Anti-elf Protection
Vicki
Radiofrequent Waves
What are radiofrequent waves?
Sources of radiofrequent waves
Radiofrequent waves hazards
Standards for radiofrequent waves
Protection against radiofrequent waves
What are radiofrequent waves?
Radiofrequent waves is electromagnetic radiation with wavelengths exceeding
1 mm. They comprise radar, radio and television waves and also industrially
and domestically used microwaves of frequency 2,450 MHz.
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Sources of radiofrequent waves
The most important sources are also the best known ones:: radio and TV
broadcast stations.
AM stations can develop about 1 MW. FM stations emit their waves
horizontally. As most of the sources are mounted on towers, the rule of
keeping distance applies to the neighbors.
Portable phones and walkie-talkies also emit radiofrequent waves.
Radar waves are used for tracing and detection.
Microwaves are used for diathermy treatment in physical medical science.
Well known 2,450 MHz microwave applications include domestic cooking and
industrial drying. They are also used in induction ovens to melt and degas
metals.
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Radiofrequent waves hazards
Radiofrequent waves feature higher penetration capacity than other non
ionizing radiation. Waves of frequencies above 3 GHz (wavelength < 30 cm)
can penetrate up to 10 cm, those below 1 GHz (wavelength < 10 cm) can
dissipate their energy in deeper tissues. Waves of wavelengths above 1 m
pass through the entire body.
The most hazardous waves have got wavelengths between 3 cm (150 MHz) and 2
m (10 GHz). Reflection of these waves on the subcutaneous fat layer can
generate resonance, and hence hot spots in the body.
Apart from burns, radiofrequent waves can overheat the gonads and disrupt
the nerve and the cardiovascular systems.
The lens can age prematurely and severely and cataract can appear, even long
after exposure.
Next to he radiation hazards, following risks have to be considered:
sources of radiofrequent waves can cause electrocution
high tension can generate X-rays in magnetrons and klystrons
strong electromagnetic fields can induce electrostatic charges in metals and
generate sparks. Radio stations can act accordingly even over 3 km distance.
induction can affect electronic equipment
radiofrequent waves can interfere with older types of pacemakers. More
recent types have EMF shielding up to 100 W/m²
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Standards for radiofrequent waves
Current Belgian standards use the specific absorption rate (SAR) as main
criteria. In fact they are identical to US regulation.
Research has demonstrated that no disadvantageous effects occur for SAR
values below 4 W/kg over the entire body. For safety reasons the standards
are drafted such that the SAR is limited to 0.4 W/kg during any 6 minute
interval.
The power density is not measurable in the vicinity of the source. Hence on
has to take recourse to the field strength. The power density PD is then:
PD = 37,700 E² where E = electrical field strength in v/m
PD = 377 H² where H = magnetic field strength in A/m
Threshold values are collected in the table.
frequency FPD in W/m²E2 in V²/m²H² in A²/m²
10 kHz to 3 MHz 1,000377,0002.65
3 MHz to 30 MHz 9,000/F²3,770 x 900/F²900/(37.7F²)
30 MHz to 100 MHz 103,7700.0265
100 MHz to 1 GHz F/103,770 x F/100F/37.7x100
1 GHz to 300 GHz 10037,7000.265
Both continuous and pulsed radiation must be averaged over 6 minutes.
The thresholds can be exceeded only if it can be demonstrated that the SAR
remains below 0.4 W/kg over the entire body and below 8 W/kg locally.
The threshold of 1,000 W/m² for waves below 3 MHz is clearly safe based
on the SAR. This threshold was introduced because of the risk of
electrocution above the threshold..
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Protection against radiofrequent waves
Adequate protection includes:
encapsulation of the danger zone. To avoid creation of secondary sources,
all metal elements used must be covered with e.g. graphite filled PUR foam.
personnel exposed to the radiation fields must wear overalls, facial screens
and gloves made out of metallized fibers. Additional gonad protection is
recommended.
reflection causing resonance and hot spots must be avoided. Similarly
crossing waves must be avoided.
the sources must be monitored continuously to detect possible unforeseen
reflections (called lobes). Measurements have to be carried out at a
distance of more than 5 cm of any object.
Glass is effective against microwaves Temperature resistant glass dishes are
commonly used in microwave ovens. The window glass is meshed however. The
size of the meshes prevents the microwaves from leaving the oven and causing
damage.
The application of adequate sun protection creams in combination with
exposure time control allows for safe sun tanning without nasty injuries.
Opaque materials cannot be penetrated by light. Laser beams can however cut
these materials, drill holes or weld them.
