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
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.
Open Access
Tripod-loop metasurfaces for terahertz-sensing applications: a comparison
(MDPI, 2020) Jáuregui López, Irati; Orazbayev, Bakhtiyar; Pacheco-Peña, Víctor; Beruete Díaz, Miguel; Ingeniería Eléctrica, Electrónica y de Comunicación; Institute of Smart Cities - ISC; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren
The high electric field intensity achieved on the surface of sensors based on metasurfaces (metasensors) makes them an excellent alternative for sensing applications where the volume of the sample to be identified is tiny (for instance, thin-film sensing devices). Various shapes and geometries have been proposed recently for the design of these metasensors unit-cells (meta-atoms) such as split ring resonators or hole arrays, among others. In this paper, we propose, design, and evaluate two types of tripod metasurfaces with different complexity in their geometry. An in-depth comparison of their performance is presented when using them as thin-film sensor devices. The meta-atoms of the proposed metasensors consist of a simple tripod and a hollow tripod structure. From numerical calculations, it is shown that the best geometry to perform thin-film sensing is the compact hollow tripod (due to the highest electric field on its surface) with a mean sensitivity of 3.72 × 10−5 nm−1. Different modifications are made to this structure to improve this value, such as introducing arms in the design and rotating the metallic pattern 30 degrees. The best sensitivity achieved for extremely thin film analytes (5–25 nm thick) has an average value of 1.42 × 10−4 nm, which translates into an extremely high improvement of 381% with respect to the initial hollow tripod structure. Finally, a comparison with other designs found in the literature shows that our design is at the top of the ranking, improving the overall performance by more than one order of magnitude. These results highlight the importance of using metastructures with more complex geometries so that a higher electric field intensity distribution and, therefore, designs with better performance can be obtained.

Beruete Díaz, Miguel

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