Phase-Variation Microwave Displacement Sensor with High Resolution, Sensitivity, and Dynamic Range

A microwave displacement sensor based on the phase of the reflection coefficient of a transmission line is presented in this paper. The proposed sensor consists of a static part, which is a microstrip line terminated with a matched load, and a movable part, consisting of two resonators with two different resonance frequencies. The movable part is placed on top of the reader (static part) with a small airgap between them, and it can move along the microstrip line. Two single-frequency (harmonic) signals with frequencies equal to the resonance frequencies of the resonators are injected into the input port of the reader. By this means, the displacement of the movable part can be extracted according to the changes in the phase of the reflection coefficient. The phase of the reflection coefficient of the signal at higher frequency is used to improve resolution and sensitivity, whereas the phase of the reflection coefficient of the signal with lower frequency is used to enhance the dynamic range. As a result, in the proposed sensor, the resolution and sensitivity are improved while it still exhibits a long dynamic range.