The field of magnetic resonance imaging (MRI) has been evolving with imaging techniques in which, for example, diffusion anisotropy serves to provide contrast.
Anisotropy is a term that the Royal Spanish Academy (RAE) presents in its dictionary as a word from the field of physics that refers to the condition of anisotropic . This word, in turn, refers to the diversity of physical properties that a body or substance can show according to the direction in which it is measured.
According to experts on this matter, anisotropic behaviors can be observed in physical properties that are represented by a tensor magnitude . It is possible, in this context, to link anisotropy with ionic conductivity , magnetism and elasticity , for example. It is constructive to consider that by appealing to a stiffness tensor of composite materials it is possible to effectively measure anisotropy .
It is also interesting to know that the concept of isotropy appears opposite to the idea of anisotropy . Isotropic bodies or substances have identical properties in any direction analyzed. In order to be able to recognize without further complications how and what anisotropic materials are, it is essential to remember that, according to theory, elements whose mechanical properties differ when appreciated in different directions are thus defined.
Types of anisotropy
There are different types of anisotropy . To establish which material a material presents, it is necessary to investigate each set of geometric symmetries that specialists in crystallography and geography classify as a point group .
Within the subgroups in which symmetry is continuous , transverse hemitropia , hemitropia and transverse isotropy are distinguished. When it comes to subdivisions characterized by a discrete symmetry, meanwhile, the anisotropies branch out as polyhedral (icosahedral, tetrahedral or octahedral) and axial (clinotropic or orthotropic).
On the other hand, it is advisable to educate oneself regarding optical anisotropy (a trait that causes some materials to exhibit different refractive indices depending on the direction of the light, whose transmission does not always occur at the same speed .
Elastic anisotropy, thermal anisotropy y crystal anisotropy son otros de los tantos ejemplos que sirven para comprobar que hay numerosos types of anisotropy.
Applications
Anisotropy is of utmost importance for numerous scientific disciplines and technological activities.
It gains prominence, to indicate a specific case as a guide, when manufacturing semiconductor devices . In this framework magnetic anisotropy comes into play. It is also present in medical practices and analysis, as well as in engineering (in order, for example, to study soil anisotropy ).
Wood exhibits different behaviors in different directions, which is why it serves as a concrete example for the idea of anisotropy.
Likewise, anisotropy is taken into account in the fields of geophysics , seismology , cosmology , astrophysics and nanotechnology , among others.
The creation of computer graphics that are characterized by their three-dimensional essence even benefits when a method called anisotropic filtering is used. Thanks to it, it is guaranteed to improve the quality of a certain texture of a surface that, compared to its projection angle, is observed from an oblique angle. An effect known as aliasing can be eliminated with this technique and, for a few years, drivers can be configured or programming tools used to specify the characteristics of anisotropic filtering on graphics cards.
More information about anisotropy
Electromagnetic plasmas , both almost homogeneous and those that have complete homogeneity, show anisotropy around the momentum space , which is conceived as a pair of temperatures that appear in different directions. In these plasmas an instability called Weibel instability is distinguishable, which is very common in astrophysical plasmas .
It is also enriching to learn about fluorescent polarization . By focusing attention on this topic, a physical phenomenon called fluorescent anisotropy gains relevance. This arises if the light emitted by a fluorophore presents, in different polarization axes, multiple intensities. This variety of anisotropy is very useful, specifically, within the field of microscopy .
Anisotropy is detected in crystals since multiple physical properties in different directions are recognized in them.
Nor can the relevance of cosmic inflation be overlooked, key to the resolution of the curvature of space , anisotropy and the horizon problem . Even the microwave background radiation that gives solidity to the Big Bang deserves consideration. This cosmological model has managed to accurately predict anisotropies detected in the cosmic microwave background . It should be noted that several seasons ago a rigorous measurement of these anisotropies was achieved thanks to a probe belonging to NASA that received the name Wilkinson Microwave Anisotropy Probe (WMAP).
Another interesting information that emerges from this topic: thanks to anisotropy , crystals can show special optical, mechanical or electrical properties that are generally not seen in polycrystals or glasses .