Stretchy, See-Through Speaker Could Revolutionise Electronic Devices

By G.P. ThomasAug 30 2013

As Jeong-Yun Sun and Christoph Keplinger, Harvard University, demonstrate here, two major advantages of ionic conductors are that they can be very stretchy and completely transparent, two properties difficult to achieve with electronics. Image credit: Photo by Eliza Grinnell, Harvard SEAS Communications.

A working transparent speaker has been produced that uses ions, rather than electrons, to carry the electrical charge.

The speaker, created at Harvard University, is made from two layers of polyacrylamide gel swollen with salt water, which act as electrolytes, sandwiching a thin rubber membrane that vibrates as a high-voltage signal is run across its surface. However, this is not any ordinary electronic device, as the electrical charge is carried by ions, not electrons.

Jeong-Yun Sun (left) and Christoph Keplinger (right), Harvard University, demonstrate their transparent ionic speaker. It uses a signal conducted by ions, rather than electrons, to vibrate a rubber membrane. Image credit: Photo by Eliza Grinnell, SEAS Communications.

Traditionally, there have been constraints that have prevented the use of ionic conductors in such applications. Firstly, ions are much larger than electrons; this means moving them through a conventional circuit takes a lot longer. On top of this, in ionic materials, high voltages can cause chemical reactions that produce gases and burn up the materials they pass through.

However, the new system may be able to overcome these issues. Jeong-Yun Sun is a postdoctoral fellow at the Harvard School of Engineering and Applied Sciences (SEAS), and a co-lead author of a paper explaining the findings, to be published in the journal Science today. Below he explains how the speaker they have created overcomes these traditional issues:

"It must seem counterintuitive to many people, that ionic conductors could be used in a system that requires very fast actuation, like our speaker, yet by exploiting the rubber layer as an insulator, we're able to control the voltage at the interfaces where the gel connects to the electrodes, so we don't have to worry about unwanted chemical reactions. The input signal is an alternating current (AC), and we use the rubber sheet as a capacitor, which blocks the flow of charge carriers through the circuit. As a result, we don't have to continuously move the ions in one direction, which would be slow; we simply redistribute them, which we can do thousands of times per second."

Further to this, using ionic conductors may even display certain advantages over current electronic systems:

•  Ionic conductors can be stretched easily without the increase in resistivity associated with stretched electronic devices.
•  The gels used are biocompatible, and as such can be readily incorporated into biological systems
•  The transparency of the system may be beneficial to the optics and photonics industry.

To make the speaker, a membrane of transparent, insulating rubber is sandwiched between two layers of transparent, conductive gel. The electrical connection to the power source is established outside of the active region of the device, where it does not need to be transparent. Image credit: Image courtesy of Christoph Keplinger, Jeong-Yun Sun, and Science/AAAS.

Now that some of these previous issues have been overcome, commercialisation of the technology, in devices from smart phones to wearable electronics, may not be too far away.

Co-lead author Christoph Keplinger talks below about the incredible potential of the new technology:

"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."

Below is a video aptly demonstrating the capabilities of the novel speaker, as it plays Grieg’s ‘Morning’ Prelude (Footage courtesy of Science/AAAS.).

Original Source: Harvard University

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