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Electro-active elastomers promise potential in vibration damping

Engineers in Germany are working on intelligent materials that can diminish vibrations and extract power from the environment. These electro-active elastomers could dampen annoying vibrations in a vehicle, for example, or supply wireless power to sensors in otherwise inaccessible places.

Engineers in Germany are working on intelligent materials that can diminish vibrations and extract power from the environment. These electro-active elastomers could dampen annoying vibrations in a vehicle, for example, or supply wireless power to sensors in otherwise inaccessible places.

A team at the Fraunhofer Institute for Structural Durability and System Reliability LBF (Darmstadt) is designing components made of such elastomers that actively respond to unwanted vibrations, and dampen them more effectively than ever before.

Electro-active elastomer could reduce vibrations in motor vehicles. Image shows lattice-shaped electrode in the foreground, and elastomer in background.

Elastomers have been used in engineering for decades, such as in shock absorbers and vehicle engine mounts. Until now, they have had a purely passive effect on vibrations or impact collisions.

It would be more effective if the elastomers were to respond proactively and counteract vibrations. In the same way a tennis player slows down the ball on a drop shot by pulling back on her racket, an active elastomer draws out the energy from the vibration in a targeted manner by swinging in precise push-pull mode. Theoretically, this would make the vibration dissipate completely.

There are already materials that are good for this purpose. "They are called 'electroactive elastomers'," explains LBF scientist William Kaal. "They are elastic substances that change their form when exposed to an electrical field." The trick: apply an alternating current, and the material starts to vibrate. If there are smart electronics controlling the elastomers, making them vibrate precisely in push-pull mode, then unwanted vibrations in equipment or an engine will dissipate for the most part. To demonstrate that the principle works, the Darmstadt-based researchers created a model. Smaller than a pack of cigarettes, it is comprised of 40 thin elastomer electrode layers and is known as a stack actuator.

"The challenge was the design of the electrodes with which we apply the electric field to the elastomer layers," as Kaal's colleague Jan Hansmann explains. Usually, electrodes are made out of metal. However, metals are relatively rigid, which impedes the deformation of the elastomer. Fraunhofer experts deliver an elegant solution to the problem: "We put microscopic-sized holes in the electrodes," says Hansmann. "If an electric voltage deforms the elastomer, then the elastomer can disperse into these holes." The result is an actuator that can rise or fall a millimeters upon command - several times a second, in fact.

The LBF engineers believe one potential application for their stack actuator can be found in vehicle construction. "An engine's vibrations can be really disruptive," says William Kaal. "The vibrations are channeled through the chassis into the car's interior, where the passengers start to feel them." Of course, engines are installed meticulously, and yet: "Active elastomers may help further reduce vibrations in the car," Kaal asserts.

Bridge monitoring

The function of the stack actuator can also be reversed: rather than produce vibrations, the device can also absorb vibrations from its surroundings to produce energy. "That would be of interest, for example, if you wanted to monitor inaccessible sites where there are vibrations but no power connections," Hansmann believes - as he cites an example: the temperature and vibration sensors that monitor bridges for their condition.

The stack actuator technology has been largely perfected: "The manufacturing process can be readily automated, which is important for industrial mass production," says Kaal. Nevertheless, endurance tests are still needed to give an indication of the long-term viability of these intelligent actuators. Ultimately, they must be able to withstand harsh environments of the kind found in the engine compartment of a car.-[email protected]

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