Strength of radio frequency signal: A better marker of mobile phone radiation
The dynamic use of mobile phone worldwide brought into a growing concern about the health hazards of cellphone radiation and long-term exposure to radiofrequency (RF) field around the phone and its implication with possible adverse health effects, particularly brain and other intracranial tumors [8, 5, 7]. Electromagnetic field produced by the antenna of mobile phone has several components. Only one of these actually propagates through space as radiofrequency signal while the other components remain near the antenna. The strength of the RF signal decreases rapidly with distance, however the entire field strength near the antenna can be relatively high and pose a hazard to the human head [6].
When the exposed head is near the antenna, the electromagnetic field is distributed due to the electric properties of the tissue. Some of the energy in the electromagnetic waves emitted by phone is absorbed by the head, mostly in superficial tissue and is quantified by the Specific Absorption Rate (SAR) [Watts/kg]. Scientific data indicate that, during exposure to radiation from a mobile phone, variety of biological effects occur at energy levels that may or may not cause local increase in temperature. Differences between experimental electroencephalography EEG, with and without the use of cell phone, have been observed [1]. The distribution of the absorbed energy in the head varies with the design of the phone and to which side of the head it is held [9]. The radiofrequency range normally used in mobile phone is 0.9 – 1.8 GHz while the maximum power that is permitted to transmit is 2W for 0.9 GHz and 1W for 1.8 GHz. These powers are reduced by the help of adaptive power control (APC) and discontinuous transmissions. The APC continually adjust the power from phone, such that the transmitted power for clear signal is a minimum [6, 10]. APC employed by the second-generation GSM (Global System for Mobile communications) networks have the ability to reduce the output power of mobile phone handsets by 2 fold on average [9].
For a phone to pass FCC certification and be sold in the United States, its maximum SAR level must be less than 1.6 Watts/kg. In Europe, the level is capped at 2 Watts/kg, while Canada allows a maximum of 1.6 Watts/kg. The SAR level varies between different transmission bands (the same phone can use multiple bands during a call), and between different models of handset that’s offered by multiple carriers. The exposure to RF signal depends on the output power of the phone, which is directly related to the exposure level (call duration) and absorbed dose, and may vary by a factor of 1000 during a call [3].
The base station will regulate the output power of the mobile phone depending on the received signal strength. Factors that may influence the APC are the distance between hand set and base station, attenuation of the signal, length of the call (the phone transmit maximum allowed signal at the onset of each call), and change of connecting base station, ‘‘handover’’ (the phone will temporarily increase output power when connecting to a new base station). Some researchers advise against using phone in areas with poor coverage since phones emit more radiation when searching for a signal. Thus, calls made in locations with larger distance to base stations such as rural areas, and while in a moving vehicle may achieve substantially higher output power [9, 4].
When the RF signal strength is weak, the emitted radiation can be 1000 fold higher as in the case of distant places from base station, moving vehicles and heavy traffic in base station. The variation of emitted radiation can best be monitored by strength of RF signal, which varies by a factor of 1000 than SAR of the specific cell phone, which differs by a maximum of 20 fold. Though the signal level does not tell the exact amount of radiation, it indicates that the radiation is higher when the signal is weak. A high or good signal level improves the safety of user from radiation related hazard. In order to ensure user safety from mobile phone radiation, a simple application is constructed that alerts the user about the lower signal level, when initiating a call. This application will prompt the user to postpone the call or switch to hands free equipment, when the signal is below the threshold. Several simple measures can be practiced to avoid cell phone radiation associated hazards, despite purchasing a handset with a low SAR. Text message instead of placing a voice call, use a wired headset or speakerphone whenever possible, and hold the phone at least one inch away from your body. Use of hands free equipment may reduce the amount of absorbed energy in the head considerably (more than a 90% reduction) [2]. Children, who have smaller and thinner skulls, should limit cell phone use, and all users, should not sleep with an active phone next to their bedside or under their pillow.
Many SAR protection software and chips are commercially available all over the world. You can buy it here:http://www.radisafe.co/
http://www.sarshield.com/
References
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[2] Bit-Babik G., Chou C.K., Faraone A., Gessner A., Kanda M., and Balzano Q. Estimation of the SAR in the head and body due to radiofrequency radiation exposure from handheld mobile phones with hands-free accessories. Radiat Res 2003: 159: 550–557.
[3] ETSI. Digital cellular telecommunications system (Phase 2+); Radio transmission and reception (3GPP).2007; ETSI TS 145 005 V7.11.0 (R7).
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[6] Morega M, Machedon A Specific Conditions for EMF Modeling in Human Exposure from mobile Phone Technology, Advanced Topics in Electrical Engineering ATEE 2002, Bucharest, Romania, Nov. 2002, 7 pg., Proc. CD-ROM
[7] Sadetzki S, Chetrit A, Jarus-Hakak A, et al. Cellular phone use and risk of benign and malignant parotid gland tumors—a nationwide case-control study. Am J Epidemiol 2008;167:457–67.
[8] Takebayashi T, Akiba S, Kikuchi Y, et al. Mobile phone use and acoustic neuroma risk in Japan. Occup Environ Med 2006;63:802–7.
[9] M Vrijheid, S Mann, P Vecchia, et al. Determinants of mobile phone output power in a multinational study: implications for exposure assessment Occup Environ Med 2009;66:664–671. doi:10.1136/oem.2008.043380
[10] Wiart J, Dale C, Bosisio AD, et al. Analysis of the influence of the power control and discontinuation transmission on RF exposure with GSM mobile phones. IEEE Transactions on Electomagnetic compatibility 2000;42:376–85.
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