Analysis and Design of Smart Electromagnetic Structures

Use of ferroelectric materials to improve antenna performance is an area of active research. Applying an electric field across a ferroelectric used as the dielectric in an antenna enables tuning the antenna performance. Ferroelectrics also have coupled electromechanical behavior due to which it is sensitive to mechanical strains and fluctuations in ambient temperature. Use of ferroelectrics in antenna structures, especially those subject to mechanical and thermal loads, requires knowledge of the phenomenological relationship between the ferroelectric properties of interest (especially dielectric permittivity) and the external physical variables, viz. electric field(s), mechanical strains and temperature. To this end, a phenomenological model of ferroelectric materials based on the Devonshire thermodynamic theory is presented. This model is then used to obtain a relationship expressing the dependence of the dielectric permittivity on the mechanical strain, applied electric field and ambient temperature. The relationship is compared with published experimental data and other models in literature. Subsequently, a relationship expressing the dependence of antenna performance on those physical quantities is described.