RF and Microwave radiation hazards

1. Microwave Antennas and
Propagation

2. Microwave Antennas
• Conventional antennas can be adapted to microwave use
• The small wavelength of microwaves allows for additional
antenna types.

3. Assignment
• Horn antenna
• Slot Antenna
• Lens Antenna
• Microstrip antenna
• Helical Antenna
• Parabolic Reflectors
• Plasma effect
• Propagation effect
• Ground effect
Refer to David M. Pozar’s book for propagation characteristics of microwave
antennas.

4. Radiation Zones
• Radiation is the energy in the form of electromagnetic waves.
• Radiation zone or field can be divided into three zones depending
upon physical size of antenna (D) and wavelength of the antenna or
transmitter or system:
1. Reactive Zone/Non- radiative near-field
𝑅 =
𝜆
2𝜋
2. Radiating Near-field/ Fresnel Zone
𝑅 =
2𝐷2
𝜆
3. Radiating far-field
𝑅 >
2𝐷2
𝜆

5. Radiation Zones
• Reactive Zone and radiative
near-field zone are hazardous.

6. Specific Absorption Rate (SAR)
• Specific absorption rate (SAR) is a measure of the rate at
which energy is absorbed by the human body when exposed
to a radio frequency (RF) electromagnetic field.
• 𝑆𝐴𝑅 =
𝜎𝐸2
𝑚 𝑑
W/kg
Where σ = conductivity
E = electric field intensity
md = mass density (kg/m2)

7. • Hazard of Electromagnetic Radiation to Personnel
(HERP)-potential of electromagnetic radiation to produce
harmful biological effects in humans.
• Hazard of Electromagnetic Radiation to Ordnance
(HERO)- potential of electro explosive devices to be
adversely effected by electromagnetic radiation
• Hazard of Electromagnetic Radiation to Fuel (HERF)-
potential of electromagnetic radiation to cause spark
ignition of volatile combustibles such as vehicles fuels.
EM RADIATION HAZARD (RADHAZ):

8. • Caused by the thermal effect of radiated energy
where the body absorbs radiation
• Significant internal heating may occur without the
individuals knowledge because the body does not
have internal sensation of heat, and tissue damage
may occur before the excess heat can be dissipated.
• Eg-if the lense of the eye is exposed to microwaves,
its circulatory system would be unable to provide
sufficient flow of blood for cooling and may cause
cataract.
HERP

9. • Eg-the stomach, intestines and bladder are
especially sensitive to thermal damage from
high power microwaves.
• Microwave frequencies for which the
wavelengths are the same order of magnitude
as the dimensions of human body produce
close coupling between the body and the
microwave field.
• A large amount of heat can be generated to
caused severe damage to the body.
• Significant energy absorption will occur even
when the body size 1/10 of the wavelength.

10. • Although the biological damage occurs mostly
due to the dielectric coupling, low frequency
magnetic field coupling also produce damage
when exposure time is large

11. Microwave energy is dangerous to ordnance like
weapon system, safety and emergency devices and
other equipment containing sensitive electro
explosive devices (EEDs).
Radiated fields can cause unintentional triggering
of EEDs
High intensity RFR fields produced by modern radio
and radar transmitting equipment can cause
sensitive electrically initiated devices (EIDs)
classically known as electro-explosive devices
(EEDs), contained in ordnance systems to actuate
prematurely.
HERO

12. Ordnance is more sensitive than human
partially because they do not have circulatory
system to dissipate internal heat.
However, EEDs can more easily be protected
from the effects of RF energy than humans by
enclosing them with metallic enclosures
which reflected back the incident microwave
energy
The potential dangers to ordnance and fuels
are obvious because there could be an
explosive "chain reaction" by exploding;
consequently, these limits are generally lower
than personnel limits.

13. • Occurs due to possibility of accidently igniting fuel vapours
by RF-induced areas during fuel handling operations
proximity to high level RF fields.(during fuel handling
operations close to high powered radar and radio
transmitting antennas. )
• The probability of ignition may be significant for more than
50 volt-ampere arc.
HERF

14. • HERF precautions are of more general concern
to fuel truck operators. However, some general
guidelines include:
• Do not energize a transmitter (radar/comm) on an
aircraft or motor vehicle being fueled or on an
adjacent aircraft or vehicle.
• Do not make or break any electrical, ground wire,
or tie down connector while fueling.
• Radars capable of illuminating fueling areas with a
peak power density of 5 W/cm2 should be shut
off.

15. • For shore stations, antennas radiating 250 watts or less
should be installed at least 50 ft from fueling areas (at
sea 500 watts is the relaxed requirement).
• For antennas which radiate more than 250 watts, the
power density at 50 ft from the fueling operation
should not be greater than the equivalent power
density of a 250 watt transmitter located at 50 ft.

16. International Radiation Protection Association
(IRPA) sets the Permissible Exposure Levels
(PEL) for the general public
IRPA guidelines are divided into 2 categories:
◦ Occupational Permissible Exposure Levels (applies
to personnel who work in the vicinity of RF for 8
hours a day)
◦ General Public Permissible Exposure Levels (applies
to resident who are exposed to the RF
electromagnetic environment throughout the year
Radiation Hazard Limit

18. FCC Safety Limit
Safe
Hazard

19. MPEL (ANSI’s 1982 RF Protection Guide)
Safe
Hazard

20. • Can be practised by preventing radiation from entering into
the beam of the transmit antenna or from coming close to
any microwave generators or propagating medium.
• In areas where high power radar are used, the service and
maintenance personnel must wear microwave absorptive
suit (made of stainless steel woven into a fire retardant
synthetic fiber)
Radiation Protection