Preface to the lecture, 1

34

 

Protection against artificial fields

 

 

system                                            used  frequency

about

 

measured 

value

 

radio broadcasting station 

(MW 2O kW)

 

6OO kHz

 

2...17 V/m

 

radio broadcasting station 

(SW 1OO kW)

 

15 MHz

 

1...25 V/m

 

SOS-transmitter 

on a ship (1OO W)

 

41O kHz

 

1...3 V/m

 

Epitaxiedevice 

(induction oven)

 

45O kHz

 

37...4OO V/m

 

HF-welting press 

(welding of plastic foils)

 

27,12 MHz

 

70...85 V/m

 

radar on a ship 

(TRN 311)

 

9,3 GHz

 

1...3O uW/cm

2

 

radar of an airplane

 

9,2 GHz

 

45O... 

28OO uW/cm

2

 

domestic appliances measured in a distance

 

of 3O cm:

 

hand mixer 

refrigerator

 

5O Hz

5O Hz

 

5O V/m 

6O V/m

 

Fig.  2.12: ____ the electric field strength resp. Power density

 

in our environment.

 

____

taken from: _____________________________________________________

 

:     E. Habiger u. a. : Elektromagnetische Vertraglichkeit, Fig. 7.2, page 146, 

2. Ed., 1992, Berlin, Munchen: Verlag Technik, ISBN 3-341-00993-0

 

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Tasks 

35

 

2.12 Protection against artificial fields

 

Artificial fields more or less always occur in the neighbourhood of electric apparatus and

 

installations. Especially problematic are those that work with the free radiation of

 

electromagnetic fields, that is all the radio broadcasting stations, handheld and radar

 

transmitters.

 

Herewith it is important that not needed parts of the antennas are shielded, that antennas

 

with little close by field pollution are used and that the stand should be situated at least 3

 

km remote from inhabited areas. For instance at radar installations damping values of 10

 

dB and more can be obtained only by using a corresponding tree growth.

 

This obviously concerns a damping of the waves in a dielectric manner. We'll have to

 

come back to this because textbook physics does not know a corresponding damping term

 

in the wave equation.

 

The radiation leaking out in case of the high-frequency welding of plastic foils and of the

 

microwave oven should be minimized.

 

In the case of induction ovens or of motors an active shielding often causes problems so

 

that for simple domestic appliances like a hand mixer and especially for the electric hair-

 

dryer non proportionally high field strength values are measured. Fig. 2.12 informs about

 

it.

 

Protective measures for the operator are hardly possible. To protect uninvolved people not

 

only the apparatus but also the rooms and eventually whole parts of buildings had to be

 

shielded and grounded.

 

Sometimes also fairly simple possibilities are helpful like e.g. the usage of a remote 

control. By clearing away the cable salat at the workplace and at the sleeping place 

induction  loops can be removed.  Alarm-clocks operated by batteries  should have

 

preference over those operated by the network. Mattresses with metal in them and spring- 

beds which clearly act as an antenna should be avoided. In extreme cases even so called 

"current-free switches" and shielded network lines are recommended (fig. 2.13).

 

In the area of the network supply lines a choking coil can help decrease the spreading of

 

high-frequency interference radiation. It is especially important that all the conducting

 

metallic objects like e.g. water pipes, heatings, steel racks, machines, switching racks,

 

steel armaments and metallic windows should be grounded properly, because otherwise

 

extremly high static charges could result instead of a shielding. Construction biologists

 

recommend to when possible do without metals when building houses and furnishing,

 

what of course is only realizable with limitation.

 

In any case numerous measures are known that to a lesser extent find their legitimation in

 

classical physics, but more likely in precaution. As long as we do not know which

 

phenomenon causes the electrosmog and we don't have a measuring-instrument at our

 

disposal, precaution is really the only thing we can do irrespective of the effectiveness of

 

the measures and of the arising costs!

 

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36

 

Unsolved tasks

 

 

Fig. 2.13:   About the circuitry and the problems involved 

with a "current-free switches" installation 

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Tasks 

37

 

2.13 Unsolved tasks

 

The report concerning the actual state of research could be continued at will. But the 

expositions should suffice, to understand what are the tasks of the electromagnetic 

environmental compatibility (fig. 2.1) and which questions still have to be supplied with a 

solution. One can get deeper into every of the addressed points and then discover that 

some questions can be expressed sharper and maybe conceivable answers can be found, 

but at the same time and unavoidable the number of new questions increases faster.

 

Let us again take up the example of the handheld wireless telephones (chapter 1.2). At 

least it now is clear to us that the usage of the built-in microwave antenna of a handy is 

problematic. In the interior of an automobile it never should be used. If, however, one uses 

the antenna installed on the outside on the sheet metal then the damping and screening 

effect of the sheet metal chassis is advantageous at least for the handy user.

 

With that of course the central question is not answered. The question of what the cause is 

for the interfering and at worst health endangering effect of the HF-radiation. Field 

freedom we can't find anywhere on this world. Possibly we even need the fields. But then 

the question is how much is necessary, how much is healthy and how much makes us ill.

 

The gap of explanation especially gets clear in the case of the static or of the low- 

frequency magnetic field: away from technical interference sources normally fields on the 

scale of 10 nT are measurable. Construction biologists say that 20 nT, so twice that value, 

should not be exceeded at the sleeping place and maybe 50 nT at the desk. These values 

however are determined purely empirical.

 

When a person is examined in a nuclear magnetic resonance tomograph that person is 

exposed to a field that lies between 0.2 and 1.5 Tesla. that is a value 7 till 8 powers often 

higher than before mentioned without this leading to the death of that person. Entirely on 

the contrary this method is regarded as especially caring and safe compared to the X-ray 

examination.

 

Here again the legitimation of the thesis put forward is entirely comfirmed. The thesis that 

the well-known physically measurable and controllable phenomena can not be considered 

as a cause and that possibly a until now undiscovered field phenomenon should be called 

to account.

 

Should such a phenomenon exist it should be derived, calculated and proved. We must go 

to endless troubles and try everything. The actual difficulties wherein the electromagnetic 

environmental compatibility is stuck are a challenge.

 

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