Their nature, their characteristics, their potential danger
When an electric charge moves (as when a current flows through a wire when turning on an electrical device) it emits both electric and magnetic energy , which can be described as either an electromagnetic field, or electromagnetic waves (or radiation) (see Glossary).
Modern physics tells us that all matter can be described as composed of atoms made up of one or more electric charges (electrons, negatively charged) gravitating around a nucleus comprising, in particular, an identical number of positive charges, protons . Electrons have the ability to circulate between several atoms and thereby create bonds between atoms, to form molecules that can be more or less complex. Chemistry can thus be considered as the physics of electronic interactions between atoms.
We can therefore see that all matter, whatever the level of detail at which it is observed, from the atom to an entire organism or even a planet, produces an electromagnetic field whose characteristics (power, frequencies) depend on the organization of the movements of electrons within it.
Apart from a few very special cases (lasers), no matter emits a single wavelength, but a set of characteristic wavelengths, called a spectrum . The specificity of these spectra is such that many “spectroscopy” techniques have been developed to very precisely identify the composition of all kinds of matter, living or not.
Effects on living things
The electromagnetic fields emitted by any material can interact with other materials, near or far, depending in particular on the intensity of the field emitted, but also, and above all, depending on the structure of the material encountered. Any matter can thus capture certain wavelengths (which can have all sorts of consequences on this matter by the energy thus transferred) or deviate them, reflect them, without being influenced, or even be crossed without there being any the least interaction and therefore the least influence of matter on waves and of waves on matter.
The fundamental element that determines whether or not there is interaction between an electromagnetic field and the matter it encounters is the concordance between the wavelength of the field and the electromagnetic structure of the matter; when this concordance is sufficiently high (that is to say that certain frequencies of the wave correspond to internal frequencies of the matter) the two can enter into “resonance” and the wave can thus transfer a part, more or less important, of its energy to the matter, which can have all sorts of consequences for the matter, in particular making it chemically more reactive or downright breaking its structure in certain specific points.
Thus, certain specific wavelengths can have a major, even dramatic, impact on living matter, even at very low intensities , while others have little or no influence, even at high intensity. intensity over very long periods. The specificity of these interactions is even such that major differences in sensitivity can exist between individuals of the same living species due to genetic differences in the structure of DNA and proteins, which thus have sufficiently different capacities to resonate or react to interaction with a field so that the biological impact is not the same for everyone .
The health consequences of these interactions are potentially endless. in their variety and very deleterious in some cases, as has long been known for example for X-rays. The rapid multiplication of technologies based on the emission of electromagnetic fields and their increasingly sustained implementation on a large scale in all sectors of human activity means that today the risk is growing, but not yet measured, of having a major negative impact on the health of all living beings.
It is no coincidence that the governments of developed countries have enacted laws and regulations highlighting the need for the precautionary principle, particularly with regard to more fragile populations such as pregnant women and children, that insurers are reluctant to cover the risks associated with the development of modern telecommunications technologies and that certain telecom operators warn their customers of potential risks.
Dr Thierry D. LEEMANN
A wave is the representation of an oscillation (or vibration) which propagates: it describes the propagation of a disturbance producing on its way a reversible variation of the local physical properties of the medium (a wave, for example).
A wave carries energy without carrying matter.
It moves with a determined speed which depends on its nature and the characteristics of the propagation medium (electromagnetic waves and sound waves, for example, are of different natures and propagate at a very different speed, in water as in air). A wave is described in particular by its frequency and its length:
- The frequency of the wave is the number of times that a periodic phenomenon (vibration, oscillation) is reproduced per unit of time (see below “Frequency of the electromagnetic field”).
- Wavelength is the distance traveled by a wave during one period of oscillation; it is inversely proportional to the frequency, i.e. the higher the frequency of a wave, the shorter it is, and the lower the frequency, the longer the length of the wave.
This principle is illustrated in the diagram opposite.
Relative to the wave i), the wave ii) has a higher frequency and its wavelength (λ) and therefore shorter.
On the contrary, wave iii) has a lower frequency than wave i) and therefore its wavelength is longer.
An electromagnetic field is the representation in space of the electromagnetic force exerted by charged particles.
The electromagnetic field is the composition of two fields, one electric and the other magnetic, which can be measured independently, but which cannot be dissociated. One does not exist without the other.
Electromagnetic fields penetrate most materials, except those made of certain metallic structures (shields).
When the local magnetic and electric fields vary with the change in position of the electric charges, this produces an electromagnetic wave.
This wave can propagate in the three directions of space.
Electromagnetic waves do not need a material to travel, unlike sound waves, for example; they propagate in a vacuum at the speed of light (visible light being a particular case of electromagnetic waves included in a well-defined frequency range, as indicated in the table below).
The frequency of an electromagnetic field (see “Frequency of a wave” above) is the number of variations of the field per second.
It is expressed in hertz (Hz) or cycles per second, and ranges from zero to infinity.
A simplified classification of frequencies is presented below, with some examples of applications.
|0Hz||Static fields||Static electricity|
|50 Hz||Extremely Low Frequency (ELF)||Power lines and house current|
|20 kHzth, |
(1 kHz = 1000 Hz)
|Intermediate frequencies||Video screens, induction hobs|
|88 – 107 MHzth, |
(1 MHz = 1000 kHz)
|Radio Frequency||FM Broadcasting|
|300 MHz – 3 GHzth, |
(1 GHz = 1000 MHz)
|Microwave radio frequencies||Mobile telephony|
|400 – 800 MHz||Analogue telephone (Radiocom 2000), television|
|900 MHz and 1800 MHz||GSM (European standard)|
|1900 MHz – 2,2 GHz||UMTS|
|2400 MHz – 2483.5 MHz||Microwave oven, Wifi, Bluetooth|
|3 – 100 GHz||Radars||Radars|
|385 – 750 THzth, |
(1 THz = 1000 GHz)
|750 THz — 30 Phzth, |
(1 Phz = 1000 THz)
|30 PHz — 30 Ehzth, |
(1 EHz = 1000 PHz)
|30 EHz and above||Gamma rays||Nuclear physics|
The intensity of an electromagnetic field can be expressed using different units:
- for the electric field, the volt per meter (V/m);
- for the magnetic field, the tesla (T)
Electromagnetic radiation, which also includes radio waves and light, is a disturbance of the electromagnetic field.
Waves from Wi-Fi (but also from mobile phones, DECT cordless phones and Bluetooth) are pulsed microwaves at low frequencies.
Wi-Fi emits waves of extremely low frequencies (extremely low frequencies ), which are “pulsed by jerks”.
They are waves emitted by chaotic multipulsation, without rhythms.
So-called “radio frequency” technologies use electromagnetic fields whose frequency range is between 10 kHz and 300 GHz (see Table above) for radio broadcasting and telecommunications.
Microwaves are the very high frequency electromagnetic waves (300 MHz to 300 GHz) generated by TV and radio transmitters, mobile phone relay stations, cell phones, cordless phones, Bluetooth technology, Wi-Fi. fi, microwave ovens…
Extremely low frequency
“Extremely Low Frequency” or ELF radiation is the band of electromagnetic radiation (radio frequencies) between 3 and 30 Hz.
These waves propagate in the air, sea water and can penetrate significant distances in the rock and the basement. Living tissues are also permeable to it: an internal organ or tissue is therefore exposed to the same field as if it were located outside the body.
Natural ELF waves are present on Earth, created by lightning strikes that trigger the oscillation of electrons in the atmosphere.
Such fields can also be induced by power lines or large transformers.
Propagation attenuation measurement: decibels
Propagation of radio waves
Radio waves (generally called RF for Radio Frequency) propagate in a straight line in several directions. The speed of wave propagation in vacuum is 3.108 m/s.
In any other medium, the signal experiences attenuation due to reflection, refraction, diffraction, or absorption.
Absorption of radio waves
When a radio wave encounters an obstacle, part of its energy is absorbed and transformed, part continues to propagate in an attenuated way and another part may possibly be reflected. We call attenuation of a signal the reduction of the power of this one during a transmission.
Attenuation is measured in bels whose symbol is B. We generally prefer to use the decibel (whose symbol is dB) and corresponds to one tenth of the value in Bels.
When the measurement is positive, we speak of amplification , when it is negative, we speak of attenuation . In the case of wireless transmissions, it is more particularly a matter of attenuations.
Attenuation increases with increasing frequency or distance. Moreover, when encountering an obstacle, the value of the attenuation strongly depends on the material making up the obstacle. Generally metallic obstacles cause a strong reflection, while water absorbs the signal.
Reflection of radio waves
When a radio wave encounters an obstacle, all or part of the wave is reflected, with a loss of power.
The weakening of the signal power is largely due to the properties of the media through which the wave passes.
|Air||None||Open space, interior courtyard|
|Wood||Low||Door, floor, partition|
|Tinted glass||Medium||Tinted windows|
|Living beings||Medium||Humans, animals, plants|
|Concrete||High||Bearing walls, floors, pillars|
|Armored Glass||High||Bulletproof Glass|
|Metal||Very high||Metal shields, Reinforced concrete, metal cabinet, elevatorshaft|
Biocompatibility is the ability of materials not to interfere with, not to degrade, the biological environment in which they are used. It is important to distinguish between biocompatibility and tolerance.
A material is biocompatible BY ITS NATURE.
We then speak of biocompatible material (biomaterial)