Indian Journal of Radio & Space Physics Vol. 37, April 2008, pp. 131-134
Interaction of electromagnetic radiation with human body Vijay Kumar Department of Physics, Sushila Devi Bansal College of Technology, Indore 452 012 (MP), India E-mail:
[email protected]
and R P Vats & Sachin Goyal Department of Physics, M S College, Saharanpur 247 001 (UP), India and
Sandeep Kumar & P P Pathak Department of Physics, Gurukula Kangri University, Haridwar 249 404 (UA), India Received 29 December 2005; revised 11 June 2007; accepted 26 February 2008 Whole body specific absorption rate (SAR) is calculated for different frequencies as a function of distance from transmission tower. Comparing with safe limits of exposure as standardized by different international agencies, safe distance of residence from transmission tower is determined. The SAR for fat at a distance of 10, 20, 30, 40, 50 and 60 m is found to be harmful for 27.12-10000 MHz, above 100, 1500, 5000, 8000 and 10,000 MHz, respectively. Harmful range for cortical bone, spongy bone and skeletal muscle is also calculated. Keywords: Electromagnetic radiation (EMR), Induced electric field, Human body, Specific absorption rate (SAR) PACS No.: 84.40. Us
1 Introduction Interaction of radio frequency (RF) electromagnetic radiation (EMR) with human body is a complex function of numerous parameters. Dissymmetric studies attempt to quantify these interactions. The EMR is characterized by its frequency, intensity of electric and magnetic fields, their direction and polarization characteristics in free space. The fields inside the tissues of biological bodies can interact with them and therefore it is necessary to determine these fields for any meaningful and general quantification of biological data obtained experimentally or theoretically. Here the authors obtain these data theoretically. There are many types of sources, which radiate EMR of different frequency and intensity. Transmission towers of TV, radio, mobile phones radiate high frequency EMW and domestic gadgets like electric blankets, hairdryers, electric shavers, television sets, stereo systems, air conditioners, fluorescent lights, refrigerators, portable heaters, cloth washers and dryers, coffee makers, microwave ovens, etc. radiate low frequency EMR. In this paper the authors discuss about the harmful frequencies of EMR
by studying the SAR of biological tissues or cells. A human body is a homogeneous, lossy dielectric, whose macroscopic electrical properties are described by its complex permittivity1. When an electric or magnetic field penetrates into the body, it is attenuated and a part of it is absorbed inside the body2. The intensity of the internal fields depends on the parameters of the external fields, i.e. the frequency, polarization, size, shape and dielectric properties of the exposed body. Numerous experimental studies on interaction of EMR with tissues have revealed the electrical properties of tissues including dependence of conductivity and permittivity of different types of tissues, which constitute different parts of our body1. On theoretical side the authors have earlier evaluated the field variation2, potential drop and induced current density3 after penetration of electric field (transmitted by TV tower) into our body. Here the authors use theoretically calculated internal fields to evaluate SAR at different distances from tower and find the safe distances of living, where SAR is within safe limits.
INDIAN J RADIO & SPACE PHYS, APRIL 2008
132
2 Specific absorption rate (SAR) The specific absorption rate is defined as the time derivative of the incremental energy (dW) absorbed by or dissipated in an incremental mass (dm) contained in a volume element (dV) of a given density (ρ). It can be defined as4 SAR = d/dt (dW/dm) = d/dt (dW/ρdV)
…(1)
and by using Poynting vector theorem for sinusoidal electromagnetic fields, one can get SAR = σEi2/ρ
…(2)
where σ is the conductivity of the material and Ei the field inside that material. In terms of the field Ei incident on the body from any transmitter/generator, Ei at a depth z can be given by exponential decrease as already used by Pathak et al.2 The expression for the incident field from a transmitter of power P at a distance r is also given by Pathak et al.2 Equation (2) represents the rate at which the electromagnetic energy is converted into heat through well-established interaction mechanisms. It provides a valid quantitative measure of all interaction mechanisms that are dependent on the intensity of the internal electric field5. At this point some additional information may be relevant. For instance, some effects of radio waves modulated in amplitude at extremely low frequency (ELF) are dependent on the electric field intensity6. Once specific interaction mechanisms are better understood, they would be expressed in terms of SAR and modulation
characteristics, even though the interaction mechanisms may not necessarily be thermal. However, the direction of electric field with respect to the biological structures should be of importance for a given interaction mechanism and the SAR would not provide full quantitative information. In spite of the limitations, SAR concept has proven to be simple and useful tool in quantifying the interactions of RF radiation with living systems. Therefore, here the SAR values are calculated for different tissues/organs of the body. The detailed process for calculations for Ei has been given by Pathak et al.2. Using the same, calculations for Ei for different conditions and tissues are made here and thus the SAR is calculated with distance from transmission tower. The calculated values for fat, cortical bone, spongy bone and skeletal muscles are given in Tables 1, 2, 3 and 4, respectively. 2.1 Safe exposure limit of SAR
Many agencies like International Commission on non-ionizing radiation protection (INIRP), International non-ionizing radiation Committee (INIRC), World Health organization (WHO), National Council on Radiation Protection and Measurements (NCRP), Standard Association of Australia (SAA), Federal Communications Commission (FCC), all agree that the exposure of general public should be kept below a whole body SAR of 0.08 W/kg. As a result of differences between approaches and frequencies used worldwide standards for the continuous exposure of the human being to RF
Table 1—The variation of specific absorption rate (SAR) of fat with different frequencies of EMW at different distances from the tower Frequency of radiation, MHz
10
27.12 40.68 100 200 300 433 750 915 1500 2450 3000 5000 5900 8000 10000
172.57 248.8 363.98 382.8 442.1 497.3 599.08 646.29 771.3 986.98 1097.3 1502.5 1671.5 2188.3 2783.6
Specific absorption rate (SAR) at different distances in metre from the tower (10-3 W/kg) Distance, m 20 30 40 50 60 70 80 90 43.14 62.2 90.99 95.7 110.5 124.3 149.8 646.3 192.8 246.7 274.3 375.6 417.9 547.08 695.9
19.18 27.65 40.44 42.54 49.13 55.26 66.57 71.82 85.71 109.68 121.9 166.96 185.75 243.18 309.33
10.76 15.55 22.7 23.88 27.58 31.02 37.37 40.31 48.11 61.57 68.45 93.72 104.27 136.5 173.6
6.89 9.94 14.54 15.3 17.67 19.87 23.94 25.83 30.82 39.44 43.86 60.05 66.81 87.46 112.5
4.78 6.9 10.09 10.62 12.26 13.79 16.62 17.93 21.93 27.38 30.44 41.68 46.37 60.71 77.22
3.52 5.07 7.42 7.81 9.02 10.03 12.22 13.18 15.74 20.14 22.39 30.66 34.11 44.65 56.8
2.67 3.86 5.64 5.94 6.86 7.63 9.29 10.02 11.96 15.31 17.02 23.31 25.93 33.95 43.19
2.1 3.04 4.44 4.68 5.4 6.08 7.32 7.9 9.43 12.06 13.41 18.36 20.43 26.75 34.03
100 1.72 2.48 3.63 3.82 4.42 4.97 5.99 6.46 7.71 9.86 10.97 15.02 16.71 21.88 27.83
KUMAR et al.: INTERACTION OF ELECTROMAGNETIC RADIATION WITH HUMAN BODY
133
Table 2—The variation of specific absorption rate (SAR) of bone cortical with different frequencies of EMW at different distances from the tower Frequency of radiation, MHz
10
27.12 40.68 100 200 300 433 750 915 1500 2450 3000 5000 5900 8000 10000
90.6 130.6 191.1 201 232.1 261.1 314.5 339.3 405.01 518.2 576.2 788.9 877.7 1149 1461.6
Specific absorption rate at different distances in metre from the tower (10-3 W/kg) Distance, m 20 30 40 50 60 70 80 90 22.72 32.76 47.9 50.4 58.21 65.47 78.87 85.09 101.5 129.9 144.4 197.8 220.08 288.1 366.5
10.0 14.43 21.1 22.2 25.6 28.84 34.74 37.5 44.7 57.23 63.64 87.13 96.94 126.9 161.4
5.4 7.8 11.4 12.0 13.86 15.6 18.78 20.26 24.18 30.94 34.4 47.1 52.4 68.6 87.2
3.51 5.07 7.41 7.8 9.0 10.13 12.2 13.17 15.7 20.11 22.36 30.61 34.06 44.6 56.7
2.43 3.51 5.13 5.4 6.23 7.01 8.45 9.11 10.9 13.9 15.5 21.2 23.58 30.87 39.26
1.9 2.73 3.99 4.2 4.85 5.45 6.57 7.09 8.46 10.83 12.04 16.48 18.34 24.01 30.54
1.35 1.95 2.85 3.0 3.46 3.9 4.7 5.06 6.04 7.73 8.6 11.77 13.1 17.15 21.81
1.08 1.56 2.28 2.4 2.77 3.12 3.75 4.05 4.83 6.19 6.88 9.42 10.48 13.72 17.45
100 .906 1.3 1.91 2.01 2.32 2.61 3.14 3.39 4.05 5.18 5.76 7.88 8.77 11.49 14.61
Table 3—The variation of specific absorption rate (SAR) of spongy bone with different frequencies of EMW at different distances from the tower Frequency of radiation, MHz
10
27.12 40.68 100 200 300 433 750 915 1500 2450 3000 5000 5900 8000 10000
129.84 187.2 273.84 288 332.6 374.16 450.7 486.24 580.3 742.56 825.6 1130.4 1257.6 1646.4 2094.2
Specific absorption rate at different distances in metre from the tower (10–3 W/kg) Distance, m 20 30 40 50 60 70 80 90 32.46 46.8 68.46 72 83.16 93.54 112.7 121.5 145.08 185.04 206.4 282.6 314.4 411.6 523.56
14.33 20.67 30.23 31.8 36.72 41.31 49.76 53.68 64.07 81.99 91.16 124.8 138.8 181.8 231.23
8.11 11.7 17.11 18.0 20.79 23.38 28.17 30.39 36.27 46.41 51.5 70.65 78.6 102.9 130.9
from base station antennas ranges from 0.2 to 1.2 mW/cm2 [www.mcw.edu/gcrc/cop/cell-phone-healthFAQ, 1999]. 3 Results and discussion From Eq. (5), it is clear that the radiated electric field varies inversely with distance from the transmission tower. One can be cautious that the values vary from about 155 V/m at 5 m to 3 V/m at 250 m from the tower. This leads to an automatic inference that SAR and hence the health effects within few meters from tower would be harmful.
5.13 7.41 10.83 11.4 13.16 14.81 17.84 19.24 22.97 29.39 32.68 44.74 49.78 65.17 82.89
3.51 5.07 7.41 7.8 9.0 10.13 12.2 13.16 15.7 20.11 22.36 30.61 34.06 44.59 56.71
2.43 3.51 5.13 5.4 6.23 7.01 8.45 9.11 10.88 13.92 15.48 21.19 23.58 30.87 39.26
2.0 2.88 4.22 4.44 5.12 5.76 6.94 7.49 8.94 11.44 12.72 17.42 19.38 25.38 32.28
1.62 2.32 3.42 3.6 4.15 4.67 5.63 6.07 7.25 9.28 10.32 14.13 15.72 20.58 26.17
100 1.29 1.87 2.73 2.88 3.32 3.74 4.5 4.86 5.8 7.42 8.25 11.3 12.5 16.46 20.94
As described in section 2 above, NCRP, INIRP, FCC, SAA and WHO, have set out the whole body exposure limit of human being as SAR of 0.08 W/kg. The values of SAR as expected inside the body for fat, cortical bone, spongy bone and skeletal muscles at different distances from the tower, are calculated from Eq. (2) with the values of ρ and frequency dependent σ taken from Stuchly and Stuchly7. These are given in Tables 1-4. The harmful values (i.e. those above 0.08 W/kg) are shown in bold face. It can be seen from Table 1 that SAR for fat at a distance of 10 m is harmful for all frequencies in the range 27.12-10000
INDIAN J RADIO & SPACE PHYS, APRIL 2008
134
Table 4—The variation of specific absorption rate (SAR) of skeletal muscles with different frequencies of EMW at different distances from the tower Frequency of radiation, MHz
10
1.0 10 27.12 40.68 100 200 300 433 750 915 1500 2450 3000 5000 5900 8000 10000
34.28 52.44 53.56 59.39 76.18 109.69 117.4 122.55 131.97 137.12 151.68 189.39 193.68 335.94 405.36 655.6 882.7
Specific absorption rate (SAR) at different distances in metre from the tower (W/kg.) Distance, m 20 30 40 50 60 70 80 90 8.56 13.09 13.37 14.83 19.02 27.39 29.31 30.6 32.95 34.24 37.87 47.29 48.36 83.88 101.22 163.71 220.42
3.8 5.82 5.95 6.59 8.46 12.18 13.04 13.61 14.66 15.23 16.85 21.03 21.51 37.31 45.02 72.82 98.05
2.14 3.27 3.34 3.7 4.75 6.84 7.32 7.65 8.23 8.56 9.46 11.82 12.09 20.97 25.3 40.92 55.1
MHz, while SAR at 20 m is harmful for frequency 100 MHz and above. Similarly at 30 m harmful range starts from 1500 MHz, at 40 m from 5000 MHz, at 50 m it is at 8000 MHz and at 60 m it is not harmful even at 10000 MHz. Similarly, harmful range of SAR can be seen for cortical bone, spongy bone and skeletal muscle from Tables 2, 3 and 4, respectively. It is noticed that SAR for skeletal muscle comes out to be harmful for all the frequency ranges from 1 MHz and for all the distances up to 100 m for which the values have been calculated. The results can be treated as significant with the view that SAR at different types of tissues/parts of body are above the permissible limit. These parts of the body are under the skin of thickness of about 3 mm. With the values of ρ and σ taken from web site on line [http://www.fcc.gov/fcc-bin], the attenuation of field by skin can be calculated from Eq. (6) to range form 7% at 900 MHz to 11% at 1800 MHz (the low frequencies used worldwide for mobile phone communication). This may reduce SAR of internal parts/tissues, but simultaneously SAR of skin will be added so that the whole body SAR will come to the same value that is much above the permitted range. 4 Conclusions From the above analysis, it is concluded that some higher frequency radiations are harmful for the human
1.36 2.09 2.13 2.37 3.04 4.37 4.68 4.89 5.23 5.47 6.05 7.55 7.72 13.4 16.1 26.1 35.2
0.95 1.45 1.48 1.65 2.1 3.04 3.26 3.4 3.66 3.8 4.2 5.2 5.37 9.32 11.2 18.2 24.5
0.7 1.09 1.07 1.21 1.55 2.24 2.39 2.5 2.7 2.8 3.09 3.3 3.9 6.86 8.27 13.38 18.02
0.53 0.82 0.83 0.93 1.19 1.71 1.83 1.91 2.06 2.14 2.37 2.96 3.02 5.25 6.33 10.25 13.8
0.42 0.64 0.65 0.727 0.933 1.34 1.44 1.5 1.61 1.68 1.85 2.32 2.37 4.11 4.96 8.03 10.8
100 0.34 0.52 0.53 0.59 0.76 1.096 1.17 1.22 1.3 1.37 1.5 1.89 1.9 3.36 4.05 6.55 8.82
health and the radiation become more harmful as the distance from the transmission tower becomes less. Higher frequency radiations are more harmful for skeletal muscles at all distances up to at least 100 m from the tower, while along with this the bone cortical and bone spongy are also affected by different frequencies at different distances from the tower. Thus it is suggested that the transmission tower, which radiate high frequency radiation should be located far away from the thickly populated areas. References 1
2
3
4
5 6 7
Foster K R & Schwan, H P, in Biological Effects of Electromagnetic Fields, Edited by C Polk and E Postow, (CRC Press, Boca Raton, USA), 1996, pp 25-102. Pathak P P, Kumar V & Vats R P, Harmful electromagnetic environment near transmission tower, Indian J Radio Space Phys, 32 (2003) 238. Kumar V, Vats R P & Pathak P P, Harmful bio-effects of high frequency electromagnetic fields, J Nat Phys Sci India, 18 (2004) 17. Adair E R & Peterson R C, Biological effects of radio frequency/microwave radiation, IEEE Trans MTT (USA), 50 (2002) 953. Guy A W, Non-ionizing radiation: dosimetry and interaction, Proc ACGIH Top Symposium, 1979, 75. Adey W R, Tissue interactions with non-ionizing electromagnetic fields, Phys Rev (USA), 61 (1981) 435. Stuchly M A & Stuchly S S, in Biological Effects of Electromagnetic Fields, Edited by C Polk and E Postow, (CRC Press, Boca Raton, USA), 1996, pp 337-402.
