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
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!
36
Unsolved tasks
Fig. 2.13: About the circuitry and the problems involved
with a "current-free switches" installation
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.