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THE NATURE OF ELECTROMAGNETIC RADIATION EMFs, EMR |
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This tells you all you need to know about Electromagnetic radiation in its various forms—it’s a long read of about 4 of these pages. But persevere!
See here for an more articles on electrosensitivity, Cellphones, EMFs, prudent avoidance, etc.
(From http://www.milligauss.com/info.html) The Author: Mr. George S. Lechter holds a BS in mechanical engineering from M.I.T. (1975) with a concentration in computers, and holds an MS degree from M.I.T.'s Sloan School of Management (1977). He has had 26 years of experience in the computer and electromagnetic field. He worked as a management consultant for Harbridge House, Inc. (then a Sears Roebuck company) and as a strategic market planning consultant for Braxton Associates in Boston. He was a minicomputer marketing specialist at Nixdorf in Waltham, MA, and worked in the software industry for 9 years. In 1988 he founded Technology Alternatives Corporation. Mr. Lechter holds several patents.
An AC electric current is defined as the movement of electrons in roughly the same direction, usually through a wire. This current, in turn, produces two types of fields: an AC electric field and an AC magnetic field, which together are called an electromagnetic field. The AC electric fields result from the strength of the charge and the AC magnetic fields result from the motion of the charge (i.e., the flow of electrons comprising the electric current). The AC electric field represents the force that electric charges exert on other charges, and this force may either repel (as with two positive charges, for example) or attract. The AC magnetic field forms a closed continuous doughnut-shaped loop around the current and radiates at a right angle to the direction of the current.
People can sense an electric field of more than about 20 kilovolts/meter (kV/m) as a slight tingling sensation on their skin. This level can be found underneath high voltage power lines. On the other hand, most people cannot feel the presence of AC magnetic fields except at extraordinarily strong levels (although some people claim they can sense even low levels of EMF).
Interestingly, while an AC electric current creates an AC magnetic field, it is also true that an AC magnetic field creates an AC electric current in a nearby conductor. This is the principle of induction, and it is how we detect and measure AC EMF fields. Induction is also the principle by which a transformer raises or lowers voltages. In a transformer, an AC electric current flowing through a coil of wire radiates an AC magnetic field, and another adjacent coil of wire picks up the AC magnetic field and converts it back into AC electric current. The number of coils on each side of the transformer determine by how much the voltage is increased or decreased.
In order to distribute electricity economically over long distances, high voltages are used. Between the power plant and your home, a series of transformers reduce the voltage along the way so that by the time it reaches your home, the voltage has been reduced to the 120/240 volt level. It is desirable to use alternating current (AC), since most transformers work only with AC. AC means that the direction of the current alternates back and forth. The frequency of the back and forth cycle is measured in Hertz (Hz), which stands for cycles per second. Hence, when we talk about a 60 Hz current, which is the standard in the United States, this means that the direction of the current is changing back and forth 60 times per second. In Europe and other parts of the world, the frequency of AC electric power is 50 Hz rather than 60 Hz.
A graph of AC current (voltage vs. time) will form a sine wave, with a positive voltage for half of the time, and a negative voltage for the other half. The same is true of the electric and magnetic fields, which travel in one direction and then the other, corresponding with the changes in direction of the AC current. Since power lines, household wiring and appliances all carry electricity with a 60 Hz cycle, the resulting AC electric and AC magnetic fields also oscillate at 60 Hz. Such frequencies are at the low end of the electromagnetic spectrum, and are referred to as extremely low frequency (ELF) fields. The 60 Hz frequency originates at the power generating station and ends up in our household appliances. Higher voltages change the strength of the fields, but not the 60 Hz frequency.
Radiation is a broad term meaning the transmission of energy in the form of waves through space or through a material medium and also the radiated energy itself. The force field associated with radiation is the region throughout which the radiation is measurable. Sometimes electromagnetic radiation is called EMR, while electromagnetic fields are frequently referred to as EMF. EMR and EMF refer to the entire range of the electromagnetic spectrum, from extremely low frequencies to radio waves. In practice, EMF is used more often than EMR because "radiation" sounds scary and its use may create confusion with more dangerous radiation from X-ray machines and radioactive material. In news reports and articles written for the general public (such as this article), EMF is used loosely to indicate the low frequency electromagnetic fields coming from power lines, home wiring, appliances, TVs and computer displays.
EMF from different sources can either add together or cancel each other out. This is due to the wave characteristics of electromagnetic radiation. If the radiation from two sources are in phase, then the peaks of each cycle will occur together, and the fields will add together. On the other hand, if the two sources are exactly out of phase, then one source will be reaching its greatest strength in one direction at exactly the same time as the other source is peaking in the opposite direction. If the magnitude of the fields is identical, then the fields will cancel each other out, and the magnetic field measurement will be zero. This is why neutral and hot wires in household wiring need to be paired close together. This characteristic also provides a mechanism for configuring power lines and VDTs so that EMF levels are reduced. EMF can be either man-made or occur naturally. Examples of electromagnetic radiation, in order of increasing frequency, are extremely low frequency (ELF), very low frequency (VLF), radio waves, microwaves, infrared (heat), visible light, ultraviolet, X-rays, and gamma rays. All electromagnetic radiation travels at the speed of light.
The frequency of the electromagnetic radiation is what determines its character. X-rays (and other forms of ionizing radiation) can strip electrons away from an atom, thereby creating an "ion." When living systems are exposed to such radiation, detrimental effects are caused by breaking apart molecular bonds. Cancer can be caused by such ionizing radiation when DNA (the molecules that make genes) is broken apart. At ELF frequencies, electromagnetic radiation is non-ionizing, meaning it cannot knock electrons away from atoms or alter molecular structures. However, low frequency electromagnetic radiation is nevertheless an energy force, and this energy force can shake atoms and molecules back and forth. The field strength of electromagnetic fields can be calculated mathematically.
Fields from compact sources containing coils or magnets (transformers, appliances, and computer displays, for example) diminish most rapidly with distance F in proportion with the distance cubed (1/d**3; d = distance). Fields from long wire conductors in power lines drop off in proportion with the distance squared (1/d**2), provided the currents flowing in opposite directions are well-balanced. The field strength drops off less quickly with secondary distribution lines, since the currents are frequently unbalanced. In practice, it is easier to measure the field strength than to calculate it, since there are usually multiple EMF sources which interact with each other in complex ways.
THEORIES ON HOW EMF AFFECTS BIOLOGICAL SYSTEMS
For many years some scientists and engineers felt that low frequency EMF could not possibly produce significant biological changes or effects. This reasoning was based upon the fact that low frequency EMF cannot break molecular bonds and it generates only a miniscule amount of heat - not enough to heat body tissue. However, this argument has turned out to be incorrect because there are other ways in which fields can interact with individual cells to produce biological changes.
If we recall that magnetic fields can induce an electric current in a nearby conductor, the implication is that AC magnetic fields will induce electric currents in our bodies (although such currents will be very small). That's because our bodies are mostly comprised of a conductive medium (salty water). Some of these currents are similar to what a salamander uses to regenerate a limb, and therefore the artificial creation of these currents in a human body are of concern.
The way in which electromagnetic radiation affects the body is not fully known. A similar state of knowledge applies to the mechanisms behind how aspirin cures a headache or reduces fever, or why asbestos causes cancer. One theory is that EMF causes the cell walls to vibrate, or to resonate, in the same way you can shake a bowl of jello and observe it oscillate back and forth at a certain frequency.
Resonance is not necessarily harmful. The body is composed of many elements that can resonate at different frequencies. The human ear is an example of a part of the body which resonates in tune with its environment. When we listen to the music of a violin, we are hearing a sound vibration of 5,000 cycles per second. The sound from a violin is transmitted by pressure waves in the air, not magnetic radiation. We know that the human body has no difficulty dealing with this kind of sound-induced resonance (unless, of course, the amplitude is very large, as with the sound of a jet engine).
In the case of EMF, resonance with cells occurs when there is a "match" between the wavelength of the radiation and the physical size of the cell. The resonance maximizes the transfer of energy into the cell, and can result in observable biological effects which may be harmful. One observable effect is a disruption in the calcium flow through cell walls.
Calcium acts as a messenger that penetrates into the cell, conveying important information and triggering proteins to carry out cell functions. Calcium also plays an important role in regulating certain body functions, such as muscle contractions, heartbeat, development of egg cells and cell division. Since cancer growth depends on cell proliferation, these findings seem to explain why EMF sometimes behaves like agents that promote, rather than initiate, cancerous growths.
Another theory is that the altered calcium flow to the cell reduces the cell's ability to fight cancer. According to Craig Byus, a biochemist at the University of California at Riverside, just because the fields are very small doesn't mean they are innocuous. Cell membranes appear to have a way of amplifying the fields. Due to the poor conductivity of the thin cell wall, small induced currents produce large voltage potentials across the cell membranes, disrupting the chemical balance.
Are weaker fields safer than stronger ones? Logically, our experience with other pollutants would lead us to answer yes, but scientists say this may not be the case because there are "windows" or ranges of biologically active frequencies and field strength. Some experiments show no effect with a strong field, but when the field strength is reduced an effect appears. Other experiments show that above a certain field strength, effects can be observed but no additional effects occur when the field strength is increased.
The resonance effect between EMF and the surfaces of cells may help explain the strange window effect. To understand why, an analogy may be made with the noisy shaking of water pipes sometimes observed when running water from a faucet. As the faucet is opened, a small flow presents no problem. Then, as the initial low flow is increased, a loud noise may occur due to pipe resonance. When the flow is increased even further, the effect doesn't get worse, and usually it stops.
The shape of the magnetic pulse also seems to play a role, too, as different pulse shapes cause different effects. The strength of a 60 Hz EMF field from power lines and household wiring increases and decreases smoothly, while the VLF field from a VDT has a saw-tooth pattern. All this complicated evidence makes it difficult to reach any conclusions on what level of EMF exposure is safe and what isn't. The consensus is that more research is needed.
ELF AND VLF RADIATION There are two frequency ranges for magnetic fields which are commonly found around our homes and businesses ELF (extremely low frequency) which radiates from a 60 Hz current, such as power lines, and VLF (very low frequency) which comes from the 15 kHz to 85 kHz scanning frequencies of TVs and cathode ray tube video displays. The full ELF frequency range is between 0 Hz and 1,000 Hz, and the VLF range extends from 1,000 Hz (1 kHz) to 500,000 Hz (500 kHz).
THE GAUSS METER A Gauss is a common unit of measurement of AC magnetic field strength. A Gauss meter is an instrument which measures the strength of AC magnetic fields. Inside a Gauss meter there is a coil of thin wire, typically with hundreds of turns. As a magnetic field radiates through the coil, it induces a current, which is amplified by the circuitry inside the Gauss meter. If a Gauss meter were to have an induction coil with approximately 40,000 turns, a relatively low magnetic field strength of 1 milliGauss (1,000 milliGauss = 1 Gauss) would induce enough current to be read directly with a voltmeter. It is more practical, however, to build a Gauss meter with fewer turns and, through operational amplification circuitry, to increase the voltage or current and then calibrate the meter to read in Gauss or milliGauss (mG).
On occasion, you may encounter different units of measurement for magnetic fields, such as a Tesla, a micro-Tesla (uT), a nano-Tesla (nT), and milliamps per meter. These units |
