Millimeter-Wave Re-entrant Cavity Resonator Sensor for Liquid Dielectric Metrology

A 3D-printed 60 GHz re-entrant cavity resonator for dielectric metrology has been developed for the characterization of low-dielectric loss fluids. A higher-order resonant mode (TM₀₂₀) at 60 GHz has been utilized owing to its high unloaded measured quality factor of 2150. A full simulation analysis of the cavity resonator for complex permittivity measurement within the V-band frequency range has been demonstrated. The cavity sensor is fabricated using Stereolithography (SLA) printing and coated with copper. The advantage of the resonator geometry over rectangular and cylindrical cavities is that it provides for a concentrated electric field at a defined gap region, enabling stronger interaction between the resonant mode and analyte, and therefore higher sensitivity. The low-cost sensing device has shown good results following a measurement of hexane as a low loss sample. This has demonstrated the potential use of the device in dielectric metrology.