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Dielectric Elastomer (DE) transducers are essentially compliant capacitors fabricated from highly flexible materials that
can be used as sensors, actuators and generators. The energy density of DE is proportional to their dielectric constant
(εr), therefore an understanding of the dielectric constant and how it can be influenced by the stretch state of the material is required to predict or optimize DE device behavior. DE often operate in a stretched state. Wissler and Mazza, Kofod
et al., and Choi et al. all measured an εr of approximately 4.7 for virgin VHB, but their results for prestretched DE
showed that the dielectric constant decayed to varying degrees. Ma and Cross measured a dielectric constant of 6 for the
same material with no mention of prestretch. In an attempt to resolve this discrepancy, εr measurements were
performed on parallel plate capacitors consisting of virgin and stretched VHB4905 tape electroded with either gold
sputtered coatings or Nyogel 756G carbon grease. For an unstretched VHB tape, an εr of 4.5 was measured with both
electrode types, but the measured εr of equibiaxially stretched carbon specimens was lower by between 10 to 15%. The
dielectric constant of VHB under high fields was assessed using blocked force measurements from a dielectric elastomer
actuator. Dielectric constants ranging from 4.6-6 for stretched VHB were calculated using the blocked force tests.
Figure of merits for DE generators and actuators that incorporate their nonlinear behavior were used to assess the
sensitivity of these systems to the dielectric constant.
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