On the Sensitivity of Reflective-Mode Phase-Variation Sensors Based on Open-Ended Stepped-Impedance Transmission Lines: Theoretical Analysis and Experimental Validation

Highly Sensitive Reflective-Mode Defect Detectors and Dielectric Constant Sensors Based on Open-Ended Stepped-Impedance Transmission Lines

“…It consists of an open-ended sensing line with phase φ s and characteristic impedance Z s , cascaded to a transmission line section (the design line) with phase φ and characteristic impedance Z. In [49], it was demonstrated that for sensitivity optimization, the phase of the design line must be set to φ = 90 • , whereas the phase of the sensing line must be set to either φ s = 90 • or φ s = 180 • . Moreover, the characteristic impedances of such line sections should be set to as much extreme values as possible.…”

“…These sensors consist of an open-ended stepped-impedance transmission line, where the sensitive region is merely the open-ended line section, which should be either a high-impedance 90 • line or a low-impedance 180 • line in order to optimize the sensitivity. The step-impedance discontinuities further contribute to enhancing the sensitivity, provided the line sections with alternating high and low impedance exhibit electrical lengths of 90 • , as demonstrated in [49]. Indeed, there is a multiplicative effect, and the sensitivity can be enhanced as one wishes, at the expense of a degradation in the linearity.…”

“…An alternative approach for sensing using a harmonic signal is phase-variation [43][44][45][46][47][48][49][50]. Phase-variation sensors are especially suited for material characterization, including dielectric constant measurements, determination of material composition, and defect detection, among others.…”

“…Recently, a different approach for the implementation of phase-variation sensors operating in reflection has been reported [49] (other reflective-mode sensors operating differentially are presented in [51]). These sensors consist of an open-ended stepped-impedance transmission line, where the sensitive region is merely the open-ended line section, which should be either a high-impedance 90 • line or a low-impedance 180 • line in order to optimize the sensitivity.…”

“…Consequently, the sensitivity can be optimized in the vicinity of such a reference dielectric constant value, ε REF . In [49], the reference dielectric constant was considered to be the one of air (ε REF = 1). In this paper, it is demonstrated that the sensitivity can be optimized for arbitrary values of ε REF .…”