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

Area of Science:

• Dielectric spectroscopy
• Biophysics
• Electromagnetic bio-interaction

Background:

• Accurate dielectric properties of biological solutions are essential for understanding electromagnetic wave interactions.
• Existing data often lacks comprehensive measurements across various biological molecules and concentrations.

Purpose of the Study:

• To experimentally determine the complex permittivity of biological solutions across a wide frequency range (2-67 GHz).
• To analyze how different biomolecules (proteins, amino acids, nucleic acids, carbohydrates) and their concentrations affect permittivity.
• To provide critical data for millimeter-wave dosimetry applications.

Main Methods:

• Utilized an open-ended coaxial probe for precise permittivity measurements.
• Investigated monomolecular solutions of proteins, amino acids, nucleic acids, and carbohydrates.
• Analyzed complex mixtures like BSA-DNA-glucose, culture medium, and yeast extract.

Main Results:

• Below 1% concentration, solutions exhibit permittivity similar to distilled water.
• Increased protein concentration (e.g., 4-20% BSA) leads to decreased permittivity.
• High concentration RNA (3%) shows a slight increase in imaginary permittivity below 10 GHz.
• Ionic conductivity significantly impacts permittivity in culture media and yeast extract at lower frequencies (<10 GHz).
• Yeast extract's complex composition lowers permittivity above 10 GHz compared to water.

Conclusions:

• Permittivity is concentration-dependent, particularly for proteins and ionic components.
• Distilled water permittivity is a reasonable model for dilute solutions (>1%) above 10 GHz.
• Ionic conductivity must be considered for accurate modeling of biological media at lower frequencies.
• The obtained experimental data are vital for advancing millimeter-wave dosimetry and bio-electromagnetic research.