ID Number		898
Study Type		Engineering & Physics
Model		Exposure [900, 1800 MHz (GSM)] from mobile phone microcell and picocell base stations and Wi-Fi devices in schools (as a prediction of potential human exposure).
Details		RF emissions measured near 20 different microcell and picocell sites in the UK to assess field strengths. A map of RF emissions was constructed indicating the level of public exposure is below the ICNIRP recommended guidelines. The minimal height at which the ICNIRP level could potentially be exceeded was 2.4 meters above ground level (average male height ~2.6 meters), although exposures were generally 0.002-2% of the ICNIRP general public reference level. Exposure near microcell base stations was generally greater than close to macrocell base stations. AUTHORS' ABSTRACT: Khalid et al. 2011 (IEEE #6069): The growing use of wireless local area networks (WLAN) in schools has prompted a study to investigate exposure to the radio frequency (RF) electromagnetic fields from Wi-Fi devices. International guidelines on limiting the adverse health effects of RF, such as those of ICNIRP, allow for time-averaging of exposure. Thus, as Wi-Fi signals consist of intermittent bursts of RF energy, it is important to consider the duty factors of devices in assessing the extent of exposure and compliance with guidelines. Using radio packet capture methods, the duty factor of Wi-Fi devices has been assessed in a sample of 6 primary and secondary schools during classroom lessons. For the 146 individual laptops investigated, the range of duty factors was from 0.02 to 0.91%, with a mean of 0.08% (SD 0.10%). The duty factors of access points from 7 networks ranged from 1.0% to 11.7% with a mean of 4.79% (SD 3.76%). Data gathered with transmit time measuring devices attached to laptops also showed similar results. Within the present limited sample, the range of duty factors from laptops and access points were found to be broadly similar for primary and secondary schools. Applying these duty factors to previously published results from this project, the maximum time-averaged power density from a laptop would be 220 ¼W m2, at a distance of 0.5 m and the peak localised SAR predicted in the torso region of a 10 year old child model, at 34 cm from the antenna, would be 80 ¼W kg1. AUTHORS' ABSTRACT: Peyman et al. 2011 (IEEE #6558): Laboratory measurements have been carried out with examples of Wi-Fi devices used in UK schools to evaluate the radiofrequency power densities around them and the total emitted powers. Unlike previous studies, a 20 MHz bandwidth signal analyzer was used, enabling the whole Wi-Fi signal to be captured and monitored. The radiation patterns of the laptops had certain similarities, including a minimum toward the torso of the user and two maxima symmetrically opposed across a vertical plane bisecting the screen and keyboard. The maxima would have resulted from separate antennas mounted behind the top left and right corners of the laptop screens. The patterns for access points were more symmetrical with generally higher power densities at a given distance. The spherically-integrated radiated power (IRP) ranged from 5 to 17 mWfor 15 laptops in the 2.45 GHz band and from 1 to 16 mW for eight laptops in the 5 GHz band. For practical reasons and because access points are generally wallmounted with beams directed into the rooms, their powers were integrated over a hemisphere. These ranged from 3 to 28 mWfor 12 access points at 2.4 GHz and from 3 to 29 mW for six access points at 5 GHz. In addition to the spherical measurements of IRP, power densities were measured at distances of 0.5 m and greater from the devices, and consistent with the low radiated powers, these were all much lower than the ICNIRP reference level.
Findings		Not Applicable to Bioeffects
Status		Completed With Publication
Principal Investigator		NRPB, UK
Funding Agency		HPA (NRPB), UK, MMF, MTHR (NRPB), UK, GSM Association, DTI, UK
Country		UNITED KINGDOM
References		Cooper, TG et al. J Radiol Prot, (2006) 26:199-211 Khalid, M et al. Progress in Biophysics and Molecular Biology., (2011) 107:412-420 Peyman, A et al. Health Physics., (2011) 100:594-612 Mann, S et al. WHO International Workshop on Base Stations and Wireless Networks: Exposures and Health Consequences (2005: Geneva, Switzerland)., (2005) :83-105
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