperial College Junior Research Fellowship.

The final publication is available at Springer via http://dx.doi.org/10.1007/s12161-017-0879-1, The aim of this research was to study the application of MIR spectroscopy as an alternative to conventional methods to determine fat and protein content. Samples of the main species used to produce meat products were analyzed, showing all of them absorption bands at similar wavenumbers though with different intensity. Correlation analysis of absorption intensities showed that bands around 2925, 2854, and 1746 cm−1 are associated with fat content, whereas bands around 3288, 1657, and 1542 cm−1 are associated with proteins. During the validation process, prediction models of fat and protein content were successfully obtained withR2 0.9173 and 0.7534, respectively. Finally, a good result (R2 =0.8829) was obtained on the estimation of the lipid content when the information at only one wavenumber was used., This work was supported by the Spanish Government
through the Consolider Engineering Metamaterials under Contract
CSD2008-00066 and Contract 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.

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., This work was supported in part by the Spanish Government under contract Consolider Engineering Metamaterials CSD2008-00066 and contract TEC2011-28664-C02-01. The work of V. Torres was supported by the Universidad Pública de Navarra. The work of B. Orazbayev was supported by the Spanish Ministerio de Economía y Competitividad under grant no. FPI BES-2012-054909. The work of V. Pacheco-Peña was supported by the Spanish Ministerio de Educación, Cultura y Deporte under grant no. FPU AP-2012-3796. The work of M. Beruete was supported by the Spanish Government via RYC-2011-08221. The work of M. Navarro-Cía was supported by the Imperial College Junior Research Fellowship.

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.

Graded index ε near-zero (GRIN-ENZ) quasi-optical components such as beam steerers and power splitters are designed, simulated and analyzed. The GRIN-ENZ medium is realized using stacked narrow hollow waveguides whose infinite array shows the first transmission peak at 1.0002 THz. Several GRIN-ENZ beam steerers to channel a normal incident plane wave to different output angles (15, 45, 65 and 80 deg) with good impedance matching (low reflection) are analytically and numerically demonstrated using planar structures with a thickness of 5λ0 = 1500 μm along z-axis. Moreover, symmetrical and asymmetrical power splitters are designed with output angles (plus/minus 45 deg) and (-80, +35 deg), respectively., This work was supported in part by the Spanish Government under contract Consolider
Engineering Metamaterials CSD2008-00066 and contract TEC2011-28664-C02-01. V.P.-P. is
sponsored by Spanish Ministerio de Educación, Cultura y Deporte under grant FPU AP-2012-3796.
V.T. is sponsored by the Universidad Pública de Navarra. M.B. is sponsored by the Spanish
Government via RYC-2011-08221. M. N.-C. is supported by the Imperial College Junior Research Fellowship.

A dual-band quarter-wave plate based on a modified extraordinary transmission hole array is numerically analyzed and experimentally demonstrated at terahertz frequencies. To control independently orthogonal polarizations, the original square holes are connected with vertical slits and their lateral straight sides are replaced by meander lines. This smart design enables dual-band operation with unprecedented fractional bandwidths in a compact structure. Considering a flattening deviation lower than 40% of the optimum value, a fractional bandwidth of 53.8% and 3.8% is theoretically obtained (16.8% and 2.9% in the experiment) at 1 and 2.2 THz, respectively. At these two frequencies, the structure is 0.13-λ and 0.29-λ thick, respectively. Given the compactness of the whole structure and the performance obtained, this quarter-wave plate is presented as a competitive device for the terahertz band., This work was supported by the Spanish Government through the Consolider Engineering Metamaterials under Contract CSD2008-00066 and Contract TEC2011-28664-C02.

We briefly review different synthesis techniques for the design of passive microwave components with arbitrary frequency response,
developed by our group during the last decade. We provide the theoretical foundations based on inverse scattering and coupledmode
theory as well as several applications where the devices designed following those techniques have been successfully tested.
The main characteristics of these synthesis methods are as follows. (a) They are direct, because it is not necessary to use lumpedelement
circuit models; just the target frequency response is the starting point. (b)They are exact, as there is neither spurious bands
nor degradation in the frequency response; hence, there is no bandwidth limitation. (c) They are flexible, because they are valid for
any causal, stable, and passive transfer function; only inviolable physical principles must be guaranteed. A myriad of examples has
been presented by our group in many different technologies for very relevant applications such as harmonic control of amplifiers,
directional couplerwith enhanced directivity and coupling, transmission-type dispersive delay lines for phase engineering, compact
design of high-power spurious free low-pass waveguide filters for satellite payloads, pulse shapers for advanced UWB radar and
communications and for novel breast cancer detection systems, transmission-type Nth-order differentiators for tunable pulse
generation, and a robust filter design tool., This work has been supported by the Spanish Ministerio de Ciencia e Innovación through the Project TEC2011-28664-C02-01. Magdalena Chudzik would like also to acknowledge Spanish Ministerio de Educación for its FPU Grant.

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., Effort sponsored by Spanish Government under contracts Consolider ‘‘Engineering Metamaterials’’ CSD2008-00066, TEC2011-28664-C02-01. B. O. is sponsored by Spanish Ministerio de Economía y Competitividad under grant FPI BES-2012-054909. M. B. is
sponsored by the Spanish Government via RYC-2011-08221. 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 Imperial College Junior Research Fellowship.

The following article appeared Pacheco-Pena, V., Orazbayev, B., Torres, V., Beruete, M., & Navarro-Cia, M. (n.d). Ultra-compact planoconcave zoned metallic lens based on the fishnet metamaterial. Applied Physics Letters, 103(18), and may be found at http://dx.doi.org/10.1063/1.4827876., A 1.5λ0 -thick planoconcave zoned lens based on the fishnet metamaterial is demonstrated experimentally at millimeter wavelengths. The zoning technique applied allows a volume reduction of 60% compared to a full fishnet metamaterial lens without any deterioration in performance. The structure is designed to exhibit an effective refractive index n = -0.25 at f = 56.7GHz (λ0 = 5.29 mm) with a focal length FL = 47.62 mm = 9λ0. The experimental enhancement achieved is 11.1dB, which is in good agreement with simulation and also with previous full fishnet metamaterial lenses and opens the door for integrated solutions., This work was supported in part by the Spanish
Government under contract Consolider Engineering
Metamaterials CSD2008-00066 and contract TEC2011-
28664-C02-01. V.P.-P. was sponsored by Spanish Ministerio
de Educacion, Cultura y Deporte under Grant No. FPU AP-
2012-3796. B.O. was sponsored by Spanish Ministerio de
Economıa y Competitividad under Grant No. FPI BES-2012-
054909. V.T. is sponsored by the Universidad Publica de
Navarra. M.B. is sponsored by the Spanish Government via
RYC-2011-08221. M.N.-C. was supported by the Imperial
College Junior Research Fellowship.

Trabajo presentado al 2014 Mediterranean Microwave Symposium. Marruecos, 2014., Here we perform numerical and experimental investigation of plano-concave all-metallic ε-near-zero (ENZ) lens with operational frequency f = 144 GHz. The ENZ lens is achieved by stacking an array of narrow hollow rectangular waveguides working near cut-off frequency. Focusing and radiation properties are numerically analyzed and measured. The enhancement of 5.61 dB and directivity of 17.6 dBi are shown. Good agreement between experimental and numerical results is demonstrated., 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 Spanish Ministerio de Economía y Competitividad under grant FPI BES-2012-054909. V.T. is sponsored by the Universidad Pública de Navarra. V.P.-P. is sponsored by Spanish Ministerio de Educación, Cultura y Deporte under grant FPU AP-2012-3796. M.B. is sponsored by the Spanish Government via RYC-2011-08221. M. N.-C. is supported by the Imperial College 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.

In this paper, a methodology is proposed for the design of EBG-assisted coupled line structures in microstrip technology, controlling independently the forward and backward coupling. It is based on the use of a single-frequency-tuned electromagnetic bandgap (EBG) structure to produce a single backward-coupled frequency band, in combination with the forward-coupled frequency bands produced by the difference between the even and odd mode propagation constants present in microstrip technology. Thus, the central frequency of the backward-coupled band is controlled by the period of the EBG structure, while the frequencies of the forward coupled bands are fixed by the length of the device. The rest of the frequencies go to the direct port giving rise to a device with the input port matched at all the frequencies and where the coupled bands are easily controllable by adjusting the corresponding design parameter. The novel methodology proposed has been successfully demonstrated by designing a triplexer intended for the GSM (900 MHz) and WLAN (2.4 GHz and 5.5 GHz) telecommunication bands., This work was supported by MINECO (Spain) under projects TEC2011-28664-C02-01 and TEC2014-51902-C2-2-R.

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., This work was supported in part by the Spanish Ministerio
de Economía y Competitividad under contracts No. TEC2014-
51902-C2-1-R and No. TEC2014- 51902-C2-2-R. 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 Ministerio de Economía y Competitividad
via Grant No. RYC-2011-08221. C.G.-M. acknowledges
support from Generalitat Valenciana through the VALi+d
postdoctoral program (Grant No. APOSTD/2014/044).

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., This work was supported by the Spanish Government under Grant
Consolider “Engineering Metamaterials” CSD2008-00066, TEC2011-28664-
C02-01. The work of V. Pacheco-Peña was supported by Spanish Ministerio
de Educación, Cultura y Deporte under Grant FPU AP-2012-3796. The work
of M. Navarro-Cía was supported by the Imperial College Junior Research
Fellowship. The work of B. Orazbayev was supported by Spanish Ministerio
de Economía y Competitividad under Grant FPI BES-2012-054909. The work
of M. Beruete was supported by the Spanish Government via RYC-2011-08221.

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

The following article appeared in Minin, I., Minin, O., Pacheco-Pena, V., & Beruete, M. (n.d). All-dielectric periodic terajet waveguide using an array of coupled cuboids. Applied Physics Letters, 106(25), and may be found at http://dx.doi.org/10.1063/1.4923186., In this paper, the recently proposed technique to produce photonic jets (terajets at terahertz (THz) frequencies) using 3D dielectric cuboids is applied in the design of a mesoscale cuboid-chain wave- guide. The chains are basically designed with several dielectric cubes with side 1 wavelength placed periodically along the axial z-axis and separated by an air-gap. Based on this, a systematic study of the focusing properties and wave guiding of this chain is performed when the air-gap between the dielectric cubes is changed from 0.25 wavelengths to 3 wavelengths with the best performance achieved at 2.5 wavelengths.An analysis when losses are included in the cubes is also done, demonstrating a robust performance. Finally, the wave guiding is experimentally demonstrated at sub-THz frequencies with a good agreement with numerical results. The simulation results of focusing and transport properties are carried out using Finite Integration Technique. The results here presented may be scaled to any frequency ranges such as millimeter, sub-millimeter, and optical frequencies., This work was supported in part by the Spanish Government under Contract No. TEC2011-28664-C02-01. V.P.-P. was sponsored by Spanish Ministerio de Educación, Cultura y Deporte under Grant No. FPU AP-2012-3796. 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.

Frozen modes arising in stacked subwavelength hole arrays are studied in detail. Their origin is proved to be connected with the interaction between the extraordinary transmission resonance and the Fabry–Perot cavity mode. The analysis is done for various situations that differ in metal plate thicknesses and sizes and shape of the holes. Dispersion results and finite-stack transmission spectra are in good agreement, both showing the features indicating hybridization. The boundaries of the hybridization are found in terms of the geometrical parameters. The effect of the number of stacked plates on the transmission has been demonstrated. Finally, it is shown that the group index of refraction ng in the considered finite structures can be larger than 200. The obtained estimates of ng, which are based on dispersion and transmission results, well coincide with each other., This work was supported in part by the Spanish Government under Contract Consolider Engineering Metamaterials CSD2008-00066 and Contract TEC2011-28664-C02-01. M.B. is sponsored by the Spanish Government via RYC-2011-08221. P.R.U. is sponsored by the Government of Navarre via program “Formación de Tecnólogos” 055/01/11. M.N.C. is supported by the Imperial College Junior Research Fellowship. A.E.S. thanks Deutsche Forschungsgemeinschaft for partial support of this work under Project No. SE1409/2-2.
In memoriam of Mario Sorolla.

The following article appeared in Pacheco-Peña, V., Torres, V., Orazbayev, B., Beruete, M., Sorolla, M., Navarro-Cía, M., & Engheta, N. (2014). Mechanical 144GHz beam steering with all-metallic epsilon-near-zero lens antenna. Applied Physics Letters, 105(24), doi:10.1063/1.4903865, and may be found at http://dx.doi.org/10.1063/1.4903865., An all-metallic steerable beam antenna composed of an ε-near-zero (ENZ) metamaterial lens is experimentally demonstrated at 144 GHz (λ0 = 2.083 mm). The ENZ lens is realized by an array of narrow hollow rectangular waveguides working just near and above the cut-off of the TE10 mode. The lens focal arc on the xz-plane is initially estimated analytically as well as numerically and compared with experimental results demonstrating good agreement. Next, an open-ended waveguide is placed along the lens focal arc to evaluate the ENZ-lens antenna steerability. A gain scan loss below 3 dB is achieved for angles up to plus/minus 15º., This work was supported in part by the Spanish
Government under Contract Consolider Engineering
Metamaterials CSD2008-00066 and Contract TEC2011-
28664-C02-01. V.P.-P. is sponsored by Spanish Ministerio
de Educacion, Cultura y Deporte under grant FPU AP-2012-
3796. V.T. is sponsored by the Universidad Publica de
Navarra. B.O. is sponsored by Spanish Ministerio de
Economıa y Competitividad under Grant FPI BES-2012-
054909. M.B. is sponsored by the Spanish Government via
RYC-2011-08221. M.N.-C. is supported by the Imperial
College Junior Research Fellowship.

Metallic plates with a two-dimensional (2D) periodic distribution of sub-wavelength apertures are known to exhibit extraordinary transmission of electromagnetic waves. Stacking two or more of such plates gives place to the so-called fishnet structures, which constitute a popular way of achieving an effective negative index medium at frequencies ranging from microwaves to optics. Unfortunately, a general wideband equivalent circuit has not yet been proposed to facilitate its understanding and design. This
work presents this circuit model with closed-form expressions for the circuit elements, thus making it possible to obtain the electrical response for this class of structures in a very efficient way. This
procedure is much faster than alternative numerical methods at the same time that it retains a high level of accuracy when compared with some other oversimplified models. The circuit model also provides a simple rationale as well as a good physical insight in order to explain the qualitative behavior of such structures, independently of the number of stacked layers., This work was supported by the Spanish Ministry of Economy and Competitiveness with European Union Feder Funds (under grants TEC2011-28664-C02-01, TEC2014-51902-C2-2-R, TEC2013-41913-P, and Consolider EMET CSD2008-00066, and by the Spanish Junta de Andalucía under Project P12-TIC-1435). The work of M. Beruete was supported by the Spanish Government via RYC-2011-08221.

The following article appeared in Pacheco-Pena, V., Orazbayev, B., Beaskoetxea, U., Beruete, M., & Navarro-Cia, M. (n.d). Zoned near-zero refractive index fishnet lens antenna: Steering millimeter waves. Journal Of Applied Physics, 115(12), and may be found at http://dx.doi.org/10.1063/1.4869436., A zoned fishnet metamaterial lens is designed, fabricated, and experimentally demonstrated at millimeter wavelengths to work as a negative near-zero refractive index lens suitable for compact lens antenna configurations. At the design frequency f=56.7GHz (wavelength = 5.29 mm), the zoned fishnet metamaterial lens, designed to have a focal length FL= 9 wavelengths, exhibits a refractive index n = 0.25. The focusing performance of the diffractive optical element is briefly compared with that of a non-zoned fishnet metamaterial lens and an isotropic homogeneous zoned lens made of a material with the same refractive index. Experimental and numerically-computed radiation diagrams of the fabricated zoned lens are presented and compared in detail with that of a simulated non-zoned lens. Simulation and experimental results are in good agreement, demonstrating an enhancement generated by the zoned lens of 10.7 dB, corresponding to a gain of 12.26 dB. Moreover, beam steering capability of the structure by shifting the feeder on the xz-plane is demonstrated., This work was supported in part by the Spanish
Government under contract Consolider Engineering
Metamaterials CSD2008-00066 and Contract No. TEC2011-
28664-C02-01. V.P.-P. is sponsored by Spanish Ministerio
de Educacion, Cultura y Deporte under Grant No. FPU AP-
2012-3796. B.O. is sponsored by Spanish Ministerio de
Economıa y Competitividad under Grant No. FPI BES-2012-
054909. M.B. is sponsored by the Spanish Government via
RYC-2011-08221. M. N.-C. is supported by the Imperial
College Junior Research Fellowship.

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.

A high-gain Bull’s-Eye leaky-wave horn antenna
working at 77 GHz with sinusoidal profile has been designed,
fabricated, and experimentally measured. The influence of the
number of periods on the gain and beamwidth is numerically
investigated. Experimental measurements show a high gain of
28.9 dB, with low sidelobe level and a very narrow beamwidth in
good agreement with results obtained from simulations., This work was supported by the Spanish Government
under Grant Consolider Engineering Metamaterials CSD2008-0066 and
Grant TEC2011-28664-C02-01. The work of M. Navarro-Cía was supported by
the Imperial College Junior Research Fellowship. The work of M. Beruete was
supported by the Spanish Government under the Research Contract Program
Ramón y Cajal RYC-2011-08221 and the European Science Foundation (ESF)
for the activity titled “New Frontiers in Millimetre/Sub-Millimetre Waves
Integrated Dielectric Focusing Systems.”

In the past, it has been demonstrated that it is possible to produce terajets with high resolution at its focus using 3D dielectric cuboids under plane-wave illumination. Here, a systematic study of the harmonic and angular response of terajets using cuboids is performed. Mutifrequency focusing is demonstrated at the fundamental frequency and two higher frequency harmonics showing an intensity enhancement of∼10, ∼18, and∼14 for each case. This capability to use 3D dielectric cuboids to produce terajets at the fundamental frequency and first harmonic is experimentally evaluated at sub-THz frequencies, with good agreement with numerical results. Moreover, a robust angular response is demonstrated numerically and experimentally showing that the intensity at the focal position is maintained in a wide angular range (from 0° to 45°), demonstrating the capability to work as a wide scanning terajet-focusing lens. The results here presented may be scaled at different frequency bands such as optical frequencies and may be used in microscopy techniques and sensors., This work was supported in part by the Spanish
Government under contract Consolider Engineering
Metamaterials CSD2008-00066 and contract TEC2011-
28664-C02-01. V. P.-P. is sponsored by Spanish Ministerio
de Educación, Cultura y Deporte under grant FPU AP-
2012-3796. M. B. is sponsored by the Spanish Government
via RYC-2011-08221.

Los metamateriales, descendientes de los dieléctricos artificiales, tienen parámetros electromagnéticos inusuales y proporcionan más posibilidades que los dieléctricos naturales para el control de la propagación de la luz. Los metamateriales han posibilitado la obtención de medios doblemente negativos, gracias a la capacidad que ofrecen para controlar tanto la permitividad y la permeabilidad. La primera realización experimental de un medio de ese tipo dio un enorme impulso a la investigación en el campo del electromagnetismo. Como resultado, se han desarrollado desde entonces muchos dispositivos electromagnéticos fascinantes, incluyendo lentes de metamateriales, dispositivos de control de dirección de haz e incluso capas de invisibilidad. Las posibles aplicaciones de los metamateriales no se limitan a estos dispositivos y se pueden aplicar en muchas áreas como las telecomunicaciones, sistemas de seguridad, detección biológica y química, la espectroscopía, nanoóptica integrada, la nanotecnología, los sistemas de imágenes médicas, etc.
El objetivo de esta tesis doctoral, realizada en la Universidad Pública de Navarra en colaboración con la Universidad de Texas en Austin, el Centro de Tecnología Nanofotónica de Valencia de la UPV y el King’s College London, es contribuir al desarrollo de dispositivos basados en metamateriales, incluyendo su fabricación y, cuando sea posible, la verificación experimental. La tesis no se centra en una sola aplicación o dispositivo, sino que trata de proporcionar una extensa exploración de diferentes dispositivos de metamateriales. Los resultados de la misma son los siguientes:
Se presentan tres lentes de diferentes diseños basados en un metamaterial fishnet: una lente zonada de ancha banda, una lente Soret y una lente de Wood. Todas las lentes han sido experimentalmente realizadas, demostrando un buen acuerdo con el análisis numérico. Por otra parte, se ha demostrado una capa de invisibilidad ultrafina basada en una metasuperficie, un caso 2D de metamaterial, construida con resonadores de anillo. Se ha realizado un análisis numérico, y experimental confirmando el comportamiento de invisibilidad dentro de un rango de frecuencias y de ángulos relativamente amplios. Además, se presenta un diseño de una capa de invisibilidad basada en la óptica de transformación para la luz difusa. Se demuestra, que mediante la restricción de la capa para trabajar en una sola dirección es posible obtener un rendimiento de camuflaje ideal bajo las condiciones de iluminación transitoria, que normalmente está fuera de alcance en los diseños típicos de capas de invisibilidad. Por último, se presenta la demostración teórica de tres diferentes dispositivos de control del haz basados en metamateriales de grafeno. El metamaterial de grafeno utilizado permite controlar dinámicamente el ángulo de salida de la radiación con velocidad ultra alta., Metamaterials, the descendants of the artificial dielectrics, have unusual electromagnetic parameters and provide more abilities than naturally available dielectrics for the control of light propagation. Being able to control both permittivity and permeability, metamaterials have opened a way to obtain a double negative medium. The first experimental realization of such medium gave an enormous impulse for research in the field of electromagnetism. As result, many fascinating electromagnetic devices have been developed since then, including metamaterial lenses, beam steerers and even invisibility cloaks. The possible applications of metamaterials are not limited to these devices and can be applied in many fields, such as telecommunications, security systems, biological and chemical sensing, spectroscopy, integrated nano-optics, nanotechnology, medical imaging systems, etc.
The aim of this doctoral thesis, performed at the Public University of Navarre in collaboration with the University of Texas at Austin, the Valencia Nanophotonics Technology Center in the UPV and King’s College London, is to contribute to the development of metamaterial based devices, including their fabrication and, when possible, experimental verification. The thesis is not focused on a single application or device, but instead tries to provide an extensive exploration of the different metamaterial devices. These results include the following:
Three different lens designs based on a fishnet metamaterial are presented: a broadband zoned fishnet metamaterial lens, a Soret fishnet metamaterial lens and a Wood zone plate fishnet metamaterial. All lenses have been experimentally realized, demonstrating a good agreement with numerical analysis. Moreover, a metasurface, a 2D case of metamaterial, built with closed ring resonators has been used to design an ultrathin carpet cloak. Numerical as well as experimental analysis is done, confirming the cloaking performance of the designed cloak in relatively wide frequency range and angle span. Also, a design of a transformation based cloak for diffusive light is presented. It is demonstrated, that by restricting the cloak to work in one direction it is possible to obtain an ideal cloaking performance under transient illumination, which is normally beyond reach in typical cloak designs. Finally, the theoretical demonstration of three different beam steering devices based on graphene metamaterial is presented. The used graphene metamaterial allows to dynamically control the output angle of the radiation with ultrahigh speed., Ministerio de Economía, Industria y Competitividad (FPI BES-2012-054909)., Programa de Doctorado en Tecnologías de las Comunicaciones, Bioingeniería y de las Energías Renovables (RD 99/2011), Bioingeniaritzako eta Komunikazioen eta Energia Berriztagarrien Teknologietako Doktoretza Programa (ED 99/2011)

An epsilon-near-zero graded-index converging lens with planar
faces is proposed and analyzed. Each perfectly-electric conducting (PEC)
waveguide comprising the lens operates slightly above its cut-off frequency
and has the same length but different cross-sectional dimensions. This
allows controlling individually the propagation constant and the normalized
characteristic impedance of each waveguide for the desired phase front at
the lens output while Fresnel reflection losses are minimized. A complete
theoretical analysis based on the waveguide theory and Fermat’s principle
is provided. This is complemented with numerical simulation results of
two-dimensional and three-dimensional lenses, made of PEC and
aluminum, respectively, and working in the terahertz regime, which show
good agreement with the analytical work., Effort sponsored by Spanish Government under contracts Consolider “Engineering
Metamaterials” CSD2008-00066 and TEC2011-28664-C02-01. P.R.-U. is sponsored by the
Government of Navarra under funding program “Formación de tecnólogos” 055/01/11. M.N.-
C. is supported by the Imperial College Junior Research Fellowship. M. B. acknowledges
funding by the Spanish Government under the research contract program Ramon y Cajal
RYC-2011-08221. N.E. acknowledges the support from the US Office of Naval Research
(ONR) Multidisciplinary University Research Initiatives (MURI) grant number N00014-10-1-
0942.

We present a method that enables the implementation of full three-dimensional
(3D) transformation media with minimized anisotropy. It is based on a special
kind of shape-preserving mapping and a subsequent optimization process. For
sufficiently smooth transformations, the resulting anisotropy can be neglected,
paving the way for practically realizable 3D devices. The method is independent
of the considered wave phenomenon and can thus be applied to any field for
which a transformational technique exists, such as acoustics or thermodynamics.
Full 3D isotropy has an additional important implication for optical transformation
media, as it eliminates the need for magnetic materials in many situations.
To illustrate the potential of the method, we design 3D counterparts of
transformation-based electromagnetic squeezers and bends., The authors acknowledge support from projects Consolider EMET (CSD2008-00066), TEC 2011-28664-C02-02 and GVA ACOMP/2013/013.

A general theory of reciprocal unidirectional transmission with tunable sign-switchable refraction and deflection of outgoing wave in structures with broken spatial inversion symmetry is presented. Several coupling scenarios connected with the diffraction-inspired asymmetry in transmission are considered for volumetric structures with one-side corrugations. They illustrate conditions of coexistence of diodelike unidirectional transmission and tunability of deflection and refraction, including change of their sign. Simulation results are presented and analyzed for nonsymmetric structures based on the stacked subwavelength hole array metamaterial. It is shown that one-way coupling can appear within a wide range of frequencies and angles of incidence, a part of which may be used to obtain different signs of deflection. Transmission results and field distributions confirm the possibility of obtaining high-contrast unidirectional transmission that can be tuned by varying incidence angle, while frequency is fixed. A pronounced unidirectional transmission is demonstrated at negative deflection in structures that are only 0.47λ0 thick, whereas a thicker structure is required in order to obtain both signs of deflection in a unidirectional regime., This work was sponsored by the Spanish Government and European Union funds under contracts Consolider “Engineering Metamaterials” CSD2008-00066 and TEC2011-28664-C02-01. P.R.-U. is sponsored by the Government of Navarre via the program “Formacion de Tecnólogos” 055/01/11. M.B. is sponsored by the Spanish Government via RYC-2011-08221. M.N.-C. is supported by the Imperial College Junior Research Fellowship. The contribution of A.E.S. was partially supported by the DFG, Project No. 1409/2-2, and by the European Science Foundation under the RNP NEWFOCUS program.

UPNa. Departamento de Ingeniería Eléctrica y Electrónica. Laboratorio de fotónica TERALAB, We present a mid-infrared inductor that when applied to an extraordinary transmission hole array produces a strong redshift of the resonant peak accompanied by an unprecedented enlargement of the operation bandwidth. The importance of the result is twofold: from a fundamental viewpoint, the direct applicability of equivalent circuit concepts borrowed from microwaves is demonstrated, in frequencies as high as 17â€...THz upholding unification of plasmonics and microwave concepts and allowing for a simplification of structure design and analysis; in practical terms, a broadband funnelling ofinfrared radiation with fractional bandwidth and efficiency as high as 97% and 48%, respectively, is achieved through an area less than one hundredth the squared wavelength, which leads to an impressive accessible strong field localization that may be of great interest in sensing applications., Effort sponsored by Spanish Government under contracts Consolider EngineeringMetamaterials CSD2008-00066, TEC2011-28664-C01 and TEC2011-28664-C02. V.T. acknowledges funding from Universidad Pública de Navarra. P.R.-U. is sponsored by the Government of Navarra under funding program Formación de tecnólogos 055/01/11. M.N.-C. is supported by the Imperial College Junior Research Fellowship. M.B. acknowledges funding by the Spanish Government under the research contract program Ramón y Cajal RYC-2011-08221.

A photonic jet (a terajet at terahertz frequencies) commonly denotes a specific, spatially localized region in the near field on the front side of a dielectric particle with a diameter comparable with the wavelength illuminated by a plane wave on its back side (i.e., the jet emerges from the shadow surface of a dielectric particle). In this Letter, the formation of a photonic jet is demonstrated using the recently proposed three-dimensional (3D) dielectric cuboids working in the “reflection” mode when the specific, spatially localized region is localized in the direction of the incident wavefront. The results of the simulations based on the Finite Integration Technique are discussed. All dimensions are given in wavelength units so that all results can be scaled to any frequency of interest, including optical frequencies, thus simplifying the fabrication process compared with spherical dielectrics. The results presented here may be of interest for novel applications, including microscopy techniques and sensors., This work was supported in part by the Spanish
Government under contract TEC2011-28664-C02-01. V.
P.-P. is sponsored by Spanish Ministerio de Educación,
Cultura y Deporte under grant FPU AP-2012-3796. M.
B. is sponsored by the Spanish Government via RYC-
2011-08221.

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.

A dual-band quarter-wave plate based on a modified extraordinary transmission hole array is numerically analyzed and experimentally demonstrated at terahertz frequencies. To control independently orthogonal polarizations, the original square holes are connected with vertical slits and their lateral straight sides are replaced by meander lines. This smart design enables dual-band operation with unprecedented fractional bandwidths in a compact structure. Considering a flattening deviation lower than 40% of the optimum value, a fractional bandwidth of 53.8% and 3.8% is theoretically obtained (16.8% and 2.9% in the experiment) at 1 and 2.2 THz, respectively. At these two frequencies, the structure is 0.13-lambda and 0.29-lambda thick, respectively. Given the compactness of the whole structure and the performance obtained, this quarter-wave plate is presented as a competitive device for the terahertz band., This work was supported by the Spanish Government through the Consolider Engineering Metamaterials under Contract CSD2008-00066 and Contract TEC2011-28664-C02.

We present a mid-infrared inductor that when applied to an extraordinary transmission hole array produces a strong redshift of the resonant peak accompanied by an unprecedented enlargement of the operation bandwidth. The importance of the result is twofold: from a fundamental viewpoint, the direct applicability of equivalent circuit concepts borrowed from microwaves is demonstrated, in frequencies as high as 17 THz upholding unification of plasmonics and microwave concepts and allowing for a simplification of structure design and analysis; in practical terms, a broadband funnelling of infrared radiation with fractional bandwidth and efficiency as high as 97% and 48%, respectively, is achieved through an area less than one hundredth the squared wavelength, which leads to an impressive accessible strong field localization that may be of great interest in sensing applications., In memoriam Prof. Mario Sorolla. Effort sponsored by Spanish Government under contracts Consolider "Engineering Metamaterials" CSD2008-00066, TEC2011-28664-C01 and TEC2011-28664-C02. V. T. acknowledges funding from Universidad Publica de Navarra. P.R.-U. is sponsored by the Government of Navarra under funding program "Formacion de tecnologos" 055/01/11. M. N.-C. is supported by the Imperial College Junior Research Fellowship. M. B. acknowledges funding by the Spanish Government under the research contract program Ramon y Cajal RYC-2011-08221.