Attenuation is the (usually) unwanted loss of signal due to
resistive heating or
radiation of the signal from its medium
magnetic energy losses in the iron or ferrite cores of inductors
electrostatic energy losses in the dielectric medium in capacitors
In fibre optic systems, light can be scattered by imperfections in the glass
The glass will not be perfectly transparent.
Attenuation makes a strong signal weaker.
Attenuation can be useful if you need to process a strong signal that would
otherwise overload your circuit.
A potential divider can be used as an attenuator.
Attenuation is usually a problem because it prevents weaker signals arriving
at their destination.
Attenuation in cables is caused by energy loss due to
- the resistance of the wire (this causes energy loss as heat P = I2R)
- radiation from the cable (this is a problem with higher frequency signals
because the cable starts to act like an antenna)
- cross talk (the signal leaks from one cable to another due to the capacitance
between the wires and due to magnetic coupling)
- skin
effect on Wikipedia. At higher frequencies, the current in a conductor prefers to
flow in the surface or skin of the conductor. Since the inner core is not
carrying the current, the effective resistance is higher. This causes greater
energy loss and attenuation. Litz wire has many thin strands. This gives
a higher surface area and the skin effect is reduced. RF burns are caused
by high frequency radio energy heating the victim's skin. This is an unpleasant
example of the skin effect.
Attenuation in optical fibres is caused by energy loss due to
- imperfections in the glass reflecting light in the wrong direction. This is called scattering.
- less than perfectly transparent glass.
- dirt or poor polishing at the fibre connectors.
Attenuation in free space is caused by
- the inverse square law (if you are transmitting in all directions equally
and you double your distance from the transmitter, the energy is spread out
over the surface of a sphere with four times the surface area so you only
receive a quarter of the energy)
- obstructions between the transmitter and receiver
- the signal can no longer be received when it becomes significantly weaker
than the background noise
