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[Image above] Credit: Dirk Knight; Flick CC BY-NC 2.0

When boomboxes came on the market in the 1970s, they were popular because of their “compact size”.

Today, most of us wouldn’t say that suitcase-sized boomboxes are compact. But whatever our comparative definition of “compact” means today, the adjective still encapsulates the name of the game when it comes to audio options.

And with advancements in 2-D materials, there’s a whole host of thin new solutions.

We already saw the first hints at this technology last year with some graphene speaker prototypes. Graphene works really well in fabricating traditional speakers—which physically move air to create sound—because the material is so thin, light, and strong.

But the need to physically move air also means that, although materials are getting thinner, such speakers can only shrink so far. So to really revolutionize audio devices, we need an entirely new way of creating sound.

Graphene to the rescue

Thankfully, where there’s a need, there’s bound to be an innovation.

University of Exeter researchers have devised a new graphene-based audio device that completely bypasses the need to move air back and forth to create sound, allowing speakers to shrink to unprecedentedly small sizes.

Instead, the new thermoacoustic device uses an electric current to rapidly heat and cool a sheet of graphene. This expands and contracts the air around the material to create sound, eliminating the need to physically move air back and forth—and allowing the device to shrink down to the size of a thumbnail.

Researchers have combined speaker, amplifier, and graphic equalizer into a thumbnail-sized chip. Credit: University of Exeter

The team’s tiny device isn’t the first to convert heat to sound, but what makes it unique is its ability to integrate several audio functions into one single device.

The first two sentences of the abstract describing the team’s new work really sum it up: “The ability to generate, amplify, mix, and modulate sound in one simple electronic device would open up a new world in acoustics. Here we show how to build such a device.”

And it’s rather simple: Using chemical vapor deposition, the scientists built their device by growing a layer of graphene onto quartz or doped-silicon substrates.

“We looked instead at the way the sound is actually produced and found that by controlling the electrical current through the graphene, we could not only produce sound but could change its volume and specify how each frequency component is amplified,” David Horsell, senior lecturer at Exeter and lead author of the new work, says in an Exeter press release. “Such amplification and control opens up a range of real-world applications we had not envisaged.”

Because graphene is so thin, the team says that its near transparency means that it could be integrated into future screens to provide both images and sound within one component. They also indicate possibilities for ultrasound imaging because of the ability to mix sounds together.

Additionally, “this could have a real impact in the telecommunications industry, which needs to combine signals this way but currently uses rather complex and, therefore, costly methods to do so,” Horsell adds in the release.

That open-access paper, published in Scientific Reports, is “Multi-frequency sound production and mixing in graphene” (DOI: 10.1038/s41598-017-01467-z).

Loudspeaker flags

Graphene is great and all, but it’s also got its fair share of commercial drawbacks—including scale-up difficulties that are just starting to be resolved.

So another group of researchers at Michigan State University is going beyond graphene and is completely rethinking how we deliver audio by getting rid of separate speaker themselves, instead integrating sound-generating devices into everyday objects.

To do so, the team developed thin nanogenerator devices that generate energy from motion, and therefore require no power supply or battery pack.

The technology, called a ferroelectret nanogenerator (FENG), consists of several layered thin-films of charge-carrying polymer foam called ferroelectret on a silicone wafer substrate.

The ferroelectret nanogenerator developed by MSU engineers. Credit: G.L. Kohuth

The team previously showed the potential of its FENG device, but the new research expands its reach even further.

“This is the first transducer that is ultrathin, flexible, scalable, and bidirectional, meaning it can convert mechanical energy to electrical energy and electrical energy to mechanical energy,” Nelson Sepulveda, MSU associate professor of electrical and computer engineering and senior author of the new research, says in an MSU press release.

The potential for such a simple yet effective technology is widespread—the team has already demonstrated how the nanogenerator can work as a microphone or a loudspeaker, depending on whether mechanical energy (sound) is collected and converted into electrical energy, or vice versa, respectively.

Hear more about the development in the short MSU video below.

Credit: MSU News; YouTube

“Imagine a day when someone could pull a lightweight loudspeaker out of their pocket, slap it against the wall, and transmit their speech to a roomful of people,” Sepulveda says in the release. “Or imagine a newspaper, where the sheets are microphones and loudspeakers. You could essentially have a voice-activated newspaper that talks back to you.”

While that thought of a newspaper that talks back may be more of a deterrent than a desirable attribute, there are plenty of rather amazing possibilities to this tech.

The MSU researchers have used the FENG device to develop a film that protects the security of your computer by recognizing the unique frequencies of your voice and a flag that can double as a music-blaring loudspeaker—the perfect addition to any sporting event.

The open-access paper, published in Nature Communications, is “Nanogenerator-based dual-functional and self-powered thin patch loudspeaker or microphone for flexible electronics” (DOI: 10.1038/ncomms15310).

Nelson Sepulveda created an ultra-thin, foldable keyboard that can harvest energy from human motion—or from the very act of pressing the keys. Credit: G.L. Kohuth