I884 IEEE TRANSACTIONS ON MlCROWAVE THEORY AND TECHNIQUES, VOL 44, NO 10, OCTOBER 1996 Electromagnetic Absorption in the Human Head and Neck for Mobile Telephones at 835 and 1900 MHz Om P. Gandhi, Fellow, IEEE, Gianluca Lazzi, Member, IEEE, and Cynthia M. Furse, Member, IEEE Abstract- We have used the finite-difference time-domain method and a new millimeter-resolution anatomically based model of the human to study electromagnetic energy coupled to the head due to mobile telephones at 835 and 1900 MHz. Assuming reduced dimensions characteristic of today’s mobile telephones, we have obtained SAR distributions for two different lengths of monopole antennas of lengths X/1 and 3X/8 for a model of the adult male and reduced-scale models of 10- and 5-year-old children and find that peak one-voxel and 1-g SAR’s are larger for the smaller models of children, particularly at 835 MHz. Also, a larger in-depth penetration of absorbed energy for these smaller models is obtained. We have also studied the effect of using the widely disparate tissue properties reported in the literature and of using homogeneous instead of the anatomically realistic heterogeneous models on the SAR distributions. Homogeneous models are shown to grossly overestimate both the peak 1-voxel and 1-g SAR’s. Last, we show that it is possible to use truncated one-half or one-third models of the human head with negligible errors in the calculated SAR distributions. This simplification will allow considerable savings in computer memory and computation times. I. INTRODUCTION ELLULAR telephones and mobile wireless communi- C cation systems are being introduced into society at a very rapid rate. This has resulted in public concern about the health hazards of RF electromagnetic fields that are emitted by these devices. In this paper, we describe a study of the electromagnetic absorption in the human body for some typical antennas used for these telephones and compare the mass- normalized rates of energy absorption (specific absorption rates or SAR’s) with the ANSIDEEE C95.1-1992 RF Safety Guidelines [I]. These safety guidelines are given in terms of the maximum permissible exposures (MPE) of electric and magnetic fields, or of power density for controlled and uncontrolled environments. Though simple to use for far-field, relatively uniform exposures, the MPE limits are not easy to use for highly nonuniform fields such as in the near-field region of a cellular telephone. An alternative procedure given in the following [I] has, therefore, been suggested to satisfy the safety guidelines for uncontrolled environments which are defined as situations where there is exposure of individuals who have no knowledge or control of their exposure. Manuscript received October 6, 1995; revised February 2, 1996. The authors are with the Department of Electrical Engincering, University Publisher Item Identifier S 001 8-9480(96)07034-2. of Utah, Salt Lake City, Utah 841 12 USA. An exposure condition can be considered to be accept- able if it can be shown that it produces SAR’s “below 0.08 Wkg, as averaged over the whole body, and spatial peak SAR values not exceeding 1.6 Wkg, as averaged over any 1 g of tissue (defined as a tissue volume in the shape of a cube).” For calculations of the SAR distributions we have used the well-established finite-difference time-domain (FDTD) numer- ical electromagnetic method which has previously been used for a number of bioelectromagnetic problems pertaining to far-field or near-field exposures from ELF to microwave fre- quencies [2]. We have also used a newly developed millimeter- resolution model of the human body obtained from the mag- netic resonance imaging (MRI) scans of a male volunteer. This whole-body model has a resolution of 1.875 mm for the two orthogonal axes in the cross-sectional planes and 3 mm along the height of the body [2]. The head and neck part of this model has previously been used to study SAR distributions for ten commercially available cellular telephones [2], [3] operating at transmission frequencies of 820-850 MHz (center frequency of 835 MHz). It has also been used to calculate electromagnetic absorption in the human head for some experimental handheld transceivers operating at 6 GHz [4]. This same anatomically based part-body model has also been used for the calculations given in this paper. We are aware of some recent publications on the SAR calculations for mobile telephones using anatomically based models of the human head [SI, [6]. Whereas a somewhat cruder model of the human head with a resolution of 6.56 mm was used in [SI, a higher-resolution MRI-based model with 2-mm cell size has been used by Dimbylow and Mann [6] for calculations with X/4 monopoles above a metal box and for X/2 dipoles. For calculations reported in this paper we have examined two different lengths of monopole antennas, X f4 and 3X f8, mounted on plastic-coated handsets of dimensions that are typical of newer mobile telephones both at 835 and 1900 MHz. We have also studied the effect of tilting the handset as for typical usage at an angle of 33” relative to vertical and compared the results with the SAR’s when the antenna is held vertically relative to the head. By scaling the model of the head and neck to obtain reduced-size models representative of 10- and 5-year-old children, we have calculated the SAR distributions and find deeper penetration of EM energy, and SAR’s for internal tissues that are several times higher than 0018-9480/96$05.00 0 1996 IEEE