Electric and electronic systems have become so pervasive that it is now difficult to imagine life without them. While they contribute to our quality of life in many ways, they also create electromagnetic fields (EMF or non-ionizing radiation) which, when emitted at sufficient levels, may warm biological tissues (as they do in microwave ovens).
Electromagnetic fields have different frequencies - expressed in Herz (Hz) suited to different uses:
Divided European Opinion
On 10/11/2012, United Nations International Telecommunications Union (ITU) announced that "Mobile-cellular subscriptions registered continuous double-digit growth in developing country markets, for a global total of 6 billion mobile subscriptions by end 2011." The rapid development of mobile telecommunications and other electronic appliances since the 1990's has substantially increased our daily exposure to electromagnetic fields. This has raised concerns about their possible adverse health effects.
Based on EU survey on EMF published in June 2007, it shows that European opinion about the potential health risks of electromagnetic fields is divided:
RFR and SAR
In this article, we'll focus on one of the EMF dissipated from wireless communication devices — radio frequency radiation (RFR).
For the purpose of radiation protection, dosimetric quantities are needed to estimate the absorbed energy and its distribution inside the body. A dosimetric quantity that is widely adopted for radio waves used in cell phones is the Specific Absorption Rate (SAR). SAR is defined as the time derivative of the incremental energy, absorbed by or dissipated in an incremental mass contained in a volume element of a given density. It is expressed in the unit watt per kilogram (W/kg).
Whole-body SAR (as expressed in W/kg) is not very easy to measure practically, consequently reference level is given in terms of the power density which is expressed in the unit W/m2 or mW/cm2.
The FCC adopted the limits from Report No. 86, "Biological Effects and Exposure Criteria for Radiofrequency Electromagnetic Fields," published in 1986 by the Congressional chartered National Council on Radiation Protection and Measurements ("NCRP"). Separate limits apply for occupational and public exposure conditions, with the latter limits generally five times more restrictive. The more recent standard, developed by the Institute of Electrical and Electronics Engineers and approved as American National StandardANSI/IEEE C95.1-2006, "Safety Levels with Respect to Human Exposure to Radio Frequency Electromagnetic Fields, 3 kHz to 300 GHz," includes similar limits. These limits apply for continuous exposures from all sources and are intended to provide a prudent margin of safety for all persons, regardless of age, gender, size, or health.
Human body interacts with radio waves at different frequencies differently. For example, the body tends to interact more strongly with radio waves at 870 MHz than at 1950 MHz. Therefore, as shown in the Figure below, a lower exposure limit is set for 870 MHz (i.e., Cell) than for 1950 MHz (i.e., PCS).
The most restrictive FCC limit for exposures of unlimited duration to radio frequency energy for several personal wireless services are as follows:
considering exposure in the context of the FCC guidelines, it is
important to recognize that the guidelines are intended to limit total exposure to radio waves from all sources and
not just that part of exposure arising from a particular source. An
example is shown in the pie chart below, which depicts measurement
proportions arising from different sources.
Wireless radiation absorption occurs at the molecular, cellular, tissue, and whole-body levels. The dominant factor for net energy absorption by an entire organism is related to the dielectric properties of bulk water, which ultimately causes transduction of electromagnetic energy into heat.
Wireless radiation effects can be classified as thermal or non-thermal. Thermal effects are well established and form the biological basis for restricting exposure to RF fields. In contrast, non-thermal effects are not well established. From recent epidemiological studies (human population studies) of long-term frequent cellular phone use, we have sufficient reasons to believe that taking precautionary steps is necessary. See the following posts: