Natural radiation was the only source of human exposure until the latter part of the nineteenth century when Thomas Edison invented the electric light. Most natural radiation of significance occurs in a small part of the lowermost frequency spectrum, electrostatic to about 5 kHz, and in the uppermost part of the spectrum above 10 THz or 1012 Hz. Man-made radiation dominates 50 Hz to 300 GHz.
Natural radiation below 5 kHz results from lightning. Average rate of global lightning strikes is about 100 bolts per second. Some natural radiation below 5 kHz results from pulsations in the earth's magnetosphere during intense solar storms causing the Aurora over one or both poles to light up.
Radiation is categorized as either non-ionizing or ionizing. Ionizing radiation has enough energy, high enough in frequency, to break atomic bonds by removing one or more electrons and creating a charged atomic particle. The higher the frequency the shorter the wavelength and the greater the energy and ionization.
Non-ionizing electromagnetic radiation is divided into three categories; electrostatic or non time-varying, low frequency such as house current, and RF or radio frequency. Natural forms of electromagnetic radiation occur above 10 THz and includes infrared heat, visible light, and ionizing radiation such as ultraviolet, X-rays, and gamma rays. All forms of radiation can have adverse health effects when intense enough or time exposure long enough.
Non-ionizing electromagnetic radiation is generally divided into three categories; electrostatic (non time-varying), low frequency (such as house current), and RF or radio frequency (greater than about 30 kHz and less than 300 GHz). Other forms of radiation electromagnetic in nature are in the uppermost part of the frequency spectrum (above 10 THz or 1013 Hz) and include IR--infrared (heat), visible light, and ionizing radiation such as ultraviolet (UV), X-rays, gamma rays and cosmic rays. All forms of radiation can have adverse health effects when intense enough and/or time exposure long enough.
|Studies and Reports|
Studies and Reports
Police microwave radar has been linked to several adverse health effects by a number of police officers who operated radars over a long period, hours at a time for years. To date the scientific community cannot establish a mechanism that links police radar to adverse health effects, that does not mean one does not exist.
Many studies on health effects and exposure to electromagnetic fields conducted since 1948 have reached varying and sometimes contradictory conclusions. Much of the early research concentrated on the thermal heating affects of electromagnetic radiation, some later studies indicated reactions to electromagnetic fields not explained by thermal heating. Experts do not always agree on the levels or types of electromagnetic fields that affect health.
US AIR FORCE STUDY
The U.S. Air Force sponsored a study of rats exposed to pulsed microwaves at 24.5 GHz. Police K band radar operates near the study frequency at 24.15 GHz. The study used pulsed microwaves and police radar is continuous.
The research was conducted by the University of Washington School of Medicine in Seattle and published in 1984. The study showed a significant increase in malignant tumors and noted affects in the adrenal glands and the entire endocrine system. The results suggests the maximum allowable exposure for humans is too low.
The London Times reported in 1998 that Dr. Henry Lai, an expert in non-ionizing radiation and professor at the School of Medicine and College of Engineering at the University of Washington, Seattle, announced that low-level microwave radiation can split DNA molecules in the brains of laboratory mice. DNA is Deoxyribonucleic acid, a complex, usually helical shaped chemical compound that is the substance that makes the organic matter of genes and chromosomes. Splitting DNA molecules in the brain is associated with Alzheimer's and Parkinson's Disease, and cancer. The cellular telephone industry supported Dr. Lai's research grant, but suppressed the report's publication.
The Air Force Research Laboratory (AFRL) has developed a non lethal antipersonnel millimeter band heat ray intended for use on battle fields or against hostile crowds. A 3 x 3 meter, about 10 x 10 feet, antenna mounted on a Humvee, aircraft, helicopter, or ship can be swept across a crowd that induces skin heating. The system radiates a 2 second burst at 95 GHz, 3.16 millimeter wavelength, that can heat the skin to 130° Fahrenheit. Officials claim the energy only penetrates the top 1/64 inch (0.4 mm) of the skin and is not harmful to internal organs, no mention about the eyes. Operating range is around 700 to 1100 yards, rain, fog and humidity will reduce range. Possible countermeasures include shielding the energy using very thick clothing, a metallic sheet such as aluminum foil, or a metal trash can lid.
|Electrical Properties of Living Matter|
Living matter exhibits many electric properties as well as generates various, relatively small, electromagnetic fields. Medical doctors use known and well-documented electrical properties of the body to determine health and diagnose problems. This section is a brief sample of some electrical properties of living matter.
|Thermal Effects of RF Radiation|
Electromagnetic energy is well known to cause thermal heating in living tissue. Microwave ovens use electromagnetic energy to heat and cook food. Microwave ovens, introduced by Raytheon in 1947, are basically magnetron oscillators, a radar transmitter cavity tube, operating at 2.45 GHz. Some microwave ovens introduced in the late 1990's operate at 5.8 GHz.
The amount of heating that takes place is a function of transmit power and duty cycle time. Maximum surface heating due to RF exposure of a typical human occurs at frequencies between 30 and 120 MHz.
Tissue heating depends on the frequency of the source and the dielectric constant, water content and thickness of the tissue. The more conductive the tissue the more energy absorbed and heat generated. It requires a relatively large amount of radiation to heat tissue. Radiation levels too low to produce heat may have other effects at a cellular level, although not all experts accept this. Some experts believe most non thermal health effects require much higher field levels compared to thermal heating effects.
Fields strong enough to cause heating require hundreds to thousands of watts. Localized heat of about 1 watt per kilogram (0.45 W/lb) can damage tumors. The temperature of the tumor is raised to between 43 and 45 degrees Celsius (109 and 113 degrees Fahrenheit). Fields that cause mild heating can promote tissue healing or relax muscles.
Specific Absorption Rate (SAR) describes the energy absorbed by tissues and is measured in power per mass, typically watts per kilogram (W/kg). Absorption is a function of tissue permittivity and conductivity, and frequency of radiator. Safe limits for human exposure are sometimes based on whole body exposure averaged over 0.1 hours (6 minutes). Some agencies consider a rate of 0.4 watts per kilogram (0.18 W/lb) a safe limit.
|Interaction of Fields and Biological Systems|
Weak RF fields insufficient to cause heating but strong enough to induce peak potentials of 1 to 1.5 millivolts per centimeter (0.10 to 0.15 V/m) can promote healing of broken bones. Experiments have shown osteoporosis, the loss of bone mass, can be halted or reversed by pulsed RF radiation. The shape and timing of pulses is extremely significant, and different, to promote bone healing or affect osteoporosis.
Some studies indicate there are reactions to RF exposure not explained by thermal heating. Strong RF fields heat tissue by vibrating molecules of the tissue. Weaker fields can induce electrical currents in or on tissue, the stronger the field the larger the induced current. Electric and magnetic fields can produce weak Lorentz forces that may affect charged particles, ions, on a molecular scale. The Lorentz force is the force on a charged particle in motion due to the presence of an electric and magnetic field, and may boost or inhabit cell chemistries by pumping ions.
Listed below is a sample of some observed affects of electromagnetic radiation on living cells. Most if not all effects depend greatly on frequency, modulation, and magnitude of the field.
RF radiation has been linked to biochemical effects, immunological effects, Alzheimer's and Parkinson's Disease, cancer, cataracts, EEG effects and behavioral changes, to name a few. Studies from the old Soviet military suggest that some frequencies and modulations cause behavioral changes in humans. In 1990 the U.S. military was reported to be planning microwave radiation experiments on animals to study behavioral effects.
Some health effects seem to take place in small bands or windows of frequencies, modulations, and magnitudes. For example, nerve tissues affected by continuous 60 hertz fields are unaffected by 55 or 65 hertz fields. Some experiments have shown for some narrow frequency bands and specific modulation types a smaller field affects cells more than a stronger field. Several factors should be considered to determine electromagnetic radiation exposure and include;
|Distance from Radiation:||Strength greatly decreases with distance|
|Exposure Time:||Exposed to large fields for short periods,
or small fields for long periods.
|Field Type:||Power, frequency, modulation|
Also see National Technical Information Service (NTIS) publication number PB95-261350, Occupational Exposure of Police Officers to Microwave Radiation from Traffic Radar Devices.