Anisotropic Meaning
Anisotropy can be defined as the property of a material that allows it to change its properties or assume different properties in different directions. It can be explained as the quality of materials that allow the materials to exhibit properties differently in different directions as measured along an axis. The property of anisotropy can be easily observed in single crystals of solid materials such as solid elements and compounds. On the other hand, it can be rarely observed in liquids and gases due to the random distribution of particles.
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Isotropic and Anisotropic Meaning
Isotropic can be defined as that property of a material that is independent of direction. On the other hand, anisotropic is the property that is primarily dependent on direction. Both isotropic and anisotropic are used to explain the properties of crystalline materials. As mentioned above, crystalline solids exhibit the property of anisotropy and are called anisotropic crystals. Other than crystalline solids, some other solids also exhibit this property and are called Anisotropic solids. Here is a brief difference between isotropic and anisotropic.
Properties of Isotropic and Anisotropic
Magnetic Anisotropy
In physics, magnetic anisotropy is the phenomena that explain how an object’s magnetic property can be different depending on directions. It is often observed that magnetically anisotropic materials will be easier or harder to magnetize depending on the direction of rotation of the object.
Magnetic anisotropy in an object can be affected by various reasons. The below are the factors on which the magnetic anisotropy of an object depends:
Magnetocrystalline Anisotropy: It is mainly found in ferromagnetic materials. A ferromagnetic material takes more energy in a specific direction to magnetize. These directions are about the principal axis of the crystalline material.
Shape Anisotropy: Anisotropy depends on the shape of the object. If a material is not perfectly spherical, then it cannot be magnetized in all the direction equally, thereby creating more than one easy axis.
Magnetoelastic Anisotropy: It is the property of a magnetic material that allows it to change its magnetizing property when subjected to an external force. In simple words, it is the property that changes the magnetization of a magnetic material.
Exchange Anisotropy: It is a phenomenon that occurs when antiferromagnetic materials react with ferromagnetic materials.
Fluorescence Anisotropy
Fluorescence Anisotropy or fluorescence polarization can be defined as the phenomenon, where the light emitted by a fluorophore is unequal when measured along different axes of polarization.
Diamagnetic Anisotropy
When a valence electron in acetylene and benzene circulate under the influence of an external field, it forms a local diamagnetic current. This local diamagnetic current helps in the deshielding of protons, and the whole process is termed Diamagnetic Anisotropy.
Applications of Anisotropy
Anisotropy has applications in different fields, and some of them are mentioned below:
In the field of computer graphics, anisotropic surfaces tend to change their appearances when rotated around their geometric normal. Anisotropic filtering is a process used in computer graphics to enhance the image quality of textures on far away surfaces.
In the field of chemistry, an anisotropic chemical filter is used to filter out particles. These filters prove to be efficient in the filtration process of particles and allow a great flow of the particles.
In Fluorescence spectroscopy, fluorescence anisotropy is used to determine the shape of a macromolecule.
The materials used in heat sources that help in the conduction and rejection of heat are often made of anisotropic materials.
In the field of medicine, anisotropy is used in medical ultrasound imaging.
FAQs on Anisotropy
1. What is anisotropy in Physics, and why is it primarily observed in crystalline solids?
Anisotropy is the property of a material exhibiting different values for a physical property when measured along different directions. For example, properties like electrical resistance, refractive index, or tensile strength can vary depending on the axis of measurement. This phenomenon is most common in crystalline solids because their atoms, ions, or molecules are arranged in a regular, ordered, but not necessarily uniform, pattern. This ordered internal structure leads to different atomic spacings and bonding strengths along different crystallographic axes, causing the directional dependence of their properties.
2. How do anisotropic materials differ from isotropic materials?
The primary difference lies in the directional dependence of their properties. Here are the key distinctions:
- Directionality: Isotropic materials show uniform properties in all directions, while anisotropic materials show direction-dependent properties.
- Internal Structure: Isotropic materials (like glass or metals) typically have a disordered or random atomic arrangement. Anisotropic materials (like quartz or wood) have an ordered, periodic internal structure.
- Refractive Index: Isotropic materials have a single refractive index. Anisotropic materials have multiple refractive indices, leading to phenomena like double refraction.
- Velocity of Light: Light travels at the same speed in all directions through an isotropic medium, but its speed varies with direction in an anisotropic medium.
3. What are some common examples of anisotropic materials?
Many materials, both natural and man-made, exhibit anisotropy. Common examples include:
- Wood: It is much stronger and easier to split along the grain than against it.
- Calcite Crystals: Famous for exhibiting double refraction, where light splits into two rays travelling in different directions at different speeds.
- Composite Materials: Materials like carbon fibre-reinforced polymers are engineered to be extremely strong along the direction of the fibres.
- Liquid Crystal Displays (LCDs): The alignment of liquid crystals, which is anisotropic, is controlled by electric fields to manipulate light and form images.
4. What is magnetic anisotropy and what factors influence it?
Magnetic anisotropy describes how a material's magnetic properties are dependent on direction. It means the material is easier or harder to magnetise along certain axes, known as 'easy' or 'hard' axes. The primary factors influencing this are:
- Magnetocrystalline Anisotropy: Arises from the material's crystal lattice structure, where the atomic structure creates preferential directions for magnetisation.
- Shape Anisotropy: Occurs in non-spherical objects. For instance, a needle-shaped magnet is easier to magnetise along its length (the easy axis) than across its width.
- Magnetoelastic Anisotropy: Induced when mechanical stress or strain is applied to a magnetic material, altering its magnetic response.
5. Why does a material's refractive index or electrical conductivity depend on direction in anisotropic substances?
The directional dependence of properties in anisotropic materials is a direct consequence of their asymmetrical internal structure. In a crystal, the spacing between atoms and the strength of the bonds connecting them are not the same in all directions.
- For electrical conductivity, electrons move more easily along axes where atoms are closely packed and orbital overlap is high. Along axes with larger atomic separation, resistance is higher.
- For the refractive index, the speed of light in a material depends on how it interacts with the material's electron cloud. Since the density and arrangement of electrons vary with direction in an anisotropic crystal, the speed of light and thus the refractive index also vary with direction.
6. How is the concept of anisotropy applied in modern technology like computer graphics and medical imaging?
Anisotropy is a crucial principle in several advanced technologies:
- Computer Graphics: A technique called anisotropic filtering is used to improve the quality of textures on surfaces that are viewed at an angle. It accounts for the distortion of the texture shape, making surfaces like roads or floors in a game look sharp and realistic even at a distance.
- Medical Imaging: In ultrasound and MRI (specifically Diffusion Tensor Imaging), the anisotropic properties of biological tissues are used for diagnostics. For example, water diffuses more easily along the length of nerve or muscle fibres than across them. Measuring this anisotropic diffusion helps in mapping neural pathways in the brain or identifying tissue damage.
7. Can a material be isotropic for one property but anisotropic for another?
Yes, this is possible and highlights the specific nature of this property. A classic example is a material with a cubic crystal structure. Due to its high degree of symmetry, it is optically isotropic, meaning its refractive index is the same in all directions, and light passes through it without being split. However, the same cubic crystal is mechanically anisotropic because its elasticity (response to stretching or compression) is different along its axes compared to along its diagonals. The arrangement of atoms provides different levels of resistance to stress in different directions.
