DRAFT Recommended Practice for Measurements and ...

1/29/98 118 C95.3-1991 Revision — 2 nd Draft
10/98 Draft
Up to frequencies of about 30 MHz, a method called the long-wavelength approximation
has been used with spheroidal models of human-sized objects. The extendedboundary-condition
method (EBCM) has been used to make calculations for spheroidal
models of man up to approximately resonance (80 MHz). The iterative extendedboundary-condition
method (IEBCM), an extension of the EBCM, has been used for
calculation up to 400 MHz for spheroidal models. The classical solution of Maxwell's
equations for cylindrical models (for human-sized objects or limbs) has been used to
obtain useful average SAR data for E-polarization from about 500 MHz to 7 GHz, and for
H-polarization from about 100 MHz to about 7 GHz. An approximation based on
geometrical optics is used to obtain useful SAR information above approximately 7 GHz.
The moment-method solution of a Green's-function integral equation for the electric field
is used up to about 400 MHz (for human- sized models). For K-polarization, a technique
called the surface-integral-equation technique (SIE) is used up to about 400 MHz with a
model consisting of a truncated cylinder capped on each end by hemispheres.
Numerical simulation techniques are now available for determining SAR and current
distributions in highly sophisticated millimeter-resolution anatomically-based models
exposed to a wide variety of far-field and near-field sources [Gandhi, 1990; Gandhi, 1995].
From a wide array of methods, including the moment method (MM) [Chen and Guru,
1977; Hagmann, et al., 1979; Spiegel, 1984; Livesay and Chen, 1974], finite element
method (FEM) [Chiba, et al., 1984; Yamashita and Takahashi, 1984; Morgan, 1981;
Lynch, et al., 1985], finite-element time-domain method (FETD) [Brauer, et al., 1989:
Chen and Lien, 1979], generalized multipole technique (GMT) [Hafner and Kuster, 1991;
Hafner, 1990; Leutchmann and Bomholt, 1990], volume-surface integral equation method
(VSIE) [Shankar et al., 1989] admittance [Armitage, et al., 1983] and impedance [Gandhi,
et al., 1984] methods and the finite-difference time-domain (FDTD) method [Gandhi,
1990; Lin and Gandhi, 1995; Sumunic, 1995; Gandhi, et al., 1992; Chen, et al., 1991;
Chen and Gandhi, 1991] has become the most widely used method of choice for
bioelectromagnetic applications in the range of a few MHz to several GHz. An extension
of the FDTD method, the frequency-dependent finite-difference time-domain method
((FD) 2 TD) [Luebbers, et al., 1990; Bui, et al., 1991; Joseph, 1991; Kunz and Luebbers,
1993; Taflove, 1995; Lee, et al., 1991, Sullivan, 1992; Sullivan, 1992a; Gandhi, et al.,
1993; Furse, et al., 1994], enables broad-band bioelectromagnetic simulations by
including the effect of the frequency dispersion of the tissues. This method has been
used to calculate SAR and current distributions in the body from ultra-short plane wave
pulses with bandwidths of the order of 1 GHz [Sullivan, 1992a; Gandhi, et al., 1993;
Furse, et al., 1994]. Several of these techniques are briefly described below.
D5.1 Long-Wavelength Approximation.
In the frequency range where the length of the irradiated object is approximately twotenths
or less of a free-space wavelength, SAR calculations are made by an
approximation based on the first-order term of a power series expansion in γ of the
electric and magnetic fields, where γ is the free-space propagation coefficient [D5]. This
is called a perturbation method because it is based on the fact that the resulting fields are
only a small change from the static fields. Equations for SAR have been derived for
homogeneous spheroidal and ellipsoidal models of humans and animals [D10, D13].
Copyright © 1998 IEEE. All rights reserved. This is an unapproved IEEE Standards Draft,
subject to change.