The dependence of electromagnetic energy absorption at 900 MHz in the human head on its anatomy and its modeling are investigated for RF-sources operating in the very close proximity of the head. Different numerical head phantoms based on MRI scans of 3 different adults were used with voxel sizes down to 1 mm/sup 3/. Simulations of the absorption were performed by distinguishing the electrical properties of up to 13 tissue types. In addition simulations with modified electric parameters and reduced degrees of complexity were performed. Thus, the phantoms greatly differ from each other in terms of shape, size, and internal anatomy. The numerical results are compared with those of measurements in a multitissue phantom and 2 homogeneous phantoms of different shapes and sizes. The results demonstrate that size and shape are of minor importance, Although local SAR values depend significantly on local inhomogeneities and electric properties, the volume-averaged spatial peak SAR obtained with the homogeneous phantoms only slightly overestimates that of the worst-case exposure in the inhomogeneous phantoms.

The dependence of EM energy absorption upon human head modeling at 900 MHz

Recently, encouraged by deregulation ultra-wideband (UWB) technology has attracted attention for use in communication and sensing applications in the commercial domain. In February 2002 the Federal Communications Commission (FCC) in the United States conditionally waived unlicensed operation of the personal UWB products in the private sector. In this paper, we constructed a prototype antenna for the FCC approved UWB frequency band (3.1-10.6 GHz). The prototype antenna was successful because it demonstrated omnidirectional radiation and low VSWR (<1.4) between 3 GHz and 20 GHz. This prototype antenna could therefore be used in the next generation of UWB wireless system measurement applications.

/pdf/an-omnidirectional-and-low-vswr-antenna-for-the-fcc-approved-4mkeiz23or.pdf

An omnidirectional and low-VSWR antenna for the FCC-approved UWB frequency band

Crawford TEM cells are often used to expose cell cultures or small animals in order to study the effects caused by high-frequency fields. They are self-contained, easy-to-use setups that provide a rather homogeneous field distribution in a large area around its center, corresponding approximately to far-field conditions. However, a number of conditions must be met if such TEM cells are intended to be used for in vitro experiments. For instance, poor interaction with the incident field must be maintained to avoid significant field disturbances in the TEM cell. This is best achieved with E-polarization, i.e., when the E-field vector is normal to the investigated cell layer lining the bottom of a synthetic Petri dish. In addition, E-polarization provides the most homogeneous field distribution of all polarizations within the entire layer of cells. In this paper, we present a detailed dosimetric assessment for 60 and 100 mm Petri dishes as well as for a 48-well titer plate at 835 MHz. The dosimetry was performed by using numerical computations. The modeling and the simplifications are validated by a second numerical technique and by experimental measurements. For thin liquid layers, an approximation formula is provided with which the induced field strength for many other experiments conducted in Petri dishes can be assessed reliably.

Numerical and experimental dosimetry of Petri dish exposure setups.

A variety of phantoms simulating the human head have been used to test compliance of mobile telecommunications equipment with safely standards. Whereas numerical compliance procedures have mostly been performed using complex anatomical phantoms based on magnetic resonance imaging (MRI) data, experimental procedures have mainly relied on homogeneous phantoms, the ears of which have often been modeled as lossless spacers. Previous studies had indeed demonstrated that the absorption in the head tissue, except the outer ear, can be well represented by a homogeneous head of appropriate shape and material. The objectives of this paper were to fill the gap of the remaining open issues, namely: to evaluate the exposure in the ear region with respect to the spatial-peak specific absorption rate and to evaluate the most appropriate modeling of the ear for experimental evaluations such that it represents the maximum exposure of a reasonable cross section of cellular phone users. This paper is based on a detailed numerical phantom produced using high-resolution MRI scans. During scanning, the ear was naturally collapsed as it occurs when using a cellular phone. The results of this study lead to the conclusion that the spatial-peak absorption occurring in the inner and outer ear can be reliably modeled either by a lossless spacer of not thicker than 3-4 mm or by partially filling the simulated pinna with head tissue simulating media, whereas the minimum distance between the device and liquid should not be larger than 3 mm.

Appropriate modeling of the ear for compliance testing of handheld MTE with SAR safety limits at 900/1800 MHz

This paper presents an exposure setup designed for in vivo studies of possible effects on the central nervous system due to the electromagnetic exposure from handheld mobile communications equipment. The setup consists of a carousel on which 10 rats, each restrained in a radially positioned tube, are exposed to the electromagnetic field emanating from a dipole antenna at the center. The rats are positioned with their snouts at a distance of 35 mm from the dipole antenna. The tubes restrain the movement of the animals to such an extent as to allow for well defined exposure conditions, yet without totally immobilizing them. Numerical and experimental dosimetric analysis of the setup was conducted using rats weighing 250-300 g at a frequency of 900 MHz. A detailed rat phantom derived from MRI scans was developed for the numerical assessment with a commercially available code based on the finite integration technique. The results were validated by measurements of the temperature rise in selected points of a rat cadaver. The dosimetric analysis shows that the setup is eminently suitable for central nervous system studies. It enables well defined field strengths to be induced in the brain tissue, whereby the variations in the specific absorption rate averaged over the brain tissue caused by movement and varying animal sizes was shown to be less than +/-16%. The specific absorption rate distribution in the brain is nonhomogeneous but comparable to that induced in the brain of a human using a handheld wireless phone. The efficiency of the exposure is about 0.20+/-0.05 mW g(-1) for the brain average value per 100 mA feedpoint current. The whole-body average specific absorption rate is considerably lower, i.e., about half of that of the brain averaged value. In addition, the setup has been proven to be practical in use, and the stress levels caused by restraining the animals in this setup are deemed by neurologists and veterinary scientists to be very low.

Exposure setup to test effects of wireless communications systems on the CNS.

A numerical approach for the solution of Maxwell's equation is presented. Based on a finite difference Yee lattice the method transforms each of the four Maxwell equations into an equivalent matrix expression that can be subsequently treated by matrix mathematics and suitable numerical methods for solving matrix problems. The algorithm, although derived from integral equations, can be considered to be a special case of finite difference formalisms

Maxwell’s grid equations

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Maxwell’s grid equations