SSPP-Integrated Multifunctional Sensor for Simultaneous and Decoupled Sensing of Dielectric Constant and Dual Displacements

This article presents a novel multifunctional microwave sensor for simultaneous and decoupled sensing of dielectric constant and dual linear displacements. The sensor is implemented using a two-layer printed circuit board (PCB) assembly. The bottom PCB features a microstrip line with a spoof surface plasmon polariton (SSPP) structure etched on its ground plane, while the top PCB is a dielectric layer serving to confine the movement of two sliding loop resonators. The integration of the SSPP converts the transmission line into a low-pass filter, whose cutoff frequency is highly sensitive to the dielectric constant of the material placed above the SSPP. Furthermore, two sliding loop resonators, operating at distinct notch frequencies, are embedded into the top dielectric layer. The reflection phase at each notch frequency exhibits a linear relationship with the displacement of its corresponding resonator block. The three underlying electromagnetic sensing mechanisms—cutoff frequency for dielectric constant, and the two reflection phases for displacements—are experimentally demonstrated to be fully independent. Both simulations and measurements validate the design, confirming its ability to serve as a compact, integrated solution for advanced applications in robotics and Internet of Things (IoT) systems.