  A predicting model for soft Dielectric Elastomer Generators (DEGs) must
consider a realistic model of the electromechanical behaviour of the elastomer
filling, the variable capacitor and of the electrical circuit connecting all
elements of the device. In this paper such an objective is achieved by
proposing a complete framework for reliable simulations of soft energy
harvesters. In particular, a simple electrical circuit is realised by
connecting the capacitor, stretched periodically by a source of mechanical
work, in parallel with a battery through a diode and with an electrical load
consuming the energy produced. The electrical model comprises resistances
simulating the effect of the electrodes and of the conductivity current
invariably present through the dielectric film. As these devices undergo a high
number of electro-mechanical loading cycles at large deformation, the
time-dependent response of the material must be taken into account as it
strongly affects the generator outcome. To this end, the viscoelastic behaviour
of the polymer and the possible change of permittivity with strains are
analysed carefully by means of a proposed coupled electro-viscoelastic
constitutive model, calibrated on experimental data available in the literature
for an incompressible polyacrilate elastomer (3M VHB4910). Numerical results
showing the importance of time-dependent behaviour on the evaluation of
performance of DEGs for different loading conditions, namely equi-biaxial and
uniaxial, are reported in the final section.
