1. Presentation by DR. Assoc. prof. VASIL TABATADZE
Human EM Exposure Study for Some Big Scenarios
Presentation by
DR. Assoc. prof.
VASIL TABATADZE

2. Overview Introduction Problem statement for the first task
Theoretical part for the first Problem
The results of numerical simulations
Problem statement for the second task
Theoretical part for the second Problem
Room wall transparence variation
Conclusions

3. Human discrete model, "Virtual Family", IT’IS Foundation
Introduction
Our group in Tbilisi have been working on EM exposure simulations for 20 years using FDTD Method and on the human discrete non-homogenous models.
This method does not fully describes the whole picture to study EM exposure in case of big models and scenarios because of very long period calculation time and powerful computer resources.
Also using FDTD Method we can’t evaluate the accuracy of the calculation.
Human discrete model, "Virtual Family", IT’IS Foundation

4. Introduction
The electromagnetic (EM) background around us increases every year. The influence of a mobile phone is maximal when it is located close to the user. It depends also on the objects around the user. Besides, it is interesting to study how radiated pattern depends on the different surrounding object scenarios, including ones with a user located in a room with a window.
Most of the building walls are made of Ferro-concrete material, which at some frequencies rooms are good resonators. These resonance frequencies are in the mobile frequency range. This means that when the user of the mobile phone during the communication is inside of the building the amplitude of the field radiated by the phone is amplified by the walls because of several reflections. As the numerical experiments show the value of this field becomes much bigger than outside of the building. Thus the presence of the walls and windows inside the room has to be considered.

5. Problem statement
We consider the diffraction problem of the EM field radiated by the mobile phone and scattered by the user and the room walls considering also, the windows. Our interest is to study the average effect on the users. There is, big difference in the shape, weight, and height of the mobile phones and different human body sizes and anatomy (there are big deviations of this parameters) and because of the simplicity of the computer simulations, we've simplified the human body geometry and as a source we considered hertz dipole.
Model geometry
In our model the human body is homogenous with the averaged permittivity and its lossy parts equals to the human’s muscle tissue. We consider a “Mummy” as a human model.
The electric dipole is located near to the user’s head. Our goal is to find the near field distribution inside of the human body as well as inside and outside of the room. We estimate also radiated far field pattern.

6. Theoretical part
From the theoretical point of view this problem corresponds to the diffraction of the harmonic in time EM wave by the homogenous dielectric surrounded by the semi open conducting surface. The stated problem is solved by the Method of Auxiliary Sources (MAS).
Application of the MAS is reduced to the construction of two couples of closed auxiliary surfaces inside and outside of the human body and also inside and outside of the semi open room surface. On these auxiliary surfaces are distributed the auxiliary sources. According to the proposed algorithm the open parts of window surface are considered as the free media with the permittivity of the air.
The unknown complex amplitudes of the auxiliary sources are found by the boundary conditions satisfaction for the scattered field on the human body model - as on the dielectric (the continuity of the electric and magnetic field tangential components). On the conducting semi open surface inside and outside (the tangential component of the electric field must be zero) and on the open parts (windows) of the room (as on the dielectric) – continuity of the fields.
So, according to the above mentioned method we construct the geometries of the auxiliary surfaces at certain distance from the body surface and the semi open surface these auxiliary surfaces repeat the form of the scattering objects.

7. Theoretical part
An auxiliary sources are chosen two mutually perpendicular combined dipoles and with the corresponding unknown complex amplitudes. The field of the combined dipole is determined by the following expression:

8. Theoretical part
The system of the auxiliary sources, distributed on each auxiliary surfaces must describe the scattered field in the opposite part of the space. Unknown field inside and outside of the dielectric body is expressed by the outer auxiliary sources.
Outside the body the field , is represented respectively as a sum of the fields radiated by the antenna , inner auxiliary sources of the human body and also outer auxiliary sources of the semi open surface:
The field outside the whole structure is represented by the inner auxiliary sources of the semi open surface:
Unknown complex amplitudes , , , , , , , , where n=1,2,…,N, m=1,2,…,M, could be found from the boundary condition satisfaction using the collocation method. For them we get the linear algebraic equation system, the number of which coincides to the number of unknowns.

9. The Results of Numerical Simulations
Based on the above mentioned algorithm we have created a program package which gives us ability to study near field inside and outside of the room and estimate far field pattern.
Using the program package we have studied several cases, changing room wall transparence, window size, source frequencies and other parameters. Obtained results are presented below. In all of the results the polarization of the source is Y - which is perpendicular to the Figures. Also we have presented the near Electric field Y component in order to well see the boundary condition satisfaction on the room surface and also on the human body.
Every calculations are carried out on the room with dimensions : 4 x 5 x 3 m
Human height cm
Human head diameter – 17.5 cm
Human body epsilon ɛ = 45 + i 2

10. The Results of Numerical Simulations
Field Distribution at 300 MHz
Near field and far field pattern in the room, window size 2.6 x 2.0 m
Near field and far field pattern in the room, with reduced window size 2.0 x 1.6 m
Near field and far field pattern in the room, window size 2.6 x 2.0 m. Auxiliary sources number is reduced.
Near field and far field pattern when there is no room

11. The Results of Numerical Simulations
Field Distribution at 450 MHz
Near field and far field pattern in the room, window size 2.6 x 2.0 m
Near field and far field pattern in the room, with reduced window size 2.0 x 1.6 m
Near field and far field pattern in the room , window size 2.6 x 2.0 m. Auxiliary sources number is reduced.
Near field and far field pattern when there is no room

12. The Results of Numerical Simulations
Field Distribution at 900 MHz
Near field and far field pattern in the room, window size 2.6 x 2.0 m
Near field and far field pattern in the room, with reduced window size 2.0 x 1.6 m
Fig.13. Near field and far field pattern in the room, window size 2.6 x 2.0 m. Auxiliary sources number is reduced.
Near field and far field pattern when there is no room

13. The Results of Numerical Simulations
Field Distribution in human head at 300 MHz
Near field in the room, with window size 2.6 x 2.0 m
Near field in the room, with reduced window size 2.0 x 1.6 m
Near field in the room, with window size 2.6 x 2.0 m
Auxiliary sources number is reduced.
Near field when there is no room

14. The Results of Numerical Simulations
SAR Distribution in human head at 300 MHz
SAR Distribution for human head, room with window size 2.6 x 2.0 m
SAR Distribution for human head, room with reduced window size 2.0 x 1.6 m
SAR Distribution for human head, room with window size 2.6 x 2.0 m. Auxiliary sources number is reduced.
SAR Distribution for human head, when there is no room

15. Statement of a Second Task
In this part our goal is to investigate the case when the electromagnetic source is the base station’s antenna. The human model is located inside of a room with a window. In this study the non homogeneity of the human tissues is not considered since it does not affect the final results so much. So, as a human model was used “Mummy”, homogenous dielectric of a human shape.
Base station has pretty high intensity radiation. If the room is nearby, the field which penetrates inside the room may be amplified because of the resonant effects. In frames of this work we plan to show that in order to determine how far the base station antenna should be located, it is important to take into account the resonant effects of the rooms considering the transparency of its walls and how the SAR value increases inside of the human.
The stated problem corresponds to the study of the diffraction of the harmonic EM wave field on a homogenous dielectric object, which is located inside of the semi open surface like room. As the base station’s EM field’s source we consider a combined dipole with definite amplitude, located outside of the room.
Our final goal is to find the near field distribution inside of the human body as well as inside and outside of the room. We have to estimate human exposure and also radiated far field pattern.

16. The Mathematical Approach
The problem is solved by the Method of Auxiliary Sources (MAS) which gives ability to solve efficiently complicated and big scenarios with minimal CPU usage.
Application of the MAS is deduced to the construction of two couples of closed auxiliary surfaces inside and outside of the “Mummy” and also inside and outside of the surrounded semi open surface like the room. Along the surfaces of the “Mummy” and so called the room, as it is possible homogeneously, are distributed the N and M numbers of combined auxiliary sources with unknown complex coefficients, which have meaning of the criterion weigh.
MAS model of cavity with using auxiliary surfaces and auxiliary sources.
These unknown complex amplitudes of the auxiliary sources must be found by the boundary conditions satisfaction using the collocation method for the scattered field on the human body model and on the open parts (windows) of the room - as on the dielectric; and on the semi open surface – as on the conductor.

17. The Mathematical Approach
The fields inside of the body is the sum of the outer auxiliary sources field:
The fields around the mummy and inside of the room , is represented respectively as a sum of the fields radiated by the antenna , inner auxiliary sources of the human body and also outer auxiliary sources of the semi open surface:
The field outside of the room is the sum of base station antenna’s field and room’s inner auxiliary sources fields:
For unknown complex coefficients we get the linear algebraic equation system, the number of which coincides to the number of unknowns.

18. The Mathematical Approach
Transmission and reflection coefficients dependence on the
collocation points and the calculation error
We introduce new approach to use the MAS methodology to easily simulate the surface transparency variations by means of the changing the accuracy of the boundary conditions satisfaction, which is necessary to study how to influence room’s walls transparency variation on the EM field exposure.
For quantitative analysis of the transparency coefficient a plane wave diffraction problem on a perfectly conducting surface has been considered. The surface has been substituted by a system of collocation points(infinite periodic lattice), where the satisfaction of the boundary conditions was required.
Transmission and reflection coefficients dependence on the collocation points, for the different lattice period, when d=0.15. T R
d=0.08
N/λ2
The dependency of the R reflection and T transparency coefficients on the collocation point’s density with N/λ2 has been investigated. By choosing the correct density, the desired transparency coefficient T can be obtained.
Transmission and reflection coefficients dependence on the collocation points, for the different d (distance between the collocation points and auxiliary surfaces)
Transmission and reflection coefficients dependence on the collocation point’s density and the calculation error, when d=0.1

19. The Results of Numerical Simulations
Structure Parameters
Several exposure scenarios with different transparency coefficients have been investigated by means of the proposed algorithm.
The human model’s dimensions:
height -1.67m
shoulder width m
head diameter m.
Room’s dimension: 4x3x2.5 (m3),
window size: 1.4x1.1 (m2).
Dielectric permittivity, ε=44+i2, (an averaged value considering blood, muscle and bones).
The calculations were conducted for two different human model positions (when human is located near the window and far from the window) at 900 MHz and 1800 MHz frequencies (main frequencies used in the mobile frequency range).
GLOBESPACE EMC & SIPI 2-3 December 2014, Tel Aviv Israel
Laboratory of Applied Electrodynamics and Radio Engineering, TSU

20. The Results of Numerical Simulations
Some numerical results when antenna is located inside of the room near the human head.
Near field distribution for two different scenarios at 900 MHz: a) user is located far from the window, b) user is located near the window, T=0.2. a) b)
For the reducing absorbed energy is optimal when user is near the window and antenna is placed in the window’s side.
This location prevents the formation of a high resonant field, so that a large part of the radiation passes through the window.
Near field distribution at 1800 MHz, when T=0.65
SAR distribution inside the human head at 900 MHz, when user is located:
a) far from the window, b) near the window, T=0.2 a) b)

21. The Results of Numerical Simulations
Base Station Antenna’s EM Field Distribution in the Room at 900 MHz
Near field distribution and far field pattern in the room at 900 MHz, when human model is located near the window; a) T=0.65, b) T=0.2 a) b)
SAR distribution inside of the human head at 900 MHz, when human model is located near the window; a) T=0.65, b) T=0.2 a) b)
Pattern of the reradiated field from the room directed to the base station position
In case of the smaller transparency because of multiple reflections of the inner field and energy storage inside the room the resonant field amplitude and also SAR are significantly higher.

22. The Results of Numerical Simulations
Base Station Antenna’s EM Field Distribution in the Room at 900 MHz
Near field distribution and far field pattern in the room at 900 MHz, when human model is located far from the window; a) T=0.65, b) T=0.2 a) b)
When the human is located near the wall far from the window, the field inside of the room amplifies more.
SAR distribution inside of the human head at 900 MHz, when human model is located far from the window; a) T=0.65, b) T=0.2 a) b)
In case of the smaller transparency the resonant field amplitude inside the room and also SAR are significantly higher.

23. The Results of Numerical Simulations
Base Station Antenna’s EM Field Distribution in the Room at 1800 MHz
Near field distribution in the room at 1800 MHz, when human model is located near window; T=0.65
Near field distribution in the room at 1800 MHz, when human model is located far window; T=0.65
When the human is located near the wall far from the window, the field inside of the room amplifies more.

24. Conclusions
In conclusion we can state that the human exposure in big rooms deserves our attention because of the possible resonant effects and high field values for enclosed and semi-open geometries, that are widely presented in our everyday life.
Some scenarios of human RF exposure inside of a room with a window has been investigated.
When using a mobile phone, the field distribution around the user is significantly different in a room compared to the open space.
A new program package for exposure simulation for semi-open geometries has been created.
We have proposed an approach for easy computer simulation methodology for modelling the variable wall transparency by means of the MAS.
It has been also shown that the resonant frequencies for such geometries are in the mobile frequency range.

25. Conclusions
A base station antenna’s field diffraction on a room with a human inside is studied. A new, MAS based, program package has been used for simulations. Numerical experiments provided by this program package showed that the field radiated by the base station antenna is amplified inside of the room because at the considered frequencies room acts as the resonator. So in order to estimate the maximal allowed value of the field the resonator properties of the room must be taken into account. The position of the human inside of the room changes significantly the field inside of the room.
In contrast to the FDTD, the MAS gives us the possibility to study the near fields around the human model, the outer objects such as walls, windows, it also makes possible to examine the resonance phenomena and control the accuracy of the solution.
A big attention is payed to the transparency of the walls, which is strictly related to the accuracy of the solution and to the number of the collocation points.
The calculations, conducted with the created program packaged, showed the presence of resonance and reactive fields in several big scenarios, which can be dangerous for a human.