What is Radiation? - Ab.ust.hk

Radiofrequency / Microwave
(RF/MW) Radiation
Example of RF sources
- Radar
- Electrical cable tower
Example of MW sources
- Microwave antenna
- Mobile phone
- Microwave oven
Specific Absorption Rate (SAR)
• Specific Absorption Rate (SAR) is a
absorption unit for the RF/MW exposure.
• Measure in vivo.
• Standard whole body limit is 0.4 W/kg based
on 6 minutes average.
Average power density
RF/MW Exposure Guidelines
Induced
current
Body
resonance
30 300
Frequency
Surface
heating
MHz
RF/MW Wavelength Are About the
Size of Humans
• People are good antennas when the
wavelengths of RF are similar in size.
• Induced AC electricity dominate close to RF
sources rather than radiation.
• Heating effect to human body caused by
microwave sources.
Power Density (Energy Flux Density)
• It is a derived limits of exposure measured in
the body-absent situation.
• The radiant power incident on a small sphere is
divided by the cross-sectional area of that
sphere.
• The SI unit of power density (S) is watt per
square meter (W/m 2 ).
Biological Effects to RF/MW
• RF/MW absorption may produce heating
effect.
• Hyperthermia (體溫過高): damage mainly to
eyes and testicles.
• Causing cataract (白內障) and temporary
sterile (短暫不育).