-Wireless communication devices such as tablets are increasing and developing rapidly. The effects of the electromagnetic (EM) waves in the human body from the wireless communication devices have been paid attention. It is well known that the absorption of electromagnetic waves on the human head for a certain period of time may lead to health problems such as headaches, or even worse, significantly increased risk of brain cancer. In this paper, the Specific Absorption Rate (SAR) in the head of tablet user's is simulated for three different head models and compared with available international recommendations. The models used are the Specific Anthropomorphic Mannequin (SAM) and two realistic models of human head (a 34 years old adult and a 6 years old child). The simulations were performed using the finite difference time domain (FDTD) method and the frequency used to feed the antenna was 2.45 GHz. All the results are below the safety recommendations set up by the International Commission Non-Ionizing Radiation Protection (ICNIRP) and the Federal Communications Committee (FCC). Among the heterogeneous models, the highest peak spatial Specific Absorption Rate (psSAR) values are estimated for the children. For 1 g psSAR the child heterogeneous model shows highest value in comparison to the SAM model.
rate; Specific time-domain
SAR evaluations in the human body from a tablet computer
is increasing in recent year. A substantial concern has risen
regarding the possible adverse effects on human health [
Two available [
These models are shown on Fig. 4. The first one is a 34
years old adult man (DUKE) and the second is a 6 years old
boy (THELONIOUS). The different tissue dielectric
parameters used in these simulations were obtained from [
Fig 3. SAM phantom (homogeneous model) with Tablet. (a) 34 years old adult man (DUKE) (b) 6 years old child
(THELONIOUS)
Tissue Fat
Bone Grey matter White matter Liquid Brain
Muscle Aqueous Humor
Skin Crystalline
Sclera Vitreous Humor
Cerebellum
Nerve εr 0.104 0.394 1.807 1.215 66.243 52.729 68.208 38.007
Some international organizations recommend the evaluations and exposure limits to electromagnetic fields generated by wireless devices near the human body (e.g., [35]). Table V shows some recommended exposure limits.
The IEEE 1528.2003 standard [
The IEC 62209-1 and IEC 62209-2 standards [
The 10 g and 1 g psSAR were estimated and are shown in
Table VII and Fig. 5-6. All the results simulated are below the
FCC psSAR limit [
In the simulations for 1 g of tissue, the highest psSAR value is in the children head model (Fig. 5).
In the simulations for 10 g of tissue, the highest psSAR value is in the SAM Phantom, and in the heterogeneous models, the highest psSAR value is in the children head model (Fig. 6). psSAR X Distances X AGE (1g)
All the simulations in this work were performed using a computer Intel Core i5 3470 at 3.4 GHz equipped with 32 GB of RAM, NVidia Tesla C1060 GPU card, and Windows 7 Professional x64 operating system, available in the communications laboratory (LACOM) of the Federal University of Rio Grande do Sul. The finite difference time domain-FDTD method was used to simulate different scenarios for the models and to estimate the SAR.
A tablet, including the antenna and the box, was simulated at 2.45 GHz assuming 30 mW normalized radiated power and the distance between the eye lens of the head models and the tablet was 150 mm. The SAR in the head models is estimated in each situation of exposure.
In Table VI the absorbed power percentages are shown in each case. The estimation with the SAM phantom shows that 5,5 % of the energy was absorbed by this model. For the Adult Head model 4,71 % of the energy was absorbed and for the Children Head model 3,97 %. In the Fig. 7 the radiation pattern as well as the SAR in a sagittal slice are shown. 0.014 0.013 0.012 0.011 0.01 0.008 0.006 0.004 0.002 0 1g SAM
psSAR X Distances X AGE (10g)
The 1 g and 10 g of tissue psSAR produced in the head of Tablet user’s was simulated when a PIFA antenna was employed in three different head models.
The homogeneous SAM phantom head model did not present the higher levels of the 1g psSAR. Therefore, according to these simulations, in 1g volume the SAM is not conservative. It is recommended that the existing mobile devices certification process should be complemented: • • • • … with an FDTD computer simulation process, … using anatomically based models, including those representatives of the children, … measuring the SAR, averaged over smaller volumes, …and in different tissues.
Then certification should be approved only if all tests result in psSAR below the recommended limits.
The psSAR simulations in heterogeneous models (adult and child) show higher levels in the children model. The possible reasons for the higher SAR estimated in the child head model compared with adult model can be due to different reasons (e.g. thinner skull, higher dielectric parameters, smaller dimensions, etc.).
It is very important to remark that the recommendations and the standards usually adopted in different countries only consider the health effects of short time of exposure. Adults, adolescents and children may use these devices for many hours a day, many days a week and many weeks each year. Then these exposures should be reduced in order to reduce the health risks and the standards should be revised again since the last review was many years ago.