Assessment of Power Absorption in Human Head Models of Adults and Children Irradiated by Cellular Phone Helical Antennas (original) (raw)
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Characteristics of power absorption in human head models exposed to normal mode helical antennas
In this paper, the coupling between various human head models and cellular phone helical antennas is studied. Canonical as well as realistic exposure problems are considered and solved using a novel accurate semianalytical method or Finite-Difference Time-Domain (FDTD) simulations. The semi-analytical method combines the theory of Green's functions with the Method of Moments (Green/MoM) and permits the analysis of the interaction between homogeneous or layered spherical human head models and arbitrarily shaped wire antennas, such as helical or linear dipoles. The accurate semi-analytical character of the Green/MoM technique provides a powerful tool for benchmarking of purely numerical techniques, such as the FDTD, which has proven to be the most efficient numerical technique for treating problems related with mobile communication dosimetric assessment. Then, FDTD simulations are carried out to evaluate the characteristics of power absorption in an anatomically detailed human head model exposed to a realistic handset equipped with a small size helix monopole. The results of Green/MoM and FDTD simulations include calculations of local and average specific absorption rates (SAR's) inside the human head, total power absorbed by the head and assessment of antenna radiation patterns at 1710 MHz. Furthermore, the results obtained for helical antennas are assessed against results obtained for linear antennas (i.e. half-wavelength linear dipole and quarter wavelength linear monopole mounted on the top of a realistic handset) using Green/MoM and FDTD simulations.
Personal dosimetry of cellular phone linear and helical antennas for adults and children
The coupling between cellular phone arbitrarily shaped wire antennas and human head models is studied through both a novel semi-analytical technique and Finite-Difference Time-Domain (FDTD) simulations. The semi-analytical technique combines the Green's functions theory with the Method of Moments (Green/MoM) and is able to model arbitrarily shaped wire antennas radiating in the close proximity of layered lossy dielectric spheres representing simplified models of the human head. The purpose of the development of an accurate semianalytical technique is to provide: (1) a powerful tool for preliminary (worst case) estimation of human head exposure to the field generated by different antenna configurations and (2) a testbed for bencmarking of purely numerical techniques, such as the FDTD which has proven to be the most efficient numerical technique for problems related with mobile communication dosimetric assessment. First, the interaction between spherical head models and a half wavelength linear dipole or a normal mode helical antenna, is studied. Then, after appropriate benchmarking, FDTD simulations are used to examine the coupling between a heterogeneous anatomically correct model of the human head exposed to either a quarter wavelength linear monopole or a normal mode helix monopole, both operating at 1710 MHz and mounted on the top of a metal box representing a realistic mobile communication terminal. The results of Green/MoM and FDTD simulations include calculations of local and average specific absorption rates (SAR's) inside the human head, total power absorbed by the head and assessment of antenna radiation patterns at 1710 MHz. Emphasis is placed on the comparative dosimetric assessment between adults and children head models.
The Environmentalist, 2005
The aim of this work is to examine the differences in power absorption in the brain of adults and children exposed to the radiation of mobile phone terminals at 1710 MHz. To this end, simulations using the Finite-Difference Time-Domain (FDTD) method have been carried out to study the interaction between heterogeneous anatomically correct models of the human head and a linear or helical monopole mounted on the top of a metal box representing a realistic mobile communication terminal. The study includes computations of specific absorption rates (SARs) inside the human head and the total power absorbed by the head. Emphasis is placed on the comparative assessment of power absorption characteristics in heads of adults and children as well as on the effect of various parameters such as the age-related changes in dielectric properties and the usage distance between the user's head and the mobile terminal.
2009
A comparative assessment of power absorption in adult and child heads exposed to a small helical antenna at 1710 MHz, is presented, emphasizing the effect of age related parameters. Finite Difference Time Domain simulations are employed to study the interaction between MRI-based head models and a mobile communication terminal equipped with a small helical monopole. A semi-analytical method, based on Green's function theory and the Method of Moments, is used to study the absorption in threelayer spherical head models exposed to a small helical dipole. SAR patterns in child head models derived by non-uniform scaling of adult ones were assessed against SAR patterns computed in child heads derived by uniform downscaling procedures. In both realistic and canonical exposure scenarios, comparable levels of absorbed power
IEEE Transactions on Microwave Theory and Techniques, 2000
A set of finite-difference time-domain (FDTD) numerical experiments modeling canonical representations of the human head/cellular phone interaction has been performed in order to investigate the effect of specific simulation details (e.g., antenna numerical representation and absorbing boundary conditions) on computed results. Furthermore, hybrid techniques based on the dyadic Green's function and the method of auxiliary sources, and on a hybrid method-of-moments-FDTD technique have been used to compute parameters of interest for comparison with the FDTD evaluated parameters. It was found that small, but potentially significant, differences in computed results could occur, even between groups that were nominally using a very similar method. However, these differences could be made to become very small when precise details of the simulation were harmonized, particularly in the regions close to the source point. Index Terms-Biological effects of electromagnetic radiation, dosimetry, error analysis, FDTD methods, hybrid numerical techniques, land mobile radio cellular systems.
Influence of the Human Head in the Radiation of a Mobile Antenna
2009
The big proliferation of mobile communication systems has caused an increased concern about the interaction between the human body and the antennas of mobile handsets. In order to study the problem, a multiband antenna was designed, fabricated and measured to operate over two frequency sub bands 900 and 1800 MHz. After that, we simulated the same antenna, but now, in the presence of a human head model to analyze the head's influence. First, the influence of the human head on the radiation efficiency of the antenna has been investigated as a function of the distance between the head and the antenna and with the inclination of the antenna. Furthermore, the relative amount of the electromagnetic power absorbed in the head has been obtained. In this study the electromagnetic analysis has been performed via FDTD (Finite Difference Time Domain).
Dosimetry in the human head for two types of mobile phone antennas at GSM frequencies
Central European Journal of Engineering, 2014
In this paper, a comparative study of dipole and patch antennas commonly used in portable telephones is investigated. The two models antennas are considered working at 900, 1800 and 2450 MHz bands. Thus, we have included different distances between the mobile phone and the human head model. This study shows the effects of electromagnetic waves on the human head model. The objective is to evaluate the SAR in simulation anatomic based model of the human head for different antenna-head distances and in many frequencies. All numerical simulations results are performed using Ansoft HFSS software.
On modeling and personal dosimetry of cellular telephone helical antennas with the FDTD code
IEEE Transactions on Antennas and Propagation, 1998
In this paper, a novel method to model helical antennas working in the normal mode, as well as helix-monopole antennas with finite-difference time-domain (FDTD) code is presented. This method is particularly useful to model antennas used for personal wireless communication handsets, where the fairly small dimensions of the helical antennas with respect to wavelength and the grid cell size do not allow an appropriate description of the antennas by the use of metal wires. By observing that a helix working in the normal mode is equivalent to a sequence of loops and dipoles, it is possible to model the helix as a stack of electric and magnetic sources with relative weights calculated using information obtained from analytical expressions for the far-fields. Dosimetry associated with wireless telephones using helical antennas is then considered by calculating the specific absorption rates (SAR's) induced by two actual devices in a 1.974 2 1.974 2 3.0-mm resolution model of the human head based on MRI scans of a male volunteer. Comparison of the computed results with experimental measurements in the near field, the far field, and the induced SAR's shows good agreement.
The Interactions Between the Mobile Handset Antenna of Various Types and the Human Head
One lingering concern is the effect of the radiation produced by the mobile handset antenna on the human head. This topic has been studied widely, but still there is no definitive answer. Since mobile telephones are typically used in close to the human head, significant levels of power can be absorbed by the head, the primary effect is to cause local heating of the brain and head tissues. This is of concern to some people who work continually with mobile telephones, and some form of ''preventative'' research should be done. This paper describes some kinds of models of antennas (dipole, monopole and patch antennas) and human, and the calculation of the Specific Absorption Rate (SAR) in the human head at 1800 MHz. Also, this paper studies the effect of the human head model on the return losses of these models of the antennas. The obtained results show that at the same frequency, the patch antenna induces SAR in the human head of smaller values than that induced by dipole and monopole antennas. In addition, the return loss of the patch antenna is affected greatly by the presence of the human model, when it is compared with the return losses of the dipole and monopole antennas.