Mechanical systems like motors and engines depend on two main types of motions of stiff components. One is linear motion in which an object moves from one point to another in a straight line, and the other is rotational motion in which an object rotates on an axis.
Nature has created much more refined forms of movement—or actuation—that can carry out complicated functions more directly and with soft components. For instance, human eyes can vary focal point by just contracting soft muscles to modify the shape of the cornea. On the contrary, cameras focus by moving solid lenses along a line, either manually or by an autofocus.
But what if shape changes and movements found in nature could be mimicked?
Currently, scientists at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have devised a technique for modifying the shape of a flat sheet of elastomer, using actuation that is reversible, quick, reconfigurable to various shapes, and controllable by an applied voltage.
The study was reported in Nature Communications.
We see this work as the first step in the development of a soft, shape shifting material that changes shape according to electrical control signals from a computer. This is akin to the very first steps taken in the 1950’s to create integrated circuits from silicon, replacing circuits made of discrete, individual components. Just as those integrated circuits were primitive compared to the capabilities of today’s electronics, our devices have a simple but integrated three-dimensional architecture of electrical conductors and dielectrics, and demonstrate the elements of programmable reconfiguration, to create large and reversible shape changes.
David Clarke, Extended Tarr Family Professor of Materials, Harvard SEAS
David Clarke is also the senior author of the paper.
The reconfigurable elastomer sheet is composed of several layers. Electrodes based on carbon nanotube and with different shapes are integrated between each layer. On applying voltage to these electrodes, a spatially varying electric field is formed within the elastomer sheet that creates uneven changes in the material geometry, enabling it to modify into a controllable three-dimensional shape.
It is possible to independently switch on various sets of electrodes, allowing different shapes depending on sets of electrodes which are off and on.
In addition to being reconfigurable and reversible, these shape-morphing actuations have a power density similar to that of natural muscles. This functionality could transform the way that mechanical devices work. There are examples of current devices that could make use of more sophisticated deformations to function more efficiently, such as optical mirrors and lenses. More importantly, this actuation method opens the door to novel devices that deemed too complicated to pursue due to the complex deformations required, such as a shape-morphing airfoil.
Ehsan Hajiesmaili, Graduate Student, SEAS
Ehsan Hajiesmaili is also the first author of the paper.
In this study, the researchers also predicted the actuation shapes by taking the applied voltage and design of the electrode arrangement into account. Next, the goal of the scientists is to deal with the inverse issue in which a desired actuation shape is given, and the team needs to predict the design of the electrodes and the required voltage that will cause it.
The intellectual property relating to this study is protected by Harvard’s Office of Technology Development, which is exploring opportunities for commercialization.
This study was supported by Harvard MRSEC through the National Science Foundation.