Abstract: The SAR（Specific Absorption Rates）distribution in human head emitted by a monopole antenna handset was simulated using the finite-difference-time-domain （FDTD） method with a three-layered human head model at the frequency of900MHz．The feasibility of the calculating method was proved by the comparison with experimental results．The calculated results show that SAR and the absorption rate of power increase when reducing the length of antenna‚and the absorption energy can be more above half of the total radiation energy．The peak and the average SARs of teenager are more than those of adult in the human head model．The average SAR （0．112W／kg） of teenager exceeds the IEEC95．1— 1991limit （0．08W／kg） when the monopole length is λ／4‚which means the harm of handset radiation to teenagers is more serious than that to adults．

Key words: handset radiation, finite-difference-time-domain method, monopole antenna