Dielectrical impermeability

In this general case, two waves of different velocity may propagate through the crystal. The relative dielectric impermeabilities are defined as the reciprocals of the principal dielectric constants ... 

Next we will introduce the optical dielectric impermeability tensor of a crystal. The coefficients (17, ) of this tensor depend on the distribution of bond charges in the material [15,71]. The 17, are found by taking the reciprocal of the relative permittivity or dielectric constant [71]. The 17, have been defined in terms of the refractive index of the crystal as [71]... 

The quantities Pjk are also dielectric material coefficients. Their dimension is obviously reciprocal to the dimension of the permittivity. They are also the coordinates of a symmetric second rank tensor for which several names have been in use. Following Thurston (1974) we call it impermittivity. (Alternatively, the names dielectric impermeability (Cady 1964, p. 163), dielectric permeability (Grindlay 1970, p. 56), vetivity , derived from the latin word vetare as the opposite to the latin permittere (Voigt 1910, p. 441) have been proposed.) The effect described by Eq. (4.31) is the inverse effect to Eq. (4.30). It is obvious that E and D have exchanged their roles as independent and dependent variables and, therefore, Sij and Pij are material coefficients derived from different thermodynamic potentials. 

In contrast to the SHG coefficient, the electro-optic coefficient r,y/t is symmetric in its first two indices for a lossless, not optically active, material. This follows from Eq. (11), which relates the electro-optical coefficient to the impermeability tensor Tiy (the matrix inverse of the dielectric permeability tensor y), a real and symmetric tensor under the stated conditions [3],... 

Also, in solid materials, microwaves are used on an industrial scale for heating purposes. The ability of the solid material to absorb microwave heating depends on two properties the dielectric constant and the loss tangent. Some materials absorb the microwave energy very easily, while others are transparent or impermeable to it. 

E is the dielectric constant or permeability the quantity Bjj has the name impermeability. 

The dielectric constant s of lithium aluminosilicate can be lowered from its bulk values of 5.6 to 2.1 by making a foam of the oxide, which has a porosity of 60%. This composite is an excellent insulator for microwave applications. The dielectric constant of the composite is some function of the dielectric constant of the components, the silicate, and air (Figure 9.1). The porosity should be of the closed type if impermeability for gas is also required. 

The relationship between the dielectric permittivity perturbation and the optical impermeability perturbation can be expressed as ... 

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