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This thesis establishes a quantitative method to extract electromechanical coupling coefficients in large-strain dielectrics, considering the intrinsic electromechanical coupling and the Maxwell effect. The analytical expressions of the relations between the harmonics obtained through Fourier transforms and high-order dielectric permittivity and electromechanical coefficients are derived. These relations serve as a basis for determining the expressions of the electromechanical coupling coefficients, and a methodology is presented to calculate them from experimental data. The complex nature of the electrostrictive coefficient implies the existence of intrinsic electrostrictive losses. Utilising the complex nature of the dielectric permittivity and electromechanical coupling coefficients, it provides the energy flow conversion from the input electrical energy to the output mechanical energy, deriving the expression of the various loss terms. This framework is then applied to composites with a polymer matrix (PDMS or P(VDF-TrFE-CFE)) and conductive inclusions (carbon black or Ti3C2Tx).The percolation threshold is not the ideal composition for electromechanical composites due to the onset of conduction mechanisms under high electric fields. Despite a two-fold improvement of the composite compared to the polymer film, the second-order strain level in polymer composites remains primarily governed by the polymer.