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Comparison of electromagnetic absorption characteristics in the head of adult and a children for 1800 MHz mobile phones

Authors:
  • Faculdade de Tecnologia Senai Porto Alegre, RGS, Brasil

Abstract and Figures

The specific absorption rate (SAR) produced by mobile phones in the head of children is simulated using an algorithm based in the finite difference time domain (FDTD) method. A new model based on a 10 year old child computed tomographic images was used. The electromagnetic parameters were fitted to this age. The results are compared to the SAR calculated in the head of adults. Comparison also were made with SAR calculated in the children model when using adult human electromagnetic parameters values. It is shown that in similar conditions, the SAR calculated for the children is higher than that for the adults. When using the 10 years old child model, values around 80% higher than those for adults were obtained
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Comparison of Electromagnetic Absorption Characteristics in the
Head of Adult and a Children for 1800 MHz Mobile Phones
Claudio R. Fernández
1,2
, Giovani Bulla
1
, A. C. Pedra
1
and Alvaro. A. A. de Salles
1
1
Electrical Engineering Department, Federal University of Rio Grande do Sul (UFRGS),
Porto Alegre, RS, 90035-190, Brazil
2
Federal Center for Technological Education of Rio Grande do Sul (CEFET-RS), Pelotas,
RS, 96015-360, Brazil
Abstract — The Specific Absorption Rate (SAR) produced
by mobile phones in the head of children is simulated using
an algorithm based in the Finite Difference Time Domain
(FDTD) method. A new model based on a 10 year old child
computed tomographic images was used. The
electromagnetic parameters were fitted to this age. The
results are compared to the SAR calculated in the head of
adults. Comparison also were made with SAR calculated in
the children model when using adult human electromagnetic
parameters values. It is shown that in similar conditions, the
SAR calculated for the children is higher than that for the
adults. When using the 10 years old child model, values
around 80% higher than those for adults were obtained.
Index Terms — Children, Mobile Phones, Cell Phones,
Specific Absorption Rate – SAR, Finite Difference Time
Domain – FDTD.
I. I
NTRODUCTION
T
HE use of mobile phone by adults, young people,
children and the elderly has grown substantially in the
last years. In parallel with this, an increased concern by
the scientific community, the authorities and the
population regarding the safety of these phones has arised.
Several authors have used the Finite Difference Time-
Domain (FDTD) method to simulate the Specific
Absorption Rate (SAR) in the cell phone user’s head [1-
10]. It is currently the most appropriate choice when
highly non-homogeneous structures are involved for
which boundary techniques have fundamental limitations.
The SAR results estimated and measured show exposure
levels close to (or even above) the limits of the available
recommendations [11, 12].
Recently the use of cell phones by young and children
has been strongly stimulated. Some authors have focused
this, and different results were presented [10, 13-16]. In
[10], the model of the children head was based on a scaled
adult model and a SAR increase (compared with adult) of
around 120 % has been obtained. In [13], the head model
was based on MRI using similar electromagnetic
parameters as those for adults, and no significant
differences between adult and children SAR results were
observed. In [15], the head model was approximated by
spheres considering some variation of the electromagnetic
parameters, and an increase of around 20 % in the
calculated SAR was shown. In [16], using also scaled
model for the children’s head with adult electromagnetic
parameters, no significant variation for the average SAR
in the whole head was observed, and when considering
the brain, an increase of around 35% in the SAR was
calculated.
In this paper the FDTD method was used to simulate
the SAR in the head of a child, and compared with the
results simulated for the adults. A new model based on a
10 year old child computed tomographic images was used.
The electromagnetic parameters were fitted to this age.
Comparison also were made with SAR calculated in the
children model when using adult human electromagnetic
parameters values. Simulations were performed using
CRAY T 94 supercomputer from CESUP [17].
All the SAR results were calculated using planar
antennas.
The use of planar antennas with moderate directivity for
mobile phones has been suggested previously [1,5,6].
These antennas radiate more in the direction opposed to
the head, and they can be very low cost, resulting
therefore in an interesting alternative to this application.
II. A
NTROPOMORPHIC
N
UMERICAL
M
ODELS
The geometric and the electromagnetic parameter
differences between the adult and the child were
considered in the simulations.
SAR simulations for the adult human are performed
using a model based on [18] as in previous works [4-9]. In
order to compare the SAR due to cell phones in adults and
children a new model based on 102 computed
tomographic images (Fig.1) from a healthy 10 years old
child was developed.
Fig.1. Computed tomographic image of the 10 years old child:
coronal cut.
Both models were rotated to put the ear-to-mouth line
vertically (Fig.2). This facilitate the cell phones antennas
positioning.
Fig.2. Saggital cut of the 10 years old child rotated model.
Three different simulation cases were implemented. In
case A, the adult model and parameters [19] were used. In
case B, the child model with adult electromagnetic
parameters was used. In case C, the child model with
fitted electromagnetic parameters was used. These were
obtained from comparison with the results obtained for
rats [20]. The electromagnetic parameters for adult human
are well established, with an accuracy better than 5% [19].
However data for children are still not available. A study
with rats [20] shows that conductivity and permittivity
decrease with age. For 10 day and younger rats the values
are around 20% higher than for sexually mature (adult)
rats (e.g. 50 days). One reason for this could be the higher
water concentration in the tissues of the young. The
measured results for adult individuals in different animal
species show that there is a parameter variation lower than
5% from animal to animal when considering the same
type of tissue. This was the rationale, and using similar
correspondence between parameters values and age for
humans as for rats, we obtained the fitted parameters for
the children. These values are shown in Table I.
TABLE I
P
HYSICAL PROPERTIES FOR THE ADULT MAN AND
FITTED FOR THE
10
YEARS OLD CHILD AT
1800 MH
Z
Age
adult 10 years old
Properties
ρ(g/cm
3
) ε
r
σ(
-1
/m) ε
r
σ(
-1
/m)
Air
0.00 1.00 0.00 1.00 0.00
Average Skull 1.85 15.56 0.43 18.48 0.54
Skin (Wet) 1.01 43.85 1.23 54.63 1.53
Average
Muscle
1.04 54.44 1.39 61.68 1.57
Average Brain 1.03 43.54 1.15 52.52 1.44
Vitreous
Humour
1.01 68.57 2.03 81.81 2.47
Fat (Mean) 0.92 11.02 0.19 13.15 0.23
Eye Tissue
(Sclera)
1.17 53.57 1.60 63.91 1.95
Brain Spinal
Fluid
1.01 67.20 2.92 80.17 3.55
Nerve (Spinal
chord)
1.04 30.87 0.84 36.83 1.02
Lens Nucleus 1.10 34.65 0.79 41.34 0.96
The cranial perimeters in both models were
approximated from ellipsis. The calculated values are in
close agreement with those shown in [13]. To adjust for
the corresponding dimensions and in order to save
memory, FDTD simulation were performed having
different cell dimensions for each of the three cases
[21,22]. Then, the distance between the antenna and the
head are slightly different. These are shown in Table II.
TABLE II
S
PATIAL DISCRETIZATION
Model Adult 10 years old
Cases A B and C
Scale factor
1 1
Cranial perimeter (mm)
563.5 523.9
x (mm)
0.764 0.946
y (mm)
1.920 1.892
z (mm)
1.920 2.044
Antenna distance (mm) 14.51 14.19
III. A
NTENNA
M
ODELS
The cell phones were modeled using patch antennas to
compare the SAR results with previous works [5,6]. The
patch antennas were designed following the cavity models
described by [23,24]. The antenna dimensions were
adjusted according to the cell grid shown in Table II.
Special care was taken to feed the antenna at the exact
resonance frequency. For example, in the simulated cases
B and C, the antenna dimensions were L = 55.19 mm, W =
32.17 mm, H = 1.89 mm, in accordance to the grid. Then
the resonance frequency estimated using the cavity model
should be f = 1832 MHz. However S
11
simulations using
FDTD and FFT show that the resonance frequency is f =
1807 MHz (Fig.3).
Fig.3. Simulated S
11
for the patch antenna used in cases B and C.
This was the frequency used to feed the antenna with a
normalized power harmonic signal. Then, even the
feeding frequencies are slightly different from case to
case, we ensure a high radiation efficiency in all the
simulated cases.
The main objective of this work is to compare the child
and adult exposures in three different situations (cases A,
B, and C). Then the obtained SAR results are normalized
for the adult (case A).
IV. R
ESULTS
In this section the peak SAR and average SAR (1 g and
10 g) are presented. The 1g-SAR and the 10g-SAR were
calculated as spatial averages of boxes with 14x × 5y ×
5z (1g-SAR, Case A), 28x × 11y × 11z (10g-SAR,
Case A), 10x × 5y × 5z (1g-SAR, Cases B and C),
21x × 12y × 10z (10g-SAR, Case B and C). Since
there is not a great variation in the densities of the
different tissues, this can be considered a reasonably
approximation.
Since the child and the adult head models were rotated
in order to a better positioning of the cell phone, then the
vertical and horizontal cuts do not correspond exactly to
coronal and frontal cuts. Fig. 4 shows the SAR calculated
in case A.
In order to make the necessary comparison, the values
are normalised to the exposure limit recommended by the
corresponding IEEE/ANSI standard [11], SAR = 1.6
W/kg for 1 g of tissue.
In Fig. 5, SAR results for the 10 years old child model
with adult parameters (Case B) for the same six vertical
and horizontal cuts and the same scale are shown.
FDTD/FFT simulation of the patch antenna ressonance
for cases B and C
In Fig. 6, SAR results for the 10 years old child model
with parameters fitted to this age (Case C) for the same six
vertical and horizontal cuts and the same scale are shown.
In Table III the maximum simulated SAR results in the
brain for the three cases are shown.
The results were compared with that obtained for the 1
g average SAR in the adult (case A) assumed to be in the
1.6 W/kg SAR recommended IEEE/ANSI exposure limit
[11].
It is observed that an increase of around 80% in the 1g-
SAR was obtained for the children model with the fitted
parameters (case C). Even when using adult parameters in
the child model (case B), an increase of around 60% is
observed. Hence, the results obtained for the child model
when using the fitted parameters were around 9% higher
than those when using adult parameters.
TABLE III
SAR
Model Adult 10 years old child
Electromagnetic
parameters
Adult
parameters
Adult
parameters
Children
parameters
Case A B C
Normalised values (W/kg)
Peak SAR
(one voxel)
1.704 3.356 3.636
1g-SAR
1.600 2.618 2.868
10g-SAR
1.319 1.984 2.119
Percentage difference
(increase/decrease)
Peak SAR
(one voxel)
+6.5% +109.7% +127.3%
1g-SAR
0% +63.6% +79.2%
10g-SAR
-18% +24.0% +32.5%
Fig.4. SAR for three vertical and horizontal cuts (Case A, adult). The color scale corresponds to 10 dB for each color. The same scale
is used in Fig.5 and Fig.6.
Fig.5. SAR for three vertical and horizontal cuts (Case B, child with adult parameters). The color scale corresponds to 10 dB for each
color. The same scale is used in Fig.4 and Fig.6.
Fig.6. SAR for three vertical and horizontal cuts (Case C, child with fitted parameters). The color scale corresponds to 10 dB for each
color. The same scale is used in Fig.4 and Fig.5.
V. D
ISCUSSIONS AND
C
ONCLUSION
S
The SAR in the 10 years old child was calculated and
compared to the results obtained for adult. SAR results
around 80% higher than those for the adults were
observed for the children. This is expected to be due to
differences in dimensions and electromagnetic parameters,
and is in accordance with the results obtained by other
authors [10].
Due to the increase of the use of mobile phones by
children, and since compliance tests use head phantoms
based exclusively on adult data, the results shown in this
paper may suggest that further theoretical and
experimental research must be done in order to evaluate
these issues aiming to reduce risks for the children. This is
in accordance to the WHO – World Health Organization –
effort, included in the WHO Children’s EMF Research
Agenda, recommending research studies relevant to the
risk of adverse health effects in children from exposure to
electromagnetic fields (EMFs) [25].
A
CKNOWLEDGMENT
The authors are grateful to MD Sonia Tozzi (from
Radicom) and Diego Mauricio Fernández Campos for
their collaboration to the 10 years old child computed
tomographic images, and also to Martin Elbern for his
contribution in the model for the head of the child.
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... Alguns autores mostraram comparações entre os valores simulados para a SAR em adultos e em crianças e em adolescentes [e.g., Gandhi, O. P. et al. , 1996, Fernández et al. ,2005. Por razões diversas, os resultados são mais críticos para os mais jovens que para os adultos. ...
... A Fig. 10 mostra as SAR simuladas para adultos (esq.) e para criança de 10 anos (dir.) [Fernández et al, 2005]. Fig. 10 -Comparações da SAR para um adulto (esq.) e para uma criança de 10 anos (dir.) ...
... Fig. 10 -Comparações da SAR para um adulto (esq.) e para uma criança de 10 anos (dir.) [Fernández et al, 2005]. ...
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The purpose of this opinion is to update the SCENIHR opinion of 21 March 2007 in the light of newly available information, and to provide a methodological framework and corresponding guidelines to evaluate available scientific evidence in order to ensure the best possible quality for risk assessment. 1. Update Radio frequency fields (RF fields) It is concluded from three independent lines of evidence (epidemiological, animal and in vitro studies) that exposure to RF fields is unlikely to lead to an increase in cancer in humans. However, as the widespread duration of exposure of humans to RF fields from mobile phones is shorter than the induction time of some cancers, further studies are required to identify whether considerably longer-term (well beyond ten years) human exposure to such phones might pose some cancer risk. Regarding non-carcinogenic outcomes, several studies were performed on subjects reporting subjective symptoms. In the previous opinion, it was concluded that scientific studies had failed to provide support for a relationship between RF exposure and selfreported symptoms. Although an association between RF exposure and single symptoms was indicated in some new studies, taken together, there is a lack of consistency in the findings. Therefore, the conclusion that scientific studies have failed to provide support for an effect of RF fields on self-reported symptoms still holds. Scientific studies have indicated that a nocebo effect (an adverse non-specific effect that is caused by expectation or belief that something is harmful) may play a role in symptom formation. As in the previous opinion, there is no evidence supporting that individuals, including those attributing symptoms to RF exposure, are able to detect RF fields. There is some evidence that RF fields can influence EEG patterns and sleep in humans. However, the health relevance is uncertain and mechanistic explanation is lacking. Further investigation of these effects is needed. Other studies on functions/aspects of the nervous system, such as cognitive functions, sensory functions, structural stability, and cellular responses show no or no consistent effects. Recent studies have not shown effects from RF fields on human or animal reproduction and development. No new data have appeared that indicate any other effects on human health. From the risk assessment perspective it is important to recognise that information on possible effects caused by RF fields in children is limited. Furthermore, there is a lack of information on diseases other than those discussed in this report. Intermediate frequency fields (IF fields) Occupational exposure to IF fields in certain areas is considerably higher than exposure to the general public. However, very little research on IF and health risks in occupational settings or for the general public have been presented since the previous opinion, and no epidemiological studies have appeared. Consequently, the data are still too limited for an appropriate risk assessment. In view of the increasing occupational exposure to IF among workers in e.g. security, shops, and certain industries it is important that research in this area is given priority. Extremely low frequency fields (ELF fields) The few new epidemiological and animal studies that have addressed ELF exposure and cancer do not change the previous assessment that ELF magnetic fields are a possible carcinogen and might contribute to an increase in childhood leukaemia. At present, in vitro studies did not provide a mechanistic explanation of this epidemiological finding. No new studies support a causal relationship between ELF fields and self-reported symptoms. Health Effects of Exposure to EMF 5 New epidemiological studies indicate a possible increase in Alzheimer's disease arising from exposure to ELF. Further epidemiological and laboratory investigations of this observation are needed. Recent animal studies provided an indication for effects on the nervous system at flux densities from 0.10-1.0 mT. However, there are still inconsistencies in the data, and no definite conclusions can be drawn concerning human health effects. Very few recent in vitro studies have investigated effects from ELF fields on diseases other than cancer and those available have very little relevance. There is a need for hypothesis-based in vitro studies to examine specific diseases. It is notable that in vivo and in vitro studies show effects at exposure levels (from 0.10 mT and above) to ELF fields that are considerably higher than the levels encountered in the epidemiological studies (μT-levels) which showed an association between exposure and diseases such as childhood leukaemia and Alzheimer's disease. This warrants further investigation. Static fields Although a fair number of studies have been published since the last opinion, the conclusion drawn there stands: there is still a lack of adequate data for a proper risk assessment of static magnetic fields. More research is necessary, especially to clarify the many mixed and sometimes contradictory results. Short term effects have been observed primarily on sensory functions for acute exposure. However, there is no consistent evidence for sustained adverse health effects from short term exposure up to several teslas. Environmental effects The current database is inadequate for the purposes of the assessment of possible risks due to environmental exposure to RF, IF and ELF. Research recommendations The scientific rationale has identified a number of areas characterised by insufficient and contradictory information regarding possible health associated effects from the various frequency bands of the EMF spectrum. It is recommended that certain knowledge gaps are filled. 2. Methodological Framework The SCENIHR is asked to provide a methodological framework and corresponding guidelines to evaluate available scientific evidence in order to ensure the best possible quality for risk assessment. The subject is covered in detail in chapter 3.8 of the opinion. The present opinion provides a methodological framework and guidelines as: - a general outline of criteria used for making EMF health risk assessment - a description of the work procedure leading to the overall evaluation - a specialised section where characteristics and quality criteria regarding dosimetry and exposure assessment, epidemiology, human laboratory studies, in vivo studies, and in vitro studies are presented.
... Researchers have developed computer-derived or MRI-derived models showing the depth of penetration of RF/MW radiation into the brain. Gandhi and others have developed models for estimating and mapping diffusion and intensity of penetration into the brain from cell phones in adults and children, taking into account the size of the skull and width of the bones (23,59,60). Most of the studies examining the penetration of radiation into tissues have focused on the brain, in regard to cellphone exposure. ...
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Background. There are reports that intense prolonged occupational exposure to non-ionizing radiation may increase risks for cancer. We previously have reported a sentinel cluster,of 7 workers with high exposures and short latent periods, and individual patients with brain cancer high occupational exposures and short latent periods. We present a sentinel case series (n=47, 40M, 7F) of cancer patients, referred to our medical unit with occupational exposures to non-ionizing radiation of all types. Objectives. Our aims were to report the findings on tumour types,age of first diagnosis, and latency, to describe their exposures and to examine the hypothesis that latencies for all tumour types (solid tissue, hematolymphatic, testicular) were coherently related to high occupational exposures starting at young ages. Methods. We divided the patients into groups by latency. We categorized each patient’s exposures in regard to types of radiation, far or near field exposure and direct body contact. For some we had data on frequencies, for others we provided assessments. We also present the patient data categorized by age of diagnosis.We used a case-case type comparison to examine latencies for tumour types [solid, hematolymphatic (HL), testicular]. Results. 15 patients developed cancer with latent periods of less than 5 years and 12 patients with latent periods between 5 and 10 years. The remaining 20 patients had longer latent periods between first occupational exposure to EMF and diagnosis of cancer. 6 patients (12.7%) had multiple tumours. 12 patients (25.5%) reported cancer cases in co-workers. In the <5 years latency group there were 8 hematolymphatic cancers, 3 testicular cancers and 6 solid tumours [head & neck (including brain) and GI tract]. In all latency groups there were patients who were exposed to intense levels of electromagnetic fields (EMF), to several types of EMF, or to EMF in combination with ionizing radiation (IR) or other exposures, and patients who had direct body contact with the equipment, were in direct focus of high radiation, or worked in small, electronically dense environments. Case classification by age showed shorter latencies with younger ages, but this association is complicated by the fact that shorter latencies co-vary with younger ages especially for testicular tumours. But patients with testicular and hematolymphatic tumours had shorter latencies than those with solid tumours. Conclusion. Man of the patients were young and had extremely short latent periods, especially for HL and testicular cancers. The fact that latent periods for testes were very short, HL longer and solid still longer suggests a coherent and biologically plausible pattern of latency in relation to the onset of exposure to EMF and other agents. The findings strengthen the hypothesis that these exposures may possibly be the major cause of many of these tumours. The findings state the case for (1) better modelling of exposure sources and penetration into the body and (2) preventive and protective measures based on control of exposure at source, barriers, and personal protection. Eur. J. Oncol., 16(1),21-54,2011 Keywords: non ionizing radiation (NIR), electromagnetic fields (EMF), occupational exposures, cancer, short latencies
... In parallel with this, an increased concern by the scientific community, the authorities and the population regarding the safety of these phones has raised. It is currently the most appropriate choice when highly non-homogeneous structures are involved for which boundary techniques have fundamental limitations [1]. The Finite-Difference Time-Domain (FDTD) is the most often used method for evaluating of electromagnetic fields in human tissue. ...
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In this paper, the power density and specific absorption rat (SAR) distribution in multi-layered life tissues and exposed to electromagnetic field emitted from handheld cellular phone operating in the 900 MHz and 1800 MHz is studied. We modeled a life tissue by four layered system to represent skin-fat-muscles-organs respectively. Matlab program and finite difference time domain (FDTD) computations were used to evaluator the electric, magnetic field, power density and specific absorption rate. A one dimensional FDTD algorithm has been built, some simulations for electromagnetic wave through the life tissue is made. Results show that electro magnetic fields penetrate the life tissues and attenuate fast to reach zero at the organs layer. The absorbent power and SAR show maximum at the skin and fat layers.
... Even though there is no evidence of extrapolating these results to human biological tissues, fitted parameters for humans based on tissue maturity and water content may be calculated. Fitted child dielectrical parameters calculated as stated above at 1800 MHz are given on [21]. In order to assess impact of size and change of dielectrical parameters values on induced SAR, two child models were built and two exposure scenarios were run: Differences between induced Spatial Peak SAR averaged over 1g and 10g of child body for Child A and Child B are given below:Table 4 Graphically on Figures 6 and 7 are shown comparative induced SAR in adult head represented by SAM phantom, where Child A and Child B are defined as above. ...
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Exposure to radio frequency electromagnetic fields has raised scientific and public concern regarding possible adverse effects to people exposed to such radiation. At cellular mobile communication frequencies, the most important parameter used to assess human exposure to electromagnetic fields is SAR (Specific Absorption Rate). This paper will firstly address two exposure scenarios related to adult exposure to GSM electromagnetic fields : Human exposure to 900 MHz GSM base station electromagnetic fields, whereby with EMR-300 is measured field strength on different points located meters away from base station antenna. Using SAR prediction formula we have calculated induced SAR values for people located near base station antenna. The obtained results are compared with maximum permissible levels and basic restrictions of international safety standards. Human exposure to mobile phone GSM electromagnetic fields, whereby with a software (FDTD code) have simulated human head exposure to mobile phone radiation and have calculated Spatial Peak SAR over 1 g and 10 g of human body biological tissues. Secondly, in order to investigate comparison of radio frequency energy absorption by head of children and adults, the Spatial Peak SAR over 1g and 10g is calculated for: uniformly down-scaled adult head with increased dielectrical parameters compared to adult ones and uniformly down-scaled adult head with adult dielectrial parameters. SAR results are presented graphically and tabulary while comparative assessment is given in order to emphasize influence of head size and change of dielectrical parameters on radio frequency energy absorption by human tissues, and give possible answer whether children should be treated as special group regarding radio frequency exposure. Even not an all inclusive approach is considered, obtained results indicate that SAM may be considered conservative for assessment of children exposure compliance to radio frequency electromagnetic fields.
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Purpose The purpose of this paper is to determine the impact of human age on the distribution of electric field and absorbed energy that originates from a mobile phone. Design/methodology/approach This research was performed for frequencies of 900, 1800 and 2100 MHz, which are used in a mobile communication system. To obtain the most accurate results, 3 D realistic model of the child’s head has been created whereby the dimensions of this model correspond to the dimensions of a seven-year-old child. Distribution of the electric field and specific absorption rate (SAR) through the child’s head was obtained by numerical analysis based on the finite integration technique. Findings The results discover that amount of absorbed energy is greater in the surface layers of the child’s head model when the electromagnetic (EM) characteristics of tissues are adjusted for the child. This deviation corresponds to different EM characteristics of biological tissues and organs of an adult person compared to a child. Research limitations/implications The study deals with penetrated electrical field and absorbed EM field energy. There is space for further studies of other EM field effects (e.g. thermal effects). Practical implications The analysis of obtained results leads to idea that mobile phones and devices aimed for children using should be modified to provide SAR values inside prescribed standards. Social implications The obtained results are foundation for future research on influence of EM fields of mobile devices on human health. Originality/value The proposed procedure offers the model for accurate estimation and quality analysis of SAR and EM field distribution inside child head tissue.
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The Specific Absorption Rate (SAR) produced by mobile phones in the head of adults and children is simulated using an algorithm based on the Finite Difference Time Domain (FDTD) method. Realistic models of the child and adult head are used. The electromagnetic parameters are fitted to these models. Comparison also are made with the SAR calculated in the children model when using adult human electromagnetic parameters values. Microstrip (or patch) antennas and quarter wavelength monopole antennas are used in the simulations. The frequencies used to feed the antennas are 1850 MHz and 850 MHz. The SAR results are compared with the available international recommendations. It is shown that under similar conditions, the 1g-SAR calculated for children is higher than that for the adults. When using the 10-year old child model, SAR values higher than 60% than those for adults are obtained.
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Resumo -Neste trabalho e apresentado 0 desenvolvimento de urn programa para calculo da Taxa de Absorcao Especifica (SAR) na cabeca e no olho de urn usuario de transceptores portateis como os telefones celulares, utilizando 0 metodo das diferencas finitas no dominio do tempo (FDTD). Sao mostrados os principais resultados obtidos com estas simulacoes e as comparacoes com os resultados simulados e medidos por outros autores. Sao tambem discutidas altemativas visando minimizar os riscos que a absorcao do campo pode representar para a saude dos usuaries, incluindo a utilizacao de antenas que emitem mais no sentido oposto acabeca. Abstract -The development of a software to estimate the Specific Absorption Rate (SAR) in the head and in the eyes of portable transmitters (such as cellular phones) user's employing the finite difference time domain (FDTD) method is shown in this work. The relevant results obtained with this model are compared with those estimated and measured by other authors. Alternatives aiming to reduce health risks are discussed, including the use of antennas radiating energy away from the user's head. Palavras-chave: Telefones Celulares, Efeitos Biologicos, Taxa de Absorcao Especifica (SAR), Diferencas Finitas no Dominio do Tempo (FDTD), Antenas em Microstrip.
Book
The discipline of antenna theory has experienced vast technological changes. In response, Constantine Balanis has updated his classic text, Antenna Theory, offering the most recent look at all the necessary topics. New material includes smart antennas and fractal antennas, along with the latest applications in wireless communications. Multimedia material on an accompanying CD presents PowerPoint viewgraphs of lecture notes, interactive review questions, Java animations and applets, and MATLAB features. Like the previous editions, Antenna Theory, Third Edition meets the needs of electrical engineering and physics students at the senior undergraduate and beginning graduate levels, and those of practicing engineers as well. It is a benchmark text for mastering the latest theory in the subject, and for better understanding the technological applications. An Instructor's Manual presenting detailed solutions to all the problems in the book is available from the Wiley editorial department.
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The thermal and the non-thermal effects of the Non-Ionizing Radiation (NIR) are briefly described. The Specific Absorption Rate (SAR) in the head of mobile phone users is simulated using the Finite Difference Time Domain (FDTD) method in three dimensions (3D) when conventional monopole and planar antennas are employed. The performance simulation of microstrip rectangular patch antennas, as well as its predicted and measured results are presented. The software Ensemble     is used to estimate the antenna voltage standing wave ratio (VSWR) and its bandwidth. An algorithm based in 3D FDTD is developed to model the radiation pattern in the horizontal plane and the electric field in the Fresnel region. Measured VSWR as well as horizontal radiation pattern are shown. It can be seen that there is a strong correlation between the measured and the FDTD simulated results when the ground plane is finite and when it is not effectively grounded. This type of antenna may be of great interest in a new generation of mobile phones, improving its performance, reducing the battery drain and the SAR in the user's head.
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Knowledge of the dielectric properties of biological materials is of importance in solving electromagnetic interaction problems. There is, as yet, no consensus on such data among scientists dealing with these issues. This project is geared towards producing a database of dielectric data based on measurements using recently developed techniques. This has been achieved through measurement over a wide frequency range. The new data were evaluated by comparison with corresponding data from the literature where available. To facilitate the incorporation of the dielectric data in numerical solutions, their frequency dependence was modelled to a spectrum characterised by 4 dispersion regions. The conductivity of tissues below 100 Hz was estimated from the recent measurements mitigated by data from the literature and used to estimate the body and of various body parts.
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The Finite-Difference Time-Domain (FDTD) method to calculate the cellular phone far and near field and the specific absorption rate (SAR) in the user's head is described. The conventional λ/4 monopole and a simple planar antenna are simulated. A multidimensional grid is developed to optimize simulations in the near and in the far field, in the presence and in the absence of the cellular phone user's head at 1.9 GHz. These calculations show that significant improvements in the antenna radiation efficiency and in the reduction of the SAR in the head are obtained when planar antennas are used.
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The Finite-Difference Time-Domain (fdtd) method is used to calculate the cellular phone far and near field and the specific absorption rate (sar) in the user’s head. The conventional λ/4 monopole and a simple planar antenna are simulated and measured. The simulated results are in good agreement with those measured for thevswr and for the radiation patterns on the horizontal and vertical planes. These results show that significant improvements in the antenna radiation efficiency and in the reduction of thesar in the head are obtained when planar antennas are used.