High Frequency Design From July 2005 High Frequency Electronics Copyright © 2005 Summit Technical Media EMR & HUMAN HEALTH Electromagnetic Radiation and Human Health: A Review of Sources and Effects By Ali Zamanian and Cy Hardiman Fluor Corporation, Industrial and Infrastructure Group adio Frequency Electromagnetic Frequency Spectrum This article provides an (RF) engineers are Wireless communication links have been extensive summary of the Rfaced many times used worldwide for many years as solutions types of electromagnetic with the following two for connectivity in point-to-point and point-to- radiation and their thermal questions: “What are the multipoint applications. The most common and molecular effects effects of radio waves on wireless solutions include AM and FM radio, on the human body human health?” and, television broadcast stations, mobile and cel- more specifically, “What lular phones, radar and microwave systems. health risks are associated with the use of cell The electromagnetic (EM) spectrum con- phones, mobile radios, microwave radios, tains an array of electromagnetic waves microwave ovens, broadcast radio and televi- increasing in frequency from Extremely Low sion transmitters, power lines and X-rays?” Frequency and Very Low Frequency In recent times, many people have (ELF/VLF), through Radio Frequency (RF) expressed an interest in learning if the use of and Microwaves, to Infrared (IR) light, Visible cell phones is associated with cancer. Many Light, Ultraviolet (UV) light, X-rays, and have heard or read about possible links Gamma rays. between cell phones and cancer, but conclu- Figure 1 is a graphical representation of sions are rarely definitive. This paper will the spectrum of electromagnetic energy or attempt to answer these questions, but first, radiation in ascending frequency (decreasing we must develop a basic understanding of wavelength). The general nature of the effects electromagnetic radiation (EMR). is noted for different ranges. Figure 1 · Electromagnetic spectrum. 16 High Frequency Electronics High Frequency Design EMR & HUMAN HEALTH Ionizing Radiation Microwave (MW) and Millimeter- made. Natural EMR includes a back- Ionizing radiation contains suffi- wave (30 kHz to 300 GHz) ground electromagnetic field created cient electromagnetic energy to strip • Infrared (IR) light, Visible light and by the earth as well as additional atoms and molecules from the tissue Ultraviolet (UV) light (above 300 EMR created by thunderstorms, as and alter chemical reactions in the GHz) well as solar and cosmic activity. The body (converting molecules totally or • [Editor’s note: the frequencies strength of an electromagnetic field partly into ions). X-Rays and Gamma between the highest microwave depends both on the power at the rays are two forms of ionizing radia- bands and infrared light are rarely source and the distance from the tion. These rays are known to cause used, but are being studied for future source. damage, which is why a lead vest applications] Exposure to man-made ELF/VLF must be worn when X-rays are taken occurs primarily due to the generation, of our bodies, and heavy shielding sur- Some heating effect is generated transmission and use of electrical rounds nuclear power plants. by all of these waves. Insufficient energy. Electromagnetic fields are cre- Human beings are constantly energy is available from most common ated whenever electricity passes exposed to low levels of ionizing radia- sources to produce any type of damage through a conductor. Actually, two tion from natural sources. This type of to human tissue, although it is proba- interdependant fields are created: an radiation is referred to as natural ble that higher power densities, such electric field and a magnetic field. The background radiation, and its main as those densities very near high-volt- strength of the electric field depends sources are: age power lines or high-power on the voltage being carried, while the (megawatt) broadcast transmitters, magnetic field strength depends on the • Visible light, ultraviolet light and could have long-term health effects. amount of current being carried infrared light (sunlight) The power density of any source of (amperage). Thus, electromagnetic • Radioactive materials on the earth’s EMR is not only related to the power fields are created by a variety of elec- surface (contained in coal, granite, level at the source, but increases trical household appliances such as etc.) rapidly as the distance from the motors in refrigerators, vacuum clean- • Radioactive gases leaking from the source decreases. A common concern ers, hair dryers, irons, electric blan- earth (radon) today, since more and more people are kets, microwaves, televisions, stereo • Cosmic rays from outer space enter- using cell phones than ever before, is receivers, and computers. In fact, ing the earth’s atmosphere through that cell phone antennas radiate near because of the individual’s proximity to the ionosphere a person’s head. Cell phones, however, household appliances, the level of elec- • Natural radioactivity in the human radiate very little power. So, even tromagnetic fields is often far greater body while close to the head, they are not than those levels produced by trans- considered a danger. mission lines strung on high towers. Non-Ionizing Radiation Some studies suggest that poten- However, the appliances only create The lower part of the frequency tial health hazards could be linked to electromagnetic fields while in use, spectrum is considered non-ionizing excessive exposure to high-power den- whereas the transmission line electro- Electromagnetic Radiation (EMR), sities of non-ionizing radiation. These magnetic fields are continuous. While with energy levels below that required health hazards include: these man-made ELF/VLF electro- for effects at the atomic level. magnetic fields may cause biological Examples of non-ionizing radiations • Cancer effects, the adverse effects on human are: • Tumors health are highly controversial. • Headaches • Static electromagnetic fields from • Fatigue Electrical Power Line Effects direct current (0 Hz) • Alzheimer’s Disease The concern over electromagnetic • Low-frequency waves from electric • Parkinson’s Disease fields emitted by power lines (Figure power (50-60 Hz) 2) has long been a topic of conversa- • Extremely Low Frequency (ELF) Researchers, however, are unsure tion in the real estate and power and Very Low Frequency (VLF) of specific long-term effects resulting industries. New studies and conflict- fields (up to 30 kHz) from prolonged exposure to non-ioniz- ing reports are published every year. • Radio Frequencies (RF), including ing radiation. While it is easy to shield a house Low Frequency (LF), Medium against the electric field generated by Frequency (MF) High Frequency ELF and VLF EM Radiation nearby power lines, it is much more (HF), Very High Frequency (VHF), EMR in the ELF and VLF range is difficult to shield against the magnet- Ultra High Frequency (UHF) and both naturally occurring and man- ic fields they generate. The magnetic 18 High Frequency Electronics High Frequency Design EMR & HUMAN HEALTH Type of mobile radio Frequency (MHz) Average radiated power Cellular/PCS 824-849 MHz A few hundred milliwatts 1850-1990 MHz Two-way, hand-held 30, 50, 150, 450 and Between 2 and 5 watts (walkie-talkie) 800 MHz bands Cordless telephone 49, 915, 2450 MHz Tens of milliwatts Table 1 · Typical portable/mobile radio equipment. sions. For the purpose of this discus- the effects are basically the same. sion, the term “RF energy” is used for An Australian group claimed to all frequencies between 30 kHz and have evidence that living near televi- 300 GHz. Some known facts about RF sion broadcast station towers causes energy are: an increase in childhood leukemia. Figure 2 · Electric power line. However, follow-up studies conducted • The biological effects of RF energy in Australia and in the UK contradict- are proportional to the rate of ener- ed this claim. The follow-up studies field can best be shielded by burying gy absorption, and the level of found no significant correlation power transmission lines, but at a absorption varies little with fre- between RF exposure and the rate of much higher cost compared to over- quency. childhood leukemia in these cases. head lines. • RF energy has the ability to heat Animal experiments, laboratory human tissue, much like the way Cellular Telephones, Cordless studies of cells, clinical studies, com- that microwave ovens heat food, and Phones and Hand-Held Radios puter simulations, and human popula- can be hazardous if the exposure is Most cellular/PCS and cordless tion (epidemiological) studies have sufficiently intense or prolonged. telephones have either a small anten- been conducted to determine the rela- • Damage to tissue may be caused by na attached or the antenna is integrat- tionship between exposure to electro- exposure to high levels of RF energy ed into the body of the telephone. magnetic fields and a number of disor- because the body is not equipped to Because the antenna of a cellular ders, including depression, childhood dissipate the excessive amounts of phone is close to the user’s head, such leukemia, central nervous system dis- heat generated. Possible injuries telephones create greater RF exposure orders, cancer, melanoma, breast can- include skin burns, deep burns, heat than other types of RF systems. Home cer, etc. In the past, numerous reports exhaustion and heat stroke. cordless telephones and other