ENERGY-ABSORPTION MECHANISM BY BIOLOGICAL BODIES IN THE NEAR-FIELD OF DIPOLE ANTENNAS ABOVE 300 MHZ

The energy absorption mechanism in the close near field of dipole antennas is studied by numerical simulations. All computations are performed and validated applying the three-dimensional multiple multipole (3DMMP) software package. The numerical model of the plane phantom is additionally checked by accurate as possible experimental measurements. For the plane phantom, the interaction mechanism can be well described by H-field induced surface currents. The spatial peak specific absorption rate (SAR) can be approximated within 3 dB by a formula given here based on the incident H-field or antenna current and on the conductivity and permittivity of the tissue. It is further shown that these findings can be generalized to heterogeneous tissues and larger biological bodies of arbitrary shape for frequencies above 300 MHz. The SAR is found to be mainly proportional to the square of the incident H-field, which implies that in the close near field, the spatial peak SAR is related to the antenna current and not to the input power. Another consequence of this study is that the exclusion clause of the ANSI C95.1-1982 standard for low-power communication equipment must be revised because it is in direct contradiction with the basic peak SAR limits.