What Is Attenuation?
When a signal propagates in a transmission medium, a part of the energy will be converted into heat energy or absorbed by the transmission medium, which will cause the signal strength to decrease continuously. This phenomenon is called attenuation. Signal attenuation is an important feature of communication transmission. The degree of signal attenuation is not only an important indicator for evaluating the quality of communication, but also directly affects the expansion and upgrade of communication systems, and the characteristics of relay distance in the layout of communication transmission cables.
In ultrasonic detection, attenuation refers to the phenomenon that the sound pressure gradually decreases as the propagation distance increases when the ultrasonic wave propagates in the medium.
The strength of the signal decreases as it travels through the cable or air. In the wired part of the communication (RF cable), the strength of the AC signal decreases due to the impedance of the coaxial cable or the influence of other components (such as connectors).
In electronic equipment, in order to prevent the input stage from being limited or blocked due to excessive signal, an attenuator is added manually.
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Attenuation TypeSelect the type of attenuation. It includes five options:
Vertical / ParallelSets the angular attenuation range between the face normal that is perpendicular to the attenuation direction and the normal that is parallel to the attenuation direction. The attenuation range is changed by 90 degrees based on the direction of the face normal. (default setting.)
Orientation / DepartureSets the angular attenuation range between the face normal facing (parallel) the attenuation direction and the normal facing away from the attenuation direction. The attenuation range is changed by 180 degrees based on the direction of the face normal.
FresnelAdjustment based on refractive index (IOR). Produces dim reflections on the surface facing the view, and brighter reflections on the angular surfaces, creating highlights just like on glass surfaces.
Shadow / LightAdjusts between two sub-textures based on the light falling on the object.
Distance BlendAdjusts between two sub-textures based on the Near Distance and Far Distance values. Uses include reducing anti-aliasing on large terrain objects and controlling shading in non-photorealistic environments. [2]
Attenuation directionSelect the direction of the attenuation. It includes five options:
Viewing direction (camera Z axis) Sets the direction of attenuation relative to the camera (or screen). Changing the object's orientation does not affect the falloff map. (default setting.)
Camera X / Y axissimilar to the camera Z axis. For example, using Camera X Axis for the Facing / Deviation attenuation type will fade from left (towards) to right (away).
ObjectPick an object whose direction determines the direction of the decay. Click Pick, and then pick the objects in the scene. The direction of attenuation is the direction from the point where the coloring is performed toward the center of the object. Points on the side facing the center of the object get the "towards" value, and points on the side facing away from the object get the "away" value.
Local X / Y / Z axisSets the attenuation direction to the local axis of one of the objects. Changing the direction of an object changes the direction of the decay. When no object is selected, the attenuation direction uses the local X, Y, or Z axis of the object being shaded.
World X / Y / Z axisSets the attenuation direction to one of the world coordinate system axes. Changing the object's orientation does not affect the falloff map.
The attenuation spectrum of the fiber is shown below. With the improvement of the optical fiber manufacturing process, the optical fiber transmission loss has been reduced year by year. There are already five low loss windows.
The average loss value of window I is 2dB / km, the average loss value of window II is 0.3dB / km ~ 0.4dB / km, the average loss value of window III is 0.19dB / km ~ 0.25dB / km, and at 1380nm of window V There is an OH-absorption peak.
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The marking, wavelength range, fiber type and application of the optical signal in the five windows are shown in the following table:
window | I | II | III | IV | V |
Marking (nm) | 850 | 1310 (O-band) | 1550 (C-band) | 1600 (L-band) | 1360 ~ 1530 (E + S band) |
Wavelength range (nm) | 600 ~ 900 | 1260 ~ 1360 | 1530 ~ 1565 | 1565 ~ 1625 | 1360 ~ 1530 |
Fiber Type | Multimode fiber | Multimode fiber / G.652 / G.653 | G.652 / G.653 / G.655 | G.652 / G.653 / G.655 | Full wave fiber |
Application occasion | Short distance, low speed | Short distance, low speed | Long distance, high speed |
The line loss of common optical fibers is shown in the following table:
Fiber Type | G.652 | G.653 | G.655 |
Typical loss value (1310nm) | 0.3dB / km ~ 0.4dB / km | - | - |
Typical loss value (1550nm) | 0.15dB / km ~ 0.25dB / km | 0.19dB / km ~ 0.25dB / km | 0.19dB / km ~ 0.25dB / km |
Working window | 1310nm and 1550nm | 1550nm | 1550nm |
