Abstract:
Dielectric Elastomer Actuators (DEAs) are classified as artificial muscles because of their muscle-like characteristics. DEAs, like muscles, possess simultaneous actuation and sensing capabilities. In the human body, receptors in muscle relay strain information to the brain, and from the brain back to the muscles; this internal feedback mechanism is known as proprioception. Similarly, the capacitance of a DEA can be used in a closed loop control scheme to control the artificial muscle. Internal sensing such as this results in fine motor control in humans and accurate displacements in DEAs. The capacitance of a DEA is a single value and can only be used to infer the area strain of a DEA. It is only interpretable as strain in a particular direction if the DEA is undergoing equi-biaxial strain, or the actuator is constrained to expand in one direction. Consequently, the actuator must be designed or modified to use it in a closed loop feedback scheme. In this study a novel technique, the Standing Wave Method (SWM), is explored to determine the strain of a DEA in its principal directions. However, because of the difficulties of implementing SWM in DEAs, the technique was explored in an electrically similar material with near ideal properties (patch antenna). Testing SWM in patch antennae means that the coupled effects of DEA expansion -- bi-directional strain, substrate thinning and electrode resistance -- can be tested separately, and independent of the electrode resistance. The study shows that SWM can infer the physical dimensions of a rectangular DEA when the conductivity of the electrodes is close to metals. Furthermore, it was shown that the thin dielectric of DEA improves the accuracy of SWM. The new technique provides an alternative to capacitive sensing and does not require modification of the DEA. SWM provides a compact sensing technique to control the position of a DEA. The technique is analogous to proprioception and has the potential to produce life-like machines with fine control.