Enhanced Cavity Sensor in SIW Technology for Material Characterization

This letter presents an enhanced solution for low-cost sensors for the determination of the dielectric permittivity and the loss tangent of materials, based on substrate-integrated waveguide (SIW) cavities. The novelty consists in a slight, yet fundamental, modification of the standard sensor topology. The typical structure is based on an SIW resonant cavity with a hole in the middle and a pipe passing through, which contains the material under test. The modification consists in adding a metal sheath that partially covers the walls of the pipe. The metal sheath enhances the penetration of the electromagnetic field into the pipe, thus increasing the sensitivity of the device. Simulation and measurement results of various liquids demonstrate the advantage of the proposed structure.