Scattering properties material particles

When the particles are chaotically scattered, the materials are called isotropic, i.e. their properties are identical in all directions. When the particles are distributed evenly within the matrix at a concentration gradient g (g -the vector indicating the direction of fastest change of particle concentration in the matrix), the composite is anisotropic and its properties depend upon the direction. The purpose of manufacturing isotropic composites is to place a respective component exactly in the site where properties of the composite article are to be realized most fully. 

Equations (B.29)-(B.33) regard the polarisability a as a scalar quantity. This holds true for isotropic materials and spherical dipoles. Anisotropy with respect to optical properties or particle shape inevitably means that the scattering of electromagnetic waves depends on the dipole s orientation. In this case the polarisability has to be expressed as tensor (cf. Bohren and Huflman 1983). 

Hollow gold spheres or core-shell particles consisting of a gold shell on a core of some other material have recently attracted attention. This is because they have interesting and tunable optical extinction properties [56]. These can be readily calculated using Mie theory [57], and there had been some scattered early interest in these shapes as a result [58, 59], but the versatility and properties of these particles only became widely... 

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