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IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 44, NO. 1, JANUARY 1996 105 Automated E-Field Scanning System for Dosimetric Assessments Thomas Schmid, Oliver Egger, and Niels Kuster Abst,ruct- The interest in accurate dosimetric measurements inside phantoms that simulate biological bodies has burgeoned since several regulatory commissions began calling for or recom- mending the testing for compliance with safety standards of low power devices. This paper presents a newly developed, robot- based system that allows automated E-field scanning in tissue simulating solutions. The distinguishing characteristics of the system are its high sensitivity and its broad dynamic range (1 pW/g )to 100 mW/g) over the entire frequency range (10 MHz to over 3 GHz) used for mobile communications. The reproducibility of the dosimetric evaluations has been shown to be considerably better than f5%. This has been accomplished by the use of an improved isotropic E-field probe connected to amplifiers with extremely low noise and drift characteristics in conjunction with digital processing of the data. Special emphasis has been placed on system reliability, user-friendliness and graphic visualization of data. I. INTRODUCTION HE question of whether low power transceivers comply T with current safety limits was first raised by Cleveland et al. [ 11. Two years later the study of the absorption mechanism in the near field of sources revealed a direct contradiction of the exclusion clause for low power devices with basic safety restrictions [2]. Additional findings of the latter study relevant for this paper were: In the close near field, induced currents are mainly caused by the inductive coupling of the high frequency (HF) current distribution on the radiating structure with the biological body. The induced specific absorption rate (SAR) depends more on the actual design and the position of the radiating structure with respect to the body than on the inhomogeneity of the tissue. Devices with an input power of considerably less than 1 W might violate the basic safety limits for partial body exposure which are: 1.6 mW/g averaged over 1 g (ANSI/IEEE [3]), 2.0 mW/g averaged over 10 g tissue (CENELEC [4]), respectively. These findings have been confirmed in the following by studies with partially homogeneous bodies exposed to dipole and helix antennas [4], [6] and by a study with largely inhomogeneous head phantoms [7]. Several recently published dosimetric studies on current mobile phones found spatial peak SAR values in the range Marmscript received April 10, 1995; revised October 2, 1995. The authors are with the Swiss Federal Institute of Technology, CH-8092, Publisher Item Identifier S 0018-9480(96)00464-4. Zurich, Switzerland. of the safety limits for uncontrolled environments [8]-[ 131.
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This note was uploaded on 06/11/2011 for the course ELECTRICAL 124 taught by Professor Ghjk during the Spring '11 term at Institute of Technology.

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