Prototype of a sensor for measuring moisture of a single rapeseed (Brassica napus L.) using microwave reflectometry

Abstract

Rapeseed moisture content is one of the key physicochemical parameters of the seeds, because of its importance for ensuring optimal conditions for seed storage, as well as for determining the time of harvesting. There are many devices available on the market for measuring rapeseed moisture content. Measurement techniques usually use a large sample of seeds (in the case of capacitance meters e.g., 100 g). Therefore, the obtained result is an average value representative for the tested sample, but does not give the range of moisture of single seeds in a given batch of material. The paper presents a prototype of a sensor and a method of measuring moisture content of individual rapeseeds. The system utilizes multiple measurements of a complex reflection coefficient that correspond to different positions and orientations of a seed under test along the sensor. As a result, the impact of non-uniform shape and inner heterogeneity of the seeds on the measurement results is limited. A novel robust algorithm for moisture determination is proposed, which does not need any calibration of the microwave measurement circuitry realized as a six-port reflectometer operating at 2.4 GHz.