electromagnetic fields. All the radio and television transmission will produce
electromagnetic field. In the applications of industrial and commercial there are also
electromagnetic fields. Human can’t have any sense in the electromagnetic fields but it is
really affect the inner of human body.
2.
Electric field intensity
（
E
）
If the charge can feel the effect of the force in a field then the field is an electric field.
The electric field intense of a point in the electric field is defined as the capacity of the
electric field control unit charge at this point. The electric potential gradient is measured
by volt per meter
（
V/M
）
.
The electric field mode should be used in following cases:
1
）
The frequency is below 30MHz
2
）
The near field region close to radiation source
3
）
In the unaware electric field
3.
Magnetic field intensity
（
H
）
It is a force field around magnetic object or around current-carrying conductor. In
this field a moving charge can feel force. The unit of magnetic field is ampere per meter
（
A/M
）
.
Only if the meter is in the far field region faraway form radiation source the
magnetic field intensity mode is suitable to be used.
4.
Power density
（
S
）
It is the power per unit area on the surface perpendicular to transmitting direction of
electromagnetic field. The unit of power density is always watt per square meter
（
W/m2
）
.
Milliwatt per square centimeter
（
mW/cm2
）
is also be used as unit for convenient
application.
5.
Characteristic of electromagnetic field
（
S
）：
1)
The electromagnetic field is transmitted by waves and the speed is the light speed
（
C
）
.
The wave length is inversely proportional to frequency.
λ（
wave length
）
=C
（
light speed
）
/f
（
frequency
）
2
）
The area in 3 wave lengths to field source is regarded as near field. The area out of 3
wave lengths is regarded as far field.
3
）
In the near field the electric field (E) intense to the magnetic (H) field intense ratio is
not a constant value. So in the near field these two values should be separately
measured. In far field measuring one value is enough and the other value can be
calculated.
2-2 Application
It is used to the cases that there are radiant electromagnetic fields in the region that the
routine operation, maintaining and servicing work are always done, Such as the broad cast. When
the other employees maybe expose to the electromagnetic field, in this case it is very important