A comparison between the energy deposition in portable radio operators at 900 MHz and 450 MHz

This paper compares the results of recent measurements at 800-900 MHz of electromagnetic energy deposition in simulated portable radio operators with results previously obtained at 450 MHz. The antenna used with the 800-900 MHz radiois a sleeve dipole, which is approximately the same size as a resonant whip of a 450 MHz portable transmitter. The mechanisms of power deposition in flat slabs of biological tissue at the two different frequencies show some similarity, although there is higher power density deposition (mW/cm³) at 800-900 MHz for equal power flow into the tissue (mW/cm²). The reason for this phenomenon resides in the fact that at the higher frequencies, the E.M. energy tends to be absorbed in the superficial layers of the tissue. The power deposition measurements at 800-900 MHz in a phantom with human features have shown the presence of a slight focusing of RF energy by the shape of the frontal surfaces of the human head. This focusing was not detected at 450 MHz and causes deeper energy deposition in the simulated brain tissue at 800-900 MHz than at 450 MHz.