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Experimental demonstration of deeply subwavelength dielectric sensing with epsilon-near-zero (ENZ) waveguides

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 TE10 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 GHz−1) and 0.6 1/RIU when considering the sensor working as a frequency- or amplitude-shift-based device, respectively.