CHAPTER 1 INTRODUCTON 1.1 EM INTERACTION WITH CONDUCTORS/DIELECTRICS

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1 CHAPTER 1 1 INTRODUCTON 1.1 EM INTERACTION WITH CONDUCTORS/DIELECTRICS Electromagnetic waves were first postulated by James Clerk Maxwell and subsequently confirmed by Heinrich Hertz. Maxwell derived a wave form of the electric and magnetic equations, revealing the wave-like nature of electric and magnetic fields, and their symmetry. Because the speed of EM waves predicted by the wave equation coincided with the measured speed of light, Maxwell concluded that light itself is an EM wave. According to Maxwell's equations, a time-varying electric field generates a magnetic field and vice versa. Therefore, as an oscillating electric field generates an oscillating magnetic field, the magnetic field in turn generates an oscillating electric field, and so on. These oscillating fields together form an electromagnetic wave. A quantum theory of the interaction between electromagnetic radiation and matter such as electrons is described by the theory of quantum electrodynamics. The physics of electromagnetic radiation is electrodynamics, a subfield of electromagnetism. Electric and magnetic fields obey the properties of superposition so that a field due to any particular particle or time-varying electric or magnetic field will contribute to the fields present in the same space due to other causes: as they are vector fields, all electric and magnetic field vectors add together according to vector addition. For instance, a travelling EM wave incident on an atomic structure induces oscillation in the atoms of that structure, thereby causing them to emit their own EM waves, emissions which alter the impinging wave through interference. These properties cause various phenomena including refraction and diffraction.

2 1.1.1 Conductors and Dielectrics 2 Most materials used in radio are required either to pass conduction current readily or to prevent the flow of conduction current as completely as possible. For this reason most materials in practice will fall into either good conductor or good insulator class. considered to be the dividing line between conductors and dielectrics. In a good conductor at radio frequencies the rate of attenuation is very great and the wave may penetrate only a short distance before being reduced to a negligibly small percentage of its original strength. A term that has significance under such the wave has been attenuated to approximately 37% of its original value [14] Reflection and Refraction In refraction, a wave crossing from one medium to another of different density alters its speed and direction upon entering the new medium. The ratio of the refractive indices of the media determines the degree of refraction, and is summarized by Snell's law. Light disperses into a visible spectrum as light is shown through a prism because of the wavelength dependant refractive index of the prism material (dispersion) Thermal Effects The basic structure of matter involves charged particles bound together in many different ways. When electromagnetic radiation is incident on matter, it causes the charged particles to oscillate and gain energy. The ultimate fate of this energy depends on the situation. It could be immediately re-radiated and appear as scattered, reflected, or transmitted radiation. It may also get dissipated into other microscopic motions within the matter, coming to thermal equilibrium and

3 3 manifesting itself as thermal energy in the material. With a few exceptions such as fluorescence, harmonic generation, photochemical reactions and the photovoltaic effect, absorbed electromagnetic radiation simply deposits its energy by heating the material. This happens both for infrared and non-infrared radiation. Intense radio waves can thermally burn living tissue and can cook food. In addition to infrared lasers, sufficiently intense visible and ultraviolet lasers can also easily set paper to fire. Ionizing electromagnetic radiation can create high-speed electrons in a material and break chemical bonds, but after these electrons collide many times with other atoms in the material eventually most of the energy gets downgraded to thermal energy, this whole process happening in a tiny fraction of a second. That infrared radiation is a form of heat and other electromagnetic radiation is not, is a widespread misconception in physics. Any electromagnetic radiation can heat a material when it is absorbed. The inverse or time-reversed process of absorption is responsible for thermal radiation. Much of the thermal energy in matter consists of random motion of charged particles, and this energy can be radiated away from the matter. The resulting radiation may subsequently be absorbed by another piece of matter, with the deposited energy heating the material. Radiation is an important mechanism of heat transfer. Electromagnetic radiation in an opaque cavity at thermal equilibrium is effectively a form of thermal energy, having maximum radiation entropy. The thermodynamic potentials of electromagnetic radiation can be well-defined for matter.

4 1.2 EM RADIATION 4 Electromagnetic radiation (EMR) is a ubiquitous phenomenon that takes the form of self-propagating waves in a vacuum or in matter. It consists of electric and magnetic field components which oscillate in phase perpendicular to each other and perpendicular to the direction of energy propagation. Electromagnetic radiation is classified into several types according to the frequency of its wave; these types include (in order of increasing frequency and decreasing wavelength): radio waves, microwaves, terahertz radiation, infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays. A small and somewhat variable window of frequencies is sensed by the eyes of various organisms; this is what we call the visible spectrum, or light. Ionizing radiation (IR) is capable of causing characteristic changes in atoms or molecules in the human body [70], which can result in radical tissue changes such as cancer. Non-ionizing radiation (NIR) does not cause immediate changes, but this can lead to oscillatory and long run changes, causing various slow toxic type of effects in the body. Mobile phone radiation is coming under non-ionizing radiation. Potential Sources of EM Radiation are Mobile phone/cell phone Walkie -Talkie, Bluetooth enabled devices, Wireless LAN, Notebook/lap top computers, Wireless PDA and Medical Telemetry Wave Model An important aspect of the nature of light is frequency. The frequency of a wave is its rate of oscillation and is measured in hertz, the SI unit of frequency, where one hertz is equal to one oscillation per second. Light usually has a spectrum of frequencies which sum together to form the resultant wave. Different frequencies undergo different angles of refraction.

5 5 A wave consists of successive troughs and crests, and the distance between two adjacent crests or troughs is called the wavelength. Waves of the electromagnetic spectrum vary in size, from very long radio waves to very short gamma rays smaller than atom nuclei. The speed of the wave v (c in a vacuum, or less in other media) is defined by f (1.1) where f between different media, their speeds change but their frequencies remain constant. Interference is the superposition of two or more waves resulting in a new wave pattern. If the fields have components in the same direction, they constructively interfere, while opposite directions cause destructive interference. The energy in electromagnetic waves is sometimes called radiant energy Photon Model Because energy of an EM wave is quantized, in the particle model of EM radiation, a wave consists of discrete packets of energy, or quanta, called photons. The frequency of the wave is proportional to the magnitude of the particle's energy. Moreover, because photons are emitted and absorbed by charged particles, they act as transporters of energy. The energy per photon[40] can be calculated from the Planck Einstein equation: E= h f (1.2) where E is the energy, h is Planck's constant, and f is frequency. This photonenergy expression is a particular case of the energy levels of the more general electromagnetic oscillator whose average energy, which is used to obtain Planck's radiation law, can be shown to differ sharply from that predicted by the

6 6 equipartition principle at low temperature, thereby establishes a failure of equipartition due to quantum effects at low temperature. As a photon is absorbed by an atom, it excites an electron, elevating it to a higher energy level. If the energy is great enough, so that the electron jumps to a high enough energy level, it may escape the positive pull of the nucleus and be liberated from the atom in a process called photo ionization. Conversely, an electron that descends to a lower energy level in an atom emits a photon of light equal to the energy difference. Since the energy levels of electrons in atoms are discrete, each element emits and absorbs its own characteristic frequencies. Together, these effects explain the absorption spectra of light. The dark bands in the spectrum are due to the atoms in the intervening medium absorbing different frequencies of the light. The composition of the medium through which the light travels determines the nature of the absorption spectrum. For instance, dark bands in the light emitted by a distant star are due to the atoms in the star's atmosphere. These bands correspond to the allowed energy levels in the atoms. A similar phenomenon occurs for emission. As the electrons descend to lower energy levels, a spectrum is emitted that represents the jumps between the energy levels of the electrons. This is manifested in the emission spectrum of nebulae. Today, scientists use this phenomenon to observe what elements a certain star is composed of. It is also used in the determination of the distance of a star, using the red shift. 1.3 MOBILE PHONE RADIATION Multi-band phones Today most telephones support multiple frequencies used in different countries. These are typically referred to as multi band phones. Dual band phones can cover GSM networks in pairs such as 900 and 1800 MHz frequencies (Europe, Asia, Australia and Brazil) or 850 and 1900 (North America and Brazil).

7 7 European tri band phones typically cover the 900, 1800 and 1900 bands giving good coverage in Europe and allowing limited use in North America, while North American tri-band phones utilize 850, 1800 and 1900 for wide-spread North American service but limited world-wide use. A new addition has been the quad band phone, supporting all four major GSM frequency groups, allowing for widespread usage globally, including in North America Power levels and Exposure levels In the GSM system up to eight users share the same frequency channel and each phone transmits only one eighth of the time. This means that the average power is one eighth of the peak power. 3G phones (UMTS/WCDMA) do not separate the signals in time or in frequency. Instead the signal from each phone is coded and sent simultaneously using the same frequency. GSM phones have a peak power of 2 W (GSM 800/900) or 1 W (GSM 1800/1900). The maximum average power is one eighth of the peak power, hence 250 mw (GSM 800/900) or 125 mw (GSM 1800/1900). For GPRS, the peak power levels are the same as for ordinary GSM but the average power when using two time slots can be up to 0.5 W for 900 MHz and 250 mw for 1800MHz. Table 1.1 shows the limits[68] for Maximum Permissible Exposure (MPE). For 3G (UMTS/WCDMA) the maximum power is W or 0.25 W depending on the terminal type. The RF field strength falls off rapidly with user who places the headset against the head/ear. Table 1.2 shows the limits[68] for General Population/Uncontrolled Exposure. Typical Base station antenna is about 30cm wide and a meter long, mounted on building or towers of height of 15 to 50m above ground. Intensity at ground directly under antenna is low. RF field

8 8 intensity increases slightly as one moves away from the base station and then decreases at greater distances. Typical power density values measured in India 2.Here is the most current Maximum Permissible Exposure number form the FCC (2007). Frequency Range (MHz) Table 1.1 Limits for Maximum Permissible Exposure (MPE) Electric Field Strength (V/m) Magnetic Field Strength (A/m) Power Density (mw/cm 2 ) /f 4.89/f 900/f f/ , Table 1.2 Limits for General Population/Uncontrolled Exposure Frequency Range (MHz) Electric Field Strength (V/m) Magnetic Field Strength (A/m) Power Density (mw/cm 2 ) /f 2.19/f 180/f f/ , Averaging Time (minutes) Averaging Time (minutes) Regulations and Standards North America: IEEE Std IEEE Recommended Practice for the Measurements and Computations with respect to Human Exposure to Radio Frequency Electromagnetic Fields, 100kHz to 300 GHz.

9 9 FCC OET 65- Supplement C Evaluating Compliance with FCC Guidelines for Human exposure to Radiofrequency Electromagnetic Fields. IC RSS-102- Radio Frequency RF Exposure Compliance of Radio communication Apparatus (All Frequency Bands) Europe: EN 50361:2001 -Basic Standard for the measurement of Specific Absorption Ratio related to human exposure to electromagnetic fields from mobile phones (300 3GHz) EN 62311:2008- Assessment of electronic and electrical equipment related to human exposure restrictions for electromagnetic fields (0 Hz GHz) International: IEC :2005 -Human exposure to radio frequency fields from handheld and body-mounted wireless communications devices Human models, instrumentation, and procedures. Part 1: Procedure to determine the specific absorption rate (SAR) for hand-held devices used in close proximity to the ear (frequency range of 300 MHz to 3 GHz) IEC Draft ( CDV )- Human exposure to radio frequency fields from hand-held and body-mounted wireless communications devices - Part 2: Procedure to determine the specific absorption rate (SAR) for wireless communication devices used in close proximity to the human body (30 MHz to 6 GHz) ACA (AS/NZS ) Radio communications (Electromagnetic Radiation Human exposure) Standard 2001.

10 10 ARIB STD-56: Specific Absorption Rate (SAR) estimation for cellular phones. Several groups have pushed recently to standardize test methods for SAR testing, including uncertainty calculations. Although new standards for measurement have been issued, the overall SAR limits have not changed. CENELEC and IEEE have produced similar specifications because the majority of people involved in writing them were on both boards. The CENELEC standard, EN 50360, has recently been published in the Official Journal of the European Communities as a harmonized standard. EN references EN 50361, which contains the test methods. SAR test method specification IEEE P1528 is already in draft format and should be due for release shortly. In Europe, a key problem with the CENELEC standard is that it is only concerned with devices held next to the human ear, that is, handset testing next to a phantom head. EN is applicable to all RF devices that are to be used in close proximity to the human ear. The standard does not contain the actual limits. Actual limits can be found in either the ICNIRP Guidelines (April 1998) or Council Recommendation 1999/519/EC. EN applies to devices transmitting with an average power greater than 20 mw and in the frequency range of 300 MHz to 3 GHz. Devices that transmit ¾20 mw(i.e., 15mW) are deemed to comply with the basic restrictions without testing. No standards have been harmonized for devices other than those such as mobile phones and cordless phones. However, manufacturers must still comply with the EU SAR limits for devices such as PDAs that have an integral RF module for GSM. Such devices are tested against flat phantoms that simulate body parts.

11 11 In the United States, the limits and applicable products are contained in Title 47 of the Code of Federal Regulations 47 CFR Part , which covers portable devices with transmitters within 20 cm of a user's body. It also includes an applicability list that encompasses virtually all radio products, depending on their output power. A full explanation of the relevant parts, SAR limits, and SAR test methods is contained in FCC OET Bulletin 65 Supplement C. A recent development in Australia has delayed plans for more-aggressive SAR requirements. The Australian Communications Authority postponed a proposal to extend the scope of SAR testing. That scope would have included all radio products except emergency beacons. Test methods have not yet been developed for implementing some of the required testing. 1.4 LITERATURE REVIEW Hussein, M. and Sebak, A. (1996) presented the review of the finitedifference time-domain (FDTD) method and then employed to model and predict the radiation patterns of three basic configurations of mobile antennas. The directive gain and the input impedance are also calculated. The antennas' configurations considered are a quarter-wavelength monopole mounted on a conducting box, a bent-slot half-wavelength dipole flush mounted on a conducting box, and a quarter-wavelength monopole mounted on the top of an automobile. The radiation patterns obtained using the FDTD are compared well with published results. According to Siegbahn, M., et. al (1997) the effort has been placed on investigations of the interaction between RF electromagnetic fields, emitted from hand-held mobile telephones, and the human user. Usually, dosimetric measurement systems incorporating liquid filled head phantoms are used to evaluate the near-field characteristics. The aim of this study has been to compare the results from measurements and corresponding FDTD calculations of both the

12 12 far-fields and near-fields emitted by mobile phones when the phone is standing free of surrounding objects and when it is placed in the close proximity of a head phantom. According to Bernardi, P., et. al (1998) wireless personal communication is a rapidly expanding sector, particularly in the field of cellular mobile phones and wireless local area networks (WLANs). In an indoor WLAN system, the user of the mobile terminal can find himself in close proximity to the radiating antenna. It is, therefore, important to consider possible health hazards due to this type of exposure. In particular, they have considered possible WLANs operating in the range between 6-30 GHz, so that the incident field can be simulated via a plane wave. Starting from the calculated SAR values, the heating distribution has been derived through the bioheat equation, which has been solved using an explicit finite-difference scheme. Temperature increases of the order of 0.04 C have been calculated in the eye lens with an incident power density of 1 mw/cm 2 at 6 GHz. The fast growth of wireless telecommunication systems has induced a public concern of the hazardous health effects of electromagnetic field. For a long time this question has been studied and protective limits have been established by international organizations such as ICNIRP (1998) and IEEE (1992) to protect the human body from RF exposure. According to Bernardi, P., et.al (2000) a complete electromagnetic and thermal analysis has been performed considering the head of a subject exposed to various kinds of cellular phones available on the market, and focusing the attention on important organs like the eye lens and brain. Attention has first been posed on a particular phone model, and a comparison between the absorbed power distribution and steady-state temperature increases has been carried out. The influence of different antennas (dipole, monopole, whip, and planar inverted F antenna) on the power absorption and on the consequent tissue heating has then

13 13 been analyzed. The obtained results show for a radiated power of 600 mw, maximum SAR values, averaged over 1 g, from 2.2 to 3.7 W/kg depending on the considered phone. Gandhi, O. P., et. al (2001) solved the bioheat equation for an anatomically based model of the human head with a resolution of mm to study the thermal implications of exposure to electromagnetic (EM) fields typical of cellular telephones both at 835 and 1900 MHz. Another objective was to study the thermal implications of the SAR limits for the occupational exposures of 8 W/kg for any 1 g, or 10 W/kg for any 10 g of tissue suggested in the commonly used safety guidelines. Such specific absorption rates (SARs) would lead to temperature elevations for the electromagnetically exposed parts of the brain up to 0.5 C with 10 W/kg for any 10 g of tissue resulting in somewhat higher temperatures and for larger volumes. According to Manteuffel, D., et. al (2001) the mechanism generating SAR from mobile phones equipped with integrated antennas has been analyzed for the 900 MHz and the 1800 MHz frequency band respectively. The lowest SAR is Additionally at this length the largest bandwidth can be reached. For 1800 MHz this effect is less dominant. The maximum SAR occurs due to currents near the shorting edge of the antenna in all configurations. IEEE Standards Coordinating Committee 28, (2002) specified the extension of IEEE Std C Below 100 MHz, the current flowing through the body to ground is measurable and can be used to determine the SAR and, therefore, a brief treatment of low frequency body current measurement is included. Ae-Kyoung Lee and Jeong-Ki Pack (2002) proposed a method to obtain a tissue volume for SAR averaging by summing node massed of the layers enclosing

14 14 the point in which the averaged SAR is wanted in a body model until the summed mass is closest to the required mass. Manteuffel, D., et. al (2002) investigated a set of mobile phones available on the market in terms of SAR and radiated power in the presence of the user. From the measured results it is hardly possible to discover (dis)advantages for a specific antenna concept used for the different phones. Especially for GSM900 this is the most significant parameter. Using the same canonical model of a mobile phone it can be found that there is no significant difference in terms of SAR whether an external or an internal antenna is used for the GSM900frequency range. The analysis comes to a different conclusion for the GSM1800 frequency range According to Shih-Huang Yeh and Kin-Lu Won (2002) antennas occupying a small volume of the system are very attractive for wireless local area network (WLAN) or Bluetooth applications. To further reduce the antenna volume and decrease the fabrication cost, the WLAN antenna using an inverted-f strip integrated on the circuit board of a communication device has been demonstrated previously. However, the antenna is capable of single-band operation only. A novel dual-band F-shaped monopole antenna, which can easily be integrated on a circuit board, is proposed. The antenna comprises a vertical metal line and two (one upper and one lower) horizontal metal lines of different lengths, which are used for tuning the antenna's first two resonant frequencies to achieve dual-band operation in the 2.4 GHz ( GHz) and 5.2 GHz ( GHz) bands for WLAN applications. Bernardi, P., et. al (2003) showed that the peak specific absorption rate (SAR) as averaged over 10 g has about a 25-fold increase in the trunk and a 50- fold increase in the limbs with respect to the whole body averaged SAR (SARWB).

15 15 Hirata, A., et. al (2003) investigated the temperature increases in a human head due to electromagnetic (EM) wave exposure from a dipole antenna in the frequency range of 900 MHz to 2.45 GHz. The maximum temperature increases in the head and brain are compared with the values of 10 C and 3.5 C (found in literature pertaining to microwave-induced physiological damage The temperature increase in the model is then calculated by substituting the SAR into the bioheat equation. Numerical results demonstrate that the temperature increase distribution in the head is largely dependent on the frequency of EM waves. This is mainly because of the frequency dependency of the SAR distribution. According to Manteuffel, D., et.al (2003) different European and international standards (e.g. ICNIRP guidelines, ANSI C95.1 standard, European Council Recommendation) define basic restrictions and reference levels for human safety in electromagnetic fields. In order to check compliance between electronic equipment and basic restrictions in human safety standards additional standards exist that specify more detailed requirements for the testing. Most of these standards are based on measurements, e.g. the European standard EN for safety of mobile phones. However there is a growing number of standards that specify requirements for numerical methods, e.g. the European standard EN for devices used in radio-frequency identification, electronic article surveillance numerical dosimetric assessment by showing a variety of applications Heberling, D., et. al (2003) presented fundamental aspects on the electromagnetic (EM) user Interaction which have to be considered in the design and optimization of mobile phones are discussed. The study is based on numerical simulations of GSM900 and GSM1800 mobile phones. The absorption mechanism is analyzed in more detail by generic models of modern cellular phones equipped with different types of antennas. The simulations are performed using EMPIRE

16 16 tool with a standardized numerical representation of the human head (SAM Specific Anthropomorphic Mannequin). Hadjem, A., et. al (2005) gave a first comparison of specific absorption rate (SAR) induced in a child-sized (CS) head and an adult head using a dual-band mobile phone. In the second study, the visible human head is considered and comparison of SAR induced in a CS or child-like (CL) head and an adult head using a dual-band mobile phone is given. Hirata, A. (2005) attempted to correlate the maximum temperature increase in the head and brain with the peak specific absorption rate (SAR) value due to handset antennas. The rationale for this study is that physiological effects and damage to humans through electromagnetic-wave exposure are induced by temperature increases, while the safety standards are regulated in terms of the local peak SAR. Jariyanorawiss, T. and Homsup, N. (2005) presented the implementation of FDTD scheme using perfectly matched layer (PML) for truncation of head model in cellular telephone simulations. The simulated physical domain containing a dipole antenna and a head model is truncated with a PML as an absorbing medium. According to Simon, W., et. al (2005) new procedures for the numerical computation of the SAR induced by mobile phones in the human head are defined and are currently evaluated using different field solvers. The standardization of these procedures intends to optimize the inter-comparison of investigations performed through different research groups. The comparison of the two investigated phantoms tend to show that the SAM phantom gives a conservative estimation of the calculated SAR value if it is compared to the inhomogeneous human head model.

17 17 Woo-Tae Kim and Jong-Gwan Yook (2005) described that bio-heat equation including the Thermoregulatory systems is solved for an anatomically based model of the human head with a resolution of 3 x 3 x 3 mm. In order to study the capability of numerical head model, the time to reach the thermal steadystate under continuous RF exposure has been examined with the variation of power of a half-wave dipole antenna operating at 835 MHz. According to Brian B. Beard, et. al (2006) the specific absorption rates (SAR) determined computationally in the specific anthropomorphic mannequin (SAM) and anatomically correct models of the human head when exposed to a mobile phone model are compared. Fujimoto, M., et. al (2006) found that the maximum temperature increases in the head can be estimated linearly in terms of peak SAR averaged over 1- or 10- g of tissue. In particular, no clear difference is observed between the adult and child models in terms of the slopes correlating the maximum temperature increase with the peak SAR. Hirata, A. et. al (2006) investigated the correlation between maximum temperature increase in the head and brain and peak spatial average SAR calculated by different average schemes and masses. The rationale for this investigation was that the temperature increase may be one of the dominant factors which induce adverse physiological effects, although peak SAR is used as a measure for human protectionfor maximum temperature increase in the head only, the average mass of 10 g was better than that of 1 g. The correlation for the brain was, however, dependent on the frequency of EM waves. This was caused by the skin depth of EM waves. Qing-Xiang Li and Gandhi, O.P. (2006) solved the bio heat equation for the temperature rise of the various tissues including the brain for three anatomical models with 1-mm resolution for exposure to cellular telephones at 835 and 1900

18 18 MHz for radiated power levels. They have used the radiated power levels so as to reach the SAR limits proposed for the non pinna tissues. Bruns, H.D., et. al (2007) reviewed the improvements in some of the most important techniques of the field: the method of moments, the finite-difference time-domain method, the finite element method, the transmission-line matrix method, and the partial-element equivalent-circuit method. Buccella, C., et. al (2007) calculated numerically SAR and temperature distributions in the human eye for several configurations and RF sources, both for near-field and far-field exposures. A triband integrated PIFA cellular phone and half-wave dipole antennas have been adopted as primary sources of near-field exposure, while the far-field exposure has been modeled by a plane-wave field. The simulation results obtained by the solution of the bio-heat equation for several mobile phone configurations have clearly shown that there are no significant temperature increases in the lens for this kind of exposure. Ilvonen, S. and Sarvas, J. (2007) made several tests to examine the uncertainties due to the method used and geometrical variation on phone positions. The results obtained are considerably lower than the basic restriction limit given in the ICNIRP guidelines. This further qualifies the previously obtained results. The suitability of the locally refined models for calculating the induced currents from small appliances held close to the body was also discussed. The use of refinements enables the use of very detailed models with moderate computational resources. Li Yang, et. al (2007) concluded that when people are wearing glasses of metal framework, the peak value of SAR is shown to be a little higher than the safety limits. It is suggested that the radiation from the mobile handset do more harmful effect on the eyes with the glasses of metal frameworks.

19 19 According to Mochizuki, S., et. al (2007) the SAR distribution depends significantly on the shape of the ear, regardless of the head model. The effects of the head size have been investigated using a 90th-percentile head model and a Japanese-average head model. The head size has considerably less effect than the ear shape. According to Tefiku, F. (2007) the effect of short pin position on the radiation characteristics of a PCS band PIFA above a finite ground is analyzed using Ansoft HFSS. The analysis showed that the impedance bandwidth varied with different ground pin positions. The change in antenna bandwidth and other radiation characteristics was due to the change in the coupling mechanism between the PIFA mode and the ground plane mode in a way similar to changing the ground plane size. It is found that PIFAs with different radiator lengths can be tuned to the PCS band by proper selection of the short pin position. Wake, K., et. al (2007) developed a new exposure system to irradiate microwaves locally on a rabbit eye using a small coaxial-to-waveguide adapter filled with low-loss dielectric material as an antenna. The temperature elevation in the exposed eye was also evaluated by solving a bio-heat equation. Wolfgang Schramm, et. al (2007) used both radio frequency (RF) and microwave (MW) ablation devices for tumour ablation. They created computer models of a cooled RF needle electrode, and a dipole MW antenna to determine differences in tissue heat transfer. They simulated RF ablation for 12 min with power controlled to keep maximum tissue temperature at 100 degree C, and MW ablation for 6 min with 75 W of power applied. Cardies, E., et. al (2008) suggested that the average RF energy absorption from mobile phones is generally highest in the temporal lobe and that this structure, on the side of the head to which the phone is held, generally absorbs at least half of all of the RF energy absorbed in the brain. Numerical simulations

20 20 performed with FDTD with various adult head models and different handsets indicate an average SAR in the cerebellum of the order of 3% of the maximum SAR over 1 g in the brain. Despite these uncertainties, however, the results appear to be fairly robust; the maximum SAR and the highest average relative SAR are seen in the temporal lobe for the vast majority of the phones measured and, although phones have become smaller and the type and position of the antenna have changed over time, this appears to have relatively little impact on the anatomical distribution of the SAR. These results suggest that analyses of risk by location of tumor are important for the interpretation of results of epidemiological studies of brain tumors in relation to mobile phone use. Togashi, T., et. al (2008) found that there was approximately a ten times difference in the average SAR depending on the distance and penetration path from the antenna to the fetal head. Moreover, in the above condition, the fetus averaged SAR and the fetal brain averaged SAR at 900 MHz were times higher than those at 2 GHz. They simulated two conditions: one in which the antenna plate was facing free space, and another where it was directly facing the body, and calculated the averaged SARs. Davis, C.C. and Balzano, Q. (2009) described the results of an international intercomparison of specific absorption rate (SAR) measurements made with actual wireless telephones, following a similar program involving standard dipole antennas and flat phantoms. This study involved 17 laboratories in 11 different countries These measurements are made using small electric field probes placed in the head phantoms. Two different wireless phones, a Motorola Model V290 and a Nokia Model 6310, were circulated to each participating laboratory, which provided its own electric field probes, head phantom, base

21 21 station emulator to activate the phones, scanning system, and a stimulant fluid prepared to a required prescription. Iikka Laakso (2009) presented finite-difference time-domain (FDTD) calculations of specific absorption rate (SAR) values in the head under plane-wave exposure from 1 to 10 GHz using a resolution of 0.5 mm in adult male and female voxel models. The results suggested that 2 mm resolution should only be used for frequencies smaller than 2.5 GHz, and 1 mm resolution only under 5 GHz. Limiting the incident plane-wave power density to smaller than 100 W m was sufficient for ensuring that the temperature rise in the eyes and brain were less than 1 C in the whole frequency range. Islam, M.T., et. al (2009) investigated the reduction of Specific Absorption Rate with ferrite sheet attachment. The methodology of SAR reduction is addressed and then the effects of attaching location, distance, size and material properties of ferrite sheet on the SAR reduction are investigated. Computational results show that the SAR averaging over 10 gm was better than that for 1 gm and SAR reduction of 57.75% is achieved for SAR 10 gm. These results show the way to choose a ferrite sheet with the maximum SAR reducing effect for phone model. Kekun Chang, et. al (2009) fabricated a high performance monopole antenna using a folded planar line as radiator is presented. A prototype of the proposed monopole antenna with a compact area size of 20 mm 9 mm is implemented, and the multi-band WLAN/Bluetooth antenna shows a wide operating bandwidth of about 200 MHz and 1000 MHz for low band and high band. An internal small antenna usually suffers from degradation in performance of narrow bandwidth and radiation efficiency.

22 22 Manapati, M.B. and Kshetrimayum, R.S. (2009) used single negative metamaterials to reduce the electromagnetic interaction between the mobile phone and human head. The specific absorption rate (SAR) in the head can be reduced by placing the metamaterials between the antenna and the head. They designed the single negative metamaterials from periodic arrangement of split ring resonators (SRRs), spiral resonators (SRs) and open split ring resonators (OSRRs). By properly designing structural parameters of SRRs, the effective medium parameter can be trade negative around 900 MHz and 1800 MHz bands Varsier, N., et. al (2009) suggested a variability of the exposure of the different parts depending on use conditions and mobile phone categories and highlighted the importance of evaluating the risk by connecting the tumour location to phone categories and use conditions. According to Ragha, L.K. and Bhatia, M.S. (2010) the most important group of ferrimagnetic materials is ferrite. In ferrite the conductivity is low which results in much smaller induced currents in the material when electromagnetic waves are applied. Also when an electromagnetic wave hits ferrite particles, the magnetic field part of the wave is canceled. 1.5 THESIS ORGANIZATION Chapter 1 provides the introduction of the thesis and discusses the related work done so far in the area of specific absorption rate, temperature rise and biological effects of electromagnetic radiation. Chapter 2 describes the analysis of specific absorption rate at different frequencies for 1 gram and 10 gram average of tissue. Chapter 3 deals with the analysis of temperature increase in human head at different power levels and the calculation of steady state temperature for various head tissues. Chapter 4 focuses on testing and measurement. Conclusions are discussed in Chapter 5.