Electromagnetic Pollution

2009-07-01T23:15:00.000+09:00

1. Introduction

Electromagnetic pollution is one kind of environmental pollution which is of electromagnetic origin. You can imagine it like a smog composed of many kinds of electromagnetic waves. For this reason the term “electromagnetic smog” or “electrosmog” is used sometimes against of the more official term of “electromagnetic pollution”.

Electromagnetic pollution is the result of electromagnetic excess of the environmental electromagnetic background that the electromagnetic waves radiated from many different technological products.

Inappropriate design of products, the need of companies for easy win, the existence of international standards and/or agreements without the correct level of focus to environmental issues, the higher safety limits, the misleading information and/or education and some kind of society problems are few of the reasons which permit the further expansion of electrosmog problems around the world.

Source of electromagnetic pollution is almost every electric, magnetic or electromagnetic device independently of size and use.

One simple example to understand the problem of electromagnetic pollution is the case of an inappropriately designed microwaves oven used for cooking. The microwaves which are produced inside it are used to heat the food. As result of inappropriate design, microwaves can usually propagate through the oven`s window to the environment. This is a kind of function which the oven does not need to have. It is not the reason was made. This useless radiation is an electromagnetic waste and it contributes to what is called electromagnetic pollution.

The electromagnetic radiation is divided to ionizing and not ionizing one, something which depends on frequency and applications (see the above picture). The sources of both kind of radiation can contribute to the existed electromagnetic environmental pollution.

Ionizing radiation is the one which can excite electrons from atoms and molecules or even to excite the nucleus of elements. It includes i.e. one part of Ultraviolet (UV) frequencies, X-ray frequencies, Gamma ray (γ-rays) frequencies and Cosmic ray frequencies.

Non-ionizing radiation is the one with no ability of ionizing. It includes i.e. visible light, Infrared (IR), Microwave (MW), Radio Frequencies (RF), Extremely Low Frequencies (ELF radiation) and the stable electric or magnetic fields (DC fields).

Non-ionizing radiation is produced by different kind of sources which exist at home, at work or outside i.e. power transmission lines, home electric devices, any kind or wireless network, any kind of radar etc. including cell phones, cell telephony base station antennas, PCs, routers and so many other.

The most important effect of non-ionizing radiation is the increase of temperature to the application area it acts i.e. human body or even the environment itself. The reason is the acceleration of charges because of the electromagnetic forces acting on them during radiation, which creates heating. In the case of human body, this heat can change the speed of biochemical reactions and possibly their function. Accidentally, it will take many years to understand bioelectromagnetic phenomena. So, the best for the time being is to understand what electromagnetic pollution is and also to keep the safety radiation limits at the acceptable level.

The activism about electromagnetic pollution should not be seen as a war between environmentalists and companies or health organizations but as a chance to improve the quality of life by using new better designed and more sophisticated technological products. It is a good chance to rebuild the existing market on a healthier basis with realistic prospects for everyone.

2. Cell Telephony Base Station Antennas Radiation

Base Station Antennas are usually located in the middle of hexagon areas named as cells, which divide a large area having a cell telephony network, as it is shown in the following picture on the right.

The density of these cells and the number of antennas is increased with the number of users per area. The Base Station Antennas located at the center of these cells look like the ones in the picture on the left.

Any cell telephony company has its own different cells network with antennas, something which increases the total electromagnetic pollution per area.

2.1. Electromagnetic Pollution by one only Base Station Antenna

There is strong interest about the level of pollution and its relation with the safety limit distance of nearest buildings from the position of one only radiating antenna.

The radiation patterns of common used antennas are anisotropic and their lobes cannot be calculated approximately by using the simple model of isotropic omnidirectional antenna.

In the picture on the left, you can observe the simulation of distribution of electromagnetic radiation of a typical base station antenna located on the wall of a tall building.

The position and kind of materials of each building around it, can give impressive results because of propagation phenomena (i.e. multi-reflections), like stronger fields (red color) even in areas far away from the antenna against closer to it (green color). This fact, and other kind of phenomena not mentioned here, make useless any proposal of a safety distance limit i.e. 300 metes, between an antenna and a building.

2.2. Electromagnetic Pollution by many Base Station Antennas

The existence of many antennas in one area makes more difficult the calculation of a standard safety distance limit from an antenna. This limit depends on each antenna (i.e. frequency, power, position, kind of antenna), the surrounding buildings construction, the weather and other factors.

In the picture on the left, you can observe one more simulation of electromagnetic radiation emitted by many antennas distributed to an urban area. The positions of maxima of this radiation are presented with red color and of minima with blue colors.

As you can see, the distribution of radiation is not the same at each area and height. So, a simple monitoring of electromagnetic fields with sensors of the emitted radiation by a cell telephony network, near or far from each antenna, is not a secure way to patrol an urban area.

2.3. Extra Covers of Cell Telephony Base Station Antennas

Extra covers of any kind to base station antennas are not permitted, neither for "extra" protection nor to "fit better" to the environment, as they can change their technical characteristics.

Good quality antennas sold by companies have their own protection materials named "radome" which have been passed specific tests i.e. weather changes, absorption behavior etc. in special labs.

In picture on the left, white and gray colored radome materials are used to cover the inside wired structure of different kind of antennas.

2.3.1. One example, which must be avoided

Greece is a less-developed country and this fact is verified every day in many aspects. Here is one…

Greek Atomic Energy Commission (GAEC) is a state authority responsible for protection of the population from electromagnetic pollution (ionic and nuclear). According to this authority base station antennas are permitted to be covered with extra covers in order to "fit better" to the environment. In the following, I show you a representative case.

In the first picture on the left, two base station antennas are installed - on the top of a building - inside two chimneys somewhere in Athens.

In the lower picture on the left, you can observe inside these chimneys big metallic elements (green circles) in front of the antennas, which make them parasitic ones.

It seems, that the members of GAEC know neither "what parasitic antenna” is nor "what radome” is.

It should be mentioned that the addition of such kind of extra materials around antennas (metalic elements or extra covers) by the cell telephony companies goes against the law. The effect of them to the radiation patterns of antennas is not included to their application study to GAEC, which checks it and gives them the permission to proceed.

The above case is a "common situation" in Greece and many antennas systems of unspecified construction have been installed on many buildings. The weight of these systems can be of great danger in case of a big earthquake.

I hope soon European Union will help Greece to undrestand the problems of this situation, by giving appropriate common instructions to all its member states.

3. Cell Phones Radiation

In order to estimate the dangers coming from the use of mobile phones, I present you a few things about it.

In the top picture on the left, you see a "classic" FDTD simulation of electromagnetic absorption inside a model “human head” made by a composite material for a mobile phone working at 915 MHz with power 1 W (SAR is the Specific Absorption Rate to electromagnetic radiation).

In the following graph on the left, you can see the change of safety limits by frequency for Electric Field, Magnetic Field and Energy Flux. In the case of the previous simulation the safety limits are not achieved.

The maximum magnetic field has been found 1.04 A/m against 0.1 A/m, which is the safety limit at frequency 915 MHz. Also, the maximum SAR has been found 1.87 W/kg against 1.6 W/kg, which is the safety limit for the same frequency.

The relation of electric field E and magnetic field H in the air is given by the formula: H = E / 376.8, with Η measured in (Α/m) and E in (V/m). This relation does not depend on frequency.

In the above graph of safety limits, the previous relation does not go along with frequencies smaller than 1 MHz. Except of that, this relation sets us a question about the need of existence of two kind of devices to measure electric and/or magnetic field in the market of electromagnetic pollution measurements devices.

3.1. SAR - measurement methods

The following methods can be used to measure SAR

a) MRI (Magnetic Resonance Imaging) known also as “magnetic tomography” is one precise technique to measure – in real time - SAR inside real human head to the radiation of a mobile phone.

b) In the picture on the right, you can see a less sophisticated method of measuring SAR by using a model human head made from composite material and an antenna located in the opposite direction.

3.2. Temperature change inside human head during a phone-call

In the top picture on the left, the calculated change of temperature at different sections of a model “human head” made by composite materials is shown, after solving arithmetically a set of electromagnetic and thermal differential equations, supposing a mobile phone-head 5 mm distance.

A temperature change about 0.5 - 1.5 °C has been found.

In the bottom picture on the left, two MRI images of the brain of a user with his cell phone at On and Off state are presented.

The existene of more expanded and more dense yellow color areas inside the curves A and B of each MRI image, verified the expected from calculation higher brain electromagnetic absorption of radiation from a cell phone at the On state.

The red arrow shows some exttra absorption phenomena ought to metalic teeth implants of the user!

It is useful to know the value of SAR of your mobile phone, which must not overpassed the safety limit of its working frequency. You can find it inside its manual.

4. Microwave Oven Radiation

A common microwave oven is made basically by a a magnetron source (2.45 GHz), a stirrer, a cooking cavity, and a control system. In the picture on the left, the structure of a microwave furnace is presented.

Microwaves are produced from the magnetron source and propagate with waveguides inside the cooking cavity. These microwaves are absorbed from the water, which exists inside the food and they heat it.

The metallic parts of the cavity act as reflectors of the microwaves. The stirrer is used to homogenize spatially the power distribution of microwaves inside the furnace.

The window of the oven is used for the reflection of microwaves, for the heat isolation and also for a direct safer observation of the food. It is usually double glazed with a metallic net inside it.

The metallic net has special coating against the oxidation and appropriate geometry to create band gaps in different angles and to increase the number of reflections. The geometry of such a net is shown in the picture on the right.

By using FDTD electromagnetic simulation with typical values of physical constants of materials used in the coating of nets, the reflection and transmission coefficients (known as S - parameters) are calculated for vertical incidence of microwaves on the window of the furnace.

Our results are presented in the picture on the left, in the form of two curves (red color for transmission and blue color for reflection). These curves do not show a big reflection at 2.45 GHz (resonance peak) as it should be.

In the same picture two more curves have been designed by hand, which correspond to the expected S-parameters of a well designed window.

In conclusion, the coating which is used to protect the net from oxidation actually iterrupts its reflection ability. This is a usual phenomenon which can be observed to the common microwave ovens used at homes and contributes to electromagnetic pollution.

5. Low Power Transmission Lines Radiation

In some countries, like i.e. Greece, there are low power transmission lines installed close to homes or apartments in larger buildings.

In the picture on the right, you can observe such a case.

There are three conductor low voltage transmission lines (230 V each) with no external grounding cover, together with a neutral and a ground conductor.

In the next picture on the left, I present you a near field FDTD simulation of one only line located close to a building in order to find out

a) how the radiated ELF waves propagate inside it and

b) to check if the values of calculated electric and magnetic field are under the safety limits.

The result is:

EM pollution propagates inside the building and under the ground.
The magnetic field does not change significantly with the distance from line.
The typical safety magnetic field limit of 500 A/m is overpassed in the area inside all the building and even behind it.

Definitely Greece and countries which use same technology of transmission lines in their power transmission network have problem of electromagnetic pollution as many lines exist in the same area.

In other countries, like i.e. UK, power lines are installed underground and cables with external grounding are used. Even in this case, the quality of grounding of the used cables is still quotable and electromagnetic fields can possibly measured over the ground.

6. High Power Transmission Lines Radiation

There is a lot of questioning worldwide about what are the biological effects of electrosmog produced by the high power transmission lines and what the minimum safety distance of pylons from houses is.

In some countries, i.e. in Greece, the safety distance is limited to 300 m.

In the picture on the right, a 7 lines pylon is shown. It has six double high power transmission lines and one line used for grounding on the top.

In the above picture on the left, I present you the results of a near field FDTD simulation of one only high power transmission line 7 kV, 60 Hz at 70 m distance from a building, to find out:

how the radiated ELF waves propagate inside it and under the ground and
if the received values of electric and magnetic field are under the safety limits.

The result is:

The electromagnetic pollution propagates over the mentioned limit of 300 m.
The magnetic field found at 300 m is 4420 A/m. This values is much larger than the safety limit of 500 A/m.
The value of the electric field is smaller than the safety limit of 10 kV/m in 300 m. I expect that the limit will be overpassed for a transmission line with voltage higher than 10 kV.
The electromagnetic pollution propagates under the ground in deeper than 50 m.
The electromagnetic pollution propagates inside the building and even behind it.
A suggested safety limit of 300 m or more is meaningless as more phenomena exist which contribute to electromagnetic pollution. Other criteria should be used to estimate safety areas.

This calculation is a typical example to help you to understand further the electromagnetic pollution because of an electric power distribution network using aerial cables.

7. Low Power Lamps as Plasma Antennas

Common light lamps used at homes and offices are recommended by many mass media and other organizations worldwide to be substituted with others of lower power consumption, which use ionized gas to produce light. In the picture on the left, we observe such kind of lamps already known to everybody.

This kind of lamps has in real higher light efficacy than the older ones which use heating coil, but they have other problems.

They behave like plasma antennas and radiate except visible light an extra electromagnetic radiation at frequency 10 - 20 kHz. This non-useful radiation, which contributes to electromagnetic pollution is ought to be from the way by which these lamps produce the "useful" for us light (see the lower picture on the left).

In these lamps, the ionized atoms of Argon gas inside it vibrate with frequency 10-20 kHz, like the electrons inside a common metallic antenna. This vibrated gas excites the atoms on the outer coated surface of the lamp and visible light is produced. The same time the ionized Argon atoms acceleration and deceleration produces an elecromagnetic radiation, the one which contributes to the electromagnetic pollution. As these lamps work for many hours inside every home etc., the problem exists.

Plasma antennas are developed for years and are used in military applications etc. as they can have stealth and jamming resistant behavior.

The level of radiation and relative characteristics should be clearly written on the surface of the lamps with lower power consumption as for the usual TV receivers.

Materials to protect from electromagnetic pollution

2008-01-01T05:47:00.000+09:00

There is a need to make certain objects invisible, or at least less visible, to radar. Such objects range from submarine periscopes to complete warships, from stealth aircraft to wind turbines.

Materials Science can meet this need, providing materials that absorb the incident microwave energy – radar absorbing materials (RAM) – or complete structures designed to do the same thing – radar absorbing structures (RAS). A number of solutions incorporate reinforced plastics, composites and metamaterials. This kind of materials can be used to protect sensitive areas from electromagnetic pollution but the high absorption they have can create problems to the functioning of cell telephony, which needs the electromagnetic waves reflections on building structures to work well.

Under writing…

Electromagnetic Smog