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Absorption of 5G radiation in brain tissue as a function of frequency, power and time

Gultekin, David H. and Siegel, Peter H. (2020) Absorption of 5G radiation in brain tissue as a function of frequency, power and time. IEEE Access, 8 . pp. 115593-115612. ISSN 2169-3536. doi:10.1109/access.2020.3002183.

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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.

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Siegel, Peter H.0000-0002-2539-4646
Additional Information:© 2020 The Author(s). This work is licensed under a Creative Commons Attribution 4.0 License. Received June 2, 2020, accepted June 7, 2020, date of publication June 12, 2020, date of current version July 2, 2020. This work was supported by THz Global. The associate editor coordinating the review of this manuscript and approving it for publication was Derek Abbott. The authors thank Dr. Kingman Fung of JPL for the GaN solid state power amplifier used for the bovine brain measurements at 39 GHz and Professor Ali Hajimiri of Caltech for the AR traveling wave tube power amplifiers used for the 1.9, 4, 29 and 39 GHz gel and the 1.9 and 4 GHz bovine brain measurements. They would like to thank JPL’s David Steinfeld for use of the Keysight probe system for measuring the dielectric constants of the brain and gel samples.
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Subject Keywords:4G, 5G, microwaves, millimeter-waves, wireless, RF absorption, RF safety, RF heating, bovine brain tissue, Triton gel
Record Number:CaltechAUTHORS:20200624-155134531
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Official Citation: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
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:104022
Deposited By: George Porter
Deposited On:25 Jun 2020 14:31
Last Modified:16 Nov 2021 18:27

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