Radiation intensity
Encyclopedia
In electromagnetism
, radiation intensity describes the power density
that an antenna
creates in a particular solid angle
. A solid angle is a section of the surface of the imaginary sphere around the antenna.
Given an antenna's power density
, radiation density is calculated by multiplying it with the square of the distance (
) from the antenna to the designated solid angle:
This is so because unlike power density, radiation intensity does not depend on distance: because radiation intensity is defined as the power through a solid angle, the decreasing power density over distance (i.e. over
of the imaginary sphere around the antenna) due to the inverse-square law
is offset by the increasing area of the solid angle due to the same law. Therefore, power density can be converted to radiation intensity by multiplying it with
.
The radiation intensity can as well characterize X-ray tube
with filtration. X-ray tube output is defined for this purpose.
Electromagnetism
Electromagnetism is one of the four fundamental interactions in nature. The other three are the strong interaction, the weak interaction and gravitation...
, radiation intensity describes the power density
Power density
Power density is the amount of power per unit volume....
that an antenna
Antenna (radio)
An antenna is an electrical device which converts electric currents into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver...
creates in a particular solid angle
Solid angle
The solid angle, Ω, is the two-dimensional angle in three-dimensional space that an object subtends at a point. It is a measure of how large that object appears to an observer looking from that point...
. A solid angle is a section of the surface of the imaginary sphere around the antenna.
Given an antenna's power density
Power density
Power density is the amount of power per unit volume....
, radiation density is calculated by multiplying it with the square of the distance () from the antenna to the designated solid angle:This is so because unlike power density, radiation intensity does not depend on distance: because radiation intensity is defined as the power through a solid angle, the decreasing power density over distance (i.e. over
of the imaginary sphere around the antenna) due to the inverse-square lawInverse-square law
In physics, an inverse-square law is any physical law stating that a specified physical quantity or strength is inversely proportional to the square of the distance from the source of that physical quantity....
is offset by the increasing area of the solid angle due to the same law. Therefore, power density can be converted to radiation intensity by multiplying it with
.The radiation intensity can as well characterize X-ray tube
X-ray tube
An X-ray tube is a vacuum tube that produces X-rays. They are used in X-ray machines. X-rays are part of the electromagnetic spectrum, an ionizing radiation with wavelengths shorter than ultraviolet light...
with filtration. X-ray tube output is defined for this purpose.