Effects of ferrite sheet attachment to portable telephone in reducing electromagnetic absorption in human head

In order to reduce the spatial peak specific absorption rate (SAR) in a human head due to a portable telephone, we have proposed attaching a ferrite sheet to the portable telephone. In this paper, the mechanism of SAR reduction is reviewed and then the effects of the attachment location and size, and the material properties of ferrite sheet on the SAR reduction are investigated by using the finite-difference time-domain (FDTD) method in conjunction with a detailed human head model. Their effects on the antenna radiation efficiency are also given. The results lead to a guide to choosing and designing a ferrite sheet with the maximum SAR reducing effect for portable telephones.