Characterization of dielectric anisotropy of small samples from plant fresh and dry biomass by microwave resonance method

The uniaxial anisotropy of small samples from plant fresh biomass has been investigated in this paper by microwave resonance method. The anisotropy means that the plant tissues have different dielectric constants in different directions according to the sample surface. The concrete investigations have been performed by determination of the relative water content and the dielectric parameters (dielectric constant and dielectric loss tangent) of disk samples extracted from fresh and dry walnut leaves normal and parallel to the sample surface. The measured dielectric constant in parallel direction is 2.75 times bigger than the normal dielectric constant of the fresh walnut leaves, but the ratio decreases twice in a dry state. The obtained results allow minimization of the measurement errors during a nondestructive characterization of the total fresh biomass associated with the entire young plant shoots by determination of the frequency shift in microwave resonators, when the leaf anisotropy is taken into account. A special experiment has been implemented to estimate the influence of the anisotropy on the measured fresh biomass by numerical simulations of a 3-D model of three-leaf plant.