Printing low-voltage dielectric elastomer actuators

Abstract

We demonstrate the fabrication of fully printed thin dielectric elastomer actuators (DEAs), reducing the operation voltage below 300 V while keeping good actuation strain. DEAs are soft actuators capable of strains greater than 100% and response times below 1 ms, but they require driving voltage in the kV range, limiting the possible applications. One way to reduce the driving voltage of DEAs is to decrease the dielectric membrane thickness, which is typically in the 20–100 μm range, as reliable fabrication becomes challenging below this thickness. We report here the use of pad-printing to produce μm thick silicone membranes, on which we pad-print μm thick compliant electrodes to create DEAs. We achieve a lateral actuation strain of 7.5% at only 245 V on a 3 μm thick pad-printed membrane. This corresponds to a ratio of 125%/kV2, by far the highest reported value for DEAs. To quantify the increasing stiffening impact of the electrodes on DEA performance as the membrane thickness decreases, we compare two circular actuators, one with 3 μm- and one with 30 μm-thick membranes. Our experimental measurements show that the strain uniformity of the 3 μm-DEA is indeed affected by the mechanical impact of the electrodes. We developed a simple DEA model that includes realistic electrodes of finite stiffness, rather than assuming zero stiffness electrodes as is commonly done. The simulation results confirm that the stiffening impact of the electrodes is an important parameter that should not be neglected in the design of thin-DEAs. This work presents a practical approach towards low-voltage DEAs, a critical step for the development of real world applications.

Inkjet printing of carbon black electrodes for dielectric elastomer actuators

“…In the past this has not been an issue because the membranes used for DEAs were relatively thick (20 µm-100 µm). However, the trend is to fabricate devices with thinner membranes to lower actuation voltages 8 . Membranes which are less than 10 µm thick are fragile and have a tendency to stick to objects which contact the surface of the membrane; thus becoming damaged in the process.…”

Assessing the degradation of compliant electrodes for soft actuators

“…As this degradation is a local process, as opposed to the global stretch value measured by the test setup, we have used an autocorrelation image processing algorithm to measure the local strain on the pictures saved at each acquisition cycle. The algorithm is the same as the one we used to investigate the strain map induced by non-homogeneous electrodes on thin membranes 16 . The analysis has been performed on an actuator activated for an initial stretch of 22 % over 11k cycles (figure 10).…”

“…Most DEAs produced in research laboratories are made with an acrylic elastomer (VHB from 3M), which is highly visco-elastic and has an extremely low mechanical cut-off frequency. Thus, the electrical resistance of the electrodes is of secondary importance compared to other properties, such as their ability to stretch 15 or their mechanical impact on the actuator stiffness 16 . Indeed, even with extremely resistive electrodes, DEAs often remain mechanically -rather than electrically -limited.…”

“…Furthermore, DEAs typically require a driving electric field in the order of 100 V µm −1 . To reduce the driving voltage of these devices (which usually lies around 5 kV), one solution consists in reducing the thickness of the dielectric 16,19 , thus increasing the capacitance of the device. The use of silicone membranes for fast applications, and/or the usage of thin membranes to decrease the actuation voltage therefore both require electrodes that have a low initial resistivity, and whose resistance doesn't increase when cyclically stretched.…”

Fully printed 3 microns thick dielectric elastomer actuator

“…We have recently reported a similar device 1 and expand here on the fabrication, characterization and modeling aspects of our work. Stretchability, biocompatibility, optical transparency and silent operation are all exciting advantages of DEAs, making this technology an ideal candidate for a wide range of applications ranging from well-established fields such as optics 2,3 and fluidics 4,5 to emerging fields such as mechanobiology 6 and soft-robotics [7][8][9] .…”