Design and Characterization of Microwave Cavity Resonators for Noninvasive Monitoring of Plant Water Distribution

We demonstrate a dedicated design of microwave cavity resonators mainly developed for high-throughput phenotyping systems of plants. Based on simulations, the field distribution of the TM010 mode inside the resonators was modified to achieve an electric field, which is homogeneously distributed in the horizontal plane and oriented in the vertical direction. Such a distribution together with large openings on top and bottom of each cavity allows to measure volumetric and dielectric properties of material that is widely distributed in space, such as plants with varying shoot branching and architecture, with no need to know its 3-D position inside the resonator. A theory was developed based on an equivalent RLC parallel circuit, showing excellent agreement with the experimental findings. For maize leaves taken as an example, it was shown that the resonator systems allow to perform precise measurements of water distribution in plant tissues.