Specific flow of absorption



The index of specific flow of absorption or SAR is an index which informs about the quantity of energy conveyed by the radio frequencies emitted towards the user by a radioelectric apparatus, when this apparatus functions with full power, under the worst conditions of use.
The unit of the SAR is Watt per kilogram (W ⁄ kg, if m2s-3).
The absorption of electromagnetic fields produces a rise in temperature of the fabrics (heating effect).
Therefore, more the SAR of a radioelectric apparatus is weak, less this apparatus is dangerous for health.
In the USA, the FCC requires that the sold telephones have a level SAR lower than 1.6 Watts per kilogram (W ⁄ kg) for a whole of 1 gram of fabric.
In the European Union, the limit of SAR of 2, is realized out of 10 grams of fabric.
For the entirety of the exposure of the human body, there exists a limit of 0,08 Watt ⁄ kg, realized on the whole of the body.
Nowadays, with some exceptions, the majority of the telephones have a SAR lower than 1 out of 10 G of fabrics: their SAR is generally located around 0.4 to 1 out of 10 G.
In addition, as the respect of these thresholds on the antennas relay is difficult to check for the general public, one then has recourse to the measurement of electric fields compared with limits of reference.
Formule
The specific flow of absorption is calculated starting from the following physical sizes :
The electric field in fabrics : SAR = σE² ⁄ ρ
Density of current in fabrics : SAR = J² ⁄ ρσ
Rise in temperature in fabrics : SAR = ci * dT ⁄ dt
E : electric field in V ⁄ m
J : density of current in A ⁄ m², obtained starting from the magnetic fields and ⁄ or electric.
ρ : density of fabric in kg ⁄ m³
σ : electric conductivity of fabric S/m
ci : heat capacity of fabric in J(kg K)
dT ⁄ dt : derived from the temperature of fabrics compared to time in K/s
Application in health
Health hazards of telecommunications.
Knowledge on the electromagnetic waves is today still to deepen.
Many scientific studies tend to prove the harmlessness of these waves with low dose (in lower part of 2 out of 10 G), but none clearly could establish this harmlessness.
Other scientific studies on the other hand highlighted dangers in the long term to the human body, such as cancers or the permeabilisation of the cellular membranes.
At present, the frequent technological changes of the cellphones do not make it possible to have a reliable knowledge of the risk. Indeed, it takes several years to undertake an epidemiological study having enough relevance to apply to low radiation dosage emitted by the cellphones.
Thus, the studies we have today relate to only the first generations of cellphones. But since, the 3G develops and the frequencies evolve ⁄ move.
Many studies conclude at the very weak risk even with their absence.
A contrario, according to a Swedish epidemiological study led by Kjell Mild, the intensive users of mobile phones would have a risk 2,9 times higher to be reached of a malignant tumor to the brain on the side where they use their telephone.
The French Agency of Public health of the Environment and Work (AFSSET) published in June 2005 a new opinion on the cellphones.
On its side the European Agency for the environment, taking into account the remaining doubts, recommends the application of the precaution principle and thus to reduce the limits of current exposures.
In the doubt, better is thus worth, on the one hand, to prefer a cellphone having a SAR relatively low and on the other hand, to telephone as much as possible under conditions of good reception and also, at the time of a communication of the type GSM ⁄ GPRS ⁄ UMTS, it is advised to move away compound from the hot areas of the body, by using for example a pedestrian kit or by activating the loudspeaker of the telephone.
Specific flow of absorption per model of cellphone
The comparative one of the SAR of the smartphones (in):
The SAR of this comparative were measured close to the ear. As the SAR differs according to waveband (GSM 900MHz - GSM 1800MHz - UMTS 2,1 GHz - Wifi 2,4 GHz), we retained the maximum value emitted with protocol UMTS for the transmissions 3G. The more important the value of the SAR is, the more the harmful effects of the electromagnetic waves are felt on the human body, particularly on the brain. Attention, a level of SAR of 2W ⁄ kg for an adult corresponds to a level of 2,19W ⁄ kg for a child of 10 years and 3,06 for a 5 year old child. Indeed, the low thickness of limps cranial of the children makes them more sensitive to the electromagnetic waves than the adults.
A study with license to know the conditions of exposures of the subjects to the antennas of mobile telephony.
According to the distance from the antennas and compared to the referent group, certain symptoms are expressed in a higher way significantly
tire up to 300 Mr.
headaches, disturbances of the sleep, feeling of discomfort up to 200 Mr.
cardiovascular irritabilities, problems, difficulty of concentration until 100m.
the women are more sensitive than the men for 7 symptoms
headaches
nauseas
loss of appetite
disturbances of the sleep
depressive tendency
feeling of discomfort
visual disturbances
Over-sensitiveness so called electrosensibility on low level, with the electromagnetic fields becomes for certain people a problem of survival.
Among the victims of the electrosensibility, one finds especially people having worked on computer during several years, but also of the inhabitants of bordering districts of lines with high voltage. And today, certain users of cellphones GSM and the inhabitants of districts where function of the antennas relay of mobile telephony test certain faintnesses which are likely to be examined under the angle of the electrosensibility.
The first researchers to be itself interested in the human electrosensibility are the Professor Cyril W Smith, Professor William Rea. These authors, as of 1985 exposed in various scientific congresses of the cases of patients reached of a curious syndrome, relatively rare, associated with the exposure to the electromagnetic fields. In the continuation, in partnership with other researchers, they published several scientific articles reporting of the observations carried out on patients presenting of the more or less serious disorders when they are subjected to various electromagnetic fields (insomnia, abnormal nervousness, state of quasi permanent stress, anguishes incoercible, depressive tendencies, nervous breakdown, losses of balance, giddinesses, nauseas, falls brutal of blood-pressure going sometimes until the collapse, disorders of the cardiac rhythm, loss of memory, losses of conscience, cutaneous eruptions, eczema, falls fast more or less abundant of hair, crises asthmatiformes, épileptiformes absences).
These symptoms can be disparate and do not appear necessarily simultaneously on a given patient.
One can consider today that over-sensitiveness with the electromagnetic fields, although not yet unanimously accepted by the medical community and academic, is well a pathology and that in certain cases, it can endanger the life of those which suffer from it (of the fatalities are described by Professor CW Smith). It is necessary to say that for majority of people, it is well difficult to conceive that an electric field or an alternate or pulsated magnetic field with low intensity, that one does not see, that one does not feel and who is measurable only thanks to very sensitive and not very widespread apparatuses, can influence certain vital functions or certain bodies.
Moreover, traditional medicine having constantly repeated us that apart from any statistics, the isolated cases observed are not to take into account, the majority of the doctors confronted with such problems of electromagnetic over-sensitiveness see possibility of treatment only in psychiatry. And these people of which we form part consequently are sometimes considered, even in their own family like hystericals, the unbalanced mental ones or like subjects nevrotic. Of course, the medicamentous treatments prescribed by the majority of the medical community are with the height of the noted symptoms : sleeping pills with massive amounts, antidepressants, euphoriant, medications of disorders of the cardiac rhythm, beta blocking. The whole having finally for effect only to deeply poison the person without solving in-depth problem and especially without establishing the true cause of it.
Certain Swedish Internet sites mention the existence of more than 600.000 électrosensibles people in Sweden, of which executives of the industry of the mobile phone. We are personally in contact with the French Association of the Electrosensibles Patients. The public authorities pretend to be unaware of their existence and yet, Professor Roger Santini, the Professor Cyril W Smith and our team of independent scientists could test these people and we could highlight thanks to simple tests this electrosensibility of the allergic type. Simple morals does not enable us to put these people at the round of applause of the company under pretext which they do not answer the standard criteria of the average of the population.
to post ⁄ mask it SAR

Cordless phone

Structure of emission
The power of maximum emission of the basic station and compound is of 250 MW. If one measures the average on a certain amount of time, the radiation seems weaker, since the signal is not emitted permanently. All the periods of 10 milliseconds (ms) are divided of 24 intervals. At the time of a conversation, a compound emits a signal during an interval and takes delivery of the signal of the basic station during the interval which is 5 ms later. The basic station can communicate simultaneously with six compounds. At rest, when there is no phone conversation, the basic station emits every 10 ms a short pulsation. Certain models of telephones comprise a basic station which does not emit any radiation when the compound is hung up again.
At the time of a phone conversation, the majority of the models of telephones DECT always emit the same radiation, whatever the distance between compound and the station basic as well as the quality of the connection. On the models consuming little energy, the power of emission is controlled and the radiation is weaker when the connection is of good quality.
Low frequency magnetic fields coming from compound, the compound is fed in electricity only during the emission or of the reception of the signal. The food by pile thus is activated and stopped all the 5ms during an telephone exchange, which generates a low frequency magnetic field of 200Hz.
Basic station : electric field
One can note the determining influence of the distance on the intensity of the field. The measured intensities are always at the lower part of the limit recommended by the ICNIRP, namely 60 V ⁄ m. Même at the time of six simultaneous phone conversations with a distance of 20cm, the electric field is lower than this limit.
At the time of an epidemiological study undertaken in the area bâloise, 166 people carried, during one week, a measuring device allowing to calculate the load released by the various radiation sources high frequency. The basic station contributed to a total value of 23% with the total load (0.22 V ⁄ m). A comparable study carried out in France showed similar results.
Electric field (field E) for various modes of fonctionnement
Seuls the results of the basic stations having généré
les the measured electric fields strongest appear on this graph.
Effects on health
Basic and combined station : short-term effects
To evaluate the medical effects in the short run magnetic fields, one can follow the limits recommended by the ICNIRP. As already mentioned, the radiation of compounds and the basic stations is quite lower than the limits. In the short run, there is not thus to fear negative effect on health, coming from compounds and the basic stations of the cordless phones.
Compound : long-term effects
The limiting values recommended by the ICNIRP do not take however counts the potential effects of them in the long run electromagnetic radiation. Several epidemiological studies currently lean on this question. In these studies, the stress is laid on the medical effects of the radiation of the cellphones, but some of them also relate to the radiation of compounds of the cordless phones. A German study in particular did not find any relationship between the use of cordless phones and the appearance of brain tumors, even during one utilization period of more than five years. On the other hand, a recent Swedish study concluded from there that a use of cordless phone over several years could cause a brain tumor. The same group of Swedish research examined the bond between the use of cordless phones and the appearance of cancers of the testicles without however being able to establish it. The study of the international research Center on cancer could not give a conclusive answer on the relationship between the radiation of the cellphones and the brain tumors. The results of the Interphone study could depending for the cordless phones. In this moment, knowledge on the subject No does not agree. Certain epidemiological studies had the aim of examining the relationship between the use of the cordless phone and the appearance of nonspecific symptoms as well as the quality of the sleep described by the people concerned. The majority of the epidemiological studies relating to the subjective quality of the sleep and the use of the cordless phone did not establish a bond between these elements. The use of a cordless phone does not seem either to have of influence on the function of the hemato-encephalic barrier.
Basic station : long-term effects
There does not exist currently any specific study on the long-term effects of the basic stations of the cordless phones. Moreover, few studies explore the question of the potential medical effects in the long run of a weak high frequency radiation, like that coming from the basic stations and no sure data could be drawn about it. Since 2007, several studies published examined the report ⁄ ratio that there could be between the subjective wellbeing and the load released by the various radiation sources high frequency, without however being able to establish this one.
Disturbance of the implants
According to a study, the basic stations and the compounds disturb neither the cardiac pacemakers nor the défibrillateurs.

Intercom baby (babyphone)

The intercoms baby are composed of a module baby and one or more modules parents. The module baby, which is posed near the child, is a transmitter, the modules parents are above all the receivers. However, certain devices act at the same time of transmitter and receiver. The majority of the intercoms babies do not emit uninterrupted, but solely when a certain noise level is reached, adjustable on the apparatus, in the room of the child.
Certain apparatuses control permanently if the module parents is still with range of emission of the module baby. With this intention, the module baby emits all both or three seconds a signal very short test, moment when it emits a radiation.
There exist various types of intercoms baby which have ranges and variable radiant intensities. The OFSP measured the radiation of two intercoms baby having different powers of emission. The radiation decreases very quickly when one moves away from the apparatus and is always at the lower part of the threshold recommended. With a distance of 20 cm, the radiation of the weakest apparatus is 28 times lower than the threshold recommended whereas that of the most powerful apparatus is three times inferior. With a distance of one meter, the radiation is 93 times inferior for weakest and nine times for most powerful compared to the threshold recommended. Even when the apparatus is in involuntary liaison with the child, the values for the measured apparatuses are lower than the threshold recommended. The radiation which generates the signal test of the control of the range is him also much weaker.
If one is based on the data above, it is not necessary to fear any risks related to the radiation, but it is however judicious to make so that the child is as not very exposed as possible there.
Place the intercom baby at least a meter of the bed of the child.
Do not use apparatuses emitting permanently. Regulate the module baby on the automatic release mode with the voice.
If the intercom baby is connected on the sector with an adapter, made so that the adapter is to at least 50 cm of the bed of your child.
Technical data
The intercoms baby can function at frequencies completely different with various powers from emission and ranges. For the majority of these frequencies, it is not allowed to use apparatuses which emit permanently. It is necessary thus that these apparatuses radiate only starting from one certain sound volume. The majority of the intercoms baby are one-way apparatuses: the module baby can only emit and that intended for the parents that to take delivery of. If this apparatus is equipped with a function of control of the range, the module baby emits all both or three seconds a signal making it possible the module parents to check that it is still with range of reception. It is also possible to decontaminate this function on the majority of the apparatuses. For the bidirectional apparatuses, the control of the range can be carried out directly starting from the module parents.
Certain apparatuses also make it possible to monitor the children by video. To function, these apparatuses must emit permanently.
The thresholds recommended by the International commission for the protection against radiation nonionizing concerning the electric fields depend on the frequency of the radiation.
Frequency (MHz) Wavelength (m) Power of maximum emission (mW) Maximum range (m) Terminology OFCOM Limit ICNIRP (V ⁄ m)
27 11 100 400 Audio application without wire, Baby monitoring 28
40,7 6,5 10 150 Application to unspecific short range 28
446 0,7 500 5000 Radiocommunication 29
865 0,35 10 400 Audio application without wire 40
1800 0,17 20   Audio application without wire 58
1900 0,16 250 300 DECT 60
2400 0,125 10 300 Application to non-specific short range 61
Low frequency fields
The intercoms baby function with piles or an adapter sector. This last also functions when the intercom is completely decontaminated. It often contains a cheap transformer having a bad output and inducing important radiated magnetic fields of 50 Hz in the immediate environment. Nevertheless, these fields are already tiny at a distance of 50 cm.
Measurements of the exposure
The best manner of characterizing the exposure is to use the concept of SAR. Value SAR indicates the power of radiation absorptive by the human body. One can measure the electric field, from which value SAR is calculated, for the apparatuses connected with at least a wavelength of the body. A study measured the electric field generated by two different intercoms baby. Even if the intercom baby should not be placed close to the body, one determined value SAR of the two apparatuses. To take these measurements, the apparatuses were regulated on a continuous signal in permanent mode, creating the most important possible radiation.
Value SAR
Value SAR was measured for the two intercoms and appeared quite lower than the limit recommended by the CIPRNI (2 W ⁄ kg).
values SAR of two different intercoms baby
Apparatus Frequency (MHz) Power of emission (MW) Value SAR (W ⁄ kg)
Intercom baby 1 863 10 0,01
Intercom baby 2 446 500 0,08
Electric field
One can note the determining influence of the distance on the intensity of the field. The measured intensities are always at the lower part of the limit recommended according to the frequency by the ICNIRP, namely 40 V ⁄ m (intercom baby 1) and 29 V ⁄ m (intercom baby 2). If one uses these apparatuses with the distance recommended of one meter, the fields reach 0,43 V ⁄ m (intercom baby 1) and 3,2 V ⁄ m (intercom baby 2).

Bluetooth


Radio connections via bluetooth are used to transmit the voice and the data on short distances by using high frequency radiations. bluetooth makes it possible to connect various wireless devices: a cellphone with a kit freehands, a laptop with a printer or a mouse, etc This technology, simple and economic, is in full rise currently and of new applications appear each day.
The apparatuses bluetooth are divided into three classes of power: 1, 2, 3. The radiations of the apparatuses of classes 2 and 3 are weak and localized. The majority of the bluetooth applications used close to the body belong to these categories. The transmitters of the most powerful class (1) can produce, if they are used in the vicinity immediate of the body, of the radiations similar to those of a cellphone.
The radiations emitted by the apparatuses bluetooth of all the classes of power are lower than the limiting values recommended to the international level. In the actual position of knowledge, these radiations do not involve an immediate health risk.
Kit freehands bluetooth in order to reduce the radiation
The use of a kit freehands bluetooth forms today also part of the measures of precaution to reduce the exposure to the radiation of the cellphone. Instead of the telephone, a transmitter bluetooth, at the radiation much weaker, is placed in the ear, thus, at the time of a call, the exposure of the head to the radiation is strongly reduced.
Detailed informations
Bluetooth (IEEE 802.15.1) is the first standard created for the vocal transmissions and the transfers of information on short distances. The transmitters bluetooth are very small, inexpensive and use little current.
Technical data
Frequency : from 2,4 to 2,4835 GHz free frequency ISM and without license
Wavelength : approx. 12,5 cm
Power of emission
For the applications, there exist three classes of power having different ranges. The class of power 3, corresponding to the lowest power, is most widespread.
The power of effective emission is most of the time lower than the maximum power : indeed, the intensity of the transmission is just sufficient to make it possible the other apparatus to receive the signal. The receiver measures the power and can require of the transmitter to increase or decrease the power of emission, if it is possible. The regulation of power makes it possible to save the battery and to decrease the disturbances of other networks bluetooth.
Classes of power of the transmitters bluetooth
Classify power Power of emission of peak (MW) Power of maximum emission (mW) Power of minimal emission (mW) Range (m)
1 100 76 1 100
2 2,5 1,9 0,25 40
3 1 0,8   10
The power of emission and thus the load of the radiation are not constant. The regulation of the power is obligatory for the class of power 1 and optional for classes 2 and 3.
Structure of emission
According to the use, there exist various profiles of communication for the apparatuses bluetooth. However, each apparatus accepts only certain profiles: two apparatuses cannot communicate and are compatible only by one and even profile.
When two aircraft bluetooth equipped with the same profile of communication are with range one of the other, a connection is established automatically. In a mini network, to eight apparatuses can be connected to each other. Under these conditions, an apparatus takes the direction and organizes the radiocommunication. This apparatus, called Master, orders the others (slaves).

Example of a periodic structure bluetooth
the Master emits on the transmission channels 12, 5, 55, 70
slaves on channels 68, 1, 17, 41
Five periods for channel 5 and three periods for channel 17
combine between them for the data transmission of significant amounts.
Each period can be more or less long according to the quantity of data which must be transmitted.
For the transmission of the data, the waveband located between 2,402 to 2,480 GHz is divided into 79 separated transmission channels, of a width of 1 MHz. Each user of the mini network has the various transmission channels according to the model which the Master establishes. In a piconet, the transmission channels change in general 1600 times a second, creating a pulsated radiation accompanied by a maximum pulse frequency of 1600 Hz. Master and slaves emit and take delivery of alternatively. The time interval during which a transmission channel is allotted to a master-slave couple is 0,625 ms. An apparatus can emit during 1, 3, 5 periods then takes delivery of again. If several periods are combined, the frequency of the impulses drops to 533 Hz or 320 Hz. In general, if there is no data transmission, the slaves do not emit and take delivery of only sporadically. On the other hand, the Master emits a screen marks out or weaves beacon so that the slaves can synchronize themselves with him.
Low frequency fields of the apparatuses bluetooth
The apparatuses bluetooth using current only during the emission or of the reception of data, the battery thus is continuously activated and stopped. It results from it from the low frequency magnetic fields, ranging between 1Hz to a few thousands of Hz.
Measurements of the exposure
Like measures basic for the load by high frequency radiation, one uses the energy of radiation absorptive by the body per unit of time and unit of weight, which one indicates like specific flow of absorption, in Watt per kilogram (W ⁄ kg). For the apparatuses bluetooth used close to the body, one measures value SAR. For the apparatuses exploited far from the body, the electric field is also significant.
A study carried out measured values SAR and the electric fields of the following applications
Two keys USB provided with an antenna of the classes 1 and 2 with flow of data and maximum power of emission
An electronic diary (personal digital assistant, ANP) of the class of power 2
Two different kits freehands, of the class of power 3
Measured values all SAR were lower than the limit of 2 W ⁄ kg recommended by the International commission of the protection against radiation nonionizing.
Values SAR of apparatuses bluetooth of categories 1, 2, 3
  Classify power Value SAR (W ⁄ kg)
Plug-in antenna (USB) 1 0,466
Plug-in antenna (USB) 2 0,0092
Electronic diary 2 0,01
Kit freehands 3 0,00117 - 0,00319
Electric field
The electric field induced near antennas USB exploited with a power of maximum emission. The field decreases quickly with the distance. The measured intensities of the apparatuses bluetooth are, as of a distance of 20 cm, more from 20 even of 150 times lower than the value of 61 V ⁄ m recommended by the CIPRNI.
Maximum electric field (field E) according to the distance for a ANP and two keys USB bluetooth of various classes of power. The electric field decreases quickly according to the distance. Measurements were carried out with maximum powers of emission.
Normally, bluetooth reduces the power of emission when the connection between the apparatuses is good and this in order to save energy and to avoid the interferences with other devices. That generates fields E and values SAR even smaller.
Effects on health
On the basis of current knowledge and measurement of exposure available, the high frequency radiation generated by the networks bluetooth is too weak to cause, by absorption and following the rise in consecutive temperature, of the acute and detectable medical effects. The long-term effects and the nonthermal effects still were studied too little. Being given the studies carried out on the effects of the high frequency CEM in the field of low dose and the very low powers of emission of the apparatuses bluetooth of classes 2 and 3, there is not to fear negative effects on health. The cellphones with transmitter bluetooth integrated class 1 constitute a special case. The effects on health due to the radiation are not known at present and are the subject of research to the international level. The OFSP published councils of precaution to limit the radiations of the cellphones, also valid for the telephones equipped with bluetooth.

WLAN
The lan without wire makes it possible to connect a laptop to a PC, or a computer with peripherals and an access point to Internet. The mobile phones and the cordless phones equipped with technology WLAN are more and more often used for Internet telephony. The data which circulate between the various apparatuses are transmitted by electromagnetic radiation of strong intensity and not by cable. The apparatuses in network are used at the same time of transmitter and receiver.
The force of the radiation depends on the power of emission and the transfer of the data. The radiation reaches its stronger intensity when there is the maximum of exchanged data. It strongly decreases according to the distance compared to the transmitter. Even when the power of radiation and the traffic of the data are with their maximum, the radiation is ten times lower than the limit recommended when one is with 20cm transmitter, and 40 times inferior when one is with 1m.
It is not known yet if the electromagnetic fields generated by network WLAN represent a danger to health. In general, the radiation of apparatuses WLAN is weak, of the measures of precaution can be recommended when the electronic laptops, agenSAR or telephones Internet are used close to the body. We advise the following measures of precaution with the people who wish to reduce to the maximum the electromagnetic fields induced in their housing or on their work place.
To start network WLAN only when one needs some really. It is in particular important to extinguish function WLAN on the laptop. Otherwise, the computer does not cease seeking a network, which causes a superfluous radiation and vacuum the battery.
Not to hold the laptop against its body during connection WLAN.
To install the access point if possible to a meter of the work places, stay or rest occupied for long periods.
To place the access point in a central way so that all the connected apparatuses have a good reception.
To prefer the standard G WLAN to the standard B, indeed, the standard G transfer more effectively the data and thus has a radiation weaker than the standard B.
If it is possible to regulate the power of emission, it should be optimized at the access point compared to the zone to be fed.
A transmitter WLAN can be used only with the antenna envisaged by the manufacturer. If the antenna does not correspond to the transmitter and has a too great profit, the power of authorized maximum emission can be exceeded.
Measurements of the OFSP for the reduction of the exposure to the radiation of the mobile phones apply to the compatible mobile phones WLAN, which are used for Internet telephony.
Installation and applications

Various apparatuses are connected between them by the access point and Internet by the modem.
In a network WLAN, one in general connects a PC to a laptop, or a computer with peripherals or an access point to Internet. The access point allows the exchange of the data between the various apparatuses and offers the access to Internet. The apparatuses in question must be equipped with technology WLAN, the PC and the modern laptops contain office a chip WLAN, whereas it is necessary to add one of them on the less recent apparatuses. The electronic agenSAR or the palm computers containing a chip WLAN can be also integrated into the wireless networking.
The mobile phones and the cordless phones equipped with technology WLAN are used for Internet telephony with voice on IP and can be connected to Internet by the access point.
Technical data
The international professional organization IEEE published various standards of family 802.11 for network WLAN. The table shows the various characteristics of radiation.
Properties of various standards WLAN of the IEEE
Normalizes IEEE 802.11a 802.11b 802.11g 802.11h
Power of maximum emission (mW) 200 100 100 200 ⁄ 1000
Power of average emission - beacon (mW) 1 0,5 0,5 0.5
Power of average emission max. (mW) < 200 < 100 < 100 < 200
Frequency (MHz) 5150 - 5250 2400 - 2483,5 2400 - 2483,5 5150 - 5350
5470 - 5725
Range (m) 50 until 200 50 50
Regulation of the power no no yes, statics yes, dynamics
Maximum flow of data gross (MBit ⁄ s) 54 11 54 54
Diffusion little out of use most widespread little
The standard 801.11g is that which is most frequently used today. The bands frequency of the standards has and H are used in Switzerland and Europe also for other services. This is why the use of apparatuses of the standard has is authorized only with one reduced power and in the buildings. The standard H was regulated for Europe in such a way that it releases the frequency at once when this one must be used by another application.
Flow of data
The standards the most recent 802.11 has, G and H has high bancs. If several apparatuses must use a connection to the access point at the same time, the line capacity of connection will be distributed and the flow for each apparatus thus will drop.
Regulation of the power of emission
With the standard H, the power of emission is automatically regulated according to the quality of the reception. Moreover, it is possible to modify by a software the power of emission according to the zone to be covered near the access points of the standard G and h.
Radiation
The effective power of radiation depends initially on the traffic of the data. Even if no data circulates, the access point continuous to emit a signal. If only the beacon is emitted access point 100 MW, the average power of radiation during time reaches 0,5 MW. On the other hand, so much of data are emitted, the average power of radiation can reach 70 MW.
The diagram of radiation is very irregular, since an apparatus can emit even without transfer of information. The beacon of the access point generates a relatively regular radiation pulsated with a repetition rate of 10Hz.
Variation according to the distance
The radiation emitted by an antenna decreases according to the distance. Moreover, it can be weakened or considered by obstacles such as walls. This is why the flow of data can fall if there are long distances or obstacles between the access point and the apparatuses in network.
In opened spaces, the range of the apparatuses corresponding to the standard H is higher, since the power of emission is stronger. However, the radiation will be more strongly attenuated by the walls because of its higher frequency, which means that its range will be reduced inside the buildings.
Networks WLAN are very sensitive, that is to say that it is still possible to put apparatuses in network even with a very weak radiation.
Measurements of the exposure
Maximum values SAR
Normalizes Apparatus Flow of data (Mb ⁄ s) SAR (W ⁄ kg)
802.11a access point 30 0,54
  chart PC 13,3 0,07
802.11b access point 6 0,73
  chart PC 6,3 0,43
  ANP 3,8 0,067
802.11g access point 26 0,27
  chart PC 21,5 0,11
Electric field
Field E according to the distance for two access points (AP), two chart PC and a ANF WLAN
The access point 2 can function as well with standard 802.11 has as with B or G, chart PC can function with 802.11 B or G
The electric fields strongly decrease according to the distance compared to the transmitter. Values SAR are always lower than the limit of 61V ⁄ m recommended by the CIPRNI. With a distance from 20cm, no apparatus reaches more than the 10% of the limiting value recommended by the CIPRNI, and to 1m, even not 2,5%.
Hotspots WLAN
The space in which an access to Internet is available via a network WLAN is called hotspot. The hotspots can be public or be accessible only to one restricted circle from users. Inside the buildings, the access points are mainly assembled to the ceiling or at the walls, sometimes in the double floors, outside, they are placed on the frontages or the roofs of the buildings. Several access points can be installed on a hostpot.
The values of immissions of the hotspots are quite lower than the limit of 61V ⁄ m, recommended by the CIPRNI.
Effects on health
According to current knowledge and on the basis of measurement of exposure available, the high frequency radiation generated by the wireless networkings is too weak to cause, by absorption and following the rise in consecutive temperature, of the acute and detectable medical effects. The long-term effects and the nonthermal effects still were studied too little. At present, the studies carried out on the effects exerted by the high frequency CEM in the field of low dose are in lower part of the limiting values into force and do not allow to conclude that the wireless networkings constitute a threat for health.
The use of certain apparatuses WLAN, like the laptops, the mobile phones and the NPA equipped with WLAN, by holding them close it body, can mean long exposure to the radiation. Many uncertainties remain today in connection with the medical effects of such apparatuses used near the body. Thorough studies are led to the international scales, being focused especially on the radiation of the mobile phones. Adapted measures of precaution, as described in the introduction, can reduce this load of radiation.

Microwawe oven


The microwawe ovens use high frequency electromagnetic radiations. These radiations are absorbed by food and are transformed into heat. The food heated with the microwaves does not contain microwaves and do not radiate. The metal case of the microwawe oven and the metal grid of the door of the furnace retain most of the radiation inside the furnace. A small portion of this radiation escapes from the furnace in the form of radiation from escape. On the surface of the furnace (0-5 cm), one can observe relatively high radiant intensities, which decrease however quickly and are already ten times lower than the limiting values to 30 cm of the furnace. In the event of defect or of clogging of the seals of the door, this radiation of escape can be higher.
On the basis of actual position of knowledge, the radiation of escape of an intact microwawe oven and correctly used does not involve any health risk. The risks can come from extreme food or on the contrary insufficiently heated so as to kill the germs which they contain. As for traditional cooking, the most important risk related to the microwawe oven is that to burn itself with food. The warm water represents an important danger if it is reversed or splashed.
Used correctly, the microwawe oven makes it possible to heat without danger of food. The following councils could be useful to you.
Consult the instructions and the regulations of safety contained in the directions for use.
Take care of the cleanliness of the framework of door and its seals, and control the good performance of the system of closing of the door, the sealing and the good state of the case of the apparatus. Do not use to in no case a defective apparatus.
Avoid the overheating and the explosive evaporation of liquids while placing a stem out of glass or a material spoon resistant to heat in the container.
The food with an envelope or a skin must be piqués before cooking or be cooked in another manner.
The food must be heated inside and outside with at least 70°C during 10 minutes, so as to be cooked well and to kill the micro-organisms. Stir up food from time to time, so that they are heated uniformly.
Heat food for babies with a conventional method, if you did not familiarize yourselves yet well with the microwawe oven. If you use one of them, are particularly careful. Heat the feeding-bottle without tétine. Shake the feeding-bottle before giving it to your child and control the temperature of food for babies, in order to ensure you that they are not nowhere too hot.
Features
Standard frequencies
0 Hz produced by the permanent magnets of the magnetron (static magnetic field)
50 Hz produced by the power supply (low frequency magnetic field)
2,45 GHz produced by the magnetron (high frequency magnetic field)
Power: 500 - 2000 Watt (domestic apparatuses)
Principle
The materials slightly conducting such as the water and of many other components of the foodstuffs absorb the energy of the microwaves. This absorption is due to the transfer of the energy on particles electrically charged and dipoles. The dipoles are molecules with which one of the ends is positively charged and the other negatively, their electric charge thus is irregularly distributed. The most frequent dipoles in the foodstuffs are the water molecules.
The ions and the dipoles inside a foodstuff are mobile. In the presence of an electromagnetic field, they tend to be directed according to their load in the direction of this field. The field of a microwawe oven changes direction at extremely high intervals, five billion times a second. The ions and the dipoles will tend to follow the changes of direction of the magnetic field. They thus will be subjected to very important movements, which will result in to raise their temperature and thus that of the foodstuffs.
This process of warming is very different from the conventional process, in which the transfer of heat is made on the surface food, heat being then transmitted inside food by conduction.
The magnetic radiation is produced by a high frequency generator, the magnetron. A transformer provides the high voltage necessary for the operation of the magnetron. The magnetron is activated and decontaminated 50 times a second. The radiation is thus of pulsated type. The typical duration of an impulse of radiation is 10 ms. The radiation is directed by the magnetron towards the interior of the furnace, in the room of cooking.
The metal walls of the furnace and the metal grid of the door reflect the radiation and maintain it in the furnace. To the opening of the door, the radiation source is immediately cut and the radiation ceases in the space of 10 µs.
The reflection of the radiation on the walls causes interferences, which increase or decrease the radiation at certain places of the furnace. The radiation inside the furnace is thus not distributed regularly. The rotary table in the furnace ensures a regular heating of food, in spite of the irregular distribution of the radiation.
1 Case
2 Transformer
3 Ventilator of the diffuser
4 Magnetron
5 Waveguide
6 Reflectors rotary
7 Reflectors metal
8 Room of cooking
9 revolving Plate
Transformer FonctionnementLe provides the high voltage necessary to the operation of the magnetron, which produces electromagnetic waves. These microwaves are concentrated in a metal tube, the waveguide, from where they are directed towards the room of cooking. There, they directly reach the dishes laid out on the rotary table either, while being distributed by reflectors rotary, or by reflection of all shares.
Suitable and inappropriate crockery
The materials electrically insulating like glass and the porcelain are practically insensitive with the microwaves and are thus appropriate very well like crockery for the microwawe ovens. It is disadvised using porcelain with metal decorations, the microwaves destroying the reasons.
The microwaves are almost entirely reflected by materials electrically conducting like metals, so that the food placed in metal containers is not heated. Moreover, one will avoid using metal containers, because they disturb the optimal distribution of the microwaves in the room of cooking. Metal parts too close to the wall of the room of cooking can cause sparks.
Measurements of exposure
High frequency electromagnetic radiation
Radiation of escape of the microwawe ovens
The high frequency radiation escaping from a microwawe oven under operation is called radiation of escape. This radiation should not exceed 5mW ⁄ cm² at a distance of 5 cm of the apparatus, which corresponds to an electric field of 137 V ⁄ m. the radiation of escape of microwawe ovens new and worn in households and restaurants was measured within the framework of studies.
Average radiation of escape of microwawe ovens to 5 cm of the apparatus
Study Average radiation of escape (mW ⁄ cm²) Many measured apparatuses Old of the apparatuses (years)
Study: apparatuses worn 0,41 106 0,1 – 14
Study : new apparatuses 0,08 60 0  
apparatuses worn 0,17 103 1 - 23
Study : apparatuses worn less than 0,062 per 50% from the apparatuses, max. 0,086 130 0,5 – 18  
These three studies conclude that the radiation of escape is most important when the seals of the door worn or are clogged, or when the door or the system of closing is worn. The acceptable radiation of escape maximum was exceeded only in one case.
Specific rate of absorption
Values SAR related to the radiation of escape of a microwawe oven were given within the framework of a study. The microwawe oven was prepared so as to emit the radiation of acceptable maximum escape. With a distance from 30cm, which corresponds to an exposure of all the body as to a distance from 5cm, which corresponds to the exposure of the head when one looks at food in the furnace, values SAR are definitely lower than the recommended limiting values. It is only with the direct contact with the furnace that the recommended limiting values are exceeded.
Outdistance (cm) Measured value SAR (W ⁄ kg) Recommended limiting values
SAR (W ⁄ kg) Exposed part of the body
< 0,1 7,95 4 members
5 0,256 2 head, body
30 0,0056 0,08 all the body
Values SAR of a microwawe oven with a radiation of maximum permissible leakage (5 mW ⁄ cm² with 5cm) and comparison with the limiting values recommended for various parts of the body.
Low frequency magnetic fields
The low frequency magnetic fields are produced by the transformer and the engine of the revolving plate, like by the transformer of strong power of the magnetron. The low frequency magnetic fields were measured for 34 microwawe ovens. The measured values do not exceed the recommended limiting value of 100 µT. The magnetic field strongly decrease when one moves away from the apparatus.
Outdistance (cm) Magnetic field (µT)
5 27,3 ± 16,7
50 1,66 ± 0,63
100 0,37 ± 0,14
Magnetic fields of 50Hz of 34 microwawe ovens studied, median value ± standard deviation
Effects on health
Effects of the electromagnetic fields
High frequency magnetic fields
The electromagnetic radiation of the microwawe ovens was studied as for its effects on the eyes. The crystalline lens of the eye being not very vascularized, the heat which accumulates there is evacuated with difficulty. The crystalline lens is consequently sensitive to the high temperatures, which can lead to a permanent opacification of this one. By observing food in the course of cooking through the door of the furnace, the eyes are very close to the apparatus, where they are exposed to the radiation of escape. The studies however showed that with closed door, the radiation is too weak to cause a significant heating.
All in all, one does not lay out, for the microwawe ovens, of indices concerning of the effects on health related to a rise in the temperature of the body.
Low frequency magnetic fields
The microwawe ovens belong to the category of domestic apparatuses in the beginning of low frequency electromagnetic fields relatively strong. In spite of that, the exposure to the magnetic fields of these apparatuses remains modest, insofar as they function only during short amounts of time. The studies carried out to date did not make it possible to highlight with certainty any effect of the microwawe ovens on health.
Dangers related to an unsuitable use of the microwawe ovens
Food warming with a hermetic envelope or skin and objects
In a microwawe oven, the warming of food is particularly fast and is accompanied by the development of an important pressure inside food reaching a certain size until 3-4cm. Food like eggs, tomatos, potatoes and sausages with an envelope or a skin can burst or explode in the furnace or after in being left. The eggs heated with the microwawe oven represent a particularly high danger and can cause light burns with low registers and wounds with the eyes. The food equipped with an envelope or a skin must consequently be sufficiently bored or peeled before their cooking with the microwawe oven. For eggs, it is preferable to cook them with water, in a conventional way.
The airtight containers like the bottles, the pots of food for babies, the vacuum packagings, etc must be open before their warming in a microwawe oven. For the feeding-bottles, one will take care to remove tétine, because the explosion of a feeding-bottle can cause serious burns.
Warming of liquids and food
In a microwawe oven, it can happen that liquids are heated beyond their point of boiling without there being formation of vapor bubbles nor. Very light jolts can cause in these overheated liquids, the almost instantaneous formation of large bubbles, which escape from the liquid in an explosive way, involving liquid and being able to cause burns. This risk can be isolated while placing a stem out of glass in the container. Spoons with coffee can also be used to this end, in so far as they are out of resistant materials like stainless steel. Do not use silver plated spoons.
Under the effect of the microwaves, the liquids, the food and the gelatinous substances are heated more quickly inside than outside. So the containers and the food can not appear hot with the first contact, at the time of leaving them the furnace. That involves a high risk of burn of the throat, in particular for the babies. It is thus recommended to mix the liquids, food and the other objects left the furnace before controlling their temperature.
Hygienic preparation of food.
In a microwawe oven, it can happen that the food is not heated in a homogeneous way
For reasons inherent in construction, important differences in temperature can exist in the room of cooking.
The various components of the food water, greases, proteins, carbohydrates are not heated at the same speed, which can involve the appearance of very hot zones and cold zones.
The very salted food is overheated on the surface.
Because of the irregular warming of food, there is a risk which the micro-organisms which they contain are not entirely killed. The preparation hygienically irreproachable of food can be assured by means of following measurements.
To increase the time of cooking. Alternation between periods of warming and rest allows a better compensation of the temperature. This process can be accelerated by stirring up food. The food must be heated inside and outside with at least 70°C during ten minutes.
The great quantities and the large pieces a thickness higher than 3-4cm cannot always be correctly cooked with the microwawe oven. In this case, to choose another method of cooking.
Modification of the chemical composition of food.
Any warming of food involves chemical modifications. New substances appear and of the existing substances are partially destroyed. These modifications depend on the duration and the temperature of cooking. The modifications of food heated in a microwawe oven are comparable with those caused by a conventional mode of cooking with regard to the food value, the digestibility of proteins, the composition of the amino-acids and the stability of the liposoluble vitamins has and E. In comparison with the conventional methods of cooking, the water-soluble vitamins C and B are preserved better by cooking at the microwaves. Greases are oxidized, which gives place to less of highly reactive toxic substances. Cooking in a microwawe oven produces generally less undesirable substances such as polycyclic aromatic hydrocarbons and heterocyclic aromatic amines that cooking with the frying pan. On the other hand, it does not make it possible to obtain an aromatic crust.

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