Reviewing and Mapping the Sources of Non-Ionizing Radiation Exposure in the Student Environment
Since 2011, the National Information and Communication Technologies (ICT) Program "Adjusting the Education System to the 21st Century" is gradually being implemented in Israeli schools. The program deploys the basic infrastructure that enables the use of advanced technologies in teaching, learning and evaluation (TLE) in a school environment. This infrastructure includes: broadband Internet, projector in every classroom, teacher laptops, classroom sound system, and means of darkness. The use of some of the program-required technologies is accompanied by exposure to non-ionizing electromagnetic radiation (RF) and low frequency electric and magnetic fields. In addition, in the student vicinity there are non-ionizing radiation sources (RF and electric and magnetic fields) due to personal devices such as mobile phones and tablets.
Given the current scientific knowledge, it is agreed that exposure should be reduced using the precautionary principle. This principle is especially valid in children considered populations at risk.
Therefore, in the following article, we have concentrated on the sources of radiation exposure in a school environment, with reference to their different characteristics, their use in the classroom, and their impact on the student's exposure to radiation.
More articles that may interest you
- Sources of Exposure to RF radiation
- Sources of Exposure to Low Frequency Magnetic and Electric Fields (ELF)
- Should a Laptop or Tablet Be Used over Cell Phones via a Wireless Network (Wi-Fi)?
- Distancing the Radiation Source from the Body
- What Is the Radiation Exposure Level in a Class of 30 Students Using End-User Devices (Cell Phone/Tablet/Desktop Computer, etc.) at the Same Time ?
Sources of Exposure to RF Radiation in the Student Environment
Cell Phone
Cell phone is a mobile device capable of holding and receiving telephone calls using electromagnetic radiation. The phone includes a transmitter and receiver, which transmits and receives non-ionizing electromagnetic radiation in the radio frequencies (RF) range.
Upon using the cellular device, the user is exposed to RF radiation, with the duration of exposure to radiation increasing as the duration of use increases and depends, among other things, on the various uses made therein.
It should be noted that mobile phones emit radio frequency radiation (RF) even when not in use, as they send signals to their base stations to inform cellular network systems about their location. Those are occasional short pulses and therefore the level of exposure is low.
Today's smartphone combines cell phone capabilities with advanced handheld capabilities and is actually a tiny laptop that on top of phone calls allows a huge variety of uses, such as calendar, photography, phone book, web browsing, messaging and photo transfer and the like.
Uses in Which Cell Phones Emit RF Radiation
- Using the cellular network for making phone calls, messaging, or web browsing
- Using the Wi-Fi network for web browsing, messaging, or making phone calls (through applications such as WhatsApp)
- Having short-term communication near the phone (such as by Bluetooth)
Transmission Characteristics of the Cell Phone
- Transmission frequency — Frequency (number of periods per second) of a carrier wave measured in hertz and expressed in megahertz (million Hertz, MHz) in the cellular frequencies range
- Transmission amplitude (power) — Expression of energy of transmission per time unit measured in watts (W)
- Specific absorption rate (SAR) — Measure of absorbed radiation inside the body (see details below)
Intensity of the Mobile Phone Radiation
The maximal power of cell phones in the various generations used today is about 250 milliwatts. This value is average over time and refers to the maximum transmission power. The better the reception, the lower the transmission power.
For second-generation phones based on GSM technology, the maximum power is up to 2 watts, but the average transmission time is limited to 250 milliwatts (those phones transmit pulses in a fragmented way). First-generation phones transmitted average power up to 600 milliwatts.
Antenna Location in Cell Phones
In modern cell phones (smartphones), as well as tablets and laptops, the antenna is internal and not visible. The antenna may be found in different locations, according to the manufacturer's design.
In smartphones, there are several antennas in different locations for cellular communication, Wi-Fi, Bluetooth, and GPS (reception only). For the most part, manufacturers prefer to place the main antenna in the lower part of the device, which is farther from the head, to reduce radiation absorption in the head (and reduce transmission power losses due to absorption).
Exposure Level from Cell Phone — SAR
Radiation absorbed in the human body is measured using a specificity called Specific Absorption Rate, or in short SAR (units of watts per kilogram).
The measurement is carried out using a simulator which contains liquid that simulates the characteristics of human tissues, which the phone is located and operated in close proximity to, similar to the exposure from the phone located near the head or in the hand (or body-mounted). The field measurement sensor scans the field developed inside the simulator. The SAR depends on the power of the transmission, distance from the source of transmission (from the cellphone and of the cellphone from base station), communication technology and amount of electromagnetic radiation absorption in the human tissue. To characterize the SAR of a mobile device under the test, the maximum possible transmission power of the device is activated to simulate the worst communication conditions in which it may operate (such as poor reception). This occurs, for example, when the phone is very far from the broadcasting station, upon entering elevator, etc. The permissible SAR for cell phones is determined based on international recommendations.
So far, recommendations for the permissible SAR levels for cell phones are based on thermal effects (of heating) rather than non-thermal effects. Accordingly, the standards do not, for example, address the possibility of developing chronic diseases (such as cancer), which may be the result of a-thermal effects.
Every cell phone manufacturer must carry out measurements of SAR for each model of cell phone. This level is set for all device models produces, and is not measured for each specific device. Measuring the SAR level for each model is conducted under laboratory conditions at the maximum power of the phone.
It should be noted that for each phone, it is possible to control (automatically) the output power of the device according to the quality of communication between it and the mobile site nearby. In fact, it is possible that a phone demonstrating a high SAR level in laboratory may emit less radiation near the mobile site than that with a low SAR level in laboratory, but distanced from the closest mobile site in its vicinity, and has poor signal quality with that mobile site. Due to the above, it is possible to determine that the SAR level for a specific phone used daily varies according to the location of the phone relative to the antennas in its vicinity. And also, that it is difficult to compare between actual exposures to different cellular phones according to their maximal SAR values.
In Israel, due to the fact that the phones are imported from different countries, two major international standards for radiation exposure from cell phones have been adopted as follows:
European standard based on ICNIRP for Europe-licensed devices — an average of 2.0 watts per kg per 10 grams of tissue.
American FCC- based standard for US-licensed devices — an average of 1.6 watts per kg per 1 gram of tissue.
Variables that Determine the Level of Exposure
The level of exposure to cell phones depends on the following variables:
- Transmission power — The intensity depends on the type of transmission (cellular, Wi-Fi and more), distance from the cellular site (for cellular transmission), the characteristics of the transmitted signal, and more
- Frequency of transmission
- Antenna location on the phone (relative to the head or body parts)
- Different characteristics of the antenna (amplification, radiation curve, behavior in the near field upon vicinity to the human body and more)
The Effect of Cell Phone Uses on the Level of Exposure
In addition to phone calls, the smartphone offers a huge variety of uses such as photography, web browsing, messaging, photo transfer and more.
It is important to note that the cell phone user has control over the level of exposure since the most important rule for reducing exposure to non-ionizing radiation is the distancing of the radiation source from the body, based on the fact that the radiation decreases significantly as the distance from the radiation source increases.
Accordingly, it is advisable to distance the radiation-emitting devices from the body as far as possible and place the device at least half a meter away upon charging (for more information, see Tips for Minimizing Exposure).
Exposure to RF Radiation when the Phone is Close to the Head Versus Exposure when the Phone is Distanced from the Head
Generally, the maximum SAR level measured by the manufacturers is obtained when the cell phone is close to the head. As the phone is distanced from the head, the SAR level in the head is lower since more power is not absorbed at the head but transmitted to the environment as radiation. In addition, when the phone is distanced from the head, the power absorbed at the head is not focused on a particular area but is scattered, so its value is lower. Those two effects result in a sharp decline in the SAR that develops in the head as the phone is distanced (for example, when using the cell phone for texting, viewing, browsing the Internet, etc.).
Cell Phone Radiation Exposure when Using Cellular Network versus Using Wi-Fi Network
This topic is quite complex. The transmission power of the phone depends on the quality of the network and the type of information transmitted (call, web browsing, or file transfer). The intensity of cellular transmission is greatly influenced by the distance of the cellular site and the existence of shielding (e.g. inside or outside a building).
Upon cellular transmission (call or using the Internet over the cellular network), the transmission power varies from hundreds of milliwatts (up to 250 milliwatts at phones of current generations) under very poor reception to single milliwatts and below under good reception. The reception inside structures is generally relatively low due to the shielding of the structures, and the transmission power may reach tens of milliwatts.
Upon using the Internet via Wi-Fi, the maximum transmission power of the phones is tens of milliwatts (and limited by 100 mW). However, Wi-Fi communication is not continuous but intermittent (pulse transmission), so that the average transmission power level over time (which is relevant in terms of the actual exposure level) is even lower. In common uses of the Internet, such as web browsing, with the exception of continuous "heavy" file transfer, and with reasonable Wi-Fi reception conditions, the average Wi-Fi transmission power is about tenths of milliwatts (hundreds of micro-watts).
To conclude, upon using cellular devices inside structures, such as classrooms (where cellular transmission is not optimal), equipped with reasonable Wi-Fi infrastructure and transmission, it is generally recommended to use Wi-Fi to reduce user exposure levels.
Radiation Exposure from Cell Phones of Adjacent Students in the Classroom
The radiation emitted near a cell phone decreases sharply upon distancing from it. In general, the decreasing is according to the square of the distance, that is, when the distance doubles, the intensity of the radiation decreases by four times, and when the distance increases by 10 times, the intensity of the radiation decreases 100 by times.
Various studies evaluated the SAR obtained from a cell phone according to the cell phone distance from the human body. According to those studies, it can be estimated that the SAR obtained from a phone at the distance of half a meter to a meter from the head is a few percent of that obtained when the phone is close to the head.
It can be estimated that the exposure of a student sitting in a vicinity to a student using the phone is about 1% of that of the student using the phone. At greater distances, the SAR decreases to thousandth and below of that of the student using the phone.
Exposure to Magnetic Fields upon Cell Phone Charging
Upon charging, cell phones local magnetic fields exist due to electric current flow, which is necessary to charge the phone's battery.
The magnetic fields near the adapter connected to the electrical outlet are of low frequencies and mainly at the power grid frequency — 50 Hz. The adapter converts the alternating voltage from the power grid to low direct voltage (DC). The level of the fields next to the adapter may reach up to tens of milligauss. However, exposure to these levels is usually brief. According to the precautionary principle, separation distance (half meter) from the adapter is recommended for extended exposures (when it comes to modern adapters the exposure level is lower).
The wire conducting the electrical current from the adapter, or from a USB connection (such as from a PC or laptop), conducts a direct current (DC) with the power of hundreds of milliamperes and above. The level of a direct (DC) magnetic field generated near the wire is very low compared to the international exposure standards. The same is true for the charging current that is conducted to the cell phone and for the magnetic field generated next to it when charging.
Use of Cell Phones by Children
Due to the increasing use of cell phones by children, and due to them being a population at risk, it has been determined that giving special emphasis to recommendations for educated use of radiation-emitting devices in children is justified and appropriate. The recommendations for educated use of cell phones reflect the desire to find a balance between the increasing use in children and safety and health considerations. See recommendations
Absorption in the Brain
There are studies in which the specific absorption ratio (SAR)l from cell phone use has been evaluated in simulations of exposure in children, taking into account their specific physiological properties.
Wi-Fi — Local Wireless Network
General
Local wireless network (Wi-Fi) uses radio waves to transmit information and data between various end-user devices (e.g. laptops, tablets, and smartphones), and from end-user devices to and from the Internet.
The end-user devices (for example, the laptop) have a wireless adapter that tranfers the data transmitted from the computer into radio signals and transmits those to the wireless router (router) via an antenna. The wireless router receives the signals from the computer, and transfers them into signals that are delivered to the Internet via cable. Of course, this process also works in the other direction: the wireless router receives information from the Internet, transfer it into radio signals that are transmitted to the computer.
Upon using a local Wi-Fi network, the information is composed on the carrier wave according to this technology and its unique protocols.
Wi-Fi technology uses frequencies around 2.4 or 5 GHz by routers and end-user devices. The maximum power of a wireless router is tens of milliwatts (and is limited in Israel to 100 mW).
Upon using the end-user device that uses a Wi-Fi network, the user is exposed to non-ionizing radio frequency (RF) radiation from both the device and the router. Exposure intensity decreases upon distancing from the device and router. The personal exposure to radiation emitted by the device is greater than that emitted by the router due to the proximity of the device to the body.
What is the Non-Ionizing Radiation Exposure Level in a Wireless Router Environment?
In general, the exposure level of radiation measured in the wireless router environment is low. The maximum estimated transmission power of a typical home wireless router is about 100 milliwatts, and at a distance of 1 m from it, the radiation exposure level is about 1 micro-watt per square centimeter, about one thousandth of the guidelines for limiting the exposure of the International Commission on Non-Ionizing Radiation Protection (ICNIRP) for the general public and about one hundredth of the thresholds recommended in Israel by the Ministry of Environmental Protection for prolonged and continuous exposure. It should be noted that in practice, the router transmits less than the maximum power due to non-continuous transmitting.
Exposure of Students to Radiation from a Wireless Router
As mentioned above, the maximum power of a wireless router is tens of milliwatts (and is limited to 100 milliwatts).
Measurements in classrooms described in articles of Khalid et al showed that the practical transmission of routers used in classrooms is usually less than that, and makes single milliwatts, as the router transmits in an intermittent way (pulses).
Radiation exposure levels to which students in a wireless router class are exposed are significantly lower than those accepted using cell phones, due to the distance of the router from the students and the sharp decrease of radiation in the distance, by the square of the distance.
For example, for a router that is 5 meters away from the students and transmits maximum power of 100 milliwatts (a very worsening assumption), the radiation exposure level is 0.04 micro-watts per square meter — 1/25,000 of the guidelines for limiting the exposure of the International Commission on Non-Ionizing Radiation Protection (ICNIRP) for the general population and 1/2,500 of the threshold recommended by the Ministry of Environmental Protection for prolonged and continuous exposure. Actually, the radiation level will be lower — millionths of the above exposure limit guidelines, as the router's transmission power is lower.
Wi-Fi Connection in Various Devices
Cell phones, tablets and laptops are able to connect to the Internet via Wi-Fi. Cell phones are also able to connect to the Internet through a cellular connection.
Some tablets are only able to connect to the Internet via Wi-Fi, and some have the ability to connect to the Internet through a cellular connection (to a network of a mobile operator). Laptops support both wired and Wi-Fi connections, and it is also possible to purchase devices that enable accessing the Internet through a cellular network connection.
Using Cell Phone or Tablet over the Cellular Network versus a Wireless Network (Wi-Fi)
Cell phones can operate over the cellular network or over a local Wi-Fi network for information delivering or receiving it, making phone calls or using the Internet.
Upon using the cellular network, the information is composited on the carrier wave by various technologies (such as WCDMA, CDMA2000, LTE), according to the generation of the cellular network and its characteristics. Phone calls or messages are transmitted over the cellular network, and the access to the Internet provided by the cellular operator allows browsing the Internet, sending and receiving messages, and even making phone calls through applications.
Upon using a local Wi-Fi network, the information is composited on the carrier wave according to this technology and its unique protocols (IEEE 802.11 standards). The network is usually connected to the Internet via cables, through an infrastructure provider, which allows browsing the Internet, sending and receiving messages, and even making phone calls through applications.
The aforementioned is also valid for a tablet.
For the cell phone radiation exposure level upon cellular versus Wi-Fi transmission, see above.
Exposure Level of Radiation in Wired Internet Connection
Radio frequency (RF) radiation generated using wired network is extremely low. This is because wired communication does not involve the use of intended radiation sources. The radiation is generated by very weak currents, which inadvertently generates minimal and very low-level radiation.
Tablet
Tablet is a laptop (see below) designed as a single surface, one side of which is generally used as a touch screen. Unlike a laptop, the tablet is comfortable to work in a variety of ways on the body, and not necessarily on a desk.
Tablet emits radiation during use of the Internet, when sending messages, etc. (via Wi-Fi or over the cellular network) or when having short-range communication (such as by Bluetooth).
To that end, tablets include a modem and antennas, which are positioned in different locations. For engineering reasons, the cellular antennas are commonly placed at the top of the device.
There are two types of tablets — tablets that have the ability to connect to the Internet via Wi-Fi, and tablets that also have the ability to connect to the Internet via cellular connection (to a network of a mobile operator). Tablets equipped with a modem for connecting the cellular network emit typical intensity radiation similar to that of smart phones, while those operating over the Wi-Fi network emit radiation of intensity typical to the Wi-Fi network (see details in section 2 “Wi-Fi — Wireless Network” above).
The level of radiation emanating from a Wi-Fi source, such as a typical home wireless router or tablet, follows the guidelines for limiting the exposure of the International Commission on Non-Ionizing Radiation Protection (ICNIRP) regarding exposure to typical Wi-Fi network frequency.
Upon communicating over a Wi-Fi network, when the browsing device (tablet) is adjacent to the body (less than 30 cm away), the personal exposure to the browsing device increases due to the small distance from the device. In accordance with the precautionary principle, the most important reducing exposure rule is to distance the radiation source from the body, since the radiation exposure level decreases significantly with distance from the radiation source. Thus, the radiant device should be kept away from the body as much as possible. Therefore, it is better not to place the tablet on the body when using it.
Radiation-emitting antenna location in different devices — Tablets and laptops are larger than cell phones and allow selection of different antenna locations.
In tablets, the preference is usually to place the cellular antennas at the top of the device, for engineering reasons, and in laptops, the antenna can be located in the body of the computer or around the screen.
Laptop
Laptop is a personal computer (PC) with relatively small physical dimensions and mobility. The laptop is portable and has a screen and keyboard. Unlike the desktop computer, it has an internal battery, which allows independent operation for a certain amount of time without connecting to an external power source.
While using the Internet (via Wi-Fi), non-ionizing radio frequency (RF) radiation is generated near the laptop.
For the Internet use, laptops include a modem and antenna, which are located in the body of the computer or around the screen. To use the cellular network, an external device (dongle) can also be used.
In general, when it comes to a laptop, there are two main types of radiation exposure:
1. Exposure to low frequency magnetic and electric fields (if plugged in)
2. Exposure to radio frequency (RF) radiation emitted from the computer while browsing the Internet using a Wi-Fi or cellular wireless network, and exposure to radio frequency (RF) radiation emitted from the wireless router when the computer is connected to a Wi-Fi wireless network.
- It should be noted that there are voltages and currents in electronic devices, which generate electric and magnetic fields near the devices. However, those are very low-intensity fields because they are generated as a by-product of the devices’ operation and not as an intended radiation through transmitters and antennas.
Regarding location of the computer, it is advisable to keep the computer away from the body. It should be noted that exposure to the radiation emitted by the router can be reduced by turning it off when not in use or connecting it to the computer via cable (wired connection).
Radiation from a laptop with a Wired Versus Wireless Internet Connection
Radio frequency (RF) radiation near a laptop connected to the Internet in a wired way is at a very low level as wired communication does not involve the activation of intended radiation sources. It is generated by very weak currents, which inadvertently create minimal and very low-level radiation. The radiation generated by connecting to the Internet through a wireless router was detailed above.
Radiation Level at Different Distances from the Laptop
The maximum radiation level expected at the distance of 1 meter from a computer, due to its maximum-power Wi-Fi communication, is about 1 micro-watt per square centimeter. This value is approximately one thousandth of the guidelines for limiting the exposure of the International Commission on Non-Ionizing Radiation Protection (ICNIRP) for the general population and about one hundredth of the threshold recommended by the Ministry of Environmental Protection for prolonged and continuous exposure.
Increasing the distance results in reducing the radiation level by the square of the distance. For example, at a distance of 2 meters, a power of about 0.25 micro-watts per square centimeter will be obtained, and at a distance of 10 meters, a power of about 0.01 micro-watts per square centimeter will be obtained.
It should be noted that this assessment is stricter and relates to the peak transmission power capability which only occurs in extreme communication situations (such as continuous transfer of "heavy" files, and when a signal is less strong).
The actual power is lower, since Wi-Fi communication is not continuous but intermittent (pulse transmission), so that the average transmission power level over time (which is relevant in terms of the permitted level) is even lower.
According to the article of Khalid et al., the radiation level at the distance of 1 m from computers connected to the network via Wi-Fi in classrooms, was estimated at the level of 0.4 micro-watts per square centimeter as a common radiation exposure level, and 0.004 micro-watts per square centimeter as an average radiation exposure level (the value that is relevant in terms of permissible level). These are values that are millionths of the exposure level allowed. Increasing the distance beyond 1 m will reduce the exposure even beyond that.
Computer Monitor Radiation
The computer screen does not include intended radiation sources. The principle of operation of the screen is optical, and therefore the non-ionizing radiation in the radio or microwave range near it is negligible and low.
Old tube screens generated magnetic fields in their rear part within the VLF band (similar to old TV screens), but the levels in the front of the screen were lower than the permissible exposure levels. It should be noted that some laptops have Wi-Fi antennas that transmit a low-power non-ionizing radiation.
Radiation Emitting Antenna Location in Tablet and Laptop
Tablets and laptops are larger than cell phones and allow selection of different antenna locations. In tablets, the preference is usually to place the cellular antennas at the top of the device, for engineering reasons, and in laptops, the antenna can be located in the body of the computer or around the screen.
Details of Low-frequency Fields Exposure Sources in the Student Environment
In this document, we will not refer to the sources of infrastructure, but to the sources to which the student is exposed from the end-user devices under the ICT program.
Desktop Computer
Exposure to non-ionizing electromagnetic radiation and to electric and magnetic fields near a desktop computer is as follows:
- As with any electronic device, there are voltages and currents in the computer, which generate electric and magnetic fields around it. However, those are very low-intensity fields because they are generated as a by-product of the computer components’ operation and not as intended radiation through transmitters and antennas. In addition, near the computer's internal power supply (which is usually at the back), there are low-frequency magnetic fields (mainly the power grid frequency). The fields may reach tens and even hundreds of Milligauss in the vicinity of the power supply, but they decrease sharply upon distancing, and at a distance of half a meter, they usually reach a value close to 1 Milligauss and even below.
- On computers with Wi-Fi connection (such as via an external device), a low-power non-ionizing radiation at radio frequencies (at the vicinity of the frequencies of 2.45 or 5 GHz) is generated near the device.
- There is an extremely weak non-ionizing radiation (at 2.45 GHz frequency) due to wirelessly connected devices such as a wireless mouse and keyboard. Radiation levels are extremely low (usually one tenth of a micro-watt per square centimeter and below), and very low compared to ICNIRP exposure guidelines (usually ppm and below).
- From the wireless router, when the computer is connected to a wireless network (Wi-Fi) — radio frequency (RF) radiation.
Charging
In the charging area, there are low frequency magnetic fields (mainly the power grid frequency) where low direct voltage (DC) is generated for charging by phone chargers or by voltage converters located behind charging jacks designated for phones and tablets. That technology (power jacks that allow direct charging of phones and tablets similar to USB jacks) came into use and is now available in public and other places.
Exposure level to fields in the charging area may reach tens of Milligauss in physical attachment. However, exposure to these values is usually brief. Upon distancing from the charging area, the level of the fields decreases sharply, down to 1 Milligauss and below at the distance of half a meter.
The wire conducting the electrical current from the adapter, or from a USB connection (such as from a stationary or laptop), conducts a direct current (DC) of hundreds of milliamperes. The level of a direct magnetic field (DC) generated near the wire is very low compared to the exposure levels at international standards.
Should a Laptop or Tablet Be Used over Cell Phones via a Wireless Network (Wi-Fi)?
Distancing the Radiation Source from the Body
Generally, in accordance with the precautionary principle, the most important reducing exposure rule is to distance the radiation source from the body, since the intensity of radiation falls significantly with distance from the radiation source.
The recommendation to distance radiation source from the body is increasingly important for children whose degree of radiation absorption may be increased and their biological sensitivity to certain diseases is different from that of adults.
The distancing principle applies to all sources of exposure listed above. The radiation generated near the cell phone/tablet/laptop, etc. decreases sharply upon distancing from the device.
Increasing the distance results in reducing the radiation level by the square of the distance, approximately.
What Is the Level of Radiation in a Class of 30 Students Using End-User Devices (e.g. Cell Phone/Tablet/Desktop Computer) at the Same Time?
An expanded and updated answer to this question will be provided later.
More articles that may interest you:
References
- ITU - International Telecommunications Union website
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