Gel speaker demonstrates viability of ionic conductors

30 August 2013
By Edd Gent
Mobile version
Share |
Jeong-Yun Sun (left) and Christoph Keplinger (right) with their transparent ionic speaker (Credit: Eliza Grinnell, Harvard SEAS)

Jeong-Yun Sun (left) and Christoph Keplinger (right) with their transparent ionic speaker (Credit: Eliza Grinnell, Harvard SEAS)

A gel-based speaker has demonstrated the viability of devices powered by electrical charges from ions rather than electrons.

The transparent device consists of a thin sheet of rubber sandwiched between two layers of a saltwater gel that can produce sounds that span the entire audible spectrum, 20 hertz to 20 kilohertz, when a high-voltage signal runs across the surfaces and through the layers, forcing the rubber to rapidly contract and vibrate.

But the speaker is not an electronic device as it relies on electrical charges carried by ions, rather than electrons. Published in journal Science today, the device represents the first demonstration that ionic conductors can be put to meaningful use in fast-moving, high-voltage devices.

“Ionic conductors could replace certain electronic systems; they even offer several advantages,” said co-lead author Jeong-Yun Sun, a postdoctoral fellow at the Harvard School of Engineering and Applied Sciences (SEAS).

Among the promising characteristics of ionic conductors is the fact that they can be stretched to many times their normal area without an increase in resistivity – a problem common in stretchable electronic devices – and they can also be transparent making them well suited for optical applications.

Ionic conductors can be very stretchy and completely transparent, two properties difficult to achieve with electronics (Credit: Eliza Grinnell)

Perhaps more importantly the gels used as electrolytes are biocompatible as signals carried by charged ions are the way the body transmits electrical signals, so it should be relatively easy to incorporate ionic devices – such as artificial muscles or skin – into biological systems.

“The big vision is soft machines,” said co-lead author Christoph Keplinger, who worked on the project as a postdoctoral fellow at SEAS in the Department of Chemistry and Chemical Biology.

“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.”

The audio speaker represents a proof of concept for ionic conductors because producing sounds across the entire audible spectrum requires both high voltage to squeeze hard on the rubber layer and high-speed actuation to vibrate quickly.

In the past researchers have found that high voltages can set off electrochemical reactions in ionic materials, producing gases and burning up the materials, and also that ions are also much larger and heavier than electrons so physically moving them through a circuit is typically slow.

By overcoming both problems the system invented at Harvard opens up a host of potential applications including biomedical devices, but also fast-moving robotics and adaptive optics.

“It must seem counterintuitive to many people, that ionic conductors could be used in a system that requires very fast actuation, like our speaker,” said Sun.

“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 electrical connection to the power source is established outside the active region of the device where it does not need to be transparent (Credit: Christoph Keplinger & Jeong-Yun Sun) “It must seem counterintuitive to many people, that ionic conductors could be used in a system that requires very fast actuation, like our speaker,” said Sun.

“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.”

The Harvard team chose to make its audio speaker out of simple materials – the electrolyte is a polyacrylamide gel swollen with salt water – but they say an entire class of ionically conductive materials is available for experimentation.

They plan to focus future work on identifying the best combinations of materials for compatibility, long life, and adhesion between the layers.

“We’d like to change people’s attitudes about where ionics can be used,” said Keplinger.

“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.”

Sam Liss, director of business development in Harvard’s Office of Technology Development, is working to commercialize the technology by working with companies involved in everything from tablet computing to smartphones, wearable electronics, consumer audio devices, and adaptive optics.

“With wearable computing devices becoming a reality, you could imagine eventually having a pair of glasses that toggles between wide-angle, telephoto, or reading modes based on voice commands or gestures,” suggested Liss.

Latest Issue

E&T cover image 1605

"We visit Barcelona, one of the smartest cities in the world, to find out what makes it so special. What does it look like and what is the future?"

E&T jobs

  • Senior Development Engineer, Electronics

    Premium job

    Helmet Integrated Systems / Gentex Corporation
    • Letchworth Garden City, Hertfordshire
    • Competitive

    We are an innovative, robust and fast growing business, whose main focus is to deliver continues improvement to existing products and offer new sol..

    • Recruiter: Helmet Integrated Systems / Gentex Corporation

    Apply for this job

  • Smart Grid Research Engineer

    Premium job

    University of Strathclyde
    • Cumbernauld, Glasgow
    • Grade: 6/7* £26,537 - £37,768*

    Work as part of a growing dynamic team on a wide range of technical projects with particular emphasis on experimental validation and testing

    • Recruiter: University of Strathclyde

    Apply for this job

  • Electrical Asset Specialist

    Affinity Water
    • Hatfield, Hertfordshire

    Responsible for updating and writing electrical engineering standards, approved codes of practice and safe systems of work

    • Recruiter: Affinity Water

    Apply for this job

  • Senior Electronics Engineer

    York Instruments
    • York, North Yorkshire

    Senior electronics engineer to work as part of a team developing an MEG imaging system; working with the engineering team and external contractors.

    • Recruiter: York Instruments

    Apply for this job

  • Manufacturing Engineer - Circuit Card Assembly

    MBDA
    • Lostock Junction
    • Competitive Salary & Benefits

    What’s the opportunity?   Manufacturing UK is an integral part of the Operations Directorate whose principal mission is to ensure that MBDA’s deliverable commitments are met...

    • Recruiter: MBDA

    Apply for this job

  • High Voltage Engineer

    Premium job

    Essex X-Ray & Medical Equipment
    • Great Dunmow, Essex

    This High Voltage Engineer will provide design leadership for high voltage cable assemblies up to one megavolt.

    • Recruiter: Essex X-Ray & Medical Equipment

    Apply for this job

  • Team Leader - Flank Arrays

    BAE Systems
    • Barrow-In-Furness, Cumbria, England
    • Negotiable

    Team Leader - Flank Arrays Would you like to work in a unique role within the construction of the Astute Class submarines? We currently have a vacancy for a Team Leader - Flank Arrays at our site in Barrow-in-Furness. As a Team Leader - Flank Arrays, you

    • Recruiter: BAE Systems

    Apply for this job

  • Electronics and Software Engineer

    Copley Scientific Ltd
    • Nottingham
    • circa £35,000 per annum + bonus

    Develop new test equipment for the pharmaceutical industry. Good opportunities to grow and develop. Successful family-owned and managed business.

    • Recruiter: Copley Scientific Ltd

    Apply for this job

  • Bridge Test Facility Manager

    BAE Systems
    • Shropshire, Telford, England
    • Negotiable

    Bridge Test Facility ManagerWe currently have a vacancy for a Bridge Test Facility Manager at our site in Telford with our Land UK business.As the Bridge Test Facility Manager, you will be part of our Test & Trials team, working closely with the Mili

    • Recruiter: BAE Systems

    Apply for this job

  • Intelligent Transport Systems Engineer - Highways Technology

    Premium job

    Mott MacDonald
    • Birmingham, West Midlands

    Our transport technology team in Birmingham is currently growing a highly skilled and customer-focused team to...

    • Recruiter: Mott MacDonald

    Apply for this job

More jobs ▶

Subscribe

Choose the way you would like to access the latest news and developments in your field.

Subscribe to E&T