Complex permittivity of representative biological solutions in the 2-67 GHz range

The main purpose of this study is to provide experimental data on the complex permittivity of some biological solutions in the 2-67 GHz range at room and human body temperatures. The permittivity measurements are performed using an open-ended coaxial probe. Permittivity spectra of several representative monomolecular solutions of proteins, amino acids, nucleic acids, and carbohydrates are analyzed and compared. Furthermore, measurements have also been performed for complex biomolecular solutions, including bovine serum albumin (BSA)-DNA-glucose mixture, culture medium, and yeast extract solution. The results demonstrate that for concentrations below 1%, the permittivity spectra of the solutions do not substantially differ from that of distilled water. Measurements carried out for 4% and 20% BSA solutions show that the presence of proteins results in a decrease in permittivity. For highly concentrated RNA solutions (3%), a slight increase in the imaginary part of the permittivity is observed below 10 GHz. Experimental data show that free water permittivity can be used for modeling of the culture medium above 10 GHz. However, at lower frequencies a substantial increase in the imaginary part of the permittivity due to ionic conductivity should be carefully taken into account. A similar increase has also been observed for the yeast extract solution in the lower frequency region of the considered spectrum. Above 10 GHz, the high concentration of proteins and other low-permittivity components of the yeast extract solution results in a decrease in the complex permittivity compared to that of water. Obtained data are of utmost importance for millimeter-wave dosimetry studies.