• Martín, Ferran
• Naqui, Jordi
• Horestani, Ali Karami

Abstract

Microwave sensors based on the symmetry properties of transmission lines loaded with metamaterial resonators are reviewed in this chapter. In most microwave sensors based on resonant elements, the physical variable to be measured modifies the resonance frequency, phase or quality factor of the sensing resonant structure. In this chapter, a novel sensing principle, based on the disruption of symmetry, is studied. The proposed sensors are implemented by loading a transmission line either with symmetric resonators (typically, although not exclusively, resonant elements useful for the implementation of metamaterials) or with symmetric configurations of resonator pairs. In the unperturbed state, the whole structure (line and resonator/s) is symmetric, and it is designed to exhibit either an all-pass behavior (Type I sensors) or a single transmission zero (Type II sensors). Conversely, when symmetry is broken by the physical effect to be sensed (e.g. a linear or angular displacement, dielectric loading, etc.), a notch appears in Type I sensors, whereas a split-off (i.e. two transmission zeros) emerges in Type II sensors. Hence, Type I and Type II sensors can be designated as resonance-based and frequency-splitting sensors, respectively. These sensors are of special interest as comparators and are robust against changes in environmental conditions. Potential applications include contactless linear and angular displacement and velocity sensors, alignment sensors, permittivity sensors, etc.

Topics

• impedance spectroscopy
• phase
• positron annihilation lifetime spectroscopy
• Photoacoustic spectroscopy
• metamaterial