In physics, attenuation (in some context also called extinction) is the gradual loss in intensity of any kind of flux through a medium. For instance, sunlight is attenuated by dark glasses, and X-rays are attenuated by lead.
In many cases, attenuation is an exponential function of the path length through the medium. In chemical spectroscopy, this is known as the Beer-Lambert law.
In engineering, 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.
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:
There are two general ways of acoustic energy losses: absorption and scattering, for instance light scattering. Ultrasound propagation through homogeneous media is associated only with absorption and can be characterised with absorption coefficient only. Propagation through heterogeneous media requires taking into account scattering.
Attenuation is caused by several different factors, but primarily scattering and absorption.The scattering of light is caused by molecular level irregularities in the glass structure. Further attenuation is caused by light absorbed by residual materials, such as metals or water ions, within the fiber core and inner cladding. Light leakage due to bending, splices, connectors, or other outside forces are other factors resulting in attenuation. 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. Attenuation in fibre optics can be quantified using the following equation:
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.
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.
"Robust Attenuation Correction System for Radar Reflectivity and Differential Reflectivity" in Patent Application Approval Process
Nov 07, 2013; By a News Reporter-Staff News Editor at Politics & Government Week -- A patent application by the inventors Venkatachalam,...