Isotropic, An-isotropic, Bi-isotropic

출처 : http://en.wikipedia.org

1. Isotropy is uniformity in all directions.
Precise definitions depend on the subject area.
The word is made up from Greek iso (equal) and tropos (direction).
Exceptions, or inequalities, are frequently indicated by the prefix an, hence anisotropy. Anisotropy is also used to describe situations where properties vary systematically, dependent on direction.
Isotropic radiation has the same intensity regardless of the direction of measurement, and an isotropic field exerts the same action regardless of how the test particle is oriented.

2. Anisotropy is the property of being directionally dependent, as opposed to isotropy, which means homogeneity in all directions.
It can be defined as a difference in a physical property (absorbance, refractive index, density, etc.) for some material when measured along different axes.
An example is the light coming through a polarizing lens.

3. bi-isotropics (or biisotropics) are any of a class of materials having the special optical property that it can twist the polarization of light in either refraction or transmission.
This does not mean all materials with twist effect fall in the Bi isotropic class.
The twist effect of the class of Bi isotropic materials is caused by the chirality and non-reciprocity of the structure of the media, in which the electric and magnetic field of an electromagnetic wave (or simply, light) interact in an unusual way.


** conventional constitutive dyadic forms