A Design Method for a Microwave-Based Moisture Sensing System for Granular Materials in Arbitrarily Shaped Containers

To estimate the moisture in an entire arbitrarily shaped workpiece, an automatic system should continuously sense moisture at all points of the workpiece. This paper proposes a design method for a microwave-based moisture sensing system for granular materials in arbitrarily shaped containers based on scanning in a moisture sensing box. The size of the moisture sensing box is first determined as the maximum size of any granular material containers based on the initial user requirements. The moisture sensing system physically consists of a pair of antennas for the microwave transmission and reception and a pair of distance sensors to scan throughout the maximum scanning range of the moisture sensing box to find the attenuation and workpiece thickness at all points of the workpiece. Then, these sensed microwave attenuations and measured workpiece thicknesses are used to calculate the moisture at all points of the workpiece. Finally, the average moisture of all points is taken as the estimated moisture of the entire workpiece. To evaluate the performance of the proposed system, experiments were performed with granular materials in containers of various shapes. The estimation results show that the proposed method of continuous moisture scanning of a workpiece can improve accuracy by approximately 7.77% compared to the antenna array approach.