Conformity Magazine - August 2008 - (Page 52)

Numerical Simulation Human Head Model The human head model has been developed by a CAD software tool starting by the atlas of human anatomy [7]. Particular attention has been devoted to the eye zone, nose and the front of the head, while for obviously reason we have paid less attention for the brain and back zone (see Figure 1a). This CAD model comprises almost the same tissues of the anatomically based models with the significant addition of the retina, choroid, lens muscles, posterior chamber, optic nerve, orbit fat and eye muscles (see Figure 1b). The advantage of the CAD model respect to the VHP or MRI models is the possibility to have a very fine resolution as 0.25 mm in the areas under investigation as the eye zone. Furthermore, the CAD model is very flexible and suitable to enhance anatomical structure and has the capability to increase the accuracy of the electro-thermal-geometrical configuration. The lens muscles and posterior chamber have been added in this paper respect to previous studies [6], and the differences in the eye model with discretization of 0.25 and 0.5 mm cell size are evident as shown in Figure 2. Numerical SAR Calculation The electromagnetic problem governed by the time-harmonic Maxwell equations must be analyzed as first step of the computational procedure. In this work the electromagnetic analysis is carried out by the commercial software tool CST Microwave Studio™ (MWS) [8]. The electro-geometrical configuration of the proposed CAD model of the whole human head has been imported in CST and then it is discretized by adopting an adaptive mesh refinement in the eye zone. The computational domain is assumed to be a cubic region containing the human head volume. Truncation boundary conditions based on perfectly matched layer (PML) have been applied on the external boundary surfaces. The SAR is calculated by: Equation 1 where Êx , Êy and Êz are the peak values of the electric field vector components, while ρ and σ are respectively the mass density and conductivity of the considered tissue. The permittivities and conductivities of all subregions corresponding to the different tissues of the human head have been obtained by [9]. It should be noted that the permittivity and conductivity of the retina have been assumed to be equal to those of the grey matter due to the high metabolic rate of the retina, while the specific constants of the choroid have been assumed to be equal to those of the blood, due to the high blood perfusion of the choroid [10]. The wireless handheld sources have been simulated in two different ways. Initially, they are simply modeled by a vertical dipole antenna with total length equal to λ/2, being λ the wavelength of the considered frequencies, i.e. f = 0.45, 0.9, 1.8, 1.9, 2.1, 2.4 and 5.4 GHz. This model has a general validity and permits to extrapolate the results obtained for dipole antenna exposure to more complex antenna configurations when the antenna characteristics are known and when the antenna-human head interaction is negligible. Then, to overcome the limitation of the simple dipole antenna model, some real handheld wireless devices are also simulated assuming the maximum admissible power and modeling the electro-geometrical configuration of the handheld transmitter body. It should be noted that the these configurations are more realistic, but the obtained results loose the general validity of the dipole antenna model. Figure 1: Human head model. (a) CAD model. (b) Detail of the eye zone. 52 Conformity AUGUSt 2008

Table of Contents Feed for the Digital Edition of Conformity Magazine - August 2008

Conformity Magazine - August 2008 Contents Editor’s Note FCC Seeks Comment on Reauction of 700 MHz D Block Commission Cracks Down (Again!) on Junk Fax Marketer Canada Levies Fees for Public Safety Radio Spectrum FDA Issues Guidance on Medical Device Tracking Greenpeace Challenges Video Game Manufacturers The IEEE EMC Society: A Proud History of Accomplishments ESD Open Forum An Update on Changes to the Automotive ESD Standard, ISO 10605 Modeling of Radiated Electromagnetic Disturbances in Automotive Applications Design Issues in Automotive Radio Frequency Systems IEEE EMC Symposium IEEE 2008 Show Preview Exhibitors Buyer’s Guide Product News Most Eco-Friendly Companies Updated Standards List For the EU’s Pressure Equipment Directive Commission Issues Updated Standards List For Directive on Gas-Fired Appliances HHS Releases Fact Sheet on U.S. Imports from China Customs Agents Seize Holiday Lights IEEE PSES Symposium Set for October CPSC Actions in the News IEC Standards Update UL Standards Update Telcordia Standards Update From Our “You Can’t Make This Stuff Up” Department Looking Back: Items from Past Issues of Conformity Product Reviews Advertisers

Conformity Magazine - August 2008

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