Martínez-Búrdalo M, Martín, Sanchis A, Villar R. FDTD assessment of human exposure to electromagnetic fields from WiFi and bluetooth devices in some operating situations. Bioelectromagnetics EPub Oct 20 2008.
This paper assessed compliance to guidelines for exposures to electromagnetic fields emanating from wireless local area networks (WLAN or WIFI) and Bluetooth devices. Although transmitted power would be lower than from mobile phones, concern arose because exposure to wireless access points is typically of longer duration.
The purpose of the paper was to analyze the field distributions in the vicinity of a person during operating conditions that would simulate everyday life.
The finite-difference time domain (FDTD) analytic method was used to compute radiofrequency (RF) energy absorption. Antennas were simulated as vertically polarized half-wavelength dipoles operating at a frequency of 2400 MHz for WLAN or Bluetooth antennas and 1800 MHz for GSM antennas.
The first part was a study of home or office environments with wireless access point antennas (based on the standard IEEE 802.11b/g) and/or laptop computers with WIFI or Bluetooth. Four geometrical configurations were considered to simulate the exposure of a person to the fields from one or two WIFI antennas operating at 2400 MHz ( (1) person in a room with antenna in a corner, (2) person with an antenna in front of eyes, (3) person with an antenna on the other side of a brick wall, (4) and person in the presence of two desktop antennas and surrounded by metallic cabinets).
The second part was a study of a situation typified by car use (simultaneous exposure by an antenna, worn inside the driver’s chest pocket, and a Bluetooth hands-free kit in the sun visor at a short distance in front of the user’s eyes).
In part one of the study, local field values for all studied configurations were below the standard reference level for a 2400 MHz exposure (listed as 61 V/m root-mean-square for the electric field). The maximum 10 gram specific absorption rates (SAR) for the four configurations listed above were, respectively (in W/kg), 0.008, 0.019, 0.008, and 0.135. The higher levels obtained in the fourth configuration can be explained by the presence of two antennas, which doubles the radiated power, and four metallic plates which increase the field for all sides of the head due to reflections.
In part two of the study, the maximum 10gm SAR was (in W/kg) 1.16 for a 1800 MHz phone (125 mW radiated power), 0.037 for a 2400 MHz phone (2.5 mW), and 0.0021 for a hands-free 2400 MHz phone (2.5 mW). In exposure plots, the GSM antenna located close to the body resulted in field hot spots with maximum averaged values within what would be first layers of tissue.
Discussion and Conclusion
Results of the study show that simulation of exposures should take into account the influence of local obstacles, which can be responsible for an increase in energy absorption. Results also show that exposure through a brick wall can produce comparable exposures to a configuration with an antenna in the same room as the person. However, in all configurations of WIFI or Bluetooth antennas, exposure was lower in comparison to mobile phone exposures.