Bioelectromagnetics 22:97^105 (2001)
Energy Deposition P rocesses in B io logical
Tissue: Nonthermal B i ohazards Seem U nlik ely
intheUltra-HighFrequencyRange
William F. Pickard
1
* and Edua rdo G . Moros
2
1
Department of E lectr i cal Engi neer ing, W as hi ngton Univ e rs ity,
Saint Louis, Missouri
2
Radiation Oncology Section, Mallinckrodt Institute of Radiology,Washington University,
Saint Louis, Missouri
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 speci®c absorption rate of micro-
waves in a biological tissue; this involves the complex Poynting vector, the mass density of the
medium, the angular frequency of the electromagnetic ®eld, 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 ®eld effects on ions; (iii) cooperative effects and/or coherent excitations. Finally, it is
concluded that the rate of energy deposition from a typical ®eld and within a typical tissue is so
small as to make unlikely any signi®cant nonthermal biological effect. Bioelectromagnetics 22:97±
105, 2001.
# 2001 Wiley-Liss, Inc.
Key words: speci®c absorption rate; constitutive parameters; SAR; magnetosomes; dielectric
relaxation; multiphoton absorption
INTRODUCTION
Within the past decade, the worldwide public
acceptance of wireless technology has been remark-
ably swift. In the United States, for example, data
collected by the Cellular Telecommunications Industry
Association (http://www.wow-com.com/statsurv/sur-
vey/199906a.cfm) and available in Fall 1999, extra-
polate to a Summer 2000 subscribership between
80 and 90 million and a doubling time of approxi-
mately 3 years. This situation has resulted in studies
related to possible bioeffects which might be as-
sociated with the many different signals available
and entering the market [Repacholi, 1998; Burkhardt
et al., 1996; 1997; Moros et al., 1998, 1999;
Repacholi et al., 1997; Moulder et al., 1999].
However, despite the considerable concern docu-
mented at a variety of websites (e.g., http://www.
microwavenews.com/ or http://www.wow-com.
com/) and a long history of investigation
[Osepchuk, 1983; Steneck, 1984], a compelling
case
1
for the ``clear and present danger'' of ultra-
high-frequency irradiation (UHF, 300±3000 MHz) has
yet to be made for SARs below overtly thermalizing
levels [e.g., Moulder et al., 1999].
In this article we shall consider ®rst the
macroscopic electromagnetic theory of energy deposi-
tion in tissue, with special reference to prospects of
ß 2001Wiley-Liss,Inc.
ÐÐÐÐÐÐ
Contract grant sponsor: Florida Corporate Electromagnetic
Research Laboratory of Motorola
*Correspondence to: William F. Pickard, Department of Electrical
Engineering, Washington University, One Brookings Drive, Saint
Louis, Missouri 63130. E-mail: wfp@ee.wustl.edu
Received 22 November 1999; Final revision received 20 March
2000
1
To be precise we shall anticipate our Discussion and de®ne
``compelling case'' as one so robust that (a) it can be reproduced at
will and (b) has had its variation with both intensity and frequency
studied in detail.