Telephones, Radiation and Everything in Between

 

There is  a lot of discussion on radiation from mobile phones that we use daily, but you cannot see the radiation or feel it, so where's the problem?  What is radiation? And what has that to do with mobile phones?

 

 

 

Illustation: sound waves passing through a megaphone   Illustration - children and mobile phones

 

Phones then and now

What are sound waves?

Sound waves are mechanical vibrations occurring in the medium (e.g. air) through which they pass.  Sound waves may be transmitted without intervening devices in conversation, at shorter or greater distances.  They may also pass through mechanical media that transmit the sound waves from one end to another (e.g. between two plastic cups connected by a string) – you can try this out….

 

In order to transmit information through conversation across large distances, sound waves are not sufficient.  The telephone converts the information contained in the   sound waves into electrical signals, transmitted as electromagnetic waves, to a receiving target.  At the other end, the electromagnetic waves carrying the information are converted back to sound waves received by the listener.

 

How do two telephones communicate?

The earliest phones were sold in pairs: two households wishing to communicate with one another purchased such a pair, and stretched a cable between them.  If one wanted to communicate with a number of households, cables would be stretched to each of them.  In order to eliminate the need to connect households directly by cables, the BELL telephone company developed the switchboard* center, through which all interested parties could communicate with one another.  By means of manually controlled connections, the telephonists at the switchboard would connect between two parties, each of which was independently connected to the switchboard center.  This process was expanded and improved until the telephone grid was invented, in the form we know it today.

 

 

Switching office   Rotary dial telephone   Push-button telephone

 

 

 

*Switching is a technique for converting an electric current into a circuit by means of electric switches.

 

What are cellular networks?

What happens when two people want to converse using wireless technologies (without the aid of wires)?  They use the same communication frequency.  But what if many people want to converse simultaneously?  To answer this question we have to understand what the cellular network consists of…..

 

The term 'cellular phone' originates from the word 'cell'.  In the cellular network, each cell possesses a certain range of frequencies, enabling a number of conversations to be carried on simultaneously.

 

Cellular phones that are connected to a single network and located within the area of one of the cells, transmit to a single transmitting/receiving station (base station) located at the center of the cell.  When one of the phones leaves the area of the cell, the base station identifies a weakening in the strength of the signal it receives from the device, and it transmits a call to all nearby base stations to check their reception from this device. The base station that receives the strongest signals from the device (the calling cellphone) allocates a frequency for it from the available range of frequencies, to enable a continuous communication (without disconnecting the call) 

 

The figure below illustrates a cellular network in urban and rural areas:

 

    Cellular networks in urban and rural areas    

 

More information on mobile phones in general and cellular networks in particular is available on the TNUDA website.

 

Today, every cellular phone company installs a network of base stations and numerous transmission centers. At each of these centers there are antennas that receive and transmit messages to the mobile phones.  The message is relayed from the antenna at the transmission center to a routing station, and by cables from the routing station to another distant routing station and then to an antenna at the transmission center nearest to the phone with which we wish to connect.  The antenna at the transmission center will relay the message through the cellular network by means of radio waves, to the appropriate mobile phone and back.

 

'Generations' of mobile phones

The use of mobile phones has changed over the years. More people subscribed, the use of phones has become ubiquitous to perform multiple tasks. If formerly they were used mainly for conversations, subsequently for text messages, today we use them in a number of different ways, encompassing all aspects of life, from personal through work-related tasks as well as for educational purposes.  The technology had to develop rapidly to keep up with the pace of changes in the extent and nature of use of the phones, both as to the technology used, and the capabilities of the device itself.

The first generation of mobile phones used analog transmission.  During the 1990s the cellular networks converted to digital transmission, by replacing the phones with more advanced models and by changing the technology of the switching stations.  At the same time, the extent of use of mobile phones increased, and the design of the phones changed.

 

The second generation of mobile phones used digital transmission for several reasons:  to block the possibility of listening in on the cellular network (a possibility that existed with analog-based networks), to improve the quality of reception, and to increase the number of channels to enable more simultaneous callers. Second generation networks were designed mainly to support conversations and low speed data transmission. 

mobile phone

The first step towards the third generation saw a change in the direction of what was termed the 2.5 generation. These systems provided data at faster speeds, and could also provide other advanced services and internet connections, such as e-mailing and internet surfing.

 

In 2001 the first phones using third generation (3G) technology were introduced.  This name, 3G, refers to devices enabling a group of applications including wireless communication for phone conversations, video connections, and communication of data through phones in motion.  The speed of transmission in 3G phones is high.  In addition, the changing standards allow the communication companies, service providers and telephone companies to provide a greater variety of services and more efficient use of their frequency allocation.

Phones - different Types

 

As from the middle of that decade, smart phones were developed, combining the properties of mobile phones with the advanced capabilities of a palm computer, and they gained popularity. Today we are already using 4th Generation technology, which is enabling the more rapid transmission of greater amounts of data and use  different applications for the end users.

 

 

*Analog and digital describe signals, where analog is based on continuous signals and digital on discrete signals – a cluster of signals composed of 0s and 1s.

 

 

[Back]

 

What is non-ionizing radiation?

Radiation….what is it?

Electromagnetic radiation may be described as a wave spreading through space or as a stream of energy-bearing particles.  This is a physical phenomenon in which electric and magnetic fields advance through space periodically.

 

Electromagnetic radiation does not need to pass through a material medium – it can also propagate through a vacuum. Electromagnetic radiation advances through a vacuum at 'the speed of light' (300,000 km/sec).

 

A number of physical attributes may describe the electromagnetic wave and its behavior:

 

 

Physical characteristics of the electromagnetic wave:

Amplitude: maximum height (peak)of a wave

Wave length: distance between two adjacent peaks

Frequency: number of cycles per time unit – the shorter

                     the wavelength, the higher the frequency

Wave energy: determined by the electromagnetic fields' amplitude

Physical characteristics of the electromagnetic wave

 

In free space, the further the source of radiation, the weaker the power of the radiation reaching the body, in quadratic proportion to distance.  For example, holding a mobile phone 50 cm from the ear instead of 5 cm increases the distance tenfold, and decreases the strength of the radiation by 100-fold.  However, in an enclosed area (most areas) the power of the radiation depends not only on the distance from the source of radiation, but also on additional factors, such as conditions in the area, the nature of the source of radiation etc.

 

Electromagnetic waves are represented by a scale known as the electromagnetic spectrum, according to the wave frequency (or alternatively, the wave length).  The scale runs from the lowest frequency (corresponding to the longest wave length) to the highest frequency (corresponding to the shortest wave length).  There is an inverse relationship between frequency and wave length, and there is a mathematical-physical relationship between frequency, wave length and the speed of light.

 

The electromagnetic spectrum

 

The electromagnetic spectrum

 

In the early days, only two types of electromagnetic radiation were known: light and radio waves.  Today we know there is a continuum of frequencies composing the electromagnetic spectrum, and different sectors of the spectrum are named according to their characteristics or the way we perceive them. Visible light is a narrow range of the spectrum (wave lengths from 380-700 nanometers).  The human eye is most sensitive at about 555 nanometers.  The ranges of visible light is is located between the infrared light (IR) with wavelengths longer than visible light (1-100 microns3) and ultraviolet light (UV) with wave lengths shorter than visible light (10-380 nanometers).

 

Radiation from visible light is absorbed by visual pigments in the eye and causes a chemical transformation which we experience as vision.  This sector of wave lengths is known as the 'visible range', since the electromagnetic rays in this sector are absorbed through our sight and recognized as 'light'.  Longer or shorter wavelengths are not perceived by our sense of vision or any other of our senses.  Despite the fact that the other wavelengths are not perceived, the frequencies of visible light do not have unique physical properties to distinguish them from other wavelengths in the electromagnetic spectrum.

 

Radiofrequency waves (RF) have frequencies lower than those of the infrared range with wavelengths longer than those in the infrared range.  The range of RFs as defined by the International Telecommunications Union (ITU) is broad, and coverswavelengths between 1 mm to 100 km.  Microwaves are part of the wide range of radiofrequency waves with wavelengths from 1mm to 1m.

 

 

Units of measurement: one nanometer = one-billionth of a meter, designated nm

One micron = one-thousandth of a millimeter.

 

 

Another important characteristic for the classification of radiation is ionization. Ionizing radiation is radiation that causes ionization of atoms, i.e. ejection of electrons.  Ionization requires high frequency radiation and is therefore characterized by the appropriate short wavelengths.  Ionization depends only on the energy of the particles (photons) and not their quantity.  When such radiation is absorbed by the body it can destroy chemical bonds and cause changes in materials.  It can cause changes in living creatures, up to damaging the hereditary material.  Examples of ionizing radiation: radioactive radiation such as X-rays and nuclear radiation.

 

In comparison to ionizing radiation, non-ionizing radiation is in the long-waves region; these waves do not have sufficient energy to ionize atoms.  Radiation frequencies of non-ionizing radiation include: Static fields, Extremely Low Frequency (ELF) emitted by electrical networks and appliances, radiofrequencies (RF) used for example in transmission and communication technologies including mobile phones, and Micro-waves radiation emitted by  appliances such as microwave ovens. Other non-ionizing radiation includes Visible light, infrared radiation, and near ultraviolet radiation (UVA part of UV).

 

What are the sources of non-ionizing radiation?

 

 

The electric grid: the electric grid we see in the street and between towns emits electromagnetic fields with extremely long wavelengths (i.e. ELF, e.g 50Hz in ISRAEL)

  Electric grid
 

Microwave ovens: These heat up or bake food with microwaves radiation that affects mainly water molecules.  Heating food by microwaves ovens is based on the fact that microwaves increase the oscillation of water molecules in the food, eventually leading to heating.

  Microwave oven
  Wireless phones: Wireless (household) phones emit non-ionizing radiation. They emit radiation in the RF range, like the frequencies of mobile phones, or in the microwave range (depending on the type of the device)   Wireless phone
 

Mobile phones: the mobile phone comprises of a transmitter and a receiver, and it emits and absorbs non-ionizing radiationatthe RF range.  While using a mobile phone the user's head is subjected to localized exposure to RF radiation. he potential effects of radiation emitted by mobile phones will be discussed in detail later).

  Mobile phone
 

Radiation from the cellular phone networks: base stations include different antennas and as such emit various levels of radiation (in the RF range) according to the size of the cell, number of subscribers in the area and RF technology used. Over time, the number of users and mode of use of the network has augmented, (e.g. access to the Internet). Moreover, the need for improved coverage throughout the country increased. In order to meet the demands, a greater number of cellular base station antennas have been installed.

  A cellular antenna

 

[Back]

 

Radiation from mobile phones

 

 

Mobile phones emit non-ionizing radiation

The mobile phone is a device that enables wireless communication by means of radio waves (i.e. non-ionizing radiation).  It comprises of a receiver and a transmitter, enabling it to establish a connection between the phone and a nearby cellular base station. The base stations are composed of antennas for transmission and reception of data.

 

In order to establish a communication path, the antennas of the base station and the mobile phones emit RF radiation. The mobile phone emits  a lower level of radiation then that of the antennas within the base station, but because the phone is located in close proximity to the user's body, the radiation power absorbed from the phone’s antenna is more substantial than that of the base stations antennas 

 

 

 

Assessment of the radiation absorbed by the body

The radiation absorbed by the human body is measured according to an index defined as Specific Absorption Rate (SAR) (in units of Watts/Kg).  The measurement is performed by a number of sensors inside an apparatus the size of a human skull, placed near the phone (simulating a person using the phone). The SAR depends on the power of the transmission, the distance from the source of transmission (the mobile phone or the relaying station), the communications technology, and the capacity of human tissue to absorb electromagnetic radiation.  To determine the SAR of the mobile phone being tested, maximal potential transmission power is activated, to simulate the most extreme communication conditions under which it can operate (such as faulty reception).  Such conditions arise, for instance, when the phone is far from the transmission station, in an elevator, etc.  The maximal acceptable levels of radiation exposure of humans from mobile phones are determined in many countries by governmental institutions.

 

To date, the maximal SAR level allowed for mobile phones is based on the thermal effects (heating) and not on non-thermal effects.  Consequently, the standards do not take into account, for example, the possibility of developing serious or fatal diseases, such as cancer, which may result from non-thermal effects.

 

Cellular communication centers

Centers for cellular communications (e.g. cellular base stations), transmit and receive radio waves essential for the operation of mobile phones, and in order to enable us to transmit and receive signals from anywhere in the country, these cellular base stations are scattered throughout the country.

 

Advanced cellular technology requires an increase in the number of cellular base stations.  Where reception is weak because of a lack of sufficient number of stations, the mobile phone 'struggles' and emits a higher power of radiation.  Moreover, lack of a sufficient number of stations requires each station to transmit with greater power, in order to serve a greater number of users, at greater distances (serve a larger cellular cover area).  It is generally agreed that in order to reduce the environmental exposure level it is preferable to install numerous cellular base stations with lower output power than installing a few more "powerful" stations 

 

  What is this comparable to?

Suppose we want to illuminate a large area such as a football field. If we install a single central light we can provide the whole area with very powerful floodlights to illuminate the whole field (including the borderlines). In comparison, we could install a large number of weaker light sources around the field. This way we can use a larger number of smaller and weaker floodlights, each of which will illuminate a smaller area, so that together they will light up the whole field.

Football stadium lighting

 

Since radiation power decreases with increasing distance from the source, most of the exposure to radiation is from the mobile phone being held close to the head, and not to the radiation emitted by the cellular base station placed at some distance from the body. It should be noted that the radiation emitted by base stations is environmental, involuntary and cannot be controlled by the user while that emitted by a device is usually voluntary and controlled by the user.

 

What are the changes in exposure levels relating to the different technologies and generations of mobile phones? 

The maximal level of radiation emitted by 3rd Generation phones is lower than that emitted by previous phone generations. However, because the pattern of use (i.e., the manner, duration and extent of use) of mobile phones has changed, it is not clear if the total amount of radiation exposure has changed and whether the exposure has decreased or increased. For instance, the use of mobile phones has grown and more people use it for longer durations; however, many people now use text messages instead of holding the phone close to the head.

 

 

 

What can we compare this with?

Suppose there is a single access road into a town and it carries a heavy load of traffic.  Urban architects will plan byroads to divert the traffic and reduce the number of vehicles on each road, for the benefit of the citizens.  At the same time, the number of cars per family has increased, so that the total number of vehicles on the roads increases significantly …What have we achieved? There are, in fact, more lanes and more roads, but the number of cars on each road has increased, and traffic jams have not been averted!

 

 

 

The effect of the 4th Generation on the level of radiation to which the individual user and the general public are exposed has not been clearly established. Environmental radiation will depend, among other factors, on the infrastructure to established

 

עכבר של מחשב

 

Under the 'list of activities' we have attached links to video clips, computer games and a variety of websites that will illustrate the concepts applying to mobile phones, radiation and everything in between.  Some of the games were originally intended for the 8-14 age group, but we believe everyone can enjoy them.

 

 

 

[Back]

 

Note for surfers

If some of the topics described above were complex and difficult to understand, the TNUDA team will be happy to receive your questions on the various subjects of interest to you.

 

For further information see:

 

 2.3.16