Microwave Resonator Orientation-Based Dual-Principle Linear Displacement Sensor

This paper reports the first dual-principle microwave displacement sensor, capable of operating in either frequency-shift or single-frequency amplitude-variation mode, thereby offering unprecedented flexibility for displacement measurement. The sensor consists of a metallic strip printed on a high-permittivity circular dielectric slab, forming a cylindrical dielectric resonator (CDR) positioned between two parallel microstrip transmission lines. A key feature is that the operating mode is selected simply by changing the orientation of the resonator relative to the feedlines, enabling effortless reconfiguration. In the frequency-shift mode (strip perpendicular to the feed lines), displacement is detected through variations in open-stub lengths on the feedlines, achieving 40 MHz/mm sensitivity over a 0–40 mm range. In the amplitude-variation mode (strip parallel to the feedlines), two resonances- strip and dielectric-resonator modes- are exploited, yielding sensitivities of 2 dB/mm (0–12 mm) and 1 dB/mm (0–17 mm), respectively. The sensor further exhibits a wide dynamic range in swept-frequency operation and simultaneous multi-resonance detection in fixed-frequency mode, with high agreement between simulations and measurements. The proposed design introduces a new class of reconfigurable resonator-based displacement sensors with strong potential for robotics, industrial automation, structural health monitoring, and aerospace vibration detection.