On the performance of an ENZ-based sensor using transmission line theory and effective medium approach

In this paper we perform an in-depth theoretical study of a 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 rigorously deduced 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 of the sensing platform response. Its performance is then evaluated by varying systematically the size, position and permittivity of the analyte, and height of the ENZ channel. It is shown that the sensor is capable of detecting changes in the permittivity/refractive index or position even with deeply subwavelength analyte sizes (∼0.05λ 0), giving a sensitivity up to 0.03 m/RIU and a figure of Merit ∼25. The effective medium approach is evaluated by treating the inhomogeneous cross-section of the analyte as a transmission line filled with a homogeneous material.