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Abstract

Contents

Introduction

Over the last half century the powerful circumstance of the environmental pollution called electromagnetic radiations of a technogenic origin is appeared [1, 2]. It was connected to use of new radiofrequency ranges, TV broadcast, different means of observation, a radio communication and so on. Such sources creates a zone of uniform radio covering which increases electromagnetic background of environment.

The analysis of a problem revealed that mobile communication most strongly influences environment and health of the person.

1 Topic relevance

The World Health Organization (WHO) embody the electromagnetic International project (WHO International EMF Project). It shows significance of this problem internationally. All developed countries have the programs for study of influence of electromagnetic radiations on the person and environment. Thanks to evolution, live organisms could adapt to a certain level of an electromagnetic radiation. A sharp increases of this level is causes tension of organism adaptation possibilities. In case of long‑time influence, the organism can not withstand and it will lead to irreversible consequences at the system level. Relevance of this problem and its high significance for society became the reasons for writing of this master's work.

2 Goal and tasks of the research

Research objective is creation of model of interaction of microwave radiation of the mobile phone with the human head.

Main objectives of research:

  1. Creation of model of the head of the person on the basis of average anatomical data, simulation of the mobile phone.
  2. Calculation of specific absorption rate of electromagnetic energy (SAR) in layers of model of the head of the person. Emitted frequencies will conform to the most widespread standards of cellular communication.
  3. Simulation of local heating of tissue from the microwave radiation of the mobile phone.
  4. Search of factors in case of which microwave radiation from the mobile phone renders less harm to health of the person.
  5. Comparison of results of simulation of the program with results of other researchers and the general conclusion on the topic.

3 Characteristics of anthropogenic sources of electromagnetic radiation

All existing sources of an electromagnetic radiation can be divided into two groups [3].

1. Sources of low frequency radiation (0–3 kHz)

This group consist of devices for production, transmission and electricity consumption — power stations, power lines, electronic devices in houses and offices, including personal computer, railway and city transport with electric drive.

2. Sources of high frequency radiation (from 3 kHz to 300 GHz)

This group is more extensive. It contains sources of reception and information transfer — TV broadcasting, amateur radio transmitters, mobile communication, cordless telephones, radar stations, communications satellites and navigation. Also the microwave technology equipment, microwave ovens, electronically ray instruments — monitors, TV sets and so on. Currents of high frequency are often applied in medicine to treatment of diseases.

The main technogenic sources are:

4 Mobile communication as a factor in the negative impact on human health.

In recent years cellular communication was very strongly developed. Levels of electromagnetic radiation are low, but their continuous impact on an organism isn't studied up to the end. The number of people who buy mobile devices grows every year. Statistical data [4] for the fourth quarter 2015 were published in the last report of the Ericsson company (Ericsson Mobility Report). In them it is specified that 68 million new subscribers were connected during this time. The total quantity of the active SIM cards in world is 7,3 billion. The actual number of subscribers of mobile communication is approximately equal 4,9 billion. It is because one person often uses several devices or uses one device with several SIM cards. Global mobile subscriptions are growing around 5 percent year‑on‑year. India grew the most in terms of net additions during the quarter (+13 million), followed by China (+7 million), the US (+6 million), Myanmar (+5 million), and Nigeria (+4 million). By results of research [5] in Russia more than 247 million people use services of cellular communication.

At the moment many megalopolises are in a difficult situation. Base stations of cellular communication emit the power equals capacities of all radio engineering objects with a frequency of operation from 300 MHz to 30 GHz [6]. Power which is emitted by a base station depends on the number of the connected subscribers in a certain interval of time. Frequency and modulation of base station depend on the standard of mobile communication. Frequency ranges such as GSM‑900 and GSM‑1800 (table 2) are used in most parts of the world [7].

Table 1 — The range of frequencies and radiated power of cellular phones and base stations
Standart Operating frequency range, MHz The maximum radiated power, W Radius of cell, km
Base station Mobile phone Base station Mobile phone
GSM‑900, digital 925–965 890–915 40 0,25 0,5–35
GSM‑1800, digital 1805–1880 1710–1785 20 0,125 0,5–35

From the table we can see that the mobile phone will emit less output power, when the frequency of its work higher.

Impact of electromagnetic radiation of the mobile phone on a human body, we will address to the medicine.

Distribution of electromagnetic radiation of the mobile phone significantly changes when the subscriber talking by phone, the human head absorbs from 10,8 to 98 % of emitting energy [8].

Bioelectric brain activity changes under the effect of mobile phone radiation. It increases activity of alpha‑2, beta‑1 and activity of beta‑2 [9], decreases amplitude of slow brain potentials during irradiation during the execution of the test job [10] and changes delta wave activity [11]. With the help of volunteers, experiments were conducted in which it was found that exposure of cellular telephone degrades performance perform tasks that require attention and manipulation of information in short‑term memory [12].

Ultra high frequency (UHF) range is distinguished by its influence on biological objects from other, lower radio frequency bands. Its radiation can directly heat the body tissue [13]. The most intensive influence is subjected to a human head portion, which is adjacent to the antenna of mobile phone. Mobile phone users often complain of a feeling of warmth in the ear, pain in the head, burning face skin, lasting about 2 hours after the call [14]. Activity of several enzymes in tissues may vary, in particular, may increase the activity of the enzyme NO‑synthase and increase production of nitric oxide that causes changes in an extracranial hemodynamics, which is regarded as one of the mechanisms of biological effect of electromagnetic radiation [15, 16].

Standing Committee of the Council of Europe Parliamentary Assembly (PACE) in report the fact that the radiation from mobile phones and Wi‑Fi have a negative impact on all living things, provoking the development of brain tumors and disrupts male reproductive function was declared [18].

4.1 Preventive measures against the harmful effects of electromagnetic radiation created by mobile phones

As a personal preventive measures against the harmful effects of microwave radiation of mobile phones, it is recommended [19]:

  1. Once you have dialed the number, not bring the phone to your ear. At this time, radiation is the strongest, as the phone communicates with the base station.
  2. After 3 or 4 minutes of conversation you need to give your body to recover for 20–25 minutes.
  3. When talking on the phone remove the glasses with metal rim. Presence of such a frame, which plays the role of emitter, can lead to an increase in the intensity of the electromagnetic radiation falling on certain areas compared with a standard situation.
  4. Use a wireless headset. In fact, the wired headset increases the radiation exposure to the ear canal. The wire from the headset not only transmits the radiation of the phone itself, but also serves as an antenna for the electromagnetic radiation from the outside.
  5. Do not use the phone in tight, trimmed metal spaces such as cars and elevators. The metal shell will act as a Faraday cage, reflecting phone radiation back to the people inside.
  6. Do not call if the signal strength indicator is almost zero. In this case, the mobile phone has more power of electromagnetic radiation.
  7. Do not bring the phone in a pocket and do not wear it on a belt when it is turned on. Tissue lower part of the human body has good electrical conductivity and absorb electromagnetic radiation faster than the tissue of head.
  8. Many people use their mobile phone as an alarm clock in the morning. In this case, it should be at a distance of at least 50 cm. This distance significantly reduces the possibility of influence on the person.
  9. Buying phone with low specific absorption rate (SAR).
  10. If possible, use SMS, follow the rules of etiquette of mobile phone use [17, 20].

5 Methods of calculation of the specific absorption rate of electromagnetic energy using CST STUDIO SUITE

CST STUDIO SUITE is a powerful complex [21] from the company Computer Simulation Technology, with which it is possible to produce three‑dimensional modeling of objects of different shapes [22]. A three‑dimensional structure is created by drawing simple geometric shapes and performing logical operations on them [23]. You can import models from third‑party programs.

After creating a construction, specifying boundary conditions and determining the location of the excitation source, the entire space of the problem is divided into a grid, and then at each point is calculated field.

Depends on the distance from the antenna, the surrounding space may be divided into a proximal zone and the radiation zone [24]. The border zone is located on the far distance:

Formula 1

(1)

where D — the largest dimension of the antenna;

λ — wavelength.

Proximal zone can be divided into two subareas: the area of radiation and reactive zone. The radiation area located closer than 2D2 / λ to the source, the radiation power is changing rapidly with distance from antenna. The area near the antenna, which is dominated by the reactive components, known as reactive domain. Law changes the field from distance depends on the type of antenna. For most antennas, transition boundary between area of radiation and reactive zone is located (0,2…0,4) D2 / λ.

Numerous results of mathematical modeling and experimental studies suggest that [24]:

These results refer to the frequencies at which the largest dimension of the body is small compared with the wavelength. Thus, for an antenna of 10 cm, operating at 900 MHz, and situated in the free space, the distance 2D2 / λ is approximately 6 cm. This means that near field of an antenna is located about radiation sources. If we consider the field of mobile phone at the time of conversation, in this zone electromagnetic energy will be absorbed in human head. It has been shown that about 40–50 % of of the radiated microwave power re reflected between the antenna and head. Most of the absorbed power is concentrated in the area near to the antenna. The anatomy of the head and heterogeneity of its tissue affect the maximum value and the SAR distribution in the cell phone user's head. However, total SAR in the head is same for a homogeneous or inhomogeneous model.

Attributes field in the near field near biological object [24]:

The field in the far field is a plane wave, regardless of the emitter configuration. Electric and magnetic fields are connected through a full environmental resistance. RF power transition from air to the planar tissue is from 20% to 60 % for radio frequencies. However, this value may be higher and the energy can reach a greater depth in the bodies with curved surfaces. In fact, the RF energy is resonance energy. This energy absorbed by a head in the range 400...1500 MHz, and the maximum of SAR value can be near the center of head. For elongate bodies in which a large ratio of height to width, RF energy interaction with biological systems depends on the polarization of the electromagnetic wave electric field

The basic idea of calculating the power absorbed in the head of mobile phone user, is to use a special mode for calculation output results of the field module: along the line (LINE), crossing construction through. In this case, we can calculate the dependence of the modulus of the field on the coordinate distance before the antenna (figure 1).

The phone is covered on all sides with plastic with dielectric constant 2,2. The thickness of this plastic, as well as the shape of the case, impact on the simulation results that is the subject of research.

Mobile phone close to the user's head

Figure 1 — Mobile phone close to the user's head

By definition, the specific absorption rate (Specific Absorption Rate — SAR) of electromagnetic energy — an indicator that determines the energy of the electromagnetic field is absorbed in the body tissue in one second. This indicator assesses the harmful effects of mobile phones per person. SAR measurement unit is W/kg.

If the field strength in the tissue is know:

Formula 2

(2)

If the current density in the tissues is know:

Formula 3

(3)

If the temperature rise in the tissues is know:

Formula 4

(4)

where Е — electric field, V/m;

ρ — density of human tissue in kg/m3;

J — current density (in A/m2), caused by electric and magnetic fields (maximum permissible level for humans which exposed to similar influences in professional work — 10 mA/м2; for the rest — 2÷10 mA/m2);

σ — the electrical conductivity of the human tissue, S/m;

c — thermal capacity of human tissues, J/(kg×K);

dT/dt — the time derivative of the temperature of the human tissue, К/с.

Formula (2) can be used, if known the values of the field intensity E in the selected points of the head model. Field Analysis is possible to limit the points most closest to the antenna system or for most characteristic directions.

Example of distribution of the SAR rate for 900 MHz per 10 gram of tissue is shown in figure 2

SAR distribution inside the mobile phone user's head

Figure 2 — SAR distribution inside the mobile phone user's head
(animation: 6 frames, 10 cycles, 144 kb)

For the analysis of wave propagation in a dielectric medium with heavy losses need to use the concept of the complex permittivity:

Formula 5

(5)

where ε — is a real part of the relative permittivity of the material;

ω = 2πf — the frequency of the propagating wave;

ε0 = 8,854×10−12 F/m.

Introduction of the complex permittivity reflects the fact that the conducting body there are socalled external currents that occur due to the excitation of the external source (as opposed to the polarization currents, which are explained only movement of dielectric charge). The value of the real part ε says about the intensity of the polarization process, while the imaginary part describes the density of conduction currents. When representing a number in the complex plane, it is possible to characterize the connection between the real and the imaginary parts of the dielectric loss angle. In practice, most commonly used by the tangent of this angle:

Formula 6

(6)

Calculated using the formula (6) the dielectric loss tangent is used in the program CST MWS.

Conclusion

Currently, the design of microwave structures associated with the selection, description and confirmation of the authenticity of the selected model. Building authentic model puts the task of calculating and analyzing the characteristics of the system, which will be implemented in the device. Modern software for the simulation and analysis of microwave devices does not guarantee the construction of a reliable model, it should be developed empirically based on independent research. It should also be stressed that despite the variety of modeling programs, they can not change the attitude to the mandatory knowledge of technical and related disciplines. In modern simulation there is a need to considering the problem in several programs (using various methods of calculation), and only in the case of getting a similar results it could be considered that model is built correctly.

This master's work is not completed yet. The turn of final completion: June 2017. The full text of the work and materials on the topic can be obtained from the author or his head after this date.

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