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Researchers build an audio speaker out of stretchy transparent gel


October 8, 2013

This is a speaker, believe it or not (Photo by Eliza Grinnell, SEAS Communications)

This is a speaker, believe it or not (Photo by Eliza Grinnell, SEAS Communications)

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Audio speakers are showing up in a variety of unusual forms these days, from the incredibly tiny to the eye-catchingly bizarre, but a research group at Harvard University may have trumped them all with a speaker that's as clear as glass. Scientists at the college's School of Engineering and Applied Sciences have built a flexible speaker out of ionic gel that is almost invisible to the naked eye and can produce high-quality sound ranging across the full audible spectrum. In doing so, they also provided a proof of concept for electronics that can transfer electric signals in a similar manner to the human nervous system.

To construct the see-through speaker, the group took a transparent rubber sheet and added a layer of conductive saltwater gel to each side. Once a voltage is applied to opposite edges of the gel layers, the entire area of the rubber flexes rapidly, producing sounds ranging from 20 Hz to 20 kHz. Because of the flexibility and ionic properties of the materials, the speaker can be stretched to several times its normal area and still function properly. The scientists believe a more refined version of their invention could be fitted over a computer or tablet screen to provide sound and haptic feedback without the need for external speakers.

A transparent speaker may be impressive on its own, but the real point of the project was to demonstrate how an electric charge passing through ions instead of electrons could be used in electronic devices. In most cases, ionic substances tend to produce slow circuit connections when a voltage is applied to them, and too high a voltage can trigger a chemical reaction that destroys the material entirely. With this new system, however, the rubber acts as an insulator, which allows scientists to better control the voltage and speed up the connection in the process.

According to the research team, if ionic conductors were perfected, they could potentially offer quite a few advantages over conductors typically used today. A common issue with most current flexible conductors is that their resistance increases the more they are stretched, which severely limits their performance in some electronic devices. Ionic conductors on the other hand don't have this problem and can be pulled to several times their regular area without affecting the circuit. An ionic conductor won't be able to match a regular electronic one in terms of resistivity any time soon, but if the goal is to build a circuit that can be warped, then they could be a feasible alternative. As a bonus, ionic conductors can be made from entirely transparent materials.

"We’d like to change people’s attitudes about where ionics can be used," says Christoph Keplinger, a co-author on the project and postdoctoral fellow at Harvard SEAS. "Our system doesn’t need a lot of power, and you can integrate it anywhere you would need a soft, transparent layer that deforms in response to electrical stimuli—for example, on the screen of a TV, laptop, or smartphone to generate sound or provide localized haptic feedback—and people are even thinking about smart windows. You could potentially place this speaker on a window and achieve active noise cancellation, with complete silence inside."

Connecting with our own biology

Aside from being clear and stretchable without hindering the circuit, the gels in the transparent speaker carry ions in much the same way as some biological systems, such as nerves in the human body. This could possibly open the door for merging biological systems with man-made ionic ones, such as artificial muscles or skin.

In the long term, the researchers see their discovery as potentially leading to more advanced "soft machines" that can alter their form on command.

"The big vision is soft machines," says Keplinger, "Engineered ionic systems can achieve a lot of functions that our body has: they can sense, they can conduct a signal, and they can actuate movement. We’re really approaching the type of soft machine that biology has to offer."

Some examples of possible projects they've described include reading glasses that can change their own focal length and robots that reshape themselves to suit different tasks. For the time being, the team plans to continue its research by performing similar experiments with other ionic substances to find which ones can function under a charge longer and which materials can be combined for greater conductivity.

The research group recently explained its ionic speaker project in a paper published in the Aug. 30, 2013 issue of Science.

Professor of Mechanics and Materials at SEAS, Zhigang Suo, put together the research group behind the transparent speaker along with George M. Whitesides, a professor in Harvard's Department of Chemistry and Chemical Biology.

Check out the video below to hear just how crisp the audio from the researchers' ionic speaker sounds.

Source: Harvard School of Engineering and Applied Sciences

About the Author
Jonathan Fincher Jonathan grew up in Norway, China, and Trinidad before graduating film school and becoming an online writer covering green technology, history and design, as well as contributing to video game news sites like Filefront and 1Up. He currently resides in Texas, where his passions include video games, comics, and boring people who don't want to talk about either of those things. All articles by Jonathan Fincher

Salah satu alternative speaker di masa datang .......speaker transparan

Bambang Wibowo

Possible, maybe ah perhaps- the reporter does his subjects a disservice by not focusing on the their actual accomplishment rather then what might be.

The reporter is clearly unaware that variable focal length glasses are not only possible they have been made with flexible materials some years ago.

The idea that a sound canceling in a room is best served at the window is utterly without merit. The temperature and insolation extremes and the wall/window sound conduction (which does not necessarily couple to the room) all strongly suggest abandoning this approach. Whether this speaker is a preferred sound canceling speaker remains to be seen.


attoman, Your clearly do the reporter an injustice by not noticing who is actually claiming or postulating what. Don't shoot the messenger.


What sound proof windows? Try a vacuum in between panels - sound and cold/heat proof.

What an awesome speaker, light weight, no copper coil or heavy magnet. I seriously hope they make this in to production, I would definitely want this for my home theater system eleven speaker surround sound.


@attoman, and you can buy variable focal length glasses where?


I'm in favor of inventors & journalists spitballing on the possibilities of research laboratory developments. I'm also in favor of attoman (or anyone) presenting complicatons to possible uses, but skip the Ad hominem, unless you are whining about OMG drivel in Yahoo, they just provoke it with thier nutty proclamations and assessments.

Adjustable eyewair for those that want to know: Formerly Trufocals covered by Gizmag Covered by Gizmag Covered by Gizmag

Also, wow. This is one of those things that is so brilliant you got to wonder how it was not tried 50 years ago, and how come we have not been using the results for 40 of them, looking forward to those.

Dave B13

This is a breathtaking innovation that comes at a good time, to address issues of sound emissions and cancellation of unwanted noises. I believe that will have multiple applications in medicine, including cardiology, as well as solving multiple technological problems. Even a PIG, used for cleaning pipes in the oil industry can be completely redesigned.

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