Particle size characterization using a high resolution planar resonator sensor in a lossy medium

In this work, a microwave planar resonator sensor with boosted quality factor is proposed for the non-contact detection and classification of particles of different diameters in gaseous and aquatic environments. This approach can be applied to rapid particle counting, particle size sensing and classification in lossy and non-lossy medium. The presented sensor operates based on variations in the dielectric properties of materials in the vicinity of a planar open-ended microstrip resonator device. Finite Element Method (FEM) analysis is performed to study the effect of particle size on the transmission response profile of the sensor. Verification of the established FEM model and the functionality of the sensor are investigated by experiment. The resolution of the sensor may be adjusted by changing the quality factor of the resonator, which is directly related to the direct current bias voltage of the active device in the local feedback loop. The initial results show the sensor to be capable of detecting the resonant frequency variations of 1 kHz over 1.5 GHz, which corresponds to a detectable frequency resolution better than 1 part per million (PPM). The reported sensor operates at 1.42 GHz and demonstrates particle classification capability within an overall 500 kHz resonant-frequency shift for different bead-diameter sizes (40-400 μm) at a distance of 5 mm, in both air and water (ε' = 78 and tanδ=0.15) using petroleum coke beads as a test material.