Bio- Thermal Effects due to Electromagnetic Radiation

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Possible temperature changes in human body exposed to the radiation emitted ... Our atmosphere is full of electromagnetic waves radiated by many types of ...
Bio- Thermal Effects due to Electromagnetic Radiation P P Pathak Department of Physics, Gurukula Kangri University Haridwar - 249404 India Email: [email protected]

Abstract Possible temperature changes in human body exposed to the radiation emitted from radio/TV/Microwave communication transmitter is evaluated. The process uses (i) propagation from transmitter, field value reducing inversely with distance (ii) penetration into a human body, field reducing exponentially with depth (iii) absorption of power, specific absorption rate (SAR) being proportional to the conductivity and square of the field value and inverse of material density (iv) temperature rise proportional to SAR and inverse to the specific heat of the body material. The results show the sufficient temperature rise to recommend the minimum distance of the transmitters from the populated areas.

1. Introduction Our atmosphere is full of electromagnetic waves radiated by many types of transmitters like those of TV/radio/microwave communication. In most countries there is no restriction or guidelines for installation these transmitters. Thus atmosphere becomes overflowing with electromagnetic fields and we are living in the sea of these fields. Bio-effects of these fields become necessary to be evaluated and guidelines be formulated.

2. Formulation Electric field at a distance r from radiating antenna at power P in air is given by [1]

  E = P 2   2πε 0 r c  where,

ε0

1

2

= 7.746 P

r

(1)

is the permittivity of air and c the speed of light. When a human body is exposed to the field, it

penetrates into the body. Inside field Ei at a given depth z is given as [2]

E i = E exp(− z )

(2)

δ

where,

δ

is skin depth for angular frequency ω to be given as

δ=

1

 µε   2

µ is permeability of body material and ε its permittivity,

 1+ p 

(

p =σ

2

εω ,

specific absorption ratio (SAR) in the body of density ρ is given by [3]

)

1

2

 − 1   

,

(3)

σ being its conductivity. Now

2

SAR = σEi

ρ

(4)

This absorption of electromagnetic waves produces temperature change ∆T, when a human body of specific heat C, otherwise in thermal equilibrium with environment, is exposed for a duration ∆t seconds to these waves, to be given by equation [4]

C∆T = SAR(∆t )

(5)

3. Calculations For calculations of SAR values for different types of tissues of the human body at 100 m from transmitter of 10 kW at 202 MHz, conductivity of the body tissues is taken from Gabriel et al. [5] and for calculation of rate of temperature change with time, mass density and heat capacity values are taken from Stuchly and Stuchly [4].

4. Results and Discussion Calculated values of SAR in different types of tissues at different depths inside human body at a distance of 100 m from transmitter of power 10 kW at frequency of 202 MHz are given in Table 1 and resulting rate of temperature rise is given in Table 2. SAR values above the values permitted by WHO and ICNIRP [6] are shown as bold. It is clear that at a distance of 100 m SAR values up to 5 mm depth are many times more than the permitted SAR values. Table 1: SAR values at different depths in different tissues of body at 100 m distance from transmitter of 10 kW at 202 MHz. Tissue Skeletal Muscle Bone cortical Bone spongy Fat

1 mm 0.525 0.00121 0.00173 0.0000023

SAR Values (W/kg) at a depth 2 mm 3 mm 4 mm 0.504 0.48 0.46 0.00120 0.001199 0.00119 0.00172 0.001719 0.00171 0.00000229 0.00000228 0.00000227

5 mm 0.444 0.00118 0.00170 0.00000226

Table 2: Rate of temperature increase at different depths in different tissues of body at 100 m distance from transmitter of 10 kW at 202 MHz. Tissue Skeletal Muscle Bone cortical Bone spongy Fat

1 mm 1.513 0.0096 0.00582 0.00001

Rate of temperature increase (in 10-4 deg C /s) at a depth 2 mm 3 mm 4 mm 5 mm 1.452 1.383 1.326 1.279 0.00952 0.00951 0.00944 0.00936 0.00579 0.00578 0.00575 0.00572 0.00001 0.00001 0.00001 0.00001

Table 2 shows that rate of temperature rise in skeletal muscle is the order of 10¯ 4 oC/s in the body which was earlier in stable condition considering all types of thermoregulation. This will give a rise of 1113 oC in one day in different depth of 5 mm to 1mm in the body. Though this may again set up

thermoregulatory process in the body but will cause additional stress in the body tissues and can cause much sickness.

4. Conclusion From the far going analysis it is clear that high frequency transmitters must not be installed in populated areas and people should keep more than 100 m away from the transmitters.

5. Acknowledgement The author is thankful to Dr. Vijay Kumar of Physics Department, S.D. Bansal College of Technology, Indore (M.P.) India for providing some data and help in calculations.

6. References 1. P.P. Pathak, V. Kumar and R.P. Vats, “Harmful Electromagnetic Environment near Transmission Tower” Indian J. Radio Space Phys. 32, August 2003. pp 238-241. 2. C. Polk, “Introduction,” in C. Polk and E. Postow (eds.), Handbook of Biological Electromagnetic Fields, Second Edition, Boca Raton, CRC Press, 1996, pp1-23.

Effects of

3. E.R. Adair and E. Peterson, “Biological Effects of Radio Frequency/Microwave Radiation ”IEEE Trans. MTT, 50, 2002, pp953. 4. M.A. Stuchly and S.S. Stuchly, “Experimental Radio wave and Microwave Dosimetry,” in C. Polk and E. Postow (eds.), Handbook of Biological Effects of Electromagnetic Fields, Second Edition, Boca Raton, CRC Press, 1996, pp295-336. 5. S. Gabriel, R.W. Lau and C. Gabriel, “The Dielectric Properties of Biological Tissues: II Measurements in the frequency range 10 Hz to 20 GHz” Phys. Med. Biol. 41, 1996, 2251-69. 6. “Guidelines for limiting exposure to time varying Electric and Magnetic and EMF’s, ICNIRP Guidelines,” Health Physics, 74(4), April 1998.