Exposure assessment in the vicinity of 900 MHz GSM base station antenna

Transcription

1 Proceedings of the 11th WSEAS International Conference on COMMUNICATIONS, Agios Nikolaos, Crete Island, Greece, July 6-8, Exposure assessent in the vicinity of 900 MHz GSM base station MIMOZA IBRANI, LUAN AHMA, ENVER HAMITI,RUZHDI SEFA Faculty of Electrical and Coputer Engineering University of Prishtina Bregu i Diellit, pn KOSOVO Abstract: Daily exposure to GSM electroagnetic fields has raised public concern of possible adverse health effects to people living in the vicinty of base station s. In this paper are presented easureents of field strength and power flux density perfored on locations few eters away fro base station, in different levels, with and without usage of obile phones, during day and in peak hours of GSM syste usage. Measureents are perfored in accordance with standards using EMR-300 radiation eter. Results are copared with ICNIPR Guidelines, IEEE and CENELEC standards. The easured were well below the axiu perissible exposure levels. Key-Words: base station s, field strength, power density, GSM, easureent 1 Introduction Increased use of cellular obile counication led to sitting of GSM base station s even in close of houses, schools etc, in densely populated areas. This raised public concern regarding safety of population exposed to such radiation. Many studies have been done and are on going regarding potential biological and theral effects of GSM electroagnetic fields. Cancer, hypertheria, neural and behavior effects of people exposed to GSM fields are being studied. Interaction of GSM electroagnetic fields and huans should include all particularities of syste : [3] The aterial (huan body)has very unusual electroagnetic properties : electric perittivity, electric conductivity These properties are not well known and depend on activity of person This aterial is an active aterial at cell scale In ost cases, the proble is actually a coupled proble: the theral effect is one of the ajor effects and it is affected by the blood circulation The geoetry is coplex and generally environent of the huan body has to be taken into account Alost all guidelines and recoended liits on huan exposure to GSM electroagnetic fields are given in ters of SAR(Specific Absorption Rate). SAR is defined as: σ E SAR = W/kg.. (1) ρ σ -Conductivity of body tissue, E- root ean square of intensity of electrical field at

2 Proceedings of the 11th WSEAS International Conference on COMMUNICATIONS, Agios Nikolaos, Crete Island, Greece, July 6-8, considered point, ρ -ass density of tissue at that point. Since SAR, tie rate of RF energy absorbed per unit ass, is very difficult and coplex to be easured in biological tissues, standards perit the use of reference levels of power flux density( W/ )s in free space. IEEE standard established the liits for rs electric and agnetic fields, so called axiu perissible exposure(mpe) and siilarly ICNIRP standard defines reference liits for free-space incident fields. Meeting these liits SAR copliance should be ensured. So instead of coplex SAR easureents, for copliance assessents above entioned standards let us use sipler field easureents as rs of electric field. In this paper we have presented results of easureents of field strength and power density flux in the vicinity of base station s. Exposure assessent is done on request of Ministry of Environent in order to give feedback regarding level of exposure, assessent of radiation, to concerned people living on the vicinity of GSM 900 MHz base station. Measureent of field strength and power density in vicinity of base station In order to have ore accurate results power flux density is easured at considerable distances fro radiating. When the huans are located in near field of, significant influence in paraeters is to be expected. If distance is greater than the huan phanto influence can be alost copletely oitted []. Assuing far-field exposure, agnitude of electrical field can be expressed as superposition of the incident field and reflected field coponents. [1-] Figure 1 shows ground-plane of suburb Eshir, Prishtina Kosovo, where is located GSM 900 MHz base station. Figure 1 H1- House Nr.1; H- House Nr.; H3- House Nr.3, H4- House Nr.4; H5- House Nr.5; H6- House Nr. 6; H7- House Nr.7; R- Road, BA- Base of Antenna. Measureents are perfored using radiation eter EMR-300, sensor type 8 E- field probe, 00 KHz -3 GHz, three axial sensors, so easureents are done independently of direction or polarization of eitter. For ore technical paraeters of instruent check at Based on given paraeters the field strength can be calculated as follows: P- Effective Isotropic Radiated S- density flux W/ Z v - Air Ipedance = 10π λ P = S..() 4π E S =. (3) Z v 10 log S = 10 log P 0 log λ + 10 log 4π (4) For downlink GSM frequency 935 MHz: 10 log S = 10 log P 0.. (5) Referring to expression (3) we obtain: 0 log E = 10 log PW (6)

3 Proceedings of the 11th WSEAS International Conference on COMMUNICATIONS, Agios Nikolaos, Crete Island, Greece, July 6-8, V ( easured+ 55.5) / 0 E (7) = 10 Technical paraeters of base station are listed on Table 1: Operational GSM downlink band Frequency ( )Mhz Nuber of sectors 3 Main radiation directions Antennas Sector A: 0 0 Sector B : 10 0 Sector C: s /sector 5 Antenna syste height Max. No. of channels 6 per sector EIRP per channel 60 db Antenna Gain 14 dbi Horizontal beawidth 65 0 Vertical bea-width 9 0 Table 1 In order to assess exposure at peak-usage tie, we have easured and presented in Table 3 of electrical field and power density and in peak usage of syste, at 1:30. In Figure are copared easureents of average intensity of electrical field at 11:30 with easureents of 1:30 at two sites, House 3, 31 far fro base of and at point 4 far fro base of. Average of electric field V/ :30 vs. 1:30 11:30 1:30 Tie of easureent Figure House nr.3 Base of Antenna In Figure 3 are presented of electric field at different sites surrounding base station. Measureents are done at sae ground level, at garden of houses. 3 Results of easureents The precise experiental deterination of power density on coplex and dynaic environent is a difficult task. This is ainly due to reflection, absorption and interference of electroagnetic waves. Different easureents can lead to quite different results due to changing of conditions[5]. In Table are presented results of easureents of instant of electrical field, average over 6 inutes, power density and power level. Presented easureents are done at 11:30 at different sites, different heights fro ground level, indoors and outdoors, with and without usage of few obile phones. In order to include worst case scenarios we have presented as well axiu of instant and axiu of average. E V/ H1 H1 H3 H4 H5 H6 H7 distance fro Figure 3 instant ax.inst.val. average ax.aver.val

4 Proceedings of the 11th WSEAS International Conference on COMMUNICATIONS, Agios Nikolaos, Crete Island, Greece, July 6-8, Nr. Place of easureent Distance fro base of () Instant Intensity of electrical field E(V/) Maxiu of instant Averag e Maxiu of average density (W/c ) Others level db Chanal of ain frequency 1. House nr House nr (second 3. House nr House nr (second 5. House nr. 66 (third House nr House nr (gardenwith usage of obile phones) 8. House nr Base of Base of House nr.5 55 ( garden) House nr.6 3 (inside a house) 13. House nr House nr.7 50 (road) Table Nr. Place of easureent 1. House nr.3. Base of Distance fro base of () 31 Instant Intensity of electrical field E(V/) Maxiu of instant Table 3 Average Maxiu of average density (W/c ) Others level db Chanal of ain frequency

5 Proceedings of the 11th WSEAS International Conference on COMMUNICATIONS, Agios Nikolaos, Crete Island, Greece, July 6-8, Conclusion Analyzing results of practical easureents perfored in liited nuber of locations, the field strength and power density levels fro GSM 900 MHz base station never exceed the reference levels as per ICNIRP guidelines. We can conclude that even in peak-tie of usage, in different sites, different heights fro ground level, indoors and outdoors, with and without usage of few obile phones, in the vicinity of base station s, easured field strength and power density levels were well below safety guidelines. References: [1] Dragan Poljak, Niksa Kovac A Siplified Electroagnetic-theral Analysis of Huan Exposure to Radiation fro Base Station Antennas, Autoatika 45(004), 1-, [] Dariusz Wojcik, Toasz Topa and Krzysztof Szczepanski, Absorption of EM energy by huan body in the vicinity of GSM base station 005 Journal of telecounications and inforation technology, pg34-38 [3] Laurent Nicolas, Interactions between Electroagnetic Fields and Biological tissues [4] J.Klia, R.Scehovic, The field strength easureent and SAR experience related to huan exposure in 110 MHz to 40 GHz, MEASUREMENT SCIENCE REVIEW, Volue 6, Section, No.4, 006 [5] S. Miclaus, P. Bechet, Estiated and easured of the radiofrequency radiation power density around cellular base stations, Ro.Journ.Phys, Vol.5, Nos.3-4 P Bucharest, 007 [6] Andre Vander Vorst, Arye Rosen and Youji Kotsuka, RF/Microwave Interaction with Biological Tissues, 006 by John Willey & Sons, Inc. pg 7-50 [7] ARRL Handbook for Radio Aateurs, 1996 Aerican Radio Relay League, Inc. Chapter 9 [8] [9] ICNIRP Guidelines for liiting exposure to tie-varying electric, agnetic, and electroagnetic fields up to 300 GHz, Health Physics 74, pg ,1998 [10] [11] Vesna Hrvoje, Wire Antenna Theory Applied ti the Assessent of the Radiation Hazard in the Vicinity of the GSM Base Station, Serbian Journal of Electrical Engineering, Vol.1, No.1, Noveber 003, 15-6 [1] Dragan Poljak, Huan Exposure to Electroagnetic Fields, Witt Press 003 [13] Outi Kivekas, Tuuka Lehtiniei, Pertti Vainiakainen; On the general energyabsorption echanis in the huan tissues, Microwave and Optical Technology Letters / Vol.43,No.3,Noveber [14] IEEE C Standard for Safety Levels with Respect to Huan Exposure to Radio Frequency Electroagnetic Fields, khz to 300 GHz, Standards Coordinating Coittees