MICROWAVE RADIATION HAZARD AND SOLUTION Chetankumar patil, AP Rajashekhargouda patil ,AP Krishakanth Adur,AP Department of E&C Department of E&C Department of E&C AGMRCET AGMRCET SITAR VARUR 581207 VARUR 581207 Chennapatna chetan.patils011@gmail.com rajashekharpatil86@gmail.com adur.krishna@gmail.com

Abstract - Health risk are there due to radiation from cell phone and cell tower. Radiation effects are divided into thermal and non-thermal effects. A cell phone transmits 1 to 2 Watt of power in the frequency range of 824 - 849 MHz (CDMA), 890 915MHz (GSM900) and 1710 1780 MHz (GSM1800). A cell phone has a SAR (Specific Absorption Rate) rating .SAR limit for cell phones is 1.6W/Kg .which is actually for 6 minutes per day usage. In India, we have adopted very relaxed radiation norms of 4.7 W/m2 for GSM900, whereas serious health effects have been noted at as low as 0.0001 W/m2 = 100 W/m2. One of the first steps to be taken is to tighten the radiation norms .In second approach LTE MIMO antennas in a mobile handset has been introduced whose radiation is very less. SAR is also presented with chassis lengths, as the SAR distribution also changes with different chassis lengths, this parameter becomes more important for MIMO antennas.

Keywords - Long Term Evolution( LTE), Specific Absorption Rate(SAR),Federal Communication Commission(FCC), Single-Input Single Output(SISO), International Commission on Non-Ionizing Radiation Protection(ICNIRP), World Health Organization(WHO), ITU-T( Telecommunication Standardization Sector of the International Telecommunications Union), Multi Input Multi Output (MIMO),CST(Computer Simulation Technology)

I. INTRODUCTION All over the world, people have been debating about associated health risk due to radiation from cell phone and cell tower. Radiation effects are divided into thermal and non-thermal effects. Thermal effects are similar to that of cooking in the microwave oven. Non-thermal effects are not well defined but it has been reported that nonthermal effects are 3 to 4 times more harmful than thermal effects. A cell phone has a SAR (Specific Absorption Rate) rating. In USA, SAR limit for cell phones is 1.6W/Kg which is actually for 6 minutes per day usage. It has a safety margin of 3 to 4, so a person should not use cell phone for more than 18 to 24 minutes per day. This information is not commonly known to the people in India, so crores of people use cell phones for more than an hour per day without realizing its associated health hazards.. Even organizations like WHO, ICNIRP, FCC, etc. have not recommended stricter safe radiation guidelines, whereas several countries have adopted radiation norms, which are 1/100th to 1/1000th of these values based on their studies. The operators providing wireless communication should consider seriously this study and ITU-T recommendations in order to keep the operation of base station transceivers in compliance with regulations concerning environmental protection against non-ionizing radiation. Further, it important to note that the present threshold limits prescribed by the ICNIRP are considered to be rather too generous. Majority of these towers are mounted near the residential and office buildings to provide good mobile phone coverage to the users. These cell towers transmit radiation 24x7, so people living within 10s of meters from the tower will receive 10,000 to 10,000,000 times stronger signal than required for mobile communicationAs we know, a small volume radiator like a cell phone antenna is fairly sensitive to its nearby environment such as the users hand and head. The antennas current density distribution, efficiency and other parameters can change a lot when the user holds the handset in different ways. At the same time, regulations exist in many countries for the radiation of a handset. Due to the great demand for high-speed wireless communication, the Multi Input Multi Output (MIMO) antenna systems have rapidly been given increased attention, as it can enhance the channel capacity effectively without consuming more power or bandwidth. So far, the MIMO antenna system has been implemented inside laptops and routers, but not yet in the area of mobile handsets. However, MIMO antennas in a mobile handset will be realized in the next few years, in order to satisfy the requirement of the LTE communications, and many studies on MIMO antennas have been done .LTE communications require that the MIMO antennas can operate in both uplink and downlink, this raises a new challenge for antenna design. how to mount multiple antennas in a limited space, and how to evaluate and optimize the interaction between the handset and the users body.Similar to a single antenna, a MIMO antenna system also emits electromagnetic energy, and the allowed level of this emission is limited in many countries. However, compared with a Single Input Single Output (SISO) antenna system, a MIMO antenna system is more complicated as it has to work under more operation modes. For example, the multiple antennas would operate simultaneously in a MIMO mode, but in some cases the antennas also need to be capable for operating as a SISO antenna system. Sometimes, these antennas even need to form an antenna array for beam forming. Furthermore, the interaction between multiple elements has to be considered, as it can change the radiation performance \as well. So far, only a few studies have been done on the SAR of MIMO antennasII. RADIATION FROM THE CELL TOWER

A GSM900 base station antenna transmits in the frequency range of 935 - 960 MHz. This frequency band of 25 MHz is divided into twenty sub-bands of 1.2 MHz, which are allocated to various operators. There may be several carrier frequencies (1 to 5) allotted to one operator with upper limit of 6.2 MHz bandwidth. Each carrier frequency may transmit 10 to 20W of power one operator may transmit 50 to 100W of power and there may be 3-4 operators on the same roof top or tower, thereby total transmitted power may be 200 to 400W. In addition, directional antennas are used, which typically may have a gain of around 17 dB (numeric value is 50), so effectively, several KW of power may be transmitted in the main beam direction.III. Radiated power density from the cell tower (1)

where, Pt = Transmitter power in Watts,Gt = Gain of transmitting antenna,R = Distance from the antenna in metersFor Pt = 20 W, Gt = 17 dB = 50, Pd for various values of R is given in Table 1.

Distance R(m)Power density Pd in W/m2Power density Pd in uW/m2

179.679,600,000

38.848,840,000

53.183,180,000

100.796796,000

500.031831,800

1000.0087,960

5000.000318318

Table 1. Power density Pd at a distance R is given

IV. Theoretical and Measured Radiated powerTo measure the power at a distance R, an antenna is used to receive the power and a spectrum analyzer or power meter is used to measure received power. Power Received Pr by an antenna at a distance R is given by:

Pr = Pt x Gt x Gr x ( / (2)Received power is directly proportional to the transmitted power, gain of transmitting and receiving antennas, and square of wavelength of the signal and it is inversely proportional to square of distance.V. Biological effects of microwave radiationWhen a human body is exposed to the electromagnetic radiation, it absorbs radiation, because human body consists of 70% liquid. It is similar to that of cooking in the microwave oven where the water in the food content is heated first. Microwave absorption effect is much more significant by the body parts which contain more fluid (water, blood, etc.), like the brain which consists of about 90% water. Effect is more pronounced where the movement of the fluid is less, for example, eyes, brain, joints, heart, abdomen, etc. Also, human height is much greater than the wavelength of the cell tower transmitting frequencies, so there will be multiple resonances in the body, which creates localized heating inside the body. This results in boils, drying up of the fluids around eyes, brain, joints, heart, abdomen, etc. There are several health hazards associated with cell phones and cell towers. VI. ESTIMATION OF EXPOSURE LEVELEstimation of exposure levels can be done either by measurement or by numerical calculations or by electromagnetic software simulations. All these methods have almost similar level of uncertainty and accuracy depending on the method and equipment or software used. Calculation of equivalent isotropically radiated power (EIRP) is an efficient method for the estimation of exposure level of a base station antenna. In this method, site survey is done and several parameters like location parameters, operating parameters, and environment parameters are recorded.Now, estimation of EIRP and threshold of EIRP (EIRPth) are done at various publicly accessible points (on ground, on rooftop, at adjacent building, etc.) in the environment surrounding the base station antenna. The EIRP for an operator service is given by EIRP of control channel (e.g. BCCH channel for GSM and common-pilot channel for CDMA/UMTS) as:EIRPBCCH = Pt - Pl -(L x CL ) +G (3)where Pt = Transmitter output power, Pl = Combiner loss, L=RF Cable length, CL=RF Cable loss per 100m length, G =Antenna gain.

Now total EIRP of the particular service of an operator is given byEIRPTotal = EIRPBCCH{1+ m x n x (N -1)} (4)where m = diversity factor, n = ATPC factor, N = number of carriers per sector in worst case, e.g., if two sectors are having three carriers while the third one has four carriers, the value of N would be four.

VII. Possible Solutions to reduce the ill effects of cell tower radiationOne of the first steps to be taken is to tighten the radiation norms and yet it should be practical enough to be cost effective without causing too much inconvenience to the users. It is recommended that maximum cumulative power density allowed should be reduced with immediate effect to 0.1 W/m, which should then be subsequently reduced to 0.01 W/m within a year, so that network planning can be carried out in a phased manner. It must be noted that a few countries have even adopted 0.001 W/m or lower, so our proposed recommendation is higher than these countries to keep it cost effective. All the operators must be strictly instructed that power density inside residential or office buildings, schools, hospitals, and at common frequently visited places should be within these guidelinesIn addition, repeaters or signal enhancers or boosters may have to be installed where signal is weak. Care must be taken that maximum power transmitted by these must not exceed 0.1W because of their close proximity to the users.VIII. Antenna Configuration and Simulation Setup to optimize the SAR performanceBased on the LTE standard, dual-element MIMO antenna in a mobile terminal is required. In this thesis, four designs of MIMO antenna with dual elements are presented and their SAR performances are studied separately: dual semi ground free PIFAs, ground free co-located antenna, dual on ground (OG) PIFAs in parallel position and dual on ground (OG) PIFAs in orthogonal position. Their schematic diagrams are shown in Fig. 1. In order to simulate the real mobile phone, a plastic box is utilized to cover each MIMO antenna.

For -6dB specification, the semi ground free PIFA and co-located antenna can cover 750MHz to 960MHz in low band, and 1700MHz to 2700MHz in high band. The bandwidth of the two designs of dual OG PIFAs is between 750MHz and 850MHz in low band, and 1700MHz to 2200MHz in high band. Considering their S parameter andthe required band for LTE, we study four frequency points for each MIMO antenna,750MHz, 850MHz, 1900Mhz and 2600MHz for semi ground free PIFA and co-located antenna; 750MHz, 850MHz, 1900Mhz and 2100MHz for parallel OG PIFA and orthogonal OG PIFA.

Fig. 1. The diagrams of the proposed antennas: (a) dual semi ground free PIFA, (b) ground free co-located antenna, (c) dual on ground PIFA in parallel position, and (d) dual on ground PIFA in vertical position.The simulation setup for the SAM(Specific Anthropomorphic Mannequin)head phantom is shown in Fig. 2.The antenna is placed in cheek touch position in accordance with the CTIA standards . The acoustic part of the cell phone needs to be placed at the middle of the pinna (in our study, the speaker of the cell phone is set to be 10.5mm lower than the top of the cell phone case), the body of the cell phone has to touch the cheek, and the perpendicular line of the mobile handset is lined up with the mouth back to pinna line on the head phantom. The antenna chassis is 4.5mm away from the pinna. For co-located antennas, dual elements are placed at the bottom of the chassis in order to optimize the SAR performance. For the vertical OG PIFA, the vertical antenna is placed at the top of the chassis. For the flat phantom, the antenna is placed 10mm above the phantom [ and radiates downward to it. Based on the LTE standard, the input powers for the antenna are set at 24dBm and 21dBm for low band (750 MHz, 850MHz) and high band (1900 MHz, 2100MHz, 2600MHz), respectively.

Fig. 2.The CST simulation model.(a)side view; (b)top view.

IX. SAR ReductionBased on the study above, we can present two examples of SAR reduction for mobile phone antennas. For stand alone SAR, as mentioned, the distribution of the current is a deciding factor. Here, we use the slot in the middle of the ground plane to change the current distribution, and reduce the SAR. The example is shown in Fig.3.

Fig. 3 Stand alone SAR in 0.75GHz for (a) original structure, and (b) improved structureIn Fig. 3, we use a monopole antenna as an example. In order to reduce the SAR, we cut a slot in the middle of the chassis, and we can see that the distribution of the SAR become more uniform and the value is reduced from 1.58 W/kg to 1.45 W/kg. The second case is for simultaneous SAR. As mentioned, the distance between hotspots is quite important; therefore, the antenna and its ports positions must be optimized. Here, in order to study these phenomena, we take a monopole with OG PIFA MIMO antenna that operates in 1.9GHz.

Fig. 4 Stand alone SAR in 0.75GHz for (a) original structure, and (b) improved structureFig. 4 in this case, for the original structure, the two hot spots are overlapping, and the simultaneous SAR can reach 3.6W/kg. In the improved structure, the OG PIFA is turned 180 degrees, and the port of the OG PIFA is moved further to the monopole.We can clearly see that the two hot spots are separated, and the simultaneous SAR is reduced to 1.3W/kg. From the example above, we can see that the current distribution and physical distance between antenna ports are two important factors for the SAR value. For the antenna engineer, these factors must be considered before they propose a new structure.

X. CONCLUSIONS In this paper, providing wireless communication should consider seriously this study and ITU-T recommendations. Even organizations like WHO, ICNIRP, FCC, etc. have to recommend stricter safe radiation guidelines. The interaction between the users body and LTE MIMO antennas in a mobile handset has been studied, which shows a lot of interesting phenomena. To meet the requirements from the governments and mobile network operators (MNO), the SAR and body loss of the antenna have to be optimized to an acceptable level.

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