A Hybrid Semi-Lumped/Cavity Multimode Resonator and Application to Sensing Based on Symmetry Truncation

This paper proposes a novel hybrid semi-lumped/cavity multimode resonator excited by a coaxial fed. The device combines a square cavity with a semi-lumped resonator implemented by the inner conductor of the coaxial fed (the inductive part) connected to a circular patch etched, and centered, on the opposite side of the cavity and providing an edge (slot) capacitance to ground. The structure exhibits a fundamental resonant mode associated with the semi-lumped resonator plus multiple cavity modes, specifically, those compatible with the considered (symmetric) excitation. By placing a movable circular dielectric on top of the circular slot, it is possible to detect lack of axial alignment between both elements through (i) the variation of the resonance frequency of the fundamental mode and (ii) the appearance of a mixed cavity mode (involving a superposition of the TE201 and TE102 modes), not excited when perfect axial alignment (symmetry) is present. With proper arrangement, the structure can be useful to detect inclination or vibration based on symmetry truncation.