A Coupled-Cavity Resonator Technique for Simultaneous Sensing of Dielectric Load and Position of Continuous Material Streams

An electromagnetic coupled-cavity resonator equipped with permanent insertion holes and designed to sense continuous dielectric material streams through the resonator is presented. The resonating structure comprises a pair of pill-box-shaped cylindrical cavities mutually coupled to each other through an aperture-loaded metal sheet of finite thickness. The input and output insertion holes in the top and bottom lids of the cavity structure form a channel for the flow of dielectric samples under test. The arrangement of aperture-coupled cavity sections results in antisymmetric and symmetric field distributions with split resonances. The resonating antisymmetric field is primarily utilized to detect dielectric load variations of the sample stream, similar to the commonly practiced permittivity based measurements in TM010 cavities. The additional resonance mode with the symmetric field distribution is more sensitive to position offsets of the sample in its concentric flow along the axis. Due to the added resonance, the arrangement provides for 2-D sensing of dielectric specimens under test (dielectric load variation and position offset) and improved accuracy can, thus, be achieved. The working principle of the coupled-cavity technique is analyzed qualitatively by numerical computations. The technique is validated by measuring samples of commercially available cotton fibers with a realized prototype.