Low-cost non-contact microwave probe design for insulating materials characterization

In this paper, we present the design, fabrication and testing of a low-cost non-contact near-field microwave probe for materials characterization operating at 5.78 GHz. The resonant probe consists of a commercial tungsten tip coupled to a dielectric resonator through a non-resonant microstrip line. Changes in the resonant frequency and quality factor of the resonant probe due to the proximity of different bulk materials to the tip are studied. The probe was simulated in the High Frequency Structure Simulator (HFSS) and a lumped-element circuit model of the microwave probe is presented. Measured results, in agreement with simulations, show a shift in the resonant frequency and quality factor as the dielectric constant of the insulating material increases. A shift of 5.84 MHz and 679 in the resonance frequency and quality factor were measured for an Alumina substrate, respectively. The tip-sample distance was fixed to be 5μm.