Open Access
Lentes metálicas basadas en el fenómeno de transmisión extraordinaria para conseguir índices de refracción negativos
(2009) Navarro Cía, Miguel; Beruete Díaz, Miguel; Sorolla Ayza, Mario; Campillo, Igor; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
In this communication we report plano-concave and bi-concave metamaterial lenses based on the close stack of subwavelegnth hole arrays. Contrary to what is expected from cut-off holes, an engineered array of holes supports Extraordinary Transmission. Moreover, the medium formed when those structures are subwavelength stacked (thus, under metamaterial condition) behaves as a medium with effective negative index of refraction, which allows designing new lenses with properties that were only guessed at not long ago such as perfect imaging, subdiffraction and free-space matching to name a few.
Open Access
Millimeter-wave extraordinary transmission: connection to metamaterials and technological applications
(2006) Beruete Díaz, Miguel; Sorolla Ayza, Mario; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
The phenomenon of Enhanced Transmission also happens in the millimeter wave range, as it happened in optical frequencies. This experimental fact shows that this is a phenomenon mostly linked to the periodic structure regardless of the model used to describe the metal. The number of illuminated holes is a key parameter to observe the Enhanced Transmission band. Measurements in Fresnel zone show a weak band, and with the farfield illumination a good level is obtained. It has been shown that ET is mainly governed by one of the transversal periodicities, the one in the direction of the electric field (under normal incidence). The presence of dielectrics can produce a great field confinement and therefore a more efficient illumination of holes. Enhancement of transmission through a narrow slot on a metallic plane achieved by corrugating the metallic plane has been experimentally proven in the range of microwaves and millimeter waves. This result links the enhancement to the geometry of the metallic substrate rather than to the metallic model. It has been checked the ability to produce a strong beaming at broadside in the configuration of corrugations drilled on the output face. Several low-profile and all-metallic antenna prototypes have been designed and measured in the microwave range. The feeding is made by means of a waveguide. By changing the central (ideally) infinite slit to a finite slot several improvements can be done, fundamentally the thickness of the antenna can be reduced and a dual-band operation can be achieved. A great variety of farfield characteristics can be obtained by changing the number of corrugations. High gain antennas can be attained by using annular corrugations, the socalled Bull’s-Eye antenna. Further improvements deal with the insertion of dielectric inside the corrugations and with changes in the shape of the corrugations, for example sinusoidal profile. An artificial waveguide defined by introducing a set of parallel electric and magnetic conductors can be employed to analyze the diffraction problem of an incident plane wave normally to a sub-wavelength hole array. Evanescent higher order modes play a key role in the ET effect. Even more unexpected results appear if a periodic structure is made by stacking several of such plates: a left-handed metamaterial can be achieved by the periodic stacking of sub-wavelength hole array plates to form a photonic band-gap structure. The stack period with LH behavior can be made much smaller than the operating wavelength, and therefore it can be safely stated that the structure works in that dimension as an effective metamaterial. Simulation and experimental results presented show that left-handed propagation effects appearing in the band where EOT happens can be allowed or inhibited by a proper engineering of the band gap position of the photonic crystal made of stacked subwavelength hole-arrays. In the transition from LH to RH behavior a nearly zero slope band is observed, which can evidence a frozen mode propagation regime inside the structure. A simplified model based on inverse line equivalent circuit has been exposed to explain the LH and RH behavior. The stacked hole array structure can be engineered to construct prisms with anomalous behavior. Other geometries such as parabolic lenses can also be achieved. It has been seen that surfaces made by the periodical arrangement of Split- Ring Resonators (SRRs) and its complementary particle (CSRRs) illuminated by a plane wave show a high variety of cross-polarization effects. The analytical discussion based on the homogenization principle has been compared with the experimental results. It is able to catch the qualitative features in the response of the screens. The complementarity in the response of SRRs and CSRRs has been checked. Applications of the studied devices to frequency selective surfaces, polarizers and polarization converters can be envisaged. The existence of electroinductive waves (EIWs) in chains of electrically coupled CSRRs has been demonstrated both theoretically and experimentally. The duality between EIWs and previously reported MIWs has been discussed, and the ability of long CSRR chains to transport electromagnetic energy along many periods has been shown. A practical transducer between electromagnetic and EIWs in planar technology has been proposed and analyzed. Regarding practical applications, EIWs can be an alternative to MIWs for the guidance of electromagnetic energy, as well as for the design of couplers, delay lines and other planar devices, when electric couplings rather than magnetic couplings are imposed, or simply desired for the design. Taking as a basis the resonators used to implement an EI waveguide, a further step has been given in the design of a UWB filter in microstrip technology. This filter can be improved by inserting CSRRs to reject the higher frequencies. A final word fundamentally related to the ET results presented here: The reported results have been achieved for the millimetre range, but similar results are expected to happen at optical frequencies since extraordinary transmission has been shown at optical frequencies and the kind of structure presented here will present low losses in higher frequency regime. The control of the EOT-LHM could lead to a new class of practical devices both in the microwave and in the optical range.
Open Access
Comportamiento de propagacion electromagnetica en el apilamiento de agujeros sublambda y agujeros propagantes
(2009) Navarro Cía, Miguel; Beruete Díaz, Miguel; Falcone Lanas, Francisco; Campillo, Igor; Sorolla Ayza, Mario; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
In this work, we provide more insight on the physics underlying the transmission through subwavelength hole arrays metaprism by comparing it with propagating hole arrays prism. We show the critical role that the size of the holes plays in this electromagnetic propagation, changing the effective index of refraction from negative to positive values as the hole diameter increases. This causes negative refraction for the zero-th order emerging beam in the metaprism whereas positive refraction in the non-cut-off holes prism. Experimental results (co- and cross-polar measurements) performed at the V-band of the millimeter waves in the Fresnel zone are well supported by numerical analyses in terms of dispersion diagram, spatial electric field distribution and power flow within the prism along with in the output air zone. As expected, higher order diffracted outgoing beams are recorded for the classical prism but not for the metaprism.
Open Access
Negative refraction in a prism made of stacked subwavelength hole arrays
(Optical Society of America, 2008) Navarro Cía, Miguel; Beruete Díaz, Miguel; Sorolla Ayza, Mario; Campillo, Igor; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
Metamaterial structures are artificial materials that show unconventional electromagnetic properties such as negative refraction index, perfect lenses, and invisibility. However, losses are one of the big challenges to be surpassed in order to design practical devices at optical wavelengths. Here we report negative refraction in a prism engineered by stacked sub-wavelength hole arrays. These structures exhibit inherently an extraordinary optical transmission which could offer a solution to the problem of losses at optical wavelengths. It is shown the possibility to obtain negative indices of refraction starting from near to zero values. Our work demonstrates by a direct experiment the feasibility of engineering negative refraction by just drilling sub-wavelength holes in metallic plates and stacking them.
Open Access
Negative refraction through an extraordinary transmission left-handed metamaterial slab
(American Physical Society, 2009) Beruete Díaz, Miguel; Navarro Cía, Miguel; Sorolla Ayza, Mario; Campillo, Igor; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
In this work we present numerical and experimental results of negative refraction through a negative index metamaterial based on miniaturized extraordinary transmission stacked subwavelength hole arrays, also known as stacked fishnet structures, working in the millimeter wave range. Analytical transmittance as a function of frequency and tangential momentum shows the conditions under which negative refraction is expected. Due to the role of the gap-surface-plasmon-polariton-like mode that gives rise to the resonant magnetic response of this structure, strong dispersion with the angle of incidence is expected. Experimental results using a quasioptical bench in the millimeter wave band demonstrate negative refraction and, besides, reasonable agreement with the simulation results is obtained. A discussion based on leaky waves serves to qualitatively explain the main features. The presented results may find application in the design of new lenses and devices both in the microwave, terahertz, and optical ranges.
Open Access
Comment on “A waveguide slit array antenna fabricated with subwavelength periodic grooves Appl. Phys. Lett. 91, 143512 (2007)”
(AIP Publishing, 2008) Beruete Díaz, Miguel; Falcone Lanas, Francisco; Sorolla Ayza, Mario; Campillo, Igor; Dolado, Jorge S.; Rodríguez Seco, J. E.; Perea, E.; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
We firmly think that it is proven that most of the ideas, results, and discussions presented in C. Huang, C. L. Du, and X. G. Luo, Appl. Phys. Lett. 91, 143512, 2007 were already present in our previous paper (M. Beruete, I. Campillo, J. S. Dolado, J. E. Rodríguez-Seco, E. Perea, F. Falcone, and M. Sorolla, IEEE Trans. Antennas Propag. 54, 340, 2006) and that the antenna design in Huang et al. cannot be considered original at all since it is identical to our design. The only innovative aspect in Huang et al. is the discussion about the multiple slit source.
Open Access
Extraordinary transmission and left-handed propagation in miniaturized stacks of doubly periodic subwavelength hole arrays
(Optical Society of America, 2007) Beruete Díaz, Miguel; Sorolla Ayza, Mario; Navarro Cía, Miguel; Falcone Lanas, Francisco; Campillo, Igor; Lomakin, Vitaliy; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
Metallic plates embedded between dielectric slabs and perforated by rectangular arrays of subwavelength holes with a dense periodicity in one of the directions support extraordinary transmission (ET) phenomena, viz. strong peaks in the transmittance frequency dependence. Stacks of such perforated plates support ET phenomena with propagation along the stack axis that is characterized by the left handed behavior. The incorporation of the dielectric materials and dense periodicity allows significantly reducing the illuminated area of the perforated plate required experimentally to observe the ET phenomena as compared to the areas required in the case of free standing rectangular hole arrays. This facilitates the experimental investigation of ET under excitation in the Fresnel zone of Gaussian beams.
Open Access
Ultra-wideband metamaterial filter based on electroinductive-wave coupling between microstrips
(EMW Publishing, 2009) Navarro Cía, Miguel; Carrasco, José Miguel; Beruete Díaz, Miguel; Falcone Lanas, Francisco; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
In this work, we analyse the frequency response of microstrip lines coupled by complementary split ring resonators (CSRRs) etched on the ground plane supporting electroinductive waves (EIWs). The single-particle configurations demonstrate the principle of operation whose bandwidths reach 67% of the central frequency. A double configuration is afterwards investigated as a further improvement of the filtering response, such as the level of the spurious lower frequency band. Finally, an ultimate prototype comprising different CSRRs along the access line, together with the aforementioned EIW-coupling is proposed for filtering undesired higher bands. Experimental results confirm numerical analysis.
Open Access
Polarized left-handed extraordinary optical transmission of subterahertz waves
(Optical Society of America, 2007) Beruete Díaz, Miguel; Navarro Cía, Miguel; Sorolla Ayza, Mario; Campillo, Igor; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
In this paper we design and measure a metamaterial polarizing device working in the sub-terahertz range. The polarizer is based on a modified version of our previous miniaturized Stacked Hole Array (SHA) structure, an arrangement that combines Extraordinary Optical Transmission (EOT) and Left-Handed Metamaterial (LHM) propagation even under Fresnel illumination. Here, we use a self complementary screen by connecting the holes of an EOT structure. Importantly, EOT remains and simultaneously total reflection is obtained for the orthogonal component. Moreover, by computing the dispersion diagram, we demonstrate that LHM propagation can be achieved for the principal polarization within the stop band of the orthogonal component, which propagates in other bands as a standard forward wave. Finally, we check our conjectures by measuring the transmission and reflection coefficients of screens milled on a low-loss microwave substrate. Measurements have been taken for 1 to 6 stacked wafers and they show clearly that the stack acts as a polarizer with lefthanded characteristic. Our results open the way to design of novel polarization control metamaterials at Terahertz wavelengths.
Open Access
Regular and anomalous extraordinary optical transmission at the THz-gap
(Optical Society of America, 2009) Kuznetsov, Sergei A.; Navarro Cía, Miguel; Kubarev, V. V.; Gelfand, A. V.; Beruete Díaz, Miguel; Campillo, Igor; Sorolla Ayza, Mario; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
In this paper Anomalous Extraordinary Transmission (ET) is reported for s-polarization of low loss doubly periodic subwavelength hole arrays patterned on polypropylene (PP) substrates by conventional contact photolithography at the so-called THz-gap (1-10 THz). The unexpected enhanced transmittance for s-polarization (i.e. without spoof plasmons) was previously numerically demonstrated in subwavelength slits arrays. However, subsequently no experimental work has been devoted to this unexpected Extraordinary Transmission neither in subwavelength slits nor in subwavelength holes. Here, numerical study and experimental results of the Anomalous ET and the symmetric and antisymmetric transmittance modes associated with the already well-known p-polarization ET are shown alongside a systematically analysis of the frequency peaks as a function of hole size for both incident polarizations.