Bi isotropic
Encyclopedia
In physics
, engineering
and materials science
, bi-isotropic materials have the special optical property that they 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.
and magnetic field
s are coupled. The constitutive relations are
D, E, B, H, ε and μ are corresponding to usual electromagnetic qualities. ξ and ζ are the coupling constants, which is the intrinsic constant of each media.
This can be generalized to the case where ε, μ, ξ and ζ are tensors (i.e. they depend on the direction within the material), in which case the media is referred to as bi-anisotropic.
(referred to as reciprocity) χ and chirality
κ parameter
after substitute the above equations into the constitutive relations, gives
into a resin. Care has been exercised to secure isotropy: the helices must be randomly oriented so that there is no special direction.
The magnetoelectric effect can be understood from the helix as it is exposed to the electromagnetic field. the helix geometry is a sort of inductor
. The magnetic component of a EM wave will induces a current on the wire and further influence the electric component of the same EM wave.
From the constitutive relations, for Pasteur media, χ = 0,
the D field was delayed the respond from the H-field by a phase i.
Tellegen media is an opposite of Pasteur media, which is electromagnetic: the electric component will cause the magnetic component to change. such a medium is not as straightforward as the concept of handedness. Electric dipoles bonded with magnets belong to this kind of media. when the dipoles are turned by the electric part of a EM wave, the magnets will also be changed, due to they bounded together. The change of magnets direction will change the magnetic component of the same EM wave.
from the constitutive relations, for Pasteur media, κ = 0,
The D field was responded immediately from the H-field.
Physics
Physics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...
, engineering
Engineering
Engineering is the discipline, art, skill and profession of acquiring and applying scientific, mathematical, economic, social, and practical knowledge, in order to design and build structures, machines, devices, systems, materials and processes that safely realize improvements to the lives of...
and materials science
Materials science
Materials science is an interdisciplinary field applying the properties of matter to various areas of science and engineering. This scientific field investigates the relationship between the structure of materials at atomic or molecular scales and their macroscopic properties. It incorporates...
, bi-isotropic materials have the special optical property that they can twist the polarization of light in either refraction
Refraction
Refraction is the change in direction of a wave due to a change in its speed. It is essentially a surface phenomenon . The phenomenon is mainly in governance to the law of conservation of energy. The proper explanation would be that due to change of medium, the phase velocity of the wave is changed...
or transmission
Transmittance
In optics and spectroscopy, transmittance is the fraction of incident light at a specified wavelength that passes through a sample. A related term is absorptance, or absorption factor, which is the fraction of radiation absorbed by a sample at a specified wavelength...
. 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
Chirality (electromagnetism)
The term chiral describes an object, especially a molecule, which has or produces a non-superimposeable mirror image of itself. In chemistry, such a molecule is called an enantiomer or is said to exhibit chirality or enantiomerism...
and non-reciprocity
Reciprocity
Reciprocity may refer to:*Reciprocity , used to describe the concept of free trade with the United States of America** Reciprocal trade agreement, entered into in order to reduce tariffs, quotas and other trade restrictions on items traded between the signatories*Reciprocity , the relationship...
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.
Definition
In bi-isotropic media, the electricElectric field
In physics, an electric field surrounds electrically charged particles and time-varying magnetic fields. The electric field depicts the force exerted on other electrically charged objects by the electrically charged particle the field is surrounding...
and magnetic field
Magnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...
s are coupled. The constitutive relations are
D, E, B, H, ε and μ are corresponding to usual electromagnetic qualities. ξ and ζ are the coupling constants, which is the intrinsic constant of each media.
This can be generalized to the case where ε, μ, ξ and ζ are tensors (i.e. they depend on the direction within the material), in which case the media is referred to as bi-anisotropic.
Coupling constant
ξ and ζ can be further related to the TellegenBernard D. H. Tellegen
Bernard D.H. Tellegen was a Dutch electrical engineer and inventor of the penthode and the gyrator...
(referred to as reciprocity) χ and chirality
Chirality (electromagnetism)
The term chiral describes an object, especially a molecule, which has or produces a non-superimposeable mirror image of itself. In chemistry, such a molecule is called an enantiomer or is said to exhibit chirality or enantiomerism...
κ parameter
after substitute the above equations into the constitutive relations, gives
Classification
non-chiral  |
chiral  |
|
|---|---|---|
reciprocal  |
simple isotropic medium | Pasteur Medium |
non-reciprocal  |
Tellegen Medium | General bi-isotropic medium |
Examples
Pasteur media can be made by mixing metal helices of one handednessHandedness
Handedness is a human attribute defined by unequal distribution of fine motor skills between the left and right hands. An individual who is more dexterous with the right hand is called right-handed and one who is more skilled with the left is said to be left-handed...
into a resin. Care has been exercised to secure isotropy: the helices must be randomly oriented so that there is no special direction.
The magnetoelectric effect can be understood from the helix as it is exposed to the electromagnetic field. the helix geometry is a sort of inductor
Inductor
An inductor is a passive two-terminal electrical component used to store energy in a magnetic field. An inductor's ability to store magnetic energy is measured by its inductance, in units of henries...
. The magnetic component of a EM wave will induces a current on the wire and further influence the electric component of the same EM wave.
From the constitutive relations, for Pasteur media, χ = 0,
the D field was delayed the respond from the H-field by a phase i.
Tellegen media is an opposite of Pasteur media, which is electromagnetic: the electric component will cause the magnetic component to change. such a medium is not as straightforward as the concept of handedness. Electric dipoles bonded with magnets belong to this kind of media. when the dipoles are turned by the electric part of a EM wave, the magnets will also be changed, due to they bounded together. The change of magnets direction will change the magnetic component of the same EM wave.
from the constitutive relations, for Pasteur media, κ = 0,
The D field was responded immediately from the H-field.
See also
- AnisotropyAnisotropyAnisotropy is the property of being directionally dependent, as opposed to isotropy, which implies identical properties in all directions. It can be defined as a difference, when measured along different axes, in a material's physical or mechanical properties An example of anisotropy is the light...
- Chirality (electromagnetism)Chirality (electromagnetism)The term chiral describes an object, especially a molecule, which has or produces a non-superimposeable mirror image of itself. In chemistry, such a molecule is called an enantiomer or is said to exhibit chirality or enantiomerism...
- MetamaterialMetamaterialMetamaterials are artificial materials engineered to have properties that may not be found in nature. Metamaterials usually gain their properties from structure rather than composition, using small inhomogeneities to create effective macroscopic behavior....
- Reciprocity (electromagnetism)Reciprocity (electromagnetism)In classical electromagnetism, reciprocity refers to a variety of related theorems involving the interchange of time-harmonic electric current densities and the resulting electromagnetic fields in Maxwell's equations for time-invariant linear media under certain constraints...
- Maxwell's equations#Constitutive relations