Attenuation
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 traveling through a medium, one can adjust the input signal amplitude to compensate for any loss of energy at the desired imaging depth.
[2] Wave equations which take acoustic attenuation into account can be written on a fractional derivative form.
[4] In homogeneous media, the main physical properties contributing to sound attenuation are viscosity [5] and thermal conductivity.
[6][7] Attenuation coefficients are used to quantify different media according to how strongly the transmitted ultrasound amplitude decreases as a function of frequency.
The attenuation coefficients of common biological materials at a frequency of 1 MHz are listed below:[8] There are two general ways of acoustic energy losses: absorption and scattering.
Chlorophyll-a absorbs light most strongly in the shortest wavelengths (blue and violet) of the visible spectrum.
The attenuation in the signal of ground motion intensity plays an important role in the assessment of possible strong groundshaking.
There are two types of dissipated energy: In porous fluid—saturated sedimentary rocks such as sandstones, intrinsic attenuation of seismic waves is primarily caused by the wave-induced flow of the pore fluid relative to the solid frame.
The primary causes of attenuation in matter are the photoelectric effect, Compton scattering, and, for photon energies of above 1.022 MeV, pair production.
The medium is typically a fiber of silica glass that confines the incident light beam to the inside.
Rough and irregular surfaces, even at the molecular level of the glass, can cause light rays to be reflected in many random directions.
Within this framework, "domains" exhibiting various degrees of short-range order become the building-blocks of both metals and alloys, as well as glasses and ceramics.
Distributed both between and within these domains are microstructural defects that will provide the most ideal locations for the occurrence of light scattering.
[17] In addition to light scattering, attenuation or signal loss can also occur due to selective absorption of specific wavelengths, in a manner similar to that responsible for the appearance of color.
This same effect is an important consideration in weather radar, as raindrops absorb a part of the emitted beam that is more or less significant, depending on the wavelength used.
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.
In addition, 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.
In computer graphics attenuation defines the local or global influence of light sources and force fields.
