whether it is safe to use cellular phone or not
...rnet Association (CTIA) are required to provide SAR information to consumers in the instructional materials that come with the phones. Antenna Restriction: FCC sets up restriction in antenna structure in order to prevent excessive radiation. Therefore, we need to understand antenna technology. Antennas transmit and receive radio waves. The focused strength of this radiated energy is measured in terms of gain in decibels (dB). Gain in microwave antennas is typically specified in dBi, which refers to the resulting decibel measurement in relation to a theoretic isotropic radiator, which is equal in all directions. The gain in the antenna focuses the transmitted signal towards the targeted area of coverage. It also focuses incoming energy on the receive side. It is important to take gain into consideration when selecting network antennas. Enough gain on both the broadcasting and receiving side will be necessary to establish stable links, but not so much as to exceed the legal radiated power limitations of 4 watts (+36 dBm) maximum effective radiated power (ERP). The ERP is the total amount of power actually transmitted through the system’s antenna and it is the product of the transmitter’s power output, the cable’s power loss and the antenna’s gain capability. Antenna manufacturers typically include various gain models in their product offering in order to accommodate differing access point gain requirements. What else prevention method we can adopt? According to ICNIRP, SAR is not a good measure for assessing absorbed energy; the incident power density of the field (in W m-2) is a more appropriate dosimetric quantity. Therefore, ICNIRP advised that a device can be installed in cellular phone to measure the electric and magnetic field constantly and provide warning to the user when it reaches to maximal level. Antenna Technology (Microstrip antennas are used for cellular phones. It can use any design, such as dipole, loop array.) Antenna technology is relatively new. The development is rapid. For longer links, an array of sector panel antennas provides a robust installation that can be used to focus the transmitted signal towards the desired areas of coverage. This can be accomplished by designing a phasor-array antenna. The picture is inserted below. This option is especially effective if the selected antennas feature efficient front-to-back ratio performance that minimizes the back reflections that contribute to co-channel interference and decreased signal strength. One of the main advantages of sector antennas is that they allow phone companies to sectorize the coverage area by transmitting the radiated signal to those areas needing coverage, and not to areas lacking subscribers. Some sector panel antennas can be adjusted according to the horizontal beamwidth needed without the need to replace or remove the antenna from the tower. As the customer base grows, additional sectors and data radios can be added to customize the radiated patterns according to the geographical region covered and the density of the population within that region. This feature allows phone companies to re-use the same frequency at another location or in another direction. This is an ideal example of cellular transmitting antenna. Phased Array Antenna in Freeport, Florida Conclusion: We can not risk our health. That could be the only or at least the best reason that we can request the law makers and FCC to keep public posted about rf radiation. We can demand better technology and more awareness from antenna and phone companies and FCC. Glossary Absorption. In radio wave propagation, attenuation of a radio wave due to dissipation of its energy, i.e., conversion of its energy into another form, such as heat. Athermal effect. Any effect of electromagnetic energy on a body that is not a heat-related effect. Blood-brain barrier. A functional concept developed to explain why many substances that are trans-ported by blood readily enter other tissues but do not enter the brain; the “barrier” functions as if it were a continuous membrane lining the vasculature of the brain. These brain capillary endothelial cells form a nearly continuous barrier to entry of substances into the brain from the vasculature. Conductance. The reciprocal of resistance. Ex-pressed in siemens (S). Conductivity, electrical. The scalar or vector quantity which, when multiplied by the electric field strength, yields the conduction current density; it is the reciprocal of resistivity. Expressed in siemens per meter (S m). Continuous wave. A wave whose successive oscillations are identical under steady-state conditions. Current density. A vector of which the integral over a given surface is equal to the current flowing through the surface; the mean density in a linear conductor is equal to the current divided by the cross-sectional area of the conductor. Expressed in ampere per square meter (A m) Depth of penetration. For a plane wave electro-magnetic field (EMF), incident on the boundary of a good conductor, depth of penetration of the wave is the depth at which the field strength of the wave has been reduced to 1/e, or to approximately 37% of its original value. Dielectric constant. See permittivity. Dosimetry. Measurement, or determination by calculation, of internal electric field strength or induced current density, of the specific energy absorption, or specific energy absorption rate distribution, in humans or animals exposed to electromagnetic fields. Electric field strength. The force (E) on a stationary unit positive charge at a point in an electric field; measured in volt per meter (V m). Electromagnetic energy. The energy stored in an electromagnetic field. Expressed in joule (J). ELF. Extremely low frequency; frequency below 300 Hz. EMF. Electric, magnetic, and electromagnetic fields. Far field. The region where the distance from a radiating antenna exceeds the wavelength of the radiated EMF; in the far-field, field components (E and H) and the direction of propagation are mutually perpendicular, and the shape of the field pattern is independent of the distance from the source at which it is taken. Frequency. The number of sinusoidal cycles completed by electromagnetic waves in 1 s; usually ex-pressed in hertz (Hz). Impedance, wave. The ratio of the complex number (vector) representing the transverse electric field at a point to that representing the transverse magnetic field at that point. Expressed in ohm (V). Magnetic field strength. An axial vector quantity, H, which, together with magnetic flux density, specifies a magnetic field at any point in space, and is expressed in ampere per meter (A m). Magnetic flux density. A vector field quantity, B, that results in a force that acts on a moving charge or charges, and is expressed in tesla (T). Magnetic permeability. The scalar or vector quantity which, when multiplied by the magnetic field strength, yields magnetic flux density; expressed in henry per meter (H m). Note: For isotropic media, magnetic permeability is a scalar; for anisotropic media, it is a tensor quantity. Microwaves. Electromagnetic radiation of sufficiently short wavelength for which practical use can be made of waveguide and associated cavity techniques in its transmission and reception. Note: The term is taken to signify radiations or fields having a frequency range of 300 MHz–300 GHz. Near field. The region where the distance from a radiating antenna is less than the wavelength of the radiated EMF. Note: The magnetic field strength (multi-plied by the impedance of space) and the electric field strength are unequal and, at distances less than one-tenth of a wavelength from an antenna, vary inversely as the square or cube of the distance if the antenna is small compared with this distance. Non-ionizing radiation (NIR). Includes all radiations and fields of the electromagnetic spectrum that do not normally have sufficient energy to produce ionization in matter; characterized by energy per photon less than about 12 eV, wavelengths greater than 100 nm, and frequencies lower than 10 Hz. Occupational exposure. All exposure to EMF experienced by individuals in the course of performing their work. Permittivity. A constant defining the influence of an isotropic medium on the forces of attraction or repulsion between electrified bodies, and expressed in farad per metre (F m); relative permittivity is the permittivity of a material or medium divided by the permittivity of vacuum. Plane wave. An electromagnetic wave in which the electric and magnetic field vectors lie in a plane perpen-dicular to the direction of wave propagation, and the magnetic field strength (multiplied by the impedance of space) and the electric field strength are equal. Power density. In radio wave propagation, the power crossing a unit area normal to the direction of wave propagation; expressed in watt per square meter (W m). Public exposure. All exposure to EMF experienced by members of the general public, excluding occupa-tional exposure and exposure during medical procedures. Radiofrequency (RF). Any frequency at which electromagnetic radiation is useful for tele communication. Note: In this publication, radio frequency refers to the frequency range 300 Hz –300 GHz. Resonance. The change in amplitude occurring as the frequency of the wave approaches or coincides with a natural frequency of the medium; whole-body absorption of electromagnetic waves presents its highest value, i.e., the resonance, for frequencies (in MHz) corresponding approximately to 114/L, where L is the height of the individual in meters. Root mean square (rms). Certain electrical effects are proportional to the square root of the mean of the square of a periodic function (over one period). This value is known as the effective, or root-mean-square (rms) value, since it is derived by first squaring the function, determining the mean value of the squares obtained, and taking the square root of that mean value. Specific energy absorption. The energy absorbed per unit mass of biological tissue, (SA) expressed in joule per kilogram (J kg); specific energy absorption is the time integral of specific energy absorption rate. Specific energy absorption rate (SAR). The rate at which energy is absorbed in body tissues, in watt per kilogram (W kg); SAR is the dosimetric measure that has been widely adopted at frequencies above about 100 kHz. Wavelength. The distance between two successive points of a periodic wave in the direction of propagation, at which the oscillation has the same phase. REFERENCES 1. IEEE C95.1-1991: "Safety Levels with Respect to Human Exposure to Radio Frequency Electromagnetic Fields, 3 kHz to 300 GHz," IEEE, Piscataway, NJ, 1992 2. NCRP: Biological effects and exposure criteria for radio frequency electromagnetic fields, Report 86, (Bethesda, MD National Council on Radiation Protection and Measurements) 1-382, 1986. 3. ICNIRP: Guidelines for limiting exposure to time-varying electric, magnetic and electromagnetic fields (up to 300GHz), Health Physics, 74(4): 494-522, 1998. 4. NRPB: Board Statement on Restrictions on Human Exposure to Static and Time-Varying Electromagnetic Fields, Documents of the PRPB, Vol. 4, No. 5, National Radiological Protection Board, Chilton, Didcot, Oxon, UK, 1993. 5. U.S. Federal Communications Commission, Office of Engineering and Technology, "Evaluating Compliance with FCC-Specified Guidelines for Human Exposure to Radiofrequency Electromagnetic Fields," OET Bulletin 65, August 1997. 6. COMAR Reports: Radio frequency interference with medical devices: A Technical Information Statement. IEEE Engineering in Medicine and Biology Magazine 17(3):111-114, 1998. 7. RF Radiation in human life, Vol XXX No. 10, Microwave News 8. A report on non-ionizing radiation, Vol XXV No. 5, Microwave News 9. Fundamental of applied electromagnetics, ISBN 0-13-185089-X 10. Antenna Theory,ISBN 0-471-59268-4 On October 20, 1999, the ABC News show “20/20” aired a story about the safety of hand-held cellular telephones and their compliance with FCC safety and testing guidelines. The ABC News story reported that certain cell telephones were tested failed to comply with FCC test guidelines. Even though FCC did not agree with the allegation and promised to work with manufacturers involved to determine if any further action was required, it is essential to look into the cell technology and how it does affect our health, so that we can understand safety standards applied by FCC which can provide safety for our cellular phone usage. FCC sets up guidelines on cellular phone radiation. The FCC's guidelines are based on recommendations by two expert organizations- Institute of Electrical and Electronics Engineers (IEEE) and International Commission on Non-Ionizing Radiation Protection (ICNIRP). The FCC's guidelines have received the support of key federal health and safety agencies, including the Food and Drug Administration (FDA), the Environmental Protection Agency (EPA), the National Institute for Occupational Safety and Health (NIOSH) and the Occupational Safety and Health Administration (OSHA). Report from IEEE and ICNIRP on cellular phone radiation In September 2000, the institute of Electrical and Electronics Engineers (IEEE) Committee on Man and Radiation (COMAR) stated in one report that there was public concern about the safety of exposure to the radio frequency (RF) and microwave (MW) fields from hand-held, portable, and mobile cellular telephones . In that report, IEEE stated that when considering possible hazards from exposure to wireless transmitters, several considerations must be taken into account. The first consideration is the power output of the transmitter and receiver, and its distance from the body. The radio waves emitted by the phone itself are referred to as the 'near field.' When we are on the phone, the field we are creating is called ‘near field.’ It is the near field "radiation" responsible for most of the cell phone health effects reported since 1993. The 'far field' radio waves are the "radiation" the cell phone requires for communication. When we receive a phone call, we create a far field. A picture is inserted below to explain near and far field. Figure 1: Far Field and Near Field The situation in the near-field region is rather more complicated because the maxima and minima of E and H fields do not occur at the same points along the direction of propagation as they do in the far field. In the near field, the electromagnetic field structure may be highly inhomogeneous, and there may be substantial variations from the plane-wave impedance ; that is, there may be almost pure E fields in some regions and almost pure H fields in others. Exposures in the near field are more difficult to specify, because both E and H fields must be measured and because the field patterns are more complicated; in this situation, power density is no longer an appropriate quantity to use in expressing exposure restrictions (as in the far field). Exposure to time-varying EMF results in internal body currents and energy absorption in tissues that depend on the coupling mechanisms and the frequency involved. Figure 2 In this diagram, we can see that electric field, E and magnetic field, H of transmitting wave have different directions. That results different polarization at different distances. In the guidelines for limiting exposure to time-varying electric, magnetic and electromagnetic fields, ICNIRP described two coupling mechanisms- 1) Coupling to low-frequency electric fields The interaction of time-varying electric fields with the human body results in the flow of electric charges (electric current), the polarization of bound charge (formation of electric dipoles), and the reorientation of electric dipoles already present in tissue. The relative magnitudes of these different effects depend on the electrical properties of the body—that is, electrical conductivity (governing the flow of electric current) and permittivity (governing the magnitude of polarization effects). Electrical conductivity and permittivity vary with the type of body tissue and also depend on the frequency of the applied field. Electric fields external to the body induce a surface charge on the body; this results in induced currents in the body, the distribution of which depends on exposure conditions, on the size and shape of the body, and on the body’s position in the field. 2) Coupling to low-frequency magnetic fields The physical interaction of time-varying magnetic fields with the human body results in induced electric fields and circulating electric currents. The magnitudes of the induced field and the current density are propor tional to the radius of the loop, the electrical conductivity of the tissue, and the rate of change and magnitude of the magnetic flux density. For a given magnitude and frequency of magnetic field, the strongest electric fields are induced where the loop dimensions are greatest. The exact path and magnitude of the resulting current induced in any part of the body will depend on the electrical conductivity of the tissue. The body is not electrically homogeneous; however, induced current densities can be calculated using anatomically and electrically realistic models of the body and computational methods, which have a high degree of anatomical resolution. The second consideration is frequency because exposure guidelines vary with frequency. Wireless communications operate in a variety of frequency ranges. Frequency Spectrum: In the guidelines for limiting exposure to time-varying electric, magnetic and electromagnetic fields, ICNIRP described that exposure to low-frequency electric and magnetic fields normally results in negligible energy absorption and no measurable temperature rise in the body. However, exposure to electromagnetic fields at frequencies above about 100 kHz can lead to significant absorption of energy and temperature increases. In general, exposure to a uniform (plane-wave) electromagnetic field results in a highly non-uniform deposition and distribution of energy within the body, which must be assessed by dosimetric measurement and calculation. As regards absorption of energy by the human body, electromagnetic fields can be divided into four ranges : - frequencies from about 100 kHz to less than about 20 MHz, at which absorption in the trunk decreases rapidly with decreasing frequency, and significant absorption may occur in the neck and legs; - frequencies in the range from about 20 MHz to 300 MHz, at which relatively high absorption can occur in the whole body, and to even higher values if partial body (e.g., head) resonances are considered; - frequencies in the range from about 300 MHz to several GHz, at which significant local, non-uniform absorption occurs; and - frequencies above about 10 GHz, at which energy absorption occurs primarily at the body surface. In tissue, Specific Absorption Rate (SAR) is proportional to the square of the internal electric field strength. Average SAR and SAR distribution can be computed or estimated from laboratory measurements. Values of SAR depend on the following factors: - the incident field parameters, i.e., the frequency, intensity, polarization, and source– object configuration (near- or far-field); - the characteristics of the exposed body, i.e., its size and internal and external geometry, and the dielectric properties of the various tissues; and - ground effects and reflector effects of other objects in the field near the exposed body. When the long axis of the human body is parallel to the electric field vector, and under plane-wave exposure conditions (i.e., far-field exposure), whole-body SAR reaches maximal values. The amount of energy absorbed depends on a number of factors, including the size of the exposed body. “Standard Reference Man” , if not grounded, has a resonant absorption frequency close to 70 MHz. For taller individuals the resonant absorption frequency is somewhat lower, and for shorter adults, children, babies, and seated individuals it may exceed 100 MHz. For some devices that operate at frequencies above 10 MHz (e.g., dielectric heaters, mobile telephones), human exposure can occur under near-field conditions. The frequency-dependence of energy absorption under these conditions is very different from that described for far-field conditions. Magnetic fields may dominate for certain devices, such as mobile telephones, under certain exposure conditions. The usefulness of numerical modeling calculations, as well as measurements of induced body current and tissue field strength, for assessment of near-field exposures has been demonstrated for mobile telephones, walkie-talkies, broadcast towers, shipboard communication sources, and dielectric heaters. The importance of these studies lies in their having shown that near-field exposure can result in high local SAR (e.g., in the head, wrists, ankles) and that whole-body and local SAR are strongly dependent on the separation distance between the high-frequency source and the body. Finally, SAR data obtained by measurement are consistent with data obtained from numerical modeling calculations. Whole-body average SAR and local SAR are convenient quantities for comparing effects observed under various exposure conditions. At frequencies greater than about 10 GHz, the depth of penetration of the field into tissues is small, and SAR is not a good measure for assessing absorbed energy; the incident power density of the field (in W m -2 ) is a more appropriate dosimetric quantity. Medical research on Cellular phone radiation University of Wisconsin medical school published a report which suggested that exposure to RF (Radio Frequency) radiation may increase the incidence of lymphoma . In this report, Dr. Lai and Singh suggested that relatively low-level exposure to RF radiation can cause DNA strand breaks in rat brain cells. The picture below was inserted in the report to show the DNA damage by near field magnetic field. FCC denies any kind of health risk even though they promise to keep up the research and investigation, IEEE shows some concern and some medical research shows some damage to animal brain cell resulting in to radio frequency radiation. If we look at cellular phone market, we can find some companies sell some products to prevent radiation from radio frequency technology. Some of them are listed below. FCC filed law suits against Comstar Communication and Stock Value to advertise product that according to the alleged companies prevent us from radiation by radio frequency . According to FCC, advertisements are not supported by valid documents and research. Since no long time research has not been done to find out the radiation affect on our health created by radio frequency, no medical or scientific data is available to FCC, IEEE, ICNIRP or any other company. Only short time research has been completed which proved some minor health affect on many children and some people . To be on the safe side, IEEE, ICNIRP and other organization admits the concern but no specific awareness has not been adopted by FCC yet. What are the prevention methods available right now? Restriction on radiation The FCC requires wireless phones to comply with a safety limit of 1.6 watts per kilogram (1.6 W/kg) in terms of SAR. Information on SAR for a specific phone model can be obtained for many recently manufactured phones using the FCC identification (ID) number for that model . The FCC ID number is usually printed somewhere on the case of the phone. Sometimes it may be necessary to remove the battery pack to find the number. Once we have the ID number, we can go to the following Web address: www.fcc.gov/oet/fccid. After we fill up the form, FCC will provide typical or maximum SAR for our phone. In addition to this, phones certified by the Cellular Telecommunications and Intern...