Search

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.

Microwave at 2.45 GHz frequency has been found to resonate in water and may attenuate on a straight line between a transmitter and receiver according to the water volume. The level of microwave attenuation is known to be used for moisture measurement on a point-to-point line inside an object. To measure moisture volume in an object in any shapes, it is required to install many antennas as moisture sensors which need to cover all areas of an object, and attenuation level obtained from all sensors are summarized for calculating total moisture of the object. This paper proposes a method to design a microwave-based moisture estimation system by using scanning with a sensor. Theoretically, the total moisture in the object can be sensed attenuation by moisture sensors installed covering an object, and attenuation obtained from all sensors is calculated into percentage of moisture in the object. This paper utilizes a moisture sensor to scan on a plane covering an object. All attenuation obtained from the moisture sensor which is scan on a plane shall calculate the average moisture on behalf of using many moisture sensors. To evaluate the performance of proposed method, experiments and simulations in water and paddy in a few container shapes have been performed, and the results confirmed its effectiveness.