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Towards a new generation of soft and conformable acoustic devices based on electroactive polymers

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Smaller, lighter devices which do many things at once

Scientists exploring the use of dielectric elastomers for loudspeakers have uncovered their ability to be multifunctional, opening the door to a whole range of new possibilities.

Industrial Technologies icon Industrial Technologies

Since the advent of smartphones and the internet of things, for many people, devices have become essential kit for both work and play. The next step will see devices becoming integrated – as wearable tech or embedded in the objects we interact with – meaning they need to become smaller, lighter, and more efficient. A new way of using a smart material known as dielectric elastomer (DE), might make a new generation of interactive devices feasible. “Dielectric elastomers, which are silicone films, have special properties – they are stretchable and electrically insulating,” says Giacomo Moretti, principal investigator on the DEtune project. Moretti, who is now assistant professor in Applied Mechanics at Italy’s University of Trento, adds: “When you apply an electric potential, DEs deform themselves so you can use them to build actuators in very diverse shapes.” The DEtune team, based at the Intelligent Material Systems Lab at Germany’s Saarland University, set out to explore whether DE can be used to make a new kind of lightweight loudspeaker. The team also looked into the movement patterns of membranes responding to low frequencies and came up with novel observations.

Intriguing new applications for dielectric elastomers

DE soft membranes can generate sound thanks to electrostatically driven vibrations. They do away with the need for the rigid moving coils or diaphragms of conventional loudspeakers. DEtune researchers, supported by the Marie Skłodowska-Curie Actions programme, used an advanced laser vibrometer to measure the patterns of deformation of membranes when electrical potentials were applied at various frequencies. They used the data to develop models which can describe a DE loudspeaker’s response in terms of dynamics and sound pressure. “We also built loudspeaker prototypes. As they have no magnet and no coil, they can be much lighter than normal devices,” notes Moretti. Looking at the potentials of DE is an area of interest at the moment. But the project’s analysis of the combination of numerical and experimental characterisations of voltage-driven vibrations in DE membranes represents the most comprehensive analysis in this area to date. Observing how the surface of a membrane moves at different frequencies led to another idea. “At low frequency, some DE actuators move in a pumping way, at high frequency, the surface of the membrane develops a set of complex motion patterns that allow sound to be generated,” explains Moretti. “We realised we could generate these different motions at the same time and make our devices multifunctional.”

Potential for multifunctional digital applications and devices

Moretti describes this as: “a kind of Eureka moment, although once you have seen it you realise it is actually very intuitive.” More prototypes demonstrated this new multifunctional potential. These include a smart button which can sense touch, vibrate in response and produce a sound. Another was an actuator which can play a tune and, at the same time, move in sync with the music. DE devices are still at a pre-commercial stage, but the DEtune team believe the ability to respond in different ways could contribute to a new generation of wearables. “It allows you to move towards applications where you do several things with one device. Integrating all these functionalities into a single device saves space and money, and allows you to do more,” notes Moretti. He foresees uses such as smart textiles which could interact with wearers – maybe warning a manual worker of risks in their environment or guiding them through complex tasks.

Keywords

DEtune, smart material, dielectric elastomers, loudspeakers, lightweight loudspeaker, multifunctional, wearable tech, smart textiles

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