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Encyclopedia > Attenuation
Frequency dependent attenuation of electromagnetic radiation in standard atmosphere.
Frequency dependent attenuation of electromagnetic radiation in standard atmosphere.

Attenuation is the reduction in amplitude and intensity of a signal. Signals may be attenuated exponentially by transmission through a medium, in which case attenuation is usually reported in dB with respect to distance traveled through the medium. Attenuation can also be understood to be the opposite of amplification. Attenuation is an important property in telecommunications and ultrasound applications because of its importance in determining signal strength as a function of distance. Attenuation is usually measured in units of decibels per unit length of medium (dB/cm, dB/km, etc) and is represented by the attenuation coefficient of the medium in question. [1] An attenuator has three distinct meanings: attenuator (electronics) is an electronic device that reduces the amplitude of a signal attenuator (genetics) refers to specific regulatory sequence transcribed into RNA impact attenuators are used on highways as a crumple zone in case of a car crash Category: ... Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... It has been suggested that pulse amplitude be merged into this article or section. ... In physics, intensity is a measure of the time-averaged energy flux. ... Generally, amplification is a basic process sometimes seen in nature, and often used in processes which involve a signal which must be made stronger. ... Telecommunication involves the transmission of signals over a distance for the purpose of communication. ... The decibel is a dimensionless unit (like percent) that is a measure of ratios on a logarithmic scale. ... In mathematics, a coefficient is a constant multiplicative factor of a certain object. ...

Contents

Ultrasound

One area of research in which attenuation figures strongly is in ultrasound physics. Attenuation in ultrasound is the reduction in amplitude of the ultrasound beam as a function of distance through the imaging medium. Accounting for attenuation effects in ultrasound is important because a reduced signal amplitude can affect the quality of the image produced. By knowing the attenuation that an ultrasound beam experiences travelling through a medium, one can adjust the input signal amplitude to compensate for any loss of energy at the desired imaging depth.[2] For other uses, see Ultrasound (disambiguation). ...


Attenuation coefficient

Attenuation coefficients are used to quantify different media according to how strongly the transmitted ultrasound amplitude decreases as a function of frequency. The attenuation coefficient (α) can be used to determine total attenuation in dB/cm in the medium using the following formula: In mathematics, a coefficient is a constant multiplicative factor of a certain object. ...

As this equation shows, besides the medium length and attenuation coefficient, attenuation is also linearly dependent on the frequency of the incident ultrasound beam. Attenuation coefficients vary widely for different media. In biomedical ultrasound imaging however, biological materials and water are the most commonly used media. The attenuation coefficients of common biological materials at a frequency of 1 MHz are listed below:[2] FreQuency is a music video game developed by Harmonix and published by SCEI. It was released in November 2001. ...

Material α(dB / MHz * cm)
Lung 41
Bone 20
Kidney 1.0
Liver 0.94
Fat 0.63
Blood 0.18
Brain 0.85
Water 0.0022

Electromagnetic

Attenuation decreases the intensity of electromagnetic radiation due to absorption or scattering of photons. Attenuation does not include the decrease in intensity due to inverse-square law geometric spreading. Therefore, calculation of the total change in intensity involves both the inverse-square law and an estimation of attenuation over the path. Electromagnetic waves can be imagined as a self-propagating transverse oscillating wave of electric and magnetic fields. ... In physics, absorption is the process by which the energy of a photon is taken up by another entity, for example, by an atom whose valence electrons make a transition between two electronic energy levels. ... Scattering is a general physical process whereby some forms of radiation, such as light, sound or moving particles, for example, are forced to deviate from a straight trajectory by one or more localized non-uniformities in the medium through which it passes. ... In modern physics the photon is the elementary particle responsible for electromagnetic phenomena. ... This diagram shows how the law works. ...


The primary causes of attenuation in matter are the photoelectric effect, compton scattering and, for photon energies of above 1.022MeV, pair production. A diagram illustrating the emission of electrons from a metal plate, requiring energy gained from an incoming photon to be more than the work function of the material. ... In physics, Compton scattering or the Compton effect, is the decrease in energy (increase in wavelength) of an X-ray or gamma ray photon, when it interacts with matter. ... Pair production refers to the creation of an elementary particle and its antiparticle, usually from a photon (or another neutral boson). ...


Optics

Attenuation of light by cloudy water is called turbidity, and by interstellar dust, extinction (astronomy). Attenuation in glass or other solid medium is usually studied by telecommunication engineers, hence is called by the same names as the attenuation of electrical signals. Turbidity standards of 5, 50, and 500 NTU Turbidity is a cloudiness or haziness of water (or other fluid) caused by individual particles (suspended solids) that are generally invisible to the naked eye, thus being much like smoke in air. ... Extinction is a term used in astronomy to describe the absorption of light from astronomical objects by matter between them and the observer. ... For the Analog Science Fiction and Science Fact publication, see Astounding Magazine. ...


Attenuation in fibre optics, also known as transmission loss, is the reduction in intensity of the light beam with respect to distance travelled through a transparent medium. Attenuation coefficients in fibre optics usually use units of dB/km through the medium due to the great transparency of modern optical media. The medium is usually a fibre of silica glass that confines the incident light beam to the inside. Attenuation is an important factor limiting the transmission of a light pulse across far distances, and as a result much research has gone into both limiting the attenuation and maximizing the amplification of the fibre optic light beam.[3] Attenuation in fibre optics can be quantified using the following equation:[4] Fiber Optic strands An optical fiber in American English or fibre in British English is a transparent thin fiber for transmitting light. ...

mathrm{Attenuation(dB)} = 10timeslog_{10}left(frac{mathrm{Output Intensity(W)}}{mathrm{Input Intensity(W)}}right)

Applications

In optical fibers, attenuation is the rate at which the signal light decreases in intensity. For this reason, glass fiber (which has a low attenuation) is used for long-distance fiber optic cables; plastic fiber has a higher attenuation and hence shorter range. There also exist optical attenuators which decrease the signal in a fiber optic cable intentionally. Optical fibers An optical fiber (or fibre) is a glass or plastic fiber designed to guide light along its length by confining as much light as possible in a propagating form. ... Optical attenuator, in optical communications, is a device used to reduce the power level of an optical signal. ...


Attenuation of light is also important in physical oceanography. Here, attenuation is the decrease in light intensity with depth due to absorption (by water molecules) and scattering (by suspended particulates). This same effect is an important consideration in weather radar as rain drops absorb a part of the emitted beam that is more or less significant depending on the wavelength used. World Oceans Physical oceanography is the study of physical conditions and physical processes within the ocean, especially the motions and physical properties of ocean waters. ... Impact from a water drop causes an upward rebound jet surrounded by circular capillary waves. ... Weather radar in Norman, Oklahoma with rainshaft (Source: NOAA) Environment Canada King City (CWKR) weather radar station. ...


The attenuation of photons, particularly of those in the x-ray spectrum, is important in the field of medical physics. Due to the damaging effects of high energy photons, it is necessary to know how much energy is deposited in tissue during diagnostic treatments involving such radiation. Additionally gamma radiation is used in cancer treatments where it is important to know how much energy will be deposited in healthy and in tumorous tissue. Medical physics is a branch of applied physics concerning the application of physics to medicine. ... Wikipedia does not yet have an article with this exact name. ...


Radio

Attenuation is an important consideration in the modern world of wireless telecommunication. People are daily affected by it as they rely more and more on mobile phones, television, satellite communication, and wireless internet. Attenuation limits the range of radio signals and is affected by the materials a signal must travel through (e.g. air, wood, concrete, rain). See the article on path loss for more information on signal loss in wireless communication. Copy of the original phone of Alexander Graham Bell at the Musée des Arts et Métiers in Paris Telecommunication is the transmission of signals over a distance for the purpose of communication. ... Path loss: In a communication system, the attenuation undergone by an electromagnetic wave in transit between a transmitter and a receiver. ...


See also

Path loss: In a communication system, the attenuation undergone by an electromagnetic wave in transit between a transmitter and a receiver. ... In satellite communications, rain fade refers to the absorption of a microwave Radio Frequency (RF) signal by rain or snow, and is especially prevalent in frequencies above 11 GHz. ... Radiation Length , High-energy electrons predominantly lose energy in matter by bremsstrahlung, and high-energy photons by pair production. ... The attenuator plays an important regulatory role in prokaryotic cells because of the absence of the nucleus in prokaryotic organisms. ... “Attenuator” redirects here. ... In nuclear and particle physics, the concept of a cross section is used to express the likelihood of interaction between particles. ... For sound waves in an enclosure, the mean free path is the average distance the wave travels between reflections off of the enclosures walls. ... A radiograph of a right elbow-joint Radiography is the use of certain types of electromagnetic radiation—usually ionizing—to view objects. ... Wave propagation refers to the ways waves travel through a medium (waveguide). ...

External links

  • NIST's XAAMDI: X-Ray Attenuation and Absorption for Materials of Dosimetric Interest Database
  • NIST's XCOM: Photon Cross Sections Database
  • NIST's FAST: Attenuation and Scattering Tables

References

  1. ^ Essentials of Ultrasound Physics, James A. Zagzebski, Mosby Inc., 1996.
  2. ^ a b Diagnostic Ultrasound, Stewart C. Bushong and Benjamin R. Archer, Mosby Inc., 1991.
  3. ^ Telecommunications: A Boost for Fibre Optics, Z. Valy Vardeny, Nature 416, 489–491, 2002.
  4. ^ "Fibre Optics", Bell College. 

  Results from FactBites:
 
Topics: Natural Attenuation (521 words)
This makes the sites where the investigations are conducted ideally suited to assessing potential long-term impacts, evaluating the potential and the limitations of remediation by monitored natural attenuation, and designing systems to monitor the performance of remediation where monitored natural attenuation is being relied upon.
The scientists are withdrawing water with a syringe from a core encased in polycarbonate tubing.
The sample was used to study the natural attenuation of hydrocarbon vapors in the unsaturated zone.
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