Earlier today I was fortunate enough to attend a seminar by Iain Anderson from the University of Auckland on Electroactive Polymers (EAP) at the Bristol Robotics Lab (BRL). Woah, That was a mouthful. The talk covered a range of applications the Auckland Biomimetics Lab are using EAPs for including rubber motors (electric motors made entirely from rubber, with no metal parts), rubber electronics (including NAND gates, capacitors and a replacement diode) with the ability for these applications to self-sense. The institute focuses on the use of a a sub-group of EAPs known as dielectric elastomers or DEs.
Research using EAPs has been carried out for a few decades but until recently has mostly focused on, as the name implies, replicating muscles found in a biological sense. Most often showing the power of them for use in linear actuation for robotic applications such as arms and tentacles. However a few interesting ideas and tweaks to the way they’re used has opened up a huge variety of applications as Anderson described in the talk. Below is a brief description on how the artificial muscles work:
Dielectric elastomers consist of a compliant electrical insulator sandwiched between two electrically conducting electrodes. The insulator is typically made of silicone rubber and the electrodes of carbon grease. When a high voltage is applied across the electrodes, charge accumulates in each electrode leaving positive charges in one and negative charges in the other. These positive and negative charges attract, squashing the insulating membrane, and, because the membrane is incompressible, they cause it to expand in area. (see Figure 1)
— Source: Auckland Bioengineering Institute
The talk began with an introduction of the history of EAPs beginning in 1880 with the experiments of Wilhelm Roentge on the effects of electric current to a rubber band and Benjamin Franklin’s electric motor way back in 1748. It moved through the work being done from different researches around the world, including some being done at the BRL.
Secondly on to the innovative work being done at the University of Auckland, Anderson showed examples of how they were using dielectric elastomer actuators to turn a gear or an axle without the use of metallic or magnetic parts, perfectly suited for environments with large magnetic fields such as an MRI machine. The process worked by activating an arrangement of DEs one at a time, pulling a cog closer to the active one. When arranged in a triangle they were able to rotate an axle.
This work lead on to the creation of rubber based electronics, capacitors, variable resistors, circuits capable of providing the same effect as diodes and NAND gates, suggesting it may one day soon be possible to create an entire computer out of rubber.
Finishing with the work being done in energy generation using similar techniques and the same DEAs. By running them in reverse the artificial muscles were able to generate power enabling applications such as self-charging prosthetics or harnessing natural energy from the sea or wind (as they were successful in doing, by hanging one from a tree).