Conformity Magazine - August 2008 - (Page 51)

t is well known that the human eye is one of the most sensitive tissues that can exhibit thermal damage due to intense radiofrequency (RF) electromagnetic (EM) wave exposure [1], [2]. Thus it is interesting to investigate on the possible ocular effects that could occur when the eye is exposed by the RF field produced by widely used handheld transmitters as walkie-talkies, mobile phones or WiFi-based devices. To this aim a numerical study based on partial differential equation (PDE) solution is proposed in order to evaluate the SAR and the thermal increase distributions in the human eye when narrowband wireless sources are located in the proximity of the exposed eye. The adopted numerical procedure is quite standard. First the electromagnetic problem is addressed and the SAR distribution is evaluated. Then the bioheat equation is solved numerically by a finite difference procedure in order to estimate the temperature increase distribution in the eye. The originality and importance of the paper is mainly concentrated in the high definition modeling of the eye. Another relevant aspect of the proposed paper is in the applications, where common handheld transmitters are assumed to be the radiation sources of the field exposure. The human eye is accurately modeled by considering several ocular tissues, such as retina, choroid and lens muscles whose thickness is less than 1 mm. These tissues are very important from a thermal point of view since they have significant values of the blood flow and metabolic rate [3]. In order to shape adequately the eye configuration with many tissues, a discretization of 0.25 mm is proposed for the thermal numerical calculation. Since the traditional models of the human head based on the Visible Human Project (VHP) [4] or on Magnetic Resonance Imaging (MRI) [5] are generally not suitable for the desired resolution of 0.25 mm cubic cell size, a CAD model of the human head is presented [6]. A three-dimensional (3D) numerical thermal model of the orbit ball, with a resolution of 0.25 mm, is developed and discussed in the following sections, with particular care on the computational aspects. In the application, the RF exposure produced in the eye by wireless handheld devices is investigated at the frequencies of walkie-talkies 450 MHz, mobile phones 0.9, 1.8, 1.9 and 2.1 GHz, and wireless local area network (WLAN) 2.4 and 5.4 GHz. The RF sources are simulated by radiating dipole antennas located in front of the eye ball at a small distance from it. The numerical results are obtained assuming unit power at the dipole antenna input and they can be easily used to estimated the thermal elevation distribution produced by real handheld transmitters when the power, gain and directivity of the handheld antenna is known and when the interaction antenna-human head can be neglected. Finally, some exposures generated by realistic handheld radiating antennas are considered in order to identify the most critical RF sources for the human eye [16] [17]. at us 09 e Se oth 7 2008 Bo EMC MI E it, IEE Detro http://www.atecorp.com http://www.atecorp.com

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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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