AM signals are transmitted from large arrays of antennas that are placed at high elevation on sites that are off limits to the general public because exposures close to the source can be high. AM radio is used for broadcasting over very long distances, whereas FM radio covers more localized areas. Radio signals are AM (amplitude-modulated) or FM (frequency-modulated). ![]() Radio and television signals. AM/FM radios and older VHF/UHF televisions operate at lower radiofrequencies than cell phones.Other common sources of radiofrequency radiation include: (For more information about cell phones, see the NCI fact sheet Cell Phones and Cancer Risk.) In the United States, cell phones currently operate in a frequency range of about 1.8 to 2.2 GHz ( 2). Radiofrequency radiation. The most common sources of radiofrequency radiation are wireless telecommunication devices and equipment, including cell phones, smart meters, and portable wireless devices, such as tablets and laptop computers ( 1). These EMFs can come from a number of sources.Įxtremely low frequency EMFs (ELF-EMFs). Sources of ELF-EMFs include power lines, electrical wiring, and electrical appliances such as shavers, hair dryers, and electric blankets. Human-made EMFs fall into both the ELF and radiofrequency categories of non-ionizing part of the electromagnetic spectrum. The earth’s magnetic field, which causes the needle on a compass to point North, is one example of a naturally occurring EMF. There are both natural and human-made sources of non-ionizing EMFs. Radiofrequency radiation is measured in watts per meter squared (W/m 2). ELF-EMFs have frequencies of up to 300 cycles per second, or hertz (Hz), and radiofrequency EMFs range from 3 kilohertz (3 kHz, or 3,000 Hz) to 300 gigahertz (300 GHz, or 300 billion Hz). Low- to mid-frequency EMFs include extremely low frequency EMFs (ELF-EMFs) and radiofrequency EMFs. These EMFs are in the non-ionizing radiation part of the electromagnetic spectrum and are not known to damage DNA or cells directly. Low- to mid-frequency EMFs, which include static fields (electric or magnetic fields that do not vary with time), magnetic fields from electric power lines and appliances, radio waves, microwaves, infrared radiation, and visible light.These EMFs are in the ionizing radiation part of the electromagnetic spectrum and can damage DNA or cells directly. Higher-frequency EMFs, which include x-rays and gamma rays.The electric and magnetic forces in EMFs are caused by electromagnetic radiation. ![]() Electric fields are easily shielded or weakened by walls and other objects, whereas magnetic fields can pass through buildings, living things, and most other materials.Įlectric and magnetic fields together are referred to as electromagnetic fields, or EMFs. Power lines produce magnetic fields continuously because current is always flowing through them. Magnetic fields are measured in microteslas (μT, or millionths of a tesla).Įlectric fields are produced whether or not a device is turned on, whereas magnetic fields are produced only when current is flowing, which usually requires a device to be turned on. The strength of a magnetic field decreases rapidly with increasing distance from its source. ![]() Electric fields are measured in volts per meter (V/m).Ī magnetic field results from the flow of current through wires or electrical devices and increases in strength as the current increases. As the voltage increases, the electric field increases in strength. Electric and magnetic fields are invisible areas of energy (also called radiation) that are produced by electricity, which is the movement of electrons, or current, through a wire.Īn electric field is produced by voltage, which is the pressure used to push the electrons through the wire, much like water being pushed through a pipe.
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