7.31 Dosimetry for Non-ionizing Electromagnetic Waves
271
7.31 Dosimetry for Non-ionizing Electromagnetic Waves
7.31.1 General Considerations of Dangers of Non-ionizing
Radiation
People living in populated areas of modern cities are bathed in man-made radio
waves from radio transmitters, and microwaves from repeater towers and cell phone
devices. We also receive such waves from natural sources, including solar radio
frequency radiation from flares and eruptions, and radio waves from the Earth’s
atmospheric electric discharges and aurora. Above frequencies of about 10 MHz to
about 10 GHz, man-made electromagnetic waves now dominate natural sources in
our environment.
There is also a pervasive background microwave radiation coming from outer
space as the relic radiation left over from the big bang. Because the Universe
cooled by expansion, that radiation is now the same as that from a blackbody at
the temperature of 2.725 ◦ C. From Stefan’s law (Eq. (7.18), the intensity of this
radiation is
I = σ T
4
= 5.67 × 10
−8 (2.725)
4 W/m
2
3 μW/m
2 .
(7.23)
But the microwave intensity near our cell phones is a million times greater, in the
range of 3 W/m 2 .
Intensities of background radio and microwaves are usually low enough that no
health effects are evident. 51 There are exceptional instances. A person accidentally
encountered dangerous levels when standing in front of a powerful microwave
antenna inadvertently turned on by a co-worker. 52
Table 7.5 shows the Federal Communication Commission recommended upper
limits for non-ionizing electromagnetic wave power densities in human tissue.
Surface power density, a term used by engineers, is simply another name for
Table 7.5 FCC
recommended upper limits to
radiation power density
impinging on humans
EM-wave
Limit
Radio
∼10 4 W/cm 2
Microwave
10 mW/cm 2
Infrared
1 W/cm 2
Visible
0.1 W/cm 2
Soft ultraviolet 0.001 W/cm 2
51 After all, we humans have lived on Earth for millions of years unaware of the existence of radio
waves. Then Maxwell predicted from pure deductive logic that radio waves must exist from his
equations for the behavior of electric and magnetic fields.
52 Joseph J. Carr, Microwave & Wireless Communications Technology p. 9, [Newnes (Elsevier),
Boston] (1997).
271
7.31 Dosimetry for Non-ionizing Electromagnetic Waves
7.31.1 General Considerations of Dangers of Non-ionizing
Radiation
People living in populated areas of modern cities are bathed in man-made radio
waves from radio transmitters, and microwaves from repeater towers and cell phone
devices. We also receive such waves from natural sources, including solar radio
frequency radiation from flares and eruptions, and radio waves from the Earth’s
atmospheric electric discharges and aurora. Above frequencies of about 10 MHz to
about 10 GHz, man-made electromagnetic waves now dominate natural sources in
our environment.
There is also a pervasive background microwave radiation coming from outer
space as the relic radiation left over from the big bang. Because the Universe
cooled by expansion, that radiation is now the same as that from a blackbody at
the temperature of 2.725 ◦ C. From Stefan’s law (Eq. (7.18), the intensity of this
radiation is
I = σ T
4
= 5.67 × 10
−8 (2.725)
4 W/m
2
3 μW/m
2 .
(7.23)
But the microwave intensity near our cell phones is a million times greater, in the
range of 3 W/m 2 .
Intensities of background radio and microwaves are usually low enough that no
health effects are evident. 51 There are exceptional instances. A person accidentally
encountered dangerous levels when standing in front of a powerful microwave
antenna inadvertently turned on by a co-worker. 52
Table 7.5 shows the Federal Communication Commission recommended upper
limits for non-ionizing electromagnetic wave power densities in human tissue.
Surface power density, a term used by engineers, is simply another name for
Table 7.5 FCC
recommended upper limits to
radiation power density
impinging on humans
EM-wave
Limit
Radio
∼10 4 W/cm 2
Microwave
10 mW/cm 2
Infrared
1 W/cm 2
Visible
0.1 W/cm 2
Soft ultraviolet 0.001 W/cm 2
51 After all, we humans have lived on Earth for millions of years unaware of the existence of radio
waves. Then Maxwell predicted from pure deductive logic that radio waves must exist from his
equations for the behavior of electric and magnetic fields.
52 Joseph J. Carr, Microwave & Wireless Communications Technology p. 9, [Newnes (Elsevier),
Boston] (1997).