IF- Intermediate Frequency
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According to the World Health Organization (WHO) definition, the IF range refers to the 300 Hz to 10 MHz frequency range, though it has recently been recommended that the lower limit should be changed to 1 kHz. The range is above the low frequency range (LF), and overlaps the radio frequency range (3 kHz to 10 MHz).
It should be noted that the International Telecommunications Union (ITU) does not have a definition for the IF range; the frequencies included in the WHO definition of the IF range are defined by the ITU as belonging to other frequency ranges. So, for example, the 30 kHz to 300 kHz frequency range that, according to the WHO definition is a part of the IF range, is defined by the ITU as being in the low frequency (LF) range; and the ranges considered medium frequency (MF) and even High Frequency (HF), according to the ITU definition, are defined by the WHO as being part of the IF range.
Exposures to this range come from various appliances in everyday surroundings (at home, at work, etc.) such as induction cooktops, electronic tags – RFID (such as tags used to identify products in stores), Compact Fluorescent Lights (CFL), devices with wireless electric charging (such as electric tooth brushes) etc. Industry and medical equipment are additional areas where exposure to the intermediate frequency range exists.
Below are a number of examples of devices that produce intermediate frequency (IF) fields:
- Induction Cooktops – this type of cooktop is used to heat food in metal utensils through the principle of magnetic induction heating. Unlike cooktops that conduct heat produced by a gas flame or by electric heating elements to the food (electric cooktops that heat via conduction of an electric current) induction cooktops create a relatively powerful magnetic field, that induces electric currents (called eddy currents because of their shape) in metal cooking utensils placed upon the cooktop. The magnetic field is an intermediate frequency alternating field that produces alternating induction currents within the cooking utensils. The currents cause heating of the metal that the cooking utensils are made of and heating of the food within them. Food can only be heated in cooking utensils made from iron or steel, not in those made from aluminum, copper or glass. Induction heating has the advantages of efficiency, uniform heating and safety (compared to gas, fires). Exposure to the magnetic fields produced in the vicinity of the cooktop, in the area where the user stands, is usually in the micro-tesla (one millionth of a tesla) range, which is usually below the maximum exposure limits set by the International Committee for Non-Iodizing Radiation Protection (ICNIRP) guidelines (though it is possible to exceed these levels by standing right next to the cooktop in certain situations). It should be noted that the magnetic fields drop sharply the more the distance from the cooktop increases. In order to implement the precautionary principle for minimizing exposure, it is recommended to maintain distance from cooktops and to use according to the manufacturer’s instructions. Amongst other things, only turn cooktops on when there are utensils on them, use only utensils that are appropriate for induction heating, and place them in the middle of the elements. For people with cardiac pacemakers (or other medical devices), it is recommended to consult with the manufacturer (or importer) or your treating physician.
- Wireless Electric Charging – wireless electricity conduction (without cables) is an idea that was tested more than a hundred years ago by Nikola Tesla and others, and its practical use has grown in recent years. Electricity can be transmitted wirelessly, though for relatively short ranges, using a number of methods, one of which is “inductive coupling”. In this method, electricity is transmitted via a magnetic field, between coils. One coil is fixed in the electric charger and fed from the electric grid (via an electronic circuit), and creates an intermediate frequency magnetic field. The magnetic field induces an electric current in the other coil, located in the device being charged (for instance, an electric tooth brush). The electric current charges the battery. In this manner, electricity can be transferred wirelessly and conveniently, without cables or electric contacts, while maintaining safety (for instance in a wet environment – for electric toothbrushes). Another example of wireless charging is cell phone charging at wireless charging stands located in public places (like airports), use of which has grown progressively with the introduction of new phone models that allow wireless charging. Wireless charging is also used for some types of electric cars. It is expected that wireless charging will be used more and more in the future for charging various devices conveniently and efficiently. Because strength of the magnetic field drops sharply with distance, exposure to magnetic fields from wireless chargers is usually relatively low.
- TV and Computer Screens – In the not too distant past (up until the last decade), screens were large and heavy, made of thick glass, filled with vacuum or thin gas, and based upon Cathode Ray Tube (CRT) technology. In this technology, an electron beam is created by a tube (“electron gun”) in the rear portion of the screen. The beam hit a screen covered with a phosphorescent substance, scanned it line by line, and created the image on the screen. In this method, relatively high exposures to low frequency magnetic and electric fields were created (the electricity grid frequency and frequencies in the VLF range), in the rear portion of the screen, that were necessary to create the beam and transmit it in a scanning movement onto the screen. Modern screens are built using LED technology. They contain many tiny LED bulbs, usually red, blue and green colored that directly fed by electronic circuits and create the picture seen on the screen. The magnetic fields created in their vicinity are very weak, and do not constitute a significant source of exposure. Higher magnetic fields may be created in the vicinity of the power supplies that feed the screens.
- Occupational exposures – there is intermediate frequency exposure from medical equipment, such as MRI systems, electrical equipment used for surgery and other therapies (such as bone treatment) etc. There is also intermediate frequency exposure in various industrial processes, for example in heating and welding.
