Tag Archives: Zettl Group

Carbon nanotubes, acoustics, and heat

I have a longstanding interest in carbon nanotubes and acoustics, which I first encountered in 2008. This latest work comes from the Michigan Technological University according to a July 28, 2015 news item on Nanowerk,

Troy Bouman reaches over, presses play, and the loudspeaker sitting on the desk starts playing the university fight song. But this is no ordinary loudspeaker. This is a carbon nanotube transducer—and it makes sound with heat.

Bouman and Mahsa Asgarisabet, both graduate students at Michigan Technological University, recently won a Best of Show Award at SAE International’s Noise and Vibration Conference and Exhibition 2015 for their acoustic research on carbon nanotube speakers. They work with Andrew Barnard, an assistant professor of mechanical engineering at Michigan Tech, to tease out the fundamental physics of these unusual loudspeakers.

While still a fledgling technology, the potential applications are nearly endless. Everything from de-icing helicopter blades to making lighter loudspeakers to doubling as a car speaker and heating filament for back windshield defrosters.

Here’s a few sound sound files featuring the students and their carbon nanotube speakers,

A July 28, 2015 Michigan Technological University news release, which originated the news item, goes on to describe how these carbon nanotubes are making sound,

The freestanding speaker itself is rather humble. In fact, it’s a bit flimsy. A teflon base props up two copper rods, and what seems like a see-through black cloth stretches between them.

“A little wind gust across them, and they would just blow away,” Barnard says. “But you could shake them as much as you want—since they have such low mass, there is virtually no inertia.”

The material is strong side to side, because what the naked eye can’t see is the collection of black nanotubes that make up that thin film.

The nanotubes are straw-like structures with walls only one carbon atom-thick and they can heat up and cool down up to 100,000 times each second. By comparison, a platinum sheet about 700 nanometers thick can only heat up and cool down about 16 times each second. The heating and cooling of the carbon nanotubes causes the adjacent air to expand and contract. That pushes air molecules around and creates sound waves.

“Traditional speakers use a moving coil, and that’s how they create sound waves,” Bouman says. “There are completely different physics behind carbon nanotube speakers.”

And because of these differences, the nearly weightless carbon nanotube speakers produce sound in a way that isn’t initially understood by our ears. Bouman’s research focuses on processing the sound waves to make them more intelligible. Take a listen.


To date, most research on carbon nanotubes has been on the materials side. Carbon nanotube speakers were discovered accidently in 2008, showing that the idea was viable. As mechanical engineers studying acoustics, Barnard, Bouman and Asgarisabet are refining the technology.

“They are very light weight and have no moving parts,” Asgarisabet says, which is ideal for her work in active noise control, where the carbon nanotube films could cancel out engine noise in airplanes or road noise in cars. But first, she says, “I want to focus first on getting a good thermal model of the speakers.”

Having an accurate model, Bouman adds, is a reflection of understanding the carbon nanotube loudspeakers themselves. The modeling work he and Asgarisabet are doing lays down the foundation to build up new applications for the technology.

While a lot of research remains on sorting out the underlying physics of carbon nanotube speakers, being able to use both the heat and sound properties makes them versatile. The thinness and weightlessness is also appealing.

“They’re basically conformable speakers,” Barnard says. The thin film could be draped over dashboards, windows, walls, seats and maybe even clothing. To get the speakers to that point, Barnard and his students will continue refining the technology’s efficiency and ruggedness, one carbon nanotube thin-film at a time.

As I mentioned earlier I’m quite interested in carbon nanotubes speakers and, for that matter, all other nanomaterial speakers. For example, there was a November 18, 2013 posting titled: World’s* smallest FM radio transmitter made out of graphene which also featured the Zettl Group’s (University of California at Berkeley) carbon nanotube radio (unfortunately those sound files are no longer accessible).

Dexter Johnson in a July 30, 2015 posting (on his Nanoclast blog on the Institute of Electrical and Electronics Engineers [IEEE] website) provides some additional insights (Note: Links have been removed),

It’s been some time since we covered the use of nanomaterials in audio speakers. While not a hotly pursued research field, there is some tradition for it dating back to the first development of carbon nanotube-based speakers in 2008. While nanomaterial-based speakers are not going to win any audiophile prize anytime soon, they do offer some unusual characteristics that mainly stem from their magnet-less design.

World’s* smallest FM radio transmitter made out of graphene

I’m always amazed at how often nanotechnology is paired with radio. The latest ‘nanoradio’ innovation is from the University of Columbia School of Engineering. According to a November 18, 2013 news item on ScienceDaily,

 A team of Columbia Engineering researchers, led by Mechanical Engineering Professor James Hone and Electrical Engineering Professor Kenneth Shepard, has taken advantage of graphene’s special properties — its mechanical strength and electrical conduction — and created a nano-mechanical system that can create FM signals, in effect the world’s smallest FM radio transmitter.

One of my first ‘nanorado’ stories (in 2007 and predating the existence of this blog) focused on carbon nanotubes and a Zettl Group (Alex Zettl) project at the University of California at Berkeley (from the Zettl Group’s Nanotube Radio: Supplementary materials webpage),

We have constructed a fully functional, fully integrated radio receiver, orders-of-magnitude smaller than any previous radio, from a single carbon nanotube. The single nanotube serves, at once, as all major components of a radio: antenna, tuner, amplifier, and demodulator. Moreover, the antenna and tuner are implemented in a radically different manner than traditional radios, receiving signals via high frequency mechanical vibrations of the nanotube rather than through traditional electrical means. We have already used the nanotube radio to receive and play music from FM radio transmissions such as Layla by Eric Clapton (Derek and the Dominos) and the Beach Boy’s Good Vibrations. The nanotube radio’s extremely small size could enable radical new applications such as radio controlled devices small enough to exist in the human bloodstream, or simply smaller, cheaper, and more efficient wireless devices such as cellular phones.

The group features four songs transmitted via their carbon nanotube radio (from the ‘supplementary materials’ webpage),

A high resolution transmission electron microscope allows us to observe the nanotube radio in action. We have recorded four videos from the electron microscope of the nanotube radio playing four different songs. At the beginning of each video, the nanotube radio is tuned to a different frequency than that of the transmitted radio signal. Thus, the nanotube does not vibrate, and only static noise can be heard. As the radio is brought into tune with the transmitted signal, the nanotube begins to vibrate, which blurs its image in the video, and at the same time, the music becomes audible. The four songs are Good Vibrations by the Beach Boys, Largo from the opera Xerxes by Handel (this was the first song ever transmitted using radio), Layla by Eric Clapton (Derek & the Dominos), and the Main Title from Star Wars by John Williams.

Good Vibrations (Quicktime, 8.06 MB)
Layla (Quicktime, 6.13 MB)
Largo (Quicktime, 8.73 MB)
Star Wars (Quicktime, 8.68 MB)

‘Layla’ is quite scrtachy and barely audible but it is there, if you care to listen to this 2007 carbon nanotube radio project. Now in 2013 we have a graphene radio receiver and this graphene radio project is intended to achieve some of the goals as the carbon nanotube radio project,. From the Nov. 17, 2013 University of Columbia news release on newswise and also on EurekAlert),

“This work is significant in that it demonstrates an application of graphene that cannot be achieved using conventional materials,” Hone says. “And it’s an important first step in advancing wireless signal processing and designing ultrathin, efficient cell phones. Our devices are much smaller than any other sources of radio signals, and can be put on the same chip that’s used for data processing.”

Graphene, a single atomic layer of carbon, is the strongest material known to man, and also has electrical properties superior to the silicon used to make the chips found in modern electronics. The combination of these properties makes graphene an ideal material for nanoelectromechanical systems (NEMS), which are scaled-down versions of the microelectromechanical systems (MEMS) used widely for sensing of vibration and acceleration. For example, Hone explains, MEMS sensors figure out how your smartphone or tablet is tilted to rotate the screen.

In this new study, the team took advantage of graphene’s mechanical ‘stretchability’ to tune the output frequency of their custom oscillator, creating a nanomechanical version of an electronic component known as a voltage controlled oscillator (VCO). With a VCO, explains Hone, it is easy to generate a frequency-modulated (FM) signal, exactly what is used for FM radio broadcasting. The team built a graphene NEMS whose frequency was about 100 megahertz, which lies right in the middle of the FM radio band (87.7 to 108 MHz). They used low-frequency musical signals (both pure tones and songs from an iPhone) to modulate the 100 MHz carrier signal from the graphene, and then retrieved the musical signals again using an ordinary FM radio receiver.

“This device is by far the smallest system that can create such FM signals,” says Hone.

While graphene NEMS will not be used to replace conventional radio transmitters, they have many applications in wireless signal processing. Explains Shepard, “Due to the continuous shrinking of electrical circuits known as ‘Moore’s Law’, today’s cell phones have more computing power than systems that used to occupy entire rooms. However, some types of devices, particularly those involved in creating and processing radio-frequency signals, are much harder to miniaturize. These ‘off-chip’ components take up a lot of space and electrical power. In addition, most of these components cannot be easily tuned in frequency, requiring multiple copies to cover the range of frequencies used for wireless communication.”

Unfortunately I haven’t seen any audio files for this ‘graphene radio’ but here’s a link to and a citation for the 2013 paper ,

Graphene mechanical oscillators with tunable frequency by Changyao Chen, Sunwoo Lee, Vikram V. Deshpande, Gwan-Hyoung Lee, Michael Lekas, Kenneth Shepard, & James Hone. Nature Nanotechnology (2013) doi:10.1038/nnano.2013.232 Published online 17 November 2013

The paper is behind a paywall.

* ‘Wolrd’s’ in headline corrected to ‘World’s’ on July 29, 2015.