Open Access
ε-near-zero (ENZ) graded index quasi-optical devices: steering and splitting millimeter waves
(IOP Publishing, 2014) Pacheco-Peña, Víctor; Torres Landívar, Víctor; Beruete Díaz, Miguel; Navarro Cía, Miguel; Engheta, Nader; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
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.
Open Access
Experimental realization of an epsilon-near-zero graded-index metalens at terahertz frequencies
(American Physical Society, 2017) Pacheco-Peña, Víctor; Engheta, Nader; Kuznetsov, Sergei A.; Gentselev, Alexandr; Beruete Díaz, Miguel; Ingeniaritza Elektrikoa eta Elektronikoa; Institute of Smart Cities - ISC; Ingeniería Eléctrica y Electrónica
The terahertz band has been historically hindered by the lack of efficient generators and detectors, but a series of recent breakthroughs have helped to effectively close the “terahertz gap.” A rapid development of terahertz technology has been possible thanks to the translation of revolutionary concepts from other regions of the electromagnetic spectrum. Among them, metamaterials stand out for their unprecedented ability to control wave propagation and manipulate electromagnetic response of matter. They have become a workhorse in the development of terahertz devices such as lenses, polarizers, etc., with fascinating features. In particular, epsilon-near-zero (ENZ) metamaterials have attracted much attention in the past several years due to their unusual properties such as squeezing, tunneling, and supercoupling where a wave traveling inside an electrically small channel filled with an ENZ medium can be tunneled through it, reducing reflections and coupling most of its energy. Here, we design and experimentally demonstrate an ENZ graded-index (GRIN) metamaterial lens operating at terahertz with a power enhancement of 16.2 dB, using an array of narrow hollow rectangular waveguides working near their cutoff frequencies. This is a demonstration of an ENZ GRIN device at terahertz and can open the path towards other realizations of similar devices enabling full quasioptical processing of terahertz signals.
Open Access
All-metallic ε-near-zero (ENZ) lens based on ultra-narrow hollow rectangular waveguides: experimental results
(IEEE, 2014) Orazbayev, Bakhtiyar; Torres Landívar, Víctor; Pacheco-Peña, Víctor; Falcone Lanas, Francisco; Teniente Vallinas, Jorge; Beruete Díaz, Miguel; Sorolla Ayza, Mario; Navarro Cía, Miguel; Engheta, Nader; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
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.
Open Access
On the performance of an ENZ-based sensor using transmission line theory and effective medium approach
(IOP Publishing, 2019) Pacheco-Peña, Víctor; Beruete Díaz, Miguel; Rodríguez Ulibarri, Pablo; Engheta, Nader; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Institute for Advanced Materials and Mathematics - INAMAT2; Ingeniería Eléctrica, Electrónica y de Comunicación
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.
Open Access
Terahertz epsilon-near-zero graded-index lens
(Optical Society of America, 2013) Torres Landívar, Víctor; Pacheco-Peña, Víctor; Rodríguez Ulibarri, Pablo; Navarro Cía, Miguel; Beruete Díaz, Miguel; Sorolla Ayza, Mario; Engheta, Nader; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa; Gobierno de Navarra / Nafarroako Gobernua, 055/01/11
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.
Open Access
Mechanical 144GHz beam steering with all-metallic epsilon-near-zero lens antenna
(AIP Publishing, 2014) Pacheco-Peña, Víctor; Torres Landívar, Víctor; Orazbayev, Bakhtiyar; Beruete Díaz, Miguel; Navarro Cía, Miguel; Sorolla Ayza, Mario; Engheta, Nader; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
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.
Open Access
Experimental demonstration of deeply subwavelength dielectric sensing with epsilon-near-zero (ENZ) waveguides
(American Institute of Physics, 2022) Beruete Díaz, Miguel; Engheta, Nader; Pacheco-Peña, Víctor; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Institute of Smart Cities - ISC; Ingeniería Eléctrica, Electrónica y de Comunicación
In this Letter, an all metallic sensor based on ε-near-zero (ENZ) metamaterials is studied both numerically and experimentally when working at microwave frequencies. To emulate an ENZ medium, a sensor is made by using a narrow hollow rectangular waveguide, working near the cutoff frequency of its fundamental TE 10 mode. The performance of the sensor is systematically evaluated by placing subwavelength dielectric analytes (with different sizes and relative permittivities) within the ENZ waveguide and moving them along the propagation and transversal axes. It is experimentally demonstrated how this ENZ sensor is able to detect deeply subwavelength dielectric bodies of sizes up to 0.04λ and height 5 × 10 −3 λ with high sensitivities (and the figure of merit) up to 0.05 1/RIU (∼0.6 1/GHz) and 0.6 1/RIU when considering the sensor working as a frequency- or amplitude-shift-based device, respectively.