Human exposure assessment using a hybrid technique based on ray-tracing and FDTD methods for a cellular base-station antenna

Mobile communications are becoming essential for our daily life. A typical example is that the base-stations installed in indoor areas such as the underground shopping centers are increasing. Due to the complicated indoor environment the electromagnetic (EM) field exposure to human beings are generally nonuniform. The IEEE and the International Commission on Non-ionizing Radiation Protection (ICNIRP), therefore, suggest to evaluate the averaged fields on a vertical surface equivalent to the projected human body area for the whole-body averaged specific absorption rate (SAR) compliance (P. Bernardi et al., IEEE Trans. Microwave Theory Tech.. vol. 51, no. 12, pp. 2409-2417, 2003), while no local SAR compliance has been established in relation to the incident electric fields. Moreover, even for the whole-body averaged SAR, the correlation between the incident electric fields and the SAR are based on uniform plane-wave exposure. In this case, the effects of non-uniformity of fields on the SAR are not clarified. In other words, it remains unknown whether or not the reference levels for free-space incident fields represent a conservative exposure situation. The objective of this study is, therefore, to establish an effective technique for dosimetric analysis in realistic, non-uniform EM environment. The end-point of the study is to attempt to establish a relationship between the incident fields and the SAR under non-uniform field environment.