Anisotropy
Anisotropy is the property of being directionally dependent. Something which is anisotropic, may appear different, or have different characteristics in different directions. An example is the
polarising lens in a pair of
polarized sunglasses, in which if you hold the lens in one direction, polarized light streams through, whereas if you hold the lens in another direction, light is blocked.
Encyclopedia
Anisotropy is the property of being directionally dependent. Something which is anisotropic, may appear different, or have different characteristics in different directions. An example is the
polarising lens in a pair of
polarized sunglasses, in which if you hold the lens in one direction, polarized light streams through, whereas if you hold the lens in another direction, light is blocked.
Fields of interest
Computer graphics
In the field of computer graphics, an anisotropic surface will change in appearance as it is rotated about its geometric
normal, as is the case with velvet.
Anisotropic filtering is a method of enhancing the image quality of textures on surfaces that are far away and steeply angled with respect to the point of view. Older techniques, such as
bilinear and trilinear filtering don't take account of the angle a surface is viewed from, which can result in
aliasing or blurring of textures. By reducing detail in one direction more than another, these effects can be reduced.
This is not to be confused with an anisotropic filter, as used to filter particles, which is a filter with increasingly smaller interstitial spaces in the direction of filtration so that the
proximal regions filter
out larger particles and
distal regions increasingly remove smaller particles, resulting in greater flow-through and more efficient filtration.
Physics
Cosmologists use the term to describe the fluctuations in the background radiation left over after the
big bang. The term refers to the difference in the temperature of the
cosmic microwave background radiation with direction.
Physicists use the term to refer to some properties of
plasmas. For example, a plasma may have a magnetic field oriented in a preferred direction, or show "filamentation" that is directional.
An anisotropic liquid is one which has the fluidity of a normal liquid, but have an average structural order relative to each other along the molecular axis, unlike water or
chloroform, which contain no structural ordering of the molecules.
Liquid crystals are examples of anisotropic liquids.
Some materials
conduct heat in a way that is isotropic, that is independent of spatial orientation around the heat source. It is more common for heat conduction to be anisotropic, which implies that detailed geometric modeling of typically diverse materials being thermally managed is required. The materials used to transfer and reject heat from the heat source in
electronics are often anisotropic.
Many
crystals are anisotropic to
light, and exhibit properties such as
birefringence. Crystal optics describes light propagation in these media. An
axis of anisotropy is defined as the axis along which isotropy is broken . Some materials can have multiple such axes.
Geology
Geological formations where distinct layers of sedimentary material are disposited can exhibit electrical anisotropy. That is electrical conductivity in one direction e.g. parallel to a layer, is different to that in another e.g. perpendicular to a layer. This property is used in the gas and oil exploration industry to identify hydrocarbon-bearing sands in sequences of
sand and
shale. Sand bearing
hydrocarbon assets have high resistivity whereas shales are much more conductive. Formation evaluation instruments measure this conductivity and resistivity and the results are used to help best site oil and gas wells.
Material Science & Engineering
Anisotropy is used to describe the phenomena of interatomic bond strengths being directionally dependent. This leads to the Young's Modulus of a material being different in different directions. Most materials exhibit anisotropic behavior, where the material is stronger when stressed in one direction, but stretches more in another.
Microfabrication
Anisotropic etching techniques are used in microfabrication processes to create well defined microscopic features with a high aspect ratio. These features are commonly used in
MEMS and
microfluidic devices, where the anisotropy of the features is needed to impart desired optical, electrical, or physical properties to the device.
See also
External links
