Microwave Resonance-Based Reflective Mode Displacement Sensor with Wide Dynamic Range

A wide dynamic range reflective mode displacement sensor is designed in this article based on the resonance frequency shift. The linearity of the sensor is enhanced using a tapered metallic patch that forms the capacitance of the sensor, leading to a better dynamic range. The sensor is designed using a coplanar waveguide (CPW) terminated with a series RLC resonator with R=50Ω . A movable dielectric slab is placed above the capacitive patch of the resonator, where displacing the dielectric slab modifies the overall capacitance of the resonator causing a shift in the resonance frequency. The sensing principle is analyzed in detail, using an accurate circuit model and full-wave electromagnetic simulations. The proposed sensing method is capable of detecting the displacement direction. Furthermore, the sensing concept can be extended to a 2-D displacement sensor as well. The sensing approach and the design concept are verified through the fabrication and measurement of a sensor prototype.