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TitleThe dielectric constant of 3M VHB: A parameter in dispute
Publication TypeConference Paper
Year of Publication2009
AuthorsMcKay, T.G., Calius E.P., and Anderson I.A.
Conference NameProceedings of SPIE - The International Society for Optical Engineering
Date Published2009
KeywordsActuators, Blocked force, Capacitance, Capacitors, Ceramic capacitors, Conducting polymers, Dielectric constant, Dielectric elastomer, Dielectric materials, Dielectric waveguides, FEA, Figure of merit, Force measurement, Modeling, Permittivity, Plastics, Rubber, Tape coatings, VHB
AbstractDielectric 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 er 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. © 2009 SPIE.

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