The specific absorption rate in a spherical head model from a dipole with metallic walls nearby

The head of the user of a mobile telephone is modeled by a lossy dielectric sphere excited by the near field of a dipole antenna and the effects of a metallic wall placed close to this system are analyzed. Three wall orientations are used and the changes in specific absorption rate (SAR) with wall or antenna distance from the sphere are investigated. When the wall is closer than 100 mm to the dipole-sphere system, it can have a strong influence on the input impedance of the antenna and can cause significant increases in the SAR in the head. When a constant radiated power of the dipole antenna is assumed, the maximum value of SAR averaged over 10 g of tissue within the sphere is increased by 60% when the wall is as close as 30 mm from the surface of the sphere. For a dipole excited by a constant current source, the increase is less than 10% and occurs when the wall is 120 mm from the surface of the sphere. Although the distances and configurations analyzed may not represent the way the majority of people use mobile telephones, it is important to examine unusual situations to determine the extent of the SAR enhancement problem.