Dynamic capacitive extensometry setup for in-situ monitoring of dielectric elastomer actuators

Dielectric elastomer actuators (DEAs) and their subcategory energy minimum structures (DEMES) are promising candidates for biomimetic robotic elements. Especially interesting for their characterization is the transient strain or stretch-response of the deforming elastomer part to high voltage driving signals, and the state of the applied compliant electrodes. However, this information can hardly be obtained by optical measurement techniques only. Especially DEMES with their complex three dimensional shapes are difficult to study. To this end, we present a setup of dynamic capacitive extensometry which is able to monitor DEAs and DEMES in situ; both the stretch dependent capacitance of the actuated elastomer part and the stretch dependent resistance of the compliant electrodes are recorded in situ during dynamic high voltage actuation. With the help of this measurement data the transient stretch response is studied with regard to the frequency, magnitude and shape of the actuation signal. Furthermore, the stretch-dependent resistance of the compliant electrodes and their percolation limit are investigated. The developed measurement technique can be applied also for actuator control with feedback loops.