anisotropic

Anisotropic is an adjective describing a property or system that varies with direction. The opposite term is isotropic, where a property is the same in all directions. Anisotropy can affect mechanical, thermal, electrical, magnetic, optical, or diffusion properties, and it often arises from internal structure, alignment, layering, or external fields.

In crystals, lattice arrangement causes directional variation in properties such as elasticity, conductivity, and refractive index. Optical anisotropy is common in birefringent materials that have different indices of refraction for different polarizations and directions. In everyday materials, wood is more stiff and strong along the grain than across it; fiber-reinforced composites are strongest along the fiber direction due to the orientation of reinforcing elements.

Geology and geophysics recognize anisotropy in rocks and sediments, where mineral alignment, layering, or stress history affects seismic wave speeds. In biology, tissues like muscle, bone, and white matter show anisotropic behavior, with transport and mechanical responses that depend on direction. Diffusion in biological media is often anisotropic, with greater transport along structural pathways such as nerve fibers.

Quantitatively, anisotropy is described using tensors rather than simple scalars, capturing how a property varies with direction and orientation. Measurements may yield an anisotropy ratio or a full tensor of components, depending on the property and medium.

Applications of anisotropy include material design, nondestructive testing, imaging methods such as diffusion tensor imaging, and the accurate modeling of physical systems where direction-dependent behavior is important.