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Relative permittivities ranging from 12 to 100 were obtained from porous titania. Relative permittivities from 8 to 30 were obtained from porous calcium magnesium titanates. Porosity was introduced as microporosity by partial sintering, as 15 μm diameter spherical pores with porogens, and by fabrication of a microcellular structure with cylindrical pores. The relative permittivity as a function of porosity was compared with effective media models. Permittivity could be fitted to the Bruggeman 1/3 power law over a porosity range from 5% to 78%.
Wing et al. (2006) studied this question.