Whole body SAR measurement technique by using Wheeler cap method for human head size phantom

In recent years, communications equipment including a personal mobile phones which used in a human body neighbourhood increases. The mobile phones are often used in a neighbourhood of human body. It is considered that a part of the radiated electromagnetic wave by mobile phones is absorbed into the human body. In order to analyse interaction between electromagnetic wave and human body a lot of researches have been performed. The quantity of energy absorption is evaluated by using SAR. SAR can be obtained by electric field as SAR = σ E²/ρ [w/kg] (1) Where ρ is density, E is electric field (rms), σ is conductivity. There are three types of SAR measurement techniques, one of which is point SAR measurement technique. Point SAR can be measured easily by using electric field probe or temperature sensor. In the case of using temperature sensor, SAR can be estimated by SAR = c ΔT/Δt [w/kg] (2) Where c is specific heat, ΔT is temperature elevation, Δt is heating time. Another type of SAR measurement techniques is surface SAR distribution. The surface SAR distribution can be measured by using thermography camera. Last SAR measurement technique is whole body SAR. Whole body SAR is total absorption power of target as human body. In order to measure whole body SAR, some techniques have been proposed. One of techniques is using electric field probe and scanning it. This technique can apply for only liquid type target as liquid phantom because the probe cannot scan if the target is solid. Another method is measuring total radiated power (TRP). A radiated power is absorbed by the human body. Therefore a part of radiated power is disappearing due to absorption by the human body. If TRP and input power of the antenna are known then WB-SAR can be measured by comparing these powers. This techniques is well known as measurement of antenna efficiency. However, large-scale equipment is required to measure TRP as 3- dimensional field scanner. Furthermore, huge measurement time is needed due to 3-dimensinal TRP measurement. Therefore a measurement technique of WB-SAR is not established yet. On the other hand, Wheeler cap method is well known as antenna efficiency measurement technique. Reflection coefficient of the antenna and shielding cap are used to measure antenna efficiency in the Wheeler cap method. This technique does not require large-scale equipment. The authors have proposed effective whole body SAR measurement technique by using wheeler cap method for small size phantom. In this paper, the proposed method is expanded to human head size phantom. Effectiveness of the method is confirmed by FDTD simulation.