The eye's cornea changes shape and curvature in order to efficiently adjust its focal length.

What if your camera optics could do the same, instead of relying on the limited movement of bulky lenses?

Mechanical systems, such as engines and motors, are frequently restricted to two simple motion options: linear and rotational.

By applying voltage, researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have expanded the configuration possibilities and discovered a way to morph their soft actuators into different shapes.

The team embedded a thin, flat circulator sheet of elastomer with embedded electrodes.

With specified electrodes activated, the sheet morphs into a variety of shapes, including the “saddle” configuration below:

(Gif courtesy of the Clarke Lab/Harvard SEAS)

The carbon nanotube-based electrodes are incorporated between each layer of the elastomer sheet. When voltage is applied to the electrodes, a spatially varying electric field is created within the elastomer, producing uneven changes in the material geometry, and initiating a desired three-dimensional shape.

“In addition to being reconfigurable and reversible, these shape-morphing actuations have a power density similar to that of natural muscles,” said Ehsan Hajiesmaili, first author of the paper and graduate student at SEAS. Hajiesmaili spoke with Tech Briefs about where he expects to see shape-changing actuators with that kind of power.

Tech Briefs: What applications are possible with this soft actuator?

Ehsan Hajiesmaili, graduate student at SEAS: Many novel devices are possible with this new class of soft actuators that were not practically possible before. A very exciting one is a shape-morphing airfoil — one that goes beyond moving a flap or bending its tail, but changes its shape completely in order to optimize for the required flying conditions. Even a shape-morphing airplane could be possible.

Another example is a shape-morphing mannequin that changes its shape to show how an item of clothing would look on different body shapes. Other examples are shape-morphing mirrors, lenses, and sculptures.

I think the first use of these actuators will be those shape-morphing soft actuators where their design and utilization are somewhat less complicated, such as soft grippers and soft tactile displays.

Tech Briefs: What was the inspiration behind this work?

Hajiesmaili: The idea of this work developed gradually, and it was inspired by a number of different things including the exciting possible applications of 1) shape-morphing mechanisms in nature, 2) other works on soft actuators, and 3) what we found missing in those works such as generalizability to complex shape-changes, high power density, and reconfigurability.

Tech Briefs: Why is this kind of actuator so valuable compared to traditional actuators?

Hajiesmaili: With this new class of soft actuators, a single integrated actuator can produce a sophisticated actuation deformation without the need of any external mechanisms. This was not possible with the traditional actuators; the motion that the traditional actuators provide comes from the relative displacement of their stiff components, which is limited to linear and rotary motions.

Producing complex actuation deformations with the traditional actuators requires prohibitively complex and bulky external mechanisms, and this has been a strong limitation on the level of complexity of the mechanical devices that we could make. This new class of soft actuators pushes this limitation by providing complex actuation deformations and high enough power for a large range of applications.

Numerous novel devices that had been deemed too complicated to pursue using the traditional actuators are possible with this new class of soft actuators.

Tech Briefs: What was the most challenging aspect of the technology design?

Hajiesmaili: In order to be suitable for real applications, a shape-morphing mechanism must be generalizable to shapes of high complexity, these shape-changes must be fast and reversible, the power density must be high enough for real applications, and the actuation stimulus must be easy to apply. The most challenging part of this work was to come up with a mechanism that meets all these criteria at once. We used dielectric elastomers because of their fast and reversible actuation, and high-power density, and we devised a method to induce spatial distribution of the actuation stimulus, which was the key to generalizable shape-morphing.

Tech Briefs: What’s next regarding the development of these actuators?

Hajiesmaili: To make novel devices using these shape-morphing actuators, a computational design tool is needed.

In our work, we answered the forward problem, which is predicting the actuation shape for a given design of electrodes and applied voltage; the more challenging problem, however, is the inverse problem: What should be the design of the electrodes and the applied voltage in order to morph into a desired actuation shape? This will lead to a computational design tool, which then we can use for making novel devices such as shape-morphing airfoils.

Also, optimizing the material and fabrication process is something that should be done along the way. Finally, integrating other elements into the actuator, such as sensors, batteries, and the electronics, will lead to higher functionality.

Hajiesmaili and his team's research was published in Nature Communications.

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