Dielectric elastomer actuators are considered as promising candidates for robotic elements. To this end, planar dielectric elastomer actuators (p-DEAs) and dielectric elastomer minimum energy structures (DEMES) are applicable. However, the knowledge of their electrical and mechanical characteristics is of major importance for engineering tasks. Therefore we study p-DEAs and DEMES by impedance spectroscopy (IS) and dynamic capacitive extensometry (DCE). We vary the boundary conditions with regard to p-DEAs (free and fixed boundaries) and fabricate various DEMES with one angular degree of freedom. A mixture of carbon black particles and silicone oil serves as compliant electrodes. We present equivalent circuit models of the actuators based on impedance spectroscopy data, the frequency ranges in which they are applicable and effects of aging on the equivalent circuit models. By DCE the electrical characteristics of dielectric elastomer actuators are monitored in situ during dynamic high voltage actuation. These electrical characteristics of the dielectric elastomer actuators such as p-DEAs and DEMES can be related to their transient stretch in response to high voltage driving signals. We study the viscoelastic response of the actuators to square driving signals of different magnitudes; furthermore we monitor the state of the compliant electrodes. By means of the DCE measurement data and the impedance spectra the p-DEAs and DEMES can be compared.
Thin polymer foams with a closed cell void-structure can be internally charged by silent or partial discharges
within the voids. The resulting material, which carries positive and negative charges on the internal void surfaces
is called a ferroelectret. Ferroelectrets behave like typical ferroelectrics, hence they provide a novel class of ferroic
materials. The soft foams are strongly piezoelectric in the 3-direction, but show negligible piezoelectric response
in the transverse direction. This, together with a very low pyroelectric coefficient, make ferroelectrets highly
suitable for flexible electroactive transducer element which can be integrated in thin bendable organic electronic
devices. Here we describe some fundamental characteristics of cellular ferroelectrets and present a number of
promising examples for a possible combination with various functional polymer systems. Our examples focus on
flexible ferroelectret field-effect transistor systems for large-area sensor skins and microphones, flexible large-array
position detectors (touchpad), and stretchable large-array pressure sensors.
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