Displacement Sensors Based on the Phase of the Reflection Coefficient of a Split Ring Resonator-Loaded Transmission Line

In this article, novel displacement sensors using a microstrip loaded with a pair of split ring resonators (SRRs) are proposed. It is shown that the phase of the reflection coefficient from the loading SRRs can be used for displacement sensing. The article also proposes a differential version of the sensor that benefits from a higher sensitivity and reference zero, which is useful for alignment purposes. It is further shown that the concept of interferometry can be used to convert the output variable of the sensor from changes in the phase to variations in the amplitude of the reflected wave, which can be easily measured. To this end, the proposed single-ended or differential sensors are used along with a branch-line coupler. The proposed sensing mechanism is validated through electromagnetic (EM) simulation of the structures. The concept is further validated through the fabrication and measurement of a prototype.