DIELECTRIC STUDY OF BOUND WATER IN GRAIN AT RADIO AND MICROWAVE FREQUENCIES

A phenomenological theoretical model of grain dielectric properties is presented for radio and microwave frequencies. On the bases of this model, an inverse problem is solved to determine the dielectric permittivity of bound water inside kernels of winter wheat using results of complex permittivity measurements for bulk grain carried out by other authors. The character of the water complex permittivity dependence on frequency and kernel moisture content is studied. For this, the permittivity was considered as a sum of five different functions, depending on moisture content explicitly, and with coefficients being subject to determination. The frequency dependence of these coefficients was analyzed, and the regions typical for the ionic conductivity and for the dipole-orientational polarization mechanism were detected. For this polarization mechanism, the relaxation frequencies are differ from those of free water. It was concluded that water microparticles inside kernels are formed not by pure water, but by aqueous solution of four different substances coming from the kernel solid phase. It is shown that bound water, for the most part, is in a state that is intermediate between that of free water and that of molecules in the monomolecular water layer on the solid phase boundary.