Analysis and design of a re-entrant microwave cavity for the characterisation of single wheat grain kernels

A re-entrant cylindrical microwave cavity is proposed as a sensor for determining moisture content and wet mass in single wheat grain kernels. The cavity structure is analysed using a finite element formulation suitably tailored for axisymmetric resonators. Full modal hierarchy and field plots are generated for this class of cavity for the first time. The third mode is selected as it has a concentrated, rotationally symmetric electric field distribution between the ridge and the end plate of the cavity. Using a linear method to relate the measured cavity characteristics and the grain parameters, good correlation was obtained for both grain moisture content and wet mass. In addition, the results show that the calculated grain characteristics are independent of mass.