General motivation for dielectric elastomer actuators
Interfacing with internal organs such as the brain, heart and lungs require a different type of electronics. Stretchable electronics will allow devices to interface with these organs without damaging them or otherwise impeding the natural state of the body. In addition they need to be able to withstand high frequencies and high voltages. Existing stretchable conductors are mostly electronic conductors such as carbon grease, microcracked gold film, serpentine-shaped metallic wires, carbon nanotubes, graphene sheets or silver nanowires. These existing conductors struggle with high frequencies, high voltages, biocompatibility, transparency and conductivity while undergoing large areal expansions, all of which are key tasks towards interfacing with the human body.
Case Study: Heart Shaped Dielectric Elastomer Actuator
As opposed to electronic conductors, many ionic conductors are biocompatible, are transparent and able to stay conductive at high areal expansions. Keplinger et al. (2013) designed a transparent large strain actuator consisting of a membrane of a dielectric elastomer sandwiched between two membranes of an electrolytic elastomer.
The team demonstrated this design by building a transparent heart shaped actuator using VHB 4910 tape as the dielectric and 100-um-thick polyacrylamide hydrogel containing NaCl as the electrolyte. The construction of the actuator is similar to the actuator described in this documentation. The dielectric was prestretched and attached to a rigid frame. Instead of carbon grease, the clear hydrogel is used for the active area.
The attached video shows the actuator in action:
Case Study: Transparent Loudspeaker
To show how dielectric elastomer actuators are able to function at very high frequencies, Kepplinger at al. (2013) built a transparent loudspeaker that produces sound across the entire audible range, from 20 Hz to 20 kHz. The loudspeaker was used to play audio from videos played on a laptop. The audio from the videos was fed to the loudspeaker as an analog voltage signal through a high voltage amplifier from the laptop's audio output. The resulting audio was recorded by a webcam's microphone and compared to the audio source. For one test that involved giving the loudspeaker a 20-s test signal of constant amplitude and a linear sine sweep from 20 Hz to 20 kHz, the loudspeaker was able to successfully reproduce the main signal, with some inconsistency coming from vibrations of the actuator's frame, which was not optimized and began vibrating at its resonance frequency.
The video below shows the loudspeaker in action: