RF Sensor for Material Delivery Monitoring in Powder Feeding Systems

Precise dielectric powder delivery is the key objective in feeding systems, such as the ones used in thermal spraying, additive manufacturing, conveying systems, and alike. In particular, the accuracy of the feeding system is determined by the accuracy of the material sensing element. Conventionally, loss-in-weight methods applied to main material storage have been used to measure the amount of material deposited into the process. This paper investigates a new sensing method devised to measure the amount of powder deposited into a flow with high resolution and accuracy. The proposed method is based on the interaction of electric field, produced within a radio-frequency resonator with the geometrical and dielectric properties of the material filling the resonator. Fundamentally, the amount of material present at any time during the feeding process is related to the resonant frequency shift of the resonator. Based on extensive numerical simulation and experimental results, it will be shown that the proposed method exhibits high agility in measuring solid material, such as sand, in sub-gram quantities.