Broadband dielectric spectroscopy on human blood

Background: Dielectric spectra of human blood reveal a rich variety of dynamic processes. Achieving a better characterization and understanding of these processes not only is of academic interest but also of high relevance for medical applications as, e.g., the determination of absorption rates of electromagnetic radiation by the human body.

Methods: The dielectric properties of human blood are studied using broadband dielectric spectroscopy, systematically investigating the dependence on temperature and hematocrit value. By covering a frequency range from 1Hz to 40GHz, information on all the typical dispersion regions of biological matter is obtained.

Results and conclusions: We find no evidence for a low-frequency relaxation ("α-relaxation") caused, e.g., by counterion diffusion effects as reported for some types of biological matter. The analysis of a strong Maxwell-Wagner relaxation arising from the polarization of the cell membranes in the 1-100MHz region ("β-relaxation") allows for the test of model predictions and the determination of various intrinsic cell properties. In the microwave region beyond 1GHz, the reorientational motion of water molecules in the blood plasma leads to another relaxation feature ("γ-relaxation"). Between β- and γ-relaxations, significant dispersion is observed, which, however, can be explained by a superposition of these relaxation processes and is not due to an additional "δ-relaxation" often found in biological matter.

General significance: Our measurements provide dielectric data on human blood of so far unsurpassed precision for a broad parameter range. All data are provided in electronic form to serve as basis for the calculation of the absorption rate of electromagnetic radiation and other medical purposes. Moreover, by investigating an exceptionally broad frequency range, valuable new information on the dynamic processes in blood is obtained.