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Energy deposition processes in biological tissue: Nonthermal biohazards seem unlikely in the ultra‐high frequency range
Author(s) -
Pickard William F.,
Moros Eduardo G.
Publication year - 2001
Publication title -
bioelectromagnetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.435
H-Index - 81
eISSN - 1521-186X
pISSN - 0197-8462
DOI - 10.1002/1521-186x(200102)22:2<97::aid-bem1012>3.0.co;2-n
Subject(s) - bioelectromagnetics , poynting vector , electromagnetic radiation , specific absorption rate , absorption (acoustics) , extremely low frequency , physics , electromagnetic field , computational physics , electric field , microwave , ultra high frequency , atomic physics , materials science , optics , telecommunications , antenna (radio) , magnetic field , quantum mechanics , computer science
The prospects of ultra high frequency (UHF, 300–3000 MHz) irradiation producing a nonthermal bioeffect are considered theoretically and found to be small. First, a general formula is derived within the framework of macroscopic electrodynamics for the specific absorption rate of microwaves in a biological tissue; this involves the complex Poynting vector, the mass density of the medium, the angular frequency of the electromagnetic field, and the three complex electromagnetic constitutive parameters of the medium. In the frequency ranges used for cellular telephony and personal communication systems, this model predicts that the chief physical loss mechanism will be ionic conduction, with increasingly important contributions from dielectric relaxation as the frequency rises. However, even in a magnetite unit cell within a magnetosome the deposition rate should not exceed 1/10 k B T per second. This supports previous arguments for the improbability of biological effects at UHF frequencies unless a mechanism can be found for accumulating energy over time and space and focussing it. Second, three possible nonthermal accumulation mechanisms are then considered and shown to be unlikely: (i) multiphoton absorption processes; (ii) direct electric field effects on ions; (iii) cooperative effects and/or coherent excitations. Finally, it is concluded that the rate of energy deposition from a typical field and within a typical tissue is so small as to make unlikely any significant nonthermal biological effect. Bioelectromagnetics 22:97–105, 2001. © 2001 Wiley‐Liss, Inc.