1P4b_0260

260 PIERS Proceedings, Kuala Lumpur, MALAYSIA, March 2730, 2012

Estimation of Electromagnetic Exposure Level Based on aMultilayered Model of the Pelvic-hip Region

M. Macedo and M. YarlequePontificia Universidad Catolica del Peru, Seccion Telecomunicaciones

Av. Universitaria 1801, Lima-32, Lima, Peru

Abstract Intensive research has been addressed to determine the effect of nonionizing radi-ation on head and human body. In this paper, a specific model for analyzing the EM exposurewithin the pelvic-hip region is proposed and simulated by FDTD method. This model includesseven layer and vital organs of the male and female anatomy. It is observed the most of theradiation is located within the outer layer, and minimum exposure in vital organs.

1. INTRODUCTION

Within the last years, mobile phones and wireless devices usage has been rapidly spread globally.When these devices are used in close proximity to any part of the human body, the electromagnetic(EM) interaction with the body could be complex and affected by many factors. One figure toevaluate this interaction is the specific absorption rate (SAR), which measure the power absorbedby a biological tissue.

SAR can be determined through numerical calculation or simulations on 3D Maxwell solvers oralternatively by employing phantoms [1]. SAR studies at the head [2, 3] were developed in the lastyears considering mobile phones as a source of radiation, whereas SAR full body calculation hasbeen developed as well, but this analysis considers a base station as radiation source [4, 5].

Nowadays, there is a trend to place wireless device close to the hip-pelvic region, for instance,mobile phones inside the pants pockets, laptop computers on the lap, and so forth. The electromag-netic emission of this device is likely to make an impact on vital organs and other tissues that arearound the hip. Then, it is important to assess the effect of this radiation. To our best knowledge,SAR determination on the pelvic region of the body has not been developed yet, and then themain aim of this paper is to determine SAR (W/kg) for the pelvic region and hip area throughsimulation software. Knowing hip anatomy, we propose a seven-layer model for the pelvic and hiptissues plus internal organs. Based on this new model, the EM exposure level is determined.

2. NUMERICAL METHOD AND MODELLING

2.1. General CharacteristicsBasic models for power absorption of tissue layer are based on the interaction of an EM waveimpinging on multiple layers interface, as it can be observed in Fig. 1. Elemental equations canbe established to determine the propagation of this wave throughout the different layers [6]. Thefundamental property in this interaction is the complex propagation constant.

The propagation constant of the wave depends on the electrical properties of each interface.The amount of energy transmitted to another interface depends on the type of the material in eachlayer. Fig. 2 shows the behavior of electrical properties in biological tissues.

Figure 1: EM wave impinging on multiple layers. Figure 2: Electrical properties of biologi-cal tissues [12].

Progress In Electromagnetics Research Symposium Proceedings, KL, MALAYSIA, March 2730, 2012 261

The conductivity () at low frequencies largely depends on the fraction occupied by the ex-tracellular fluid in the tissues. Over 100MHz, conductivity has dissimilar properties in tissues;and exists a relaxation at frequencies below 1GHz. Moreover, conductivity increases directly withrespect to frequency [7]. On the other hand, the permittivity () decreases with frequency incre-ment. dispersion at low frequencies is due to several physical processes, meanwhile dispersionis notable for the frequency range from 0.1 to 10MHz. dispersion takes place at 25GHz at bodytemperature, in which water is distributed in 80% of the volume of most tissues [7].

Considering the tissue layer model and their electrical properties, the electromagnetic fields canbe solved. Then, the specific absorption rate could be defined as in (1).

SAR =

2|Etiss|2 = 2pif02 |Etiss|

2 (1)

where is the volume density and Etiss is the peak value of electric field present in that portionof tissue. SAR units are then watts per kilogram (W/kg). Actually, (1) defines the local SAR, theaverage SAR could be determined as in (2)

AverageSAR =(SARdv)V

(2)

where V is the volume of the model and dv the volume of each cell. The integral could be calculatedover the whole exposed object, as well as, over samples of 1 gram or 10 grams, which determinethe volume of each sample. The average values for 1 gram and 10 grams mass are employed inthis work. The concept of SAR is very useful to quantify the interaction of RF radiation on livingtissues and extends up to 10GHz.

2.2. Male and Female Model StructureThe pelvic-hip region has been modeled in different ways. For instance, a planar distribution oftissues was developed in [7] while, a three-layer cylindrical structure was employed in [8]. Thedeveloped model consists of seven layers, which represent all the tissues between the organs andthe skin surface, plus five organs. These layers are modeled as a cylindrical structure (see Figs. 3(a).and 3(b).).

The cylindrical structure consists of an elliptical base with diameter ratio of 1.6 for male andfemale 7-layer model. Skin tissue (including penis only for male model), adipose tissue, muscletissue, bone tissue, nervous system, blood, body fluid are considered for the structure. The followingorgans are considered for male model: colon (1) bladder (2), prostate (3), kidney (4), and testis (5)as shown in Fig. 3(a) Similarly, the following organs are considered for female model: colon (1),uterus (2), bladder (3), kidney (4), and ovaries (5), as shown in Fig. 3(b).

The thickness values of each layer of the model are detailed in Table 1(a) [7]. The organs shapesare modeled as a flattened ellipsoid and spheres, and the sizes of these are according in proportionto the cylindrical structure, and are reported in Table 1(a). Density values of tissues and organsare established as is described in [5], and are reported in Table 1(b) Colon, prostates, ovaries anduterus are not specified in [5]; nevertheless these organs have similarly characteristics with the

(a) (b)

Figure 3: (a) Male model on EMPro agilent. (b)Female model on EMPro agilent.

(a) (b)

Figure 4: SAR distribution over tissues at 900MHz.(a) View of slice where the maximum SAR is located.(b) Monopole antenna tuned at 900MHz radiates overthe whole model.


Table 1: (a) Thickness values for biological tissues. (b) Volume density values for biological tissues.

(a) (b)Table 2: Permittivity and conductivity values for biological tissues [10].

muscular layer, as it is explained in [9]. The electrical properties of the tissues layers and organsare shown in Table 2. These conductivity (S/m) and relative permittivity values for each tissue ofhuman body are calculated from [10].

3. RESULTS AND DISCUSSION

To evaluate the SAR in the pelvic-hip region, the following sceneries will be analyzed:Mobile phone radiation in the 900 and 1800MHz bands.Laptop radiation in 2.4GHz, through Wi-Fi and Bluetooth wireless connection. Mobile phones

also can establish connections through these technologies.Two-way radio handheld radiation in 150MHz (VHF) and 450MHz (UHF) band.The devices operating at these frequencies commonly cause EM radiation over the regions that

are analyzed in this work. The simulation is executed in Agilent EMPro with the following param-eter: FDTD solver, perfectly matched layer (PML) absorbing boundaries, base cell size of 1.3mmand 1GB of memory required for the simulations.

3.1. Mobile Phones Band Radiation

A quarter-wavelength monopole antenna is used as radiator for both 900MHz and 1800MHz, withdifferent sizes at each frequency (8.16 and 4.07 cm respectively). It is provided at the antennaoutput a radiation power of 0.25W at 900MHz and 0.125W at 1800MHz. The distance betweenthe antenna and the object in radiation exposure is 3 cms. Once the simulation is executed, thedistribution of specific absorption rate, at 900MHz, is obtained and is shown in Fig. 4. The smallred objects observed in Fig. 4 and Fig. 5 corresponds to the ground plane of the monopole. Themonopole can not be observed because is very thin SAR peak of 1.1W/Kg is located at the first

Progress In Electromagnetics Research Symposium Proceedings, KL, MALAYSIA, March 2730, 2012 263

(a) (b)

Figure 5: SAR distribution over tissues at1800MHz. (a) Monopole antenna tuned at1800MHz radiates over the whole model. (b) Viewof slice where the maximum SAR is located.

(a) (b)Figure 6: SAR distribution over tissues at 150MHz.(a) Monopole antenna tuned at 150MHz radiatesover the whole model. (b) View of slice where themaximum SAR is located.

Table 3: Final results.

outer layer, i.e., within the skin. It is observed that radiation attenuates rapidly, passed the skinlayer. These results are obtained from the male model; similar results are obtained for the femalemodel (see Table 3).

At 1800MHz, the characteristics of permittivity and conductivity of the model layers and organschange, with higher conductivity and lower relative permittivity (see Fig. 2 and Table 2). The modelwas updated with these new values and the simulation output is presented in Fig. 5. In this case,a SAR maximum of 0.38W/Kg is observed in the second outer layer (adipose tissue). Likewise,the radiation attenuates rapidly, passed this adipose layer. These results, obtained from the malemodel, are approximately similar to the ones obtained for the female model (see Table 3).

3.2. Wi-Fi and Bluetooth RadiationAt 2.4GHz, a half-wave dipole antenna is commonly used for Wi-Fi technologies and Bluetoothconnections, and it is employed as a radiator (5.4 cm of length) for SAR calculation in this case. Aradiation power of 0.45W for WiFi antenna, and 0.12W for Bluetooth, is provided for the analysis.The distance between the radiator and the object is of 10 cms. From the Wi-Fi simulation, amaximum SAR value of 0.147W/kg is obtained, and is located within the skin layer. In the caseof Bluetooth radiation, a maximum SAR of 0.058W/kg is determined, which is lower than Wi-Fivalue, as expected. The values for male and female are similar (see Table 3).

3.3. Two-way Radio Handheld RadiationThere are two frequency bands to be analyzed. At VHF, two-way radios operate at frequen-cies around 150MHz, while at UHF, these devices can be tuned from 410 to 450MHz, being thefrequency of 450MHz chosen for the analysis. Larger monopole antennas (50 and 16.66 cm respec-tively) were designed. The distance between the antenna and the object is 9 cms. A radiationpower of 4W and 3W is provided for the VHF and UHF simulation.

At 150MHz, it is observed that the maximum SAR of 0.678W/kg is located in the kidney tissuefor the female model (this can be visualized in Fig. 6), while in the male model is located in thefirst outer layer. The small red object observed in Fig. 6 corresponds to the ground plane of themonopole. Definitely the wavelength at 150MHz is larger than the structure of simulation; and thelayer and interfaces of the skin, fat, muscle, bone and so forth, are not large enough to mitigatethis long wave.


At 450MHz a maximum SAR value of 0.797W/kg is calculated from the male model. Thismaximum is within the skin layer, the first outer layer, which absorbs a large amount of power.Similar values are obtained for the female model (see Table 3). The SAR values obtained are greaterthan in the case of 150MHz, and this is consequence of the shorter wavelength and the interactionwith the different layers sizes and conductivity.

Finally, a summary of the results obtained for all cases is reported in Table 3.All these simulations and results are obtained by employing short EM pulses (for instance

0,0001s). This pulse contains several harmonics components; however only the harmonic com-ponent at which the antenna is tuned will be radiated to the object. As part of the radiation isabsorbed and converted into heat, the authors considers that temperature may increase slightlyin the body and the dielectric properties may vary, as a result the exposure time may affect theanalysis of the SAR value.

The results of the specific absorption rate (SAR) averaged for the pelvic region and hip areaare lower than the value recommended in the standards of ICNIRP [11]. In addition the maximumSAR value was always lower than the exposure limit value specified by the ICNIRP (2W/kg).

4. CONCLUSION

In this paper, a model of seven layers and vital organs of the pelvic-region for the male and femalehas been proposed and simulated. The EM exposure within the pelvis is calculated from differentradiation devices. The maximum and average SAR value are obtained and it is observed that mostof the radiation is localized in the outer tissue layer, with minimum exposure within vital organs,except for a particular case (at 150MHz and in the female model). The latter will be furtheranalyzed in a following research.

REFERENCES

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2. Ghandi, O. P., G. Lazzi, and C. M. Furse, Electromagnetic absorption in the human head andneck for mobile telephones at 835 and 1900MHz, IEEE Transactions on Microwave Theoryand Techniques, Vol. 44, 18841897, 1996.

3. Dimbylow, P. J. and S. M. Mann, SAR calculations in an anatomically realistic model of thehead for mobile communication transceivers at 900MHz and 1.8GHz, Physics in Medicineand Biology, Vol. 39, 15371553, 1994.

4. Bernardi, P., M Cavagnaro, S. Piza, and E. Piuzzi, Human exposure to radio base-stationantennas in urban environment, IEEE Transactions on Microwave Theory and Techniques,Vol 48, 19962003, 2000.

5. Martnez-Burdalo, M., A. Martn, M. Anguiano, and R. Villar, On the safety assessment ofhuman exposure in the proximity of cellular communications base-station antennas at 900,1800, 2170MHz, Physics in Medicine and Biology, Vol. 50, 41254137, 2003.

6. Hayt, W., Electromagnetic Theory, 7th Edition, McGraw Hill, 2006.7. Polk, C. and P. Elliot, Handbook of Biological Effects of Electromagnetic Fields, 2nd Edition,

CRC Press, 1996.8. Nishizawa, S. and O. Hashimoto, Effectiveness analysis of lossy dielectric shields for a three-

layered human model, IEEE Transactions on Microwave Theory, Vol. 4, 277283, 1999.9. Carpi, A., Basic anatomy Tissues and organs, John Jay College of Criminal Justice, 1999,

http://web.jjay.cuny.edu/acarpi/NSC/14-anatomy.htm.10. Gabriel, C., Compilation of the dielectric properties of body tissues at RF and microwave

frequencies, Report N.AL/OE-TR- 1996-0037, Occupational and Environmental Health Di-rectorate, Radiofrequency Radiation Division, Brooks Air Force Base, Texas, USA, June 1996.

11. ICNIRP, Guidelines for limiting exposure to time-varying electric, magnetic and electromag-netic fields, International Commission of Non-ionizing Radiation Protection, 1998.

12. Sebastian, J., Medicion en radiacion de seres vivos, Investigacion y Ciencia, Madrid, 2006.

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