Oliver Spathmann

Effects of Early-Onset Radiofrequency Electromagnetic Field Exposure (GSM 900 MHz) on Behavior and Memory in Rats

Female Wistar rats, from an age of 14 days to 19 months, were exposed in the head region for 2 h per day, 5 days per week, to a GSM-modulated 900 MHz radiofrequency electromagnetic field (RF-EMF). The average specific absorption rates (SAR) in the brain were 0 (sham), 0.7, 2.5 and 10 W/kg. To ensure a primary exposure of the head region, rats were fixed in restraining tubes of different sizes according to their increasing body weight. During the experiment, a set of 4 behavioral and learning tests (rotarod, Morris water maze, 8-arm radial maze, open field) were performed 3 times in juvenile, adult and presenile rats. In these tests, no profound differences could be identified between the groups. Only presenile rats of the cage control group showed a lower activity in two of these tests compared to the other groups presumably due to the lack of daily handling. The rotarod data revealed on some testing days significantly longer holding times for the sham-exposed rat vs. the exposed rat, but these findings were not consistent. During the first year, body weights of sham-exposed and exposed rats were not different from those of the cage controls, and thereafter only marginally lower, so that the effect of stress as confounder was probably negligible. The results of this study do not indicate harmful effects of long-term RF-EMF exposure even when begun at an early age on subsequent development, learning skills and behavior in rats, even at relatively high SAR values.

Theoretical Estimations of Safety Thresholds for Terahertz Exposure of Surface Tissues

This paper contributes to the topic of radiation safety in the THz band by providing theoretical estimations of the permissible incident power densities over 100 GHz-10 THz. Microthermal absorption has been characterized and a worst-case analysis has been done to provide thresholds for the tissue-internal electric field strength at THz frequencies. Dielectric models for the skin and the cornea of the eye as exposed surface tissues have been constructed and used to estimate the corresponding thresholds for incident power densities. The findings of this study shall be useful as a new theoretical framework for future studies related to THz radiation safety and regulation.

Numerical Computation of Temperature Elevation in Human Skin Due to Electromagnetic Exposure in the THz Frequency Range

The ongoing development of new applications in the terahertz (THz) frequency range, such as wireless communication systems, full-body scanners, or other imaging procedures for biological and medical techniques, rapidly increases the number of persons who are potentially exposed to the electromagnetic radiation of those devices. Studies of thermal effects in humans caused by electromagnetic (EM) exposure with frequencies in the THz frequency range can rarely be found in the literature. In this paper, a method for the numerical computation of a potential thermal response in human skin due to EM fields between 0.1 and 10 THz is introduced. The method starts with the development of adequate simulation models for EM fields with penetration depths less than 1 mm. In a further step, it covers the provision of absolutely needed dielectric tissue parameters with help of the “effective medium theory,” since material properties above 100 GHz are not listed in the commonly consulted databases. The absorbed power in EM exposed human skin models of different complexity is calculated and subsequently used as heat source for temperature simulations. Spatial and time-dependent temperature profiles in the tissue are analyzed for transient and continuous exposures.

Numerical Verification of the Applicability of the Effective Medium Theory With Respect to Dielectric Properties of Biological Tissue

Especially in the THz region, little data is available regarding material properties based on measurements. It has been argued that the effective medium theory could provide a useful tool to estimate material data needed for electromagnetic field computations. In this paper, two numerical approaches are presented to test the applicability of the effective medium theory (EMT) with special regard to mm- and sub-mm-wavelengths. One approach is based on the well-known free-space method and the other one on a power loss evaluation scheme. Within the scope of application of the free-space method, the usability of the EMT is proven for two sets of dielectric tissue parameters on a longitudinally homogeneous and transversely structured sample. Moreover, power loss evaluation is a suitable method to show the applicability of the EMT. Analysis of layered models at 1-10 THz confirms that the EMT is a suitable tool to develop equivalent homogenized models with maximum errors for the dissipated powers of about 1%. In a more realistic example for a physiological fluid with spherical inclusions, the EMT yields an error of less than 1%.

High Resolution Numerical Electromagnetic Dosimetry Simulations Using a Coupled Two-Step Approach

For numerical dosimetric simulations of complex electromagnetic human exposure situations the method of moments (MoM) is coupled with a finite integration time domain (FITD) scheme: The MoM simulation features a simple model of the body under test and computes the field distribution on a closed surface around the body. This field information is used to define equivalent sources on the surface for a full three-dimensional FITD simulation featuring a high-resolution body under test. First numerical results are presented for this novel approach.