New Paper “Absorption of 5G Radiation in Brain Tissue as a Function of Frequency, Power and Time,”
D. H. Gultekin and P. H. Siegel, “Absorption of 5G Radiation in Brain Tissue as a Function of Frequency, Power and Time,” in IEEE Access, vol. 8, pp. 115593-115612, 2020, doi: 10.1109/ACCESS.2020.3002183.
Link to the full paper
Abstract:
The rapid release of 5G wireless communications networks has spurred renewed concerns regarding the interactions of higher radiofrequency (RF) radiation with living species. We examine RF exposure and absorption in ex vivo bovine brain tissue and a brain simulating gel at three frequencies: 1.9 GHz, 4 GHz and 39 GHz that are relevant to current (4G), and upcoming (5G) spectra.
We introduce a highly sensitive thermal method for the assessment of radiation exposure, and derive experimentally, accurate relations between the temperature rise ( ΔT ), specific absorption rate (SAR) and the incident power density ( F ), and tabulate the coefficients, ΔT/ΔF and Δ (SAR)/ ΔF , as a function of frequency, depth and time. This new method provides both ΔT and SAR applicable to the frequency range below and above 6 GHz as shown at 1.9, 4 and 39 GHz, and demonstrates the most sensitive experimental assessment of brain tissue exposure to millimeter-wave radiation to date, with a detection limit of 1 mW.
We examine the beam penetration, absorption and thermal diffusion at representative 4G and 5G frequencies and show that the RF heating increases rapidly with frequency due to decreasing RF source wavelength and increasing power density with the same incident power and exposure time. We also show the temperature effects of continuous wave, rapid pulse sequences and single pulses with varying pulse duration, and we employ electromagnetic modeling to map the field distributions in the tissue. Finally, using this new methodology, we measure the thermal diffusivity of ex vivo bovine brain tissue experimentally.
Excerpts
The impinging RF radiation causes complex simultaneous dynamic effects inside the brain tissue as a result of beam penetration, absorption and thermal diffusion, that need to be taken into account to assess the impact of exposure accurately as a function of frequency, power and time. Although, the overall temperature rise is nonlinear with time, it is linear over short intervals, as is the absorbed RF power at discrete exposure times and depths inside the tissue at each frequency we measured.”
“Compared to the lower frequency, at 39 GHz the RF heating is higher at every depth while RF absorption is very confined to the surface of the sample (see Appendix) and the resultant rapid changes in the heating and cooling curves are very apparent in both the brain and gel.”
“We also note that the impact of relatively modest incident RF power (1 W) and short exposure times (6 minutes CW and 30 second pulsed) at 39 GHz using a single mode waveguide source for the exposure, results in extremely large power density (16.5 kW/m2) and temperature rise (=60°C for CW, =35°C for 30 s pulse) in both bovine brain tissue and gel. This same temperature rise can be expected on skin (which has very similar dielectric properties) when such large surface power densities are present in very close proximity to the RF source or antenna, perhaps emanating from millimeter-wave base stations, handsets, or wireless-enabled appliances or kiosks.”
D. H. Gultekin and P. H. Siegel, “Absorption of 5G Radiation in Brain Tissue as a Function of Frequency, Power and Time,” in IEEE Access, vol. 8, pp. 115593-115612, 2020, doi: 10.1109/ACCESS.2020.3002183.
