User Manual

Application Note: SAR Sensitivities
Schmid & Partner Engineering AG, Zurich, Switzerland
Application Note: SAR Sensitivities
Introduction
The measured SAR-values in homogeneous phantoms depend strongly on the electrical
parameters of the liquid. Liquids with exactly matching parameters are difficult to produce;
there is always a small error involved in the production or measurement of the liquid
parameters. The following sensitivities allow the estimation of the influence of small
parameter errors on the measured SAR values. The calculations are based on an
approximation formula [1] for the SAR of an electrical dipole near the phantom surface and
a adapted plane wave approximation for the penetration depth. The sensitivities are given in
percent SAR change per percent change in the controlling parameter:
d SAR / SAR
S(x) = ———————
d x / x
The controlling parameters x are:
• ε : permitivity
• σ : conductivity
• ρ : brain density (= one over integration volume)
For example: If The liquid permitivity increases by 2 percent and the sensitivity of the SAR
to permitivity is -0.6 then the SAR will decrease by 1.2 percent.
The sensitivities are given for surface SAR values and averaged SAR values for 1 g and 10
g cubes and for dipole distances d of 10mm (for frequencies below 1000 MHz) and 15mm
(for frequencies above 1000 MHz) from the liquid surface.
Liquid parameters are as proposed in the new standards (e.g., IEEE 1528).
References
[1] N. Kuster and Q. Balzano, “Energy absorption mechanism by biological bodies in the
near field of dipole antennas above 300 MHz”, IEEE Transacions on Vehicular
Technology, vol. 41(1), pp. 17-23, 1992.