RF SAFETY in EMC LABS

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RF SAFETY in EMC LABS
Thank you
Rohde Schwarz Belgium jos westhof-jacobs senior
sales engineer systems projects - test
measurement

• ABLE - 29/11/2002

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EMF
EMF is the measurement of electromagnetic
radiation in terms of the consequences for humans
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Electrosmog
Artificial E- and H-fields 'Electrosmog' is a
term used to designate artificially generated
electromagnetic pollution, meaning electric (E)
fields and magnetic (H) fields. Such fields
arise wherever there is a voltage or a current.
All types of radio broadcasting and TV
transmitters produce electromagnetic fields, and
they also arise in industry, business and the
home, where they affect us even if our sense
organs perceive nothing. Unit of electric field
strength Volts per meter (V/m) Units of magnetic
field strength Amperes per meter (A/m) or
magnetic flux density (B) in Tesla (T) or Gauss
(G)
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Electromagnetic Fields

• Constant fields Here, the direction does not
  change. Examples include the Earths natural
  electric and magnetic fields, the magnetic fields
  used to run subways and streetcars, and the
  fields used in magnetic resonance imaging (MRI).
• Alternating fields Here, the direction does
  change. The number of periods per second is equal
  to the frequency, and the unit of frequency is
  Hertz (Hz).
• Low-frequency fields (LF) Alternating fields up
  to 30 kHz.
• HF, RF and microwave fields Alternating fields
  from 30 kHz to 300 GHz

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Properties of EM Fields
Electromagnetic fields propagate as waves and
travel at the speed of light (c). The wavelength
is proportional to the frequency. If the
distance to the field source is less than one
wavelength, then we are usually in the near field
(almost always the case in the low frequency
range up to 30 kHz). If the distance is more than
one wavelength, then far field conditions usually
hold. In the near field, the ratio of electric
field strength (E V/m) and magnetic field
strength (H A/m) is not constant, so we have to
measure each separately. In the far field,
however, it is enough to just measure one field
quantity since we can compute the other, their
ratio being a known constant. An electric field
is easily shielded, e.g. using a thin, grounded
metal foil. However, a magnetic field will
penetrate almost all known materials.
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Occurrences of overexposure
Broadcast facilities for radio, TV and
telecommunications Radar installations
Industrial facilities making use of electric
discharge machining, induction heating, plastics
bonding, microwave applications, aluminum
processing Medical equipment for diathermy,
electrosurgery, hyperthermy, magnetic resonance
imaging (MRI) EMC Sites when applying radiated
immunity testing (producing high fieldstrengths
mainly in case of military, avionics, automotive
applications)
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Effects on the human body
Low-frequency fields induce currents in the human
body that can have an effect on the sensory,
nerve and muscle cells. The greater the field
strength, the more pronounced the effects.
However, field strength decreases at increasing
distance from the source of radiation.
High-frequency fields heat the human body. The
degree of absorption of electromagnetic waves is
a function of the frequency and intensity of the
field and the type of tissue. The organs with the
least blood flow are most endangered, e.g. the
eyes. In contrast, the heart and brain are better
at handling heat due to their better blood flow.
Besides obvious damage such as burns, long-term
effects are also under discussion, e.g. increased
risk of cancer, influences on hormone balance,
cell growth and the immune system.
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Effects on the human body
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The Limits LF (EN50166-1)
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The Limits HF (EN50166-2)
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Unit Conversions
E SQRT (30 x G x P) / Deff E Fieldstrength
(V/m) G linear antenna gain P antenna input
power (W) Deff Effective distance (m)
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Quick Conversions
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Quick Conversions
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Quick Conversions
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Quick Conversions
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More info on http//www.narda-sts.com Rohde
Schwarz Belgium jos westhof-jacobs senior sales
engineer systems projects test measurement
division jos.westhof_at_rsb.rohde-schwarz.com phone
32 2 721 50 02 fax [phone]
36 http//www.rohde-schwarz.com
Thank you for your attention !