A Reflective-Mode Phase-Variation Displacement Sensor

Abstract

In this paper, a displacement sensor based on an open-ended step-impedance transmission line is reported. The sensor operates in reflection, and the output variable is the phase of the reflection coefficient. The static part of the sensor is the step-impedance transmission line, where the open-ended line section is the sensitive part (sensing line). The movable part is a dielectric slab, e.g., an uncladded microwave substrate. When such slab, located on top of the sensing line, is in relative motion to the line, in the direction of the line axis, the portion of the sensing line covered by the slab varies, and this results in a change in the phase of the reflection coefficient of the line. The step impedance discontinuity contributes to optimize the sensor sensitivity, the key parameter. A detailed analysis providing the design guidelines is carried out and used to design a prototype displacement sensor. The characterization of the fabricated device points out the potential of the approach to implement highly sensitive displacement sensors. The sensor is a one-port device and operates at a single frequency.

Planar Phase-Variation Microwave Sensors for Material Characterization: A Review and Comparison of Various Approaches

“…Several phase-variation sensors devoted to the measurement of angular or linear displacements have been reported in the literature [ 65 , 66 , 67 ]. In this paper, one of such sensors is succinctly reviewed.…”

“…The main objective of this review paper is to point out, discuss and compare different sensing strategies devoted to performance optimization (specifically sensitivity enhancement, the typical challenging aspect) in phase-variation microwave sensors [ 36 , 37 , 38 , 45 , 46 , 61 , 62 , 63 , 64 ]. Even though examples of planar phase-variation microwave sensors focused on sensing spatial variables have been reported [ 65 , 66 , 67 ], the sensors to be discussed in the present paper are mainly devoted to material characterization. Nevertheless, an example of a rotation sensor based on phase variation is also included in the paper (other sensing strategies different than phase variation are not discussed in the paper).…”

“…Even though examples of planar phase-variation microwave sensors focused on sensing spatial variables have been reported [65][66][67], the sensors to be discussed in the present paper are mainly devoted to material characterization. Nevertheless, an example of a rotation sensor based on phase variation is also included in the paper (other sensing strategies different than phase variation are not discussed in the paper).…”

Highly Sensitive Reflective-Mode Phase-Variation Permittivity Sensor Based on a Coplanar Waveguide Terminated With an Open Complementary Split Ring Resonator (OCSRR)

“…Most planar reflective-mode phase-variation sensors are based on open-ended transmission lines [1], [2], and are devoted to the characterization of solid or liquid samples (excellent sensitivities are reported in [1]). An exception is the phase-variation sensor presented in [51], which is applied to the measurement of small displacements between a movable slab and the static part of the sensor (the open-ended line). Phase-variation sensors based on electrically small single resonant elements (the sensitive part) have also been reported, but in such sensors the focus is the measurement of spatial variables [52], [53] (other sensors based on chains of resonant elements acting as electro-inductive-wave transmission lines, which also exploit phase-variation, have been recently reported [40]).…”

Characterization of the Denaturation of Bovine Serum Albumin (BSA) Protein by Means of a Differential-Mode Microwave Microfluidic Sensor Based on Slot Resonators

“…Additionally, differential sensors are robust to crosssensitivities potentially caused by changing ambient factors (e.g., temperature or humidity), since these environmental variables are seen as common-mode stimuli by such sensors. By contrast single-ended sensors, typically based on frequency variation [25], [48]- [57] or phase variation [16], [19], [58]- [62], are less tolerant to the effects of changing ambient factors (though they are, in general, smaller).…”