Epsilon-Near-Zero Microwave Sensors

Abstract

This chapter introduces epsilon-near-zero (ENZ) waveguide-based sensors as used for dielectric testing of materials. The ENZ waveguide is inherently robust to losses and provides electromagnetic wave (EM) tunneling through the narrow ENZ channel. The theory of the two-port ENZ waveguide is explained using both circuit and numerical analysis. The theoretical and numerical analysis of the electric field under various rectangular waveguide modes inside the ENZ channel suggest that the required features of the ENZ effect are manifested in the TE10 mode. The characteristics of the ENZ waveguides viz. the uniform and intensified electric field as well as the high-quality factor, make them a potential candidate for microwave sensor applications. The analytical solution and the conditions related to the dielectric sensing effect are explained using a transmission line model for the ENZ waveguide sensor. Since the ENZ waveguide works around the cutoff frequency of the ENZ channel, tailoring the broader dimension of the waveguide or the dielectric constant of the substrate can help in designing a multifrequency dielectric sensor. Such a multifrequency ENZ sensor could be achieved using multilayer planar technology, which enables single-mode multi-frequency measurement, and is a unique characteristic of the ENZ effect and advantageous for the testing of dispersive materials.