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.

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.

In this paper, a linearly polarized low profile and asymmetric Bull’s-Eye leaky wave antenna fed by a monopole operating at 13 GHz is presented. Broadside radiation from the monopole is achieved by surrounding it with an asymmetric array of semicircular metallic strips on a grounded dielectric slab. With this implementation we demonstrate high gain with a weight of less than 80 g and lower side lobe levels compared to previous designs fed by a resonant slot. The measured antenna shows an experimental gain of 19.4 dBi with only 5 periods and a side lobe level of −16 dB (−20.3 dB for the numerical ideal case at f = 12.6 GHz), along with a narrow 6º beamwidth, This
work was supported by the Spanish Ministerio de Economía y Competitividad
(MINECO) with contract TEC2014-51902-C2-2-R. U.B and A.T. acknowledge the funding provided by UPNA via the FPI PhD grant program.

In this paper, we propose a novel synthesis strategy
for the design of one dimensional electromagnetic bandgap (1-
D-EBG) structures where all the performance parameters of
these devices can fully be controlled, i.e., the central frequency
of the forbidden band, its attenuation level and bandwidth,
and the ripple level at the passbands. The novel synthesis
strategy employs a new inverse-scattering technique to accurately
synthesize the 1-D-EBG structure, targeting a properly
interpolated version of a classical periodic filter fulfilling the
required frequency specifications. The new inverse-scattering
technique follows a continuous layer peeling approach and relies
on the coupled-mode theory to precisely model the microwave
structures. Telecommunication and radar systems, as well as
material characterization devices, will be profited by this proposal
with which enhanced filters, sensors, power dividers, couplers,
mixers, oscillators, and amplifiers can be designed in many
different technologies. As a proof of concept, a 1-D-EBG structure
in microstrip technology with a single forbidden band (free of
spurious stopband replicas), with attenuation level of 30 dB,
fractional bandwidth larger than 100%, and return loss level
at the passbands of 20 dB, has been designed and fabricated.
The measurements obtained are in very good agreement with
the simulations and target specifications, being free of spurious
replicas up to the 15th harmonic, showing the robustness and
very good performance of the novel design strategy proposed., This work was supported by MINECO (Spain) under Projects TEC2014-51902-C2-2-R and TEC2014-55735-C3-R.

A concept of quasiplanar one-way transparent terahertz absorbers made of linear isotropic materials is presented. The resulting structure consists of a homogeneous absorbing layer of polar dielectric, GaAs, a dispersion-free substrate, and an ultrathin frequency-selective reflector. It is demonstrated that perfect absorption can be obtained for forward illumination, along with total reflection at backward illumination and transparency windows in the adjacent bands. The design is particularized for the polaritonic gap range where permittivity of GaAs varies in a wide range and includes epsilon-near-zero and transparency regimes. The underlying physics can be explained with the aid of a unified equivalent-circuit (EC) analytical model. Perfect matching of input impedance in forward operation and, simultaneously, strong mismatch in the backward case are the universal criteria of one-way absorption. It is shown that perfect one-way absorption can be achieved at rather arbitrary permittivity values, provided these criteria are fulfilled. The EC results are in good agreement with full-wave simulations in a wide range of material and geometrical parameters. The resulting one-way absorbers are very compact and geometrically simple, and enable transparency in the neighboring frequency ranges and, hence, multifunctionality that utilizes both absorption- and transmission-related regimes., This work is supported by the Spanish Ministerio de
Economía y Competitividad (MINECO) (TEC2014-51902-
C2-2-R). P.R.U. is sponsored by the Public University of
Navarra via a predoctoral scholarship, and A.E.S. is sup-
ported by the National Science Center of Poland (NCN)
(MetaSel DEC-2015/17/B/ST3/00118). We are very thankful
to Prof. S. Nojima, YCU (Yokohama, Japan), for valuable
discussions.

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.

In this work, the fishnet metamaterial is applied to several converging metalenses by combining the zoning, reference phase, and phase reversal techniques. First, the zoning and reference phase techniques are implemented in several metalenses at 55 GHz ( λ 0 = 5.45 m m ) with a short focal length of 1.5 λ 0 . Then, the phase reversal technique is applied to these metalenses by switching from a concave to a convex profile in order to change the phase distribution inside of them. The designs are evaluated both numerically and experimentally demonstrating that chromatic dispersion (the shift of the position of the focus at different frequencies) is reduced when using the phase-reversed profiles. It is shown how the position of the focus remains at the same location within a relatively broadband frequency range of ~4% around the design frequency without affecting the overall behaviour of the metalenses. The best performance is achieved with the design that combines both reference phase and phase reversal techniques, with an experimental position of the focus of 1.75 λ 0 , reduced side lobes, and a power enhancement of 6.5 dB. The metalenses designed here may find applications in situations where a wideband response and low side lobes are required because of the reduced chromatic aberrations of the focus., This work was partially supported by the Spanish Ministerio de Economía y Competitividad with European Union Fondo Europeo de Desarrollo Regional (FEDER) funds (TEC2014-51902-C2-2-R). Victor Pacheco-Peña is supported by Newcastle University (Newcastle University Research Fellow). Igor V. Minin and Oleg V. Minin were partially supported by the Mendeleev scientific fund of Tomsk State University.

In this letter, several converging fishnet metalenses are designed using both the zoning and reference phase techniques. They are engineered with a focal length of 1.5λ0 at the design frequency of 55 GHz (λ0 = 5.45 mm) at which the fishnet metamaterial has an effective refractive index of nlens = ∼0.68. Three metalenses are analyzed—with positive, negative, and without reference phase—in order to compare their performance. The focal properties are evaluated both numerically and experimentally, demonstrating a good agreement between them. The best performance is achieved for the zoned metalens with positive reference phase,with an experimental power enhancement at the focal length of 6.2 dB, better axial resolution (0.65λ0 ), and reduced lateral lobes compared to other designs, This work was supported by the Spanish
Ministerio de Economía y Competitividad under contract TEC2014-51902-
C2-2-R and partially by the Tomsk State University Competitiveness
Improvement Program Nº 8.1.23.2015. 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 Ministerio de Economía y Competitividad
via RYC-2011-08221.

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).

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].

In this paper we perform an in-depth theoretical studyofa sensing platform based on epsilon-near- zero (ENZ) metamaterials. The structure proposed for sensing is a narrow metallic waveguide channel. An equivalent circuit model is rigorouslydeduced using transmission line theory, considering several configurations for a dielectric body (analyte sample) inserted within the narrow channel, showing good agreement with results obtained from numerical simulations. The transmission line model is able to reproduce even the most peculiar details ofthe sensing platform response. Its performance is then evaluated byvarying systematically the size, position and permittivity ofthe analyte, and height ofthe ENZ channel. It is shown that the sensor is capable ofdetecting changes in the permittivity/ refractive index or position even with deeplysubwavelength analyte sizes (∼0.05λ0), giving a sensitivity up to 0.03m/RIU and a figure ofMerit∼25. The effective medium approach is evaluated by treating the inhomogeneous cross-section ofthe analyte as a transmission line filled with a homogeneous material., VP-P is supported by the Newcastle University (Newcastle University Research Fellow). MB acknowledges
support by the Spanish Ministerio de Economía y Competitividad under contract TEC2014-51902-C2-2-R.
PR-U was sponsored by Public University of Navarra via a predoctoral scholarship. NE acknowledges the partial
support from the Vannevar Bush Faculty Fellowship program sponsored by the Basic Research Office of the
Assistant Secretary of Defense for Research and Engineering and funded by the Office of Naval Research through
grant N00014-16-1-2029.

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

Tunable deflection of obliquely incident, linearly polarized terahertz waves is theoretically studied in a wide frequency range around 20 THz, by combining a thin slab of graphene-dielectric metamaterial (with ten layers of graphene), a dielectric grating, and a uniform polar-dielectric slab operating in the epsilon-near-zero (ENZ) regime. The modulation of the deflection intensity and deflection angle is done by varying the chemical potential of graphene, and is realized with or without connection to the asymmetric transmission. It is shown to depend on the location of the graphene-dielectric metamaterial slab, as well as on the incidence angle. Four scenarios of tunable deflection are found, including the ones realizable in two-component structures without an ENZ slab., Narodowe Centrum Nauki (NCN), Poland (DEC-2015/17/B/ST3/00118 – Metasel); TUBITAK
(113E331, 114E374, 115F560); EU Horizon-2020 via Marie Sklodowska-Curie IF program
(grant no. 708200 – ADVANTA); Ministerio de Economía, Industria y Competitividad, Spain
(TEC2014-51902-C2-2-R).

This is the peer reviewed version of the following article: M. Navarro-Cía, V. Pacheco-Peña, S. A. Kuznetsov, M. Beruete: Extraordinary THz Transmission with a Small Beam Spot: The Leaky Wave Mechanism. Advanced Optical Materials 2018, 1701312, which has been published in final form at https://doi.org/10.1002/adom.201701312. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving., The discovery of extraordinary optical transmission (EOT) through patterned
metallic foils in the late 1990s was decisive for the development of plasmonics
and cleared the path to employ small apertures for a variety of interesting
applications all along the electromagnetic spectrum. However, a typical
drawback often found in practical EOT structures is the large size needed to
obtain high transmittance peaks. Consequently, practical EOT arrays are usually
illuminated using an expanded (mimicking a plane wave) beam. Here, it
is shown with numerical and experimental results in the THz range that high
transmittance peaks can be obtained even with a reduced illumination spot
exciting a small number of holes, provided that the structure has a sufficient
number of lateral holes out of the illumination spot. These results shed more
light on the prominent role of leaky waves in the underlying physics of EOT
and have a direct impact on potential applications., This work was partially supported by the Spanish Ministerio de
Economía y Competitividad with European Union Fondo Europeo de
Desarrollo Regional (FEDER) funds [TEC2014-51902-C2-2-R]. M.N.-C.
acknowledges support from University of Birmingham [Birmingham
Fellowship]. V.P.-P. was sponsored by Spanish Ministerio de Educación,
Cultura y Deporte [formación de profesorado universitario (FPU)
AP-2012-3796]. S.A.K. acknowledges support from the Novosibirsk State
University (NSU) program 5-100 established by the Russian Ministry of
Education and Science.

In this work, a labyrinth metasurface sensor operating at the low‐frequency edge of the THz band is presented. Its intricate shape leads to a high electric field confinement on the surface of the structure, resulting in ultrasensitive performance, able to detect samples of the order of tens of nanometers at a wavelength of the order of millimeters (i.e., five orders of magnitude larger). The sensing capabilities of the labyrinth metasurface are evaluated numerically and experimentally by covering the metallic face with tin dioxide (SnO2) thin films with thicknesses ranging from 24 to 345 nm. A redshift of the resonant frequency is observed as the analyte thickness increases, until reaching a thickness of 20 μm, where the response saturates. A maximum sensitivity of more than 800 and a figure of merit near 4500 nm−1 are achieved, allowing discriminating differences in the SnO2 thickness of less than 25 nm, and improving previous works by a factor of 35. This result can open a new paradigm of ultrasensitive devices based on intricate metageometries overcoming the limitations of classical metasurface sensor designs based on periodic metaatoms., The authors acknowledge support from the Spanish Ministerio de Economía y Competitividad (MINECO) under Contract TEC2014-51902-C2-2-R, the NSU program 5-100 established by the Russian Ministry of Education and Science, and the State Assignment Program of the Rzhanov Institute of Semiconductor Physics SB RAS (Project No. 0306-2016-0020).

In this work, a metasurface with unconventional angular performance and composed by a nonbianisotropic complementary split ring resonator (NB-CSRR) is analyzed numerically and experimentally. A numerical study comparing the performance with the original complementary split ring resonator is conducted, showing very interesting transmission properties, such as complete filtering under normal incidence and high transmission peaks at oblique incidence for the NB-CSRR metasurface. A bilayered NB-CSRR prototype working at millimeter waves with a total thickness of 100
μm (0.1 times the operation wavelength) is fabricated and tested with a good agreement between simulation results and experiments. Very exciting applications based on the presented structure, such as advanced angular selectivity devices with great rejection levels at normal incidence and angular sensing devices, can be envisaged., Ministerio de Economía y Competitividad
(MINECO) (RYC-2011-08221, TEC2014-51902-C2-2-R).

A 2-D periodic array of annular apertures (or ring slots) is studied using an accurate circuit model. The model accounts for distributed and dynamic effects associated with the excitation of high-order modes operating above or below cutoff but not far from their cutoff frequencies. This paper allows to ascertain the substantial differences of the underlying physics when this structure operates as a classical frequency selective surface or in the extraordinary-transmission (ET) regime. A discussion of two different designs working at each regime is provided by means of the equivalent circuit approach (ECA), full wave simulation results, and experimental characterization. The agreement between the equivalent circuit calculation applied here and the simulation and experimental results is very good in all the considered cases. This validates the ECA as an efficient minimal-order model and a low computational-cost design tool for frequency selective surfaces and ET-based devices. Additional scenarios such as oblique incidence and parametric studies of the structural geometry are also considered., This work was supported in part by the Spanish Ministerio
de Economía y Competitividad with the European Union FEDER funds
under Project TEC2013-41913-P and Project TEC2014-51902-C2-2-R and in
part by the Spanish Junta de Andalucía under Project P12-TIC-1435. The
work of P. Rodríguez-Ulibarri was supported by the Universidad Pública
de Navarra under a Pre-Doctoral Scholarship. The work of M. Navarro Cía
was supported by the University of Birmingham under the Birmingham
Fellowship

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. The following article appeared in V. Pacheco-Peña and M. Beruete. Photonic nanojets with mesoscale high-index dielectric particles. J. Appl. Phys.125, 084104 (2019).
doi: 10.1063/1.5086175 and may be found at doi: http://dx.doi.org/10.1063/1.5086175., In this work, we demonstrate the ability of high-index dielectric particles immersed in air to generate photonic nanojets with extreme resolution (∼0.06λ0). Both 2D (cylindrical) and 3D (spherical) particles are analyzed, and their profile is truncated using the Weierstrass formulation for solid immersion lenses to produce a photonic nanojet at the output surface under plane wave illumination. Their focusing capability is evaluated in terms of the spatial resolution achieving subwavelength values of ∼0.14λ0 and ∼0.06λ0 for a truncated cylinder and sphere, respectively. The capability of the truncated sphere to enhance the backscattering produced by two small metallic spherical scatterers placed near the photonic nanojet is evaluated by using a scanning-probe microscopy configuration. The imaging capabilities of this technique are also analyzed by moving the metallic spheres in the transversal plane where the photonic nanojet is produced. The results presented here improve greatly the typical resolution of photonic nanojets generated with dielectric particles with a small index contrast. In addition, the high-index material allows using mesoscale particles, leading to a more compact setup. These results may find applications in areas such as microscopy, imaging, and sensing devices where a subwavelength resolution below the diffraction limit is needed., V.P.-P. is supported by the Newcastle University
(Newcastle University Research Fellow). M.B. acknowledges
the support by the Spanish Ministerio de Economía y
Competitividad under Contract No. TEC2014-51902-C2-2-R.

In this paper, a novel waffle-iron filter with
transmission zeros at multiple frequencies, along with its design
procedure, is presented. The proposed filter features a high-power
behavior and a wide rejected band in a single compact structure
by means of a set of transmission zeros that can also be placed close
to the passband. Its design method rests on a divide-and-rule
strategy, where the physical dimensions of the constituent design
entities (DEs) can be easily computed in a very short time. A novel
high-power compact waffle-iron filter with transmission zeros at
multiple frequencies has been designed as well as several classical
waffle-iron filters with transmission zeros at one frequency only,
using a detailed step-by-step procedure which avoids the bruteforce
optimizations needed until now. Multipactor and corona
simulations have been conducted proving a high-power handling
capability of 1.8 kW and 78.6 W, respectively. A prototype of the
novel filter has been fabricated, obtaining a remarkable
accordance between the simulated and measured results., This work was supported in part by the ESA’s
Networking/Partnering Initiati
ve under Contract 4000114859/15/NL/HK and
in part by the MINECO (Spain) under Project TEC2017-85529-C3-2-R,
Project TEC2014-55735-C3-R, and Project TEC2014-51902-C2-2-R. This
paper is an expanded version from the
2018 International Microwave Sym-
posium, Philadelphia, PA, USA, June 10–15 2018.
(Corresponding author:
Fernando Teberio.)

This is the peer reviewed version of the following article: B. Orazbayev, N. Mohammadi Estakhri, A. Alù, M. Beruete, Advanced Optical Materials 2017, 5, 1600606, which has been published in final form at http://dx.doi.org/10.1002/adom.201600606. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving., 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., This work
was founded by the Spanish Ministerio de Economía y Competitividad with project
TEC2014-51902-C2-2-R. M.B. acknowledges funding by the Spanish Ministerio de
Economía y Competitividad with contract 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.

Subwavelength hole array (HA) metasurfaces support the so-called extraordinary optical transmission (EOT) resonance that has already been exploited for sensing. In this work, we demonstrate the superior performance of a different resonant regime of HA metasurfaces called anomalous EOT, by doing a thorough numerical and experimental study of its ability in thin-film label-free sensing applications in the terahertz (THz) band. A comprehensive analysis using both the regular and anomalous EOT resonances is done by depositing thin layers of dielectric analyte slabs of different thicknesses on the structures in different scenarios. We carry out a detailed comparison and demonstrate that the best sensing performance is achieved when the structure operates in the anomalous EOT resonance and the analyte is deposited on the non-patterned side of the metasurface, improving by a factor between 2 and 3 the results of the EOT resonance in any of the considered scenarios. This can be explained by the comparatively narrower linewidth of the anomalous EOT resonance. The results presented expand the reach of subwavelength HAs for sensing applications by considering the anomalous EOT regime that is usually overlooked in the literature., 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. The work
was partially supported by the Russian Foundation for Basic Research (Project No. 17-32-80039, experimental
study; Project No. 18-29-20066, technological implementation).

The following article appeared in Pérez-Escudero, J. M., Jarauta, E., Falcone, F., & Beruete, M. (2017). Response of complementary split ring resonators in composite stratified substrate integrated waveguide. Journal of Applied Physics, 121(19), 1. doi:10.1063/1.4983709 and may be found at http://dx.doi.org/10.1063/1.4983709., In this work, the behavior of a Complementary Split Ring Resonator (CSRR) operating within the
quasi-static resonance regime and embedded in a composite stratified Substrate Integrated
Waveguide (SIW) with two different dielectric layers is analyzed. In these conditions, the propagating
modes within the SIW combined with the imposed non-symmetrical structure lead to the excitation
of the CSRR elements inside the SIW at difference with conventional excitation. Several cases
of CSRR loaded SIW are proposed, and their electromagnetic field components as well as their frequency
response are analyzed, providing insight into the CSRR resonance excitation. A test prototype
has been designed, fabricated, and measured, showing a good agreement with simulation results
and providing a new alternative for the implementation of compact frequency selective devices compatible
with planar technology and without undesired radiation loss., This work was sponsored by the Spanish Government
under Contract No. TEC2014-51902-C2-2-R. M.B. was
sponsored by the Spanish Government via RYC-2011-08221.

We investigate collective resonators made of dielectric cylinders assembled as two-dimensional regular octagons and decagons. These structures exhibit collective resonance states that change their intensity with the incident radiation angle. While most parts of the spectra present small or even null variation, one of these resonances presents high-sensitivity to the incidence angle. This strong variation is well characterized in terms of the electric field intensity distribution of a resonant state where all the cylinders show the lowest order Mie resonance and the neighbors alternate their polarities. The collective state is optimally excited when radiation impinges on a vertex of the polygonal arrangement of cylinders, while the response decreases to its minimum when the incident field hits an edge (two cylinders at the same time). The resonant state and its high dependence on the excitation incidence angle have been found in both octagonal and decagonal configurations for different dielectric permittivity values. In addition, the scalability of Maxwell equations warranties the same behavior if the whole system is downscaled to terahertz or optic frequencies. The study was performed by finite integration time domain calculations of scattering and transmission for different incidence angles. Experimental measures in the microwave range were taken from photonic molecule prototypes made of centimeter-scale glass cylinders (ϵ = 4.5). We find an overall excellent agreement between measurements and simulations. We propose that photonic molecules made of polygonal rings of dielectric cylinders are an ideal structure to build angle sensors using the strongly varying state that they present., This work has been supported by the Ministerio de Economía y Competitividad of Spain via Project No. TEC2014-51902-C2-2-R.

Backscattering reduction is usually achieved by using either absorbers or diffractions gratings at the expense of a narrow bandwidth. In this paper, we propose a different strategy based on a metallic compound reflection grating (CRG). We demonstrate that this structure allows a strong and broadband (fractional bandwidth, FBW ≈57%) backscattering reduction in the terahertz (THz) range by efficiently transferring the incident energy to the diffracted modes. The design is analyzed in terms of equivalent circuit and numerical simulations and the results are corroborated by a manufactured prototype operating at 0.35 THz., MINECO (Project TEC2014-51902-C2-2-R); P.R.-U. sponsored by UPNA FPI PhD grant.

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.

In this paper, a new topology for rectangular
waveguide bandpass and low-pass filters is presented. A simple,
accurate, and robust design technique for these novel meandered
waveguide filters is provided. The proposed filters employ a
concatenation of ±90° E-plane mitered bends (±90° EMBs) with
different heights and lengths, whose dimensions are consecutively
and independently calculated. Each ±90° EMB satisfies a local
target reflection coefficient along the device so that they can
be calculated separately. The novel structures allow drastically
reduce the total length of the filters and embed bends if
desired, or even to provide routing capabilities. Furthermore,
the new meandered topology allows the introduction of transmission
zeros above the passband of the low-pass filter, which can be
controlled by the free parameters of the ±90° EMBs. A bandpass
and a low-pass filter with meandered topology have been designed
following the proposed novel technique. Measurements of the
manufactured prototypes are also included to validate the novel
topology and design technique, achieving excellent agreement
with the simulation results., This work was supported by ESA’s Networking/Partnering Initiative (NPI)
under Contract 4000114859/15/NL/HK, Gobierno de Navarra under Project
0011-1365-2017-000130, and MINECO (Spain) under Projects TEC2014-
51902-C2-2-R and TEC2017-85529-C3-2-R.

A very simple design method to embed routing capabilities in classical corrugated filters
is presented in this paper. The method is based on the calculation of the heights and lengths of the
so-called filters design building blocks, by means of a consecutive and separate extraction of their local
reflection coefficients along the device. The proposed technique is proved with a 17th-order Zolotarev filter
whose topology is bent twice so that the input and output ports are in the same plane while
preserving the in-line filters behaviour. This new filter allows the possibility of eliminating subsequent
bending structures, reducing the insertion loss, weight, and PIM., This work was supported by MINECO (Spain) (grant TEC2014-55735-C3-R, TEC2014-51902-C2-2-R,
and TEC2017-85529-C3-2-R).

The unprecedented advance experienced by nano- fabrication techniques and plasmonics research over the past few years has made possible the realization of nanophotonic systems entering into the so-called strong coupling regime between localized surface plasmon (LSP) modes and quantum emitters. Unfortunately, from a theoretical point of view, the field is hindered by the lack of analytical descriptions of the electro- magnetic interaction between strongly hybridized LSP modes and nanoemitters even within the Markovian approximation. This gap is tackled here by exploiting a conformal transformation where a bow-tie nanoantenna excited by a dipole is mapped into a periodic slab−dipole framework whose analytical solution is available. Solving the problem in the transformed space not only provides a straightforward analytical explanation for the original problem (validated using full-wave simulations) but also grants a deep physical insight and simple design guidelines to maximize the coupling between localized dipoles and the bow-tie LSP modes. The results presented here therefore pave the way for a full analytical description of realistic scenarios where quantum dots or dye molecules (modeled beyond a two-level system) are placed near a metallic bow-tie nanoantenna., This work was supported in part by the
Spanish Government 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.B. is
sponsored by the Spanish Government via RYC-2011-08221.
A.I.F.-D. acknowledges funding from EU Seventh Framework
Programme under grant agreement FP7-PEOPLE-2013-CIG63099. Y.L. would like to acknowledge the funding support
from Singapore Ministry of Education (MOE) under grant no.
MOE2015-T2-1-145, and NTU-A*STAR Silicon Technologies
Centre of Excellence under the program grant no.
11235150003. M.N.-C. was supported by an Imperial College
Junior Research Fellowship and is now supported by a
Birmingham Fellowship.

In this paper, a novel quasi-periodic structure for rectangular waveguide technology is
proposed. The constituent unit cells of the structure feature a resonant behavior, providing high
attenuation levels in the stopband with a compact (small period) size. By applying a smooth taper-like
variation to the height of the periodic structure, very good matching is achieved in the passband while
the bandwidth of the stopband is strongly increased. Moreover, by smoothly tapering the width of the
structure, a band-pass frequency behavior is obtained. In order to demonstrate the capabilities of the
novel quasi-periodic structure proposed, a band-pass structure with good matching, wide rejected band,
and high-power handling capability has been designed, fabricated, and measured obtaining very good
results., This work was supported by MINECO (Spain) under projects TEC2014-51902-C2-2-R and TEC2014-
55735-C3-R.

In this paper we study the excitation of photonic nanojets (PNJ) in 3D dielectric cuboids by surface plasmons at telecommunication wavelengths. The analysis is done using the effective refractive index approach. It is shown that the refractive index contrast between the regions with and without cuboid should be roughly less than 2 in order to generate jets at the output of the cuboid. The best performance at λ0 = 1550 nm is obtained when the height of the cuboid is 160 nm producing a jet just at the output interface with a subwavelength resolution of 0.68λ0 and a high intensity enhancement (×5) at the focus. The multi‐wavelength response is also studied demonstrating that it is possible to use the proposed structure at different wavelengths. Finally, the backscattering enhancement is numerically evaluated by inserting a metal particle within the PNJ region, demonstrating a maximum value of ∼2.44 dB for a gold sphere of radius 0.1λ0., This work was supported by the Spanish Ministerio de Economía y Competitividad under contract TEC2014‐51902‐C2‐2‐R and partially was supported by the Mendeleev scientific fund of Tomsk State University № 8.2.48.2015. 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.

A structure based on periodically arranged 3D dielectric cuboids connected by photonic nanojets (PNJs) is proposed with the aim of increasing the propagation distance of surface plasmon polaritons (SPPs) at the telecom wavelength of 1550 nm. The performance of the structure is evaluated and compared with the case without the cuboids demonstrating that the SPPs propagation length is enhanced by a factor greater than 2, reaching a value of approximately 190, when the gap between the cuboids is 2.50. Also, the dependence of the propagation length with the height of the cubes is evaluated, showing that this parameter is critical for a good performance of the chain. A subwavelength resolution is obtained for all the jets generated at the output of the cuboids., This work was supported by the Spanish Ministerio de Economía y Competitividad under contract TEC2014-51902-C2-2-R and partially was supported by the Mendeleev scientific fund of Tomsk State University No 8.2.48.2015. 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.

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.

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

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.

Esta es la version no revisada del artículo: Orazbayev, B., Estakhri, N. Mohammadi, Alù, A., Beruete, M., Experimental Demonstration of Metasurface‐Based Ultrathin Carpet Cloaks for Millimeter Waves. Advanced Optical Materials 2017, 5, 1600606. Se puede consultar la versión publicada en https://doi.org/10.1002/adom.201600606, A metasurface carpet cloak for millimetre-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 TE and TM
polarizations, with a relatively wide frequency and angular widths response., This work
was founded by the Spanish Ministerio de Economía y Competitividad with project
TEC2014-51902-C2-2-R. M.B. acknowledges funding by the Spanish Ministerio de
Economía y Competitividad with contract 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.

The following article appeared in Torres, V., Beruete, M., Del Villar, I., & Sánchez, P. (2016). Indium tin oxide refractometer in the visible and near infrared via lossy mode and surface plasmon resonances with Kretschmann configuration. Applied Physics Letters, 108(4), doi:10.1063/1.4941077, and may be found at http://dx.doi.org/10.1063/1.4941077., An indium tin oxide (ITO) refractometer based on the generation of lossy mode resonances (LMRs) and surface plasmon resonances (SPRs) is presented. Both LMRs and SPRs are excited, in a single setup, under grazing angle incidence with Kretschmann configuration in an ITO thin- film deposited on a glass slide. The sensing capabilities of the device are demonstrated using several solutions of glycerin and water with refractive indices ranging from 1.33 to 1.47. LMRs are excited in the visible range, from 617 nm to 682 nm under TE polarization and from 533nm to 637nm under TM polarization, with a maximum sensitivity of 700 nm/RIU and 1200 nm/RIU, respectively. For the SPRs, a sensing range between 1375 nm and 2494 nm with a maximum sensitivity of 8300 nm/RIU is measured under TM polarization. Experimental results are supported with numerical simulations based on a modification of the plane-wave method for a one- dimensional multilayer waveguide., This work was supported in part by the Spanish Ministry of Education and Science-under Contracts FEDER TEC2013-43679-R and TEC2014-51902-C2-2-R. 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.

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 Economia 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 Economia y Competitividad under Grant No. FPI BES-2012-054909. M.B. is sponsored by the Spanish Ministerio de Economia 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).