Future phones and laptops could have speakers made of carbon nanotubes

For the past year, researchers at Tsinghua University in Beijing have been listening to music on a laptop through a pair of unusual earphones. Although the earphones look ordinary, they do not contain the typical metal coil speaker found in…

For the past year, researchers at Tsinghua University in Beijing have been listening to music on a laptop through a pair of unusual earphones. Although the earphones look ordinary, they do not contain the typical metal coil speaker found in most earphones, but rather a chip made of many string-like carbon nanotube (CNT) yarns with grooves etched in them. Because they are easy to fabricate, operate on 60 mW of power, and provide clear sound quality, the CNT-based chips could be used as components in a wide variety of speakers, including those found in cell phones and laptops.

“The CNT thermoacoustic chip is silicon-based, vibration-free, thin, and magnetic-free,” Yang Wei of Tsinghua University told Phys.org. “It introduces CNT-based nanotechnology into the conventional semiconductor industry. This breakthrough will greatly lower the cost and thus promote the commercialization of nanotechnology. More functionalized devices can be integrated into the thermoacoustic chip, as it is based on a silicon wafer. The CNT speaker can work for a long time thanks to its vibration-free characteristic. The small thickness allows it to meet the demand of device miniaturization. The disadvantage is the low efficiency, as indicated by the sensitivity. But the power consumption of the CNT earphone is acceptable for consumer electronics.”

In their paper published in a recent issue of Nano Letters, the researchers explain that the CNT speakers operate completely differently than conventional speakers. Most loudspeakers produce sounds by the mechanical vibration of a physical material, such as metal, paper, or plastic, which then causes surrounding air particles to vibrate. In contrast, the CNT speakers produce sounds due to an alternating current that periodically heats the CNT yarn array, which creates temperature waves in the surrounding air. The thermal expansion and contraction of the surrounding air generates sound. Despite the differences between these two methods of sound production, the sound from the CNT speakers is essentially the same as that generated by mechanical vibration.
Thermoacoustic effects were known about as far back as 1917, when physicists H.D. Arnold and I.B. Crandall, working at the Research Laboratory of the American Telephone and Telegraph Co. and Western Electric Company, Inc., which later became Bell Labs, observed that feeding an electric current into a thin conductor could produce sounds and act as a thermophone.

Enlarge

An illustration (left) and image (right) of a CNT thermoacoustic chip. Credit: Yang Wei, et al. ©2013 American Chemical Society
However, there was no significant progress on thermoacoustic effects until 2008, when a team of researchers from China, including some of the authors of the current paper, fabricated a thermoacoustic loudspeaker made of a piece of aligned CNT film. The researchers found that using the CNT material in place of a conventional conductor can greatly amplify the thermoacoustic effect due to the CNT film’s ultrasmall heat capacity per unit area. In this way, the nanoscale properties of CNT films have made the old thermophone concept practical.
In the current paper, the physicists replaced the aligned multiwalled CNT film with multiwalled CNT thin yarn arrays, which have a high mechanical strength and fast thermal response similar to the film. The CNT yarn arrays were suspended across a series of grooves that were patterned on a silicon wafer, and silver electrodes were pasted on the sides of each chip. The scientists found that the sound pressure level is highly dependent on the groove depth, which here ranged from 5 to 200 ?m, with deeper grooves providing higher sound pressure levels.
This video is not supported by your browser at this time.
Demonstration of sound produced by the CNT thermoacoustic earphone. The song is “Welcome to Beijing,” which was popular during the 2008 Olympics. Because the earphone is used in the ear, the sound is weak and difficult to record, so the researchers picked the earphone up and put it very close to the microphone of the camera at the beginning of the video. Video credit: Credit: Yang Wei, et al.The researchers also determined that, according to temperature wave theory, a substrate or other object that is within one thermal wavelength of the array could possibly cause heat loss and suppress the sound. But as long as the substrate is at least one thermal wavelength away from the array, it does not interfere with sound production.
The size of each thermoacoustic chip is 9.5 mm x 9.5 mm, about the size of a fingernail. A single chip can replace the conventional coil speaker in an earphone, with the thermoacoustic chip having the advantage of being much thinner than the coil. Conventional earphone casing usually has small holes on the backside to release pressure generated by the vibrating coil. However, these holes are unnecessary for the thermoacoustic earphone, since there is no vibrational component, and the researchers found that sealing these holes decreases sound leakage, especially at low frequencies.
The thermoacoustic earphone at this stage has an efficiency of 48 dB/mW, which is not as efficient as a conventional earphone, which has a value of about 100 dB/mW. However, as the physicists mentioned, the power consumption of 60 mW is suitable for practical devices.
The researchers demonstrated that the thermoacoustic chip can be assembled into an integrated circuit and powered by a USB. Since the chip involves a silicon wafer, the scientists could package the chip into standard semiconductor casing, which can be easily assembled into PCB board by soldering. In the future, it may be possible to integrate additional features such as memory devices and music players.
The researchers also demonstrated a 4-inch chip array, consisting of 69 chips on one silicon wafer. Larger thermoacoustic speakers could have different applications, which may include long-range acoustic devices and underwater acoustic communication.
“We have proven that a CNT thermoacoustic chip is suitable to be applied in consumer electronics, but there is still a lot of work to be done to commercialize this technology,” Yang Wei said. “We will make efforts to optimize the device design and acoustic design and further reduce the cost. More attention from industry will be helpful for the technology promotion, as there is no specialized IC to drive the thermoacoustic speakers, and the CNT earphone is still incompatible with the conventional audio output.”

Explore further:

Carbon nanotube logic device operates on subnanowatt power

More information: Yang Wei, et al. “Thermoacoustic Chips with Carbon Nanotube Thin Yarn Arrays.” Nano Letters. DOI: 10.1021/nl402408

Journal reference:

Nano Letters

view popular

5 /5 (1 vote)

© 2013 Phys.org. All rights reserved.

Related Stories

Carbon nanotube logic device operates on subnanowatt power

Sep 23, 2013

(Phys.org) —Researchers have demonstrated a new carbon nanotube (CNT)-based logic device that consumes just 0.1 nanowatts (nW) in its static ON and OFF states, representing the lowest reported value by …

First success in real time observation of process of solubilization of CNT by polymer

Feb 26, 2013

NIMS researchers have succeeded for the first time in the world in real-time analysis of the “polymer wrapping” process by which polymers (polymers of molecules) wrap around single-walled carbon nanotubes, which are a next-generation …

Tiny Music Player Made from Wire Bridge (w/ Video)

Nov 04, 2009

(PhysOrg.com) — In 2008, scientists built a loudspeaker made of carbon nanotubes that produced sound and music based on the thermoacoustic effect. Now, a different team of scientists has built a loudspeaker …

Folding batteries increases their areal energy density by up to 14 times

Oct 08, 2013

(Phys.org) —By folding a paper-based Li-ion battery in a Miura-ori pattern (similar to how some maps are folded), scientists have shown that the battery exhibits a 14x increase in areal energy density and …

New techniques stretch carbon nanotubes, make stronger composites

Oct 15, 2012

(Phys.org)—Researchers from North Carolina State University have developed new techniques for stretching carbon nanotubes (CNT) and using them to create carbon composites that can be used as stronger, lighter …

Strengthening fragile forests of carbon nanotubes for new MEMS applications

Oct 26, 2012

Microelectromechanical systems (MEMS) are incredibly tiny devices, often built on the scale of millionths of a meter. Conventional MEMS structures tend to be made out of silicon-based materials familiar to the micro-electronics …

Recommended for you

Carbon’s new champion: Theorists calculate atom-thick carbyne chains may be strongest material ever

13 minutes ago

(Phys.org) —Carbyne will be the strongest of a new class of microscopic materials if and when anyone can make it in bulk.

Folding batteries increases their areal energy density by up to 14 times

Oct 08, 2013

(Phys.org) —By folding a paper-based Li-ion battery in a Miura-ori pattern (similar to how some maps are folded), scientists have shown that the battery exhibits a 14x increase in areal energy density and …

New microfluidic approach for the directed assembly of functional materials

Oct 07, 2013

(Phys.org) —Researchers from the University of Illinois at Urbana-Champaign have developed a new approach with applications in materials development for energy capture and storage and for optoelectronic …

New biomimetic material to develop nanosensors

Oct 03, 2013

The new features of this biomimetic material will allow us to develop multiple nanometer-sized chemical sensors over the same substrate by electron beam lithography, as a result, multifunctional biochips …

Researchers apply transmission electron microscopy through unique graphene liquid cell (w/ Video)

Oct 03, 2013

(Phys.org) —Autumn is usually not such a great time for big special effects movies as the summer blockbusters have faded and those for the holiday season have not yet opened. Fall is more often the time …

Graphene-based discs ensure safe storage

Oct 03, 2013

(Phys.org) —Swinburne University of Technology researchers have shown the potential of a new material for transforming secure optical information storage.

User comments : 0

More news stories

Carbon’s new champion: Theorists calculate atom-thick carbyne chains may be strongest material ever

(Phys.org) —Carbyne will be the strongest of a new class of microscopic materials if and when anyone can make it in bulk.

A tiny, time-released treatment

Omid Farokhzad’s vision of medicine’s future sounds a lot like science fiction. He sees medicine scaled down, with vanishingly small nanoparticles playing a big role, delivering drug doses measured in molecules …

Nanoparticles: A simpler route to hollow carbon spheres

Hollow carbon nanoparticles are strong, conduct electricity well and have a remarkably large surface area. They show promise in applications such as water filtration, hydrogen storage and battery electrodes—but …

Folding batteries increases their areal energy density by up to 14 times

(Phys.org) —By folding a paper-based Li-ion battery in a Miura-ori pattern (similar to how some maps are folded), scientists have shown that the battery exhibits a 14x increase in areal energy density and …

‘White graphene’ halts rust in high temps

(Phys.org) —Atomically thin sheets of hexagonal boron nitride (h-BN) have the handy benefit of protecting what’s underneath from oxidizing even at very high temperatures, Rice University researchers have …

A strange lonely planet found without a star

(Phys.org) —An international team of astronomers has discovered an exotic young planet that is not orbiting a star. This free-floating planet, dubbed PSO J318.5-22, is just 80 light-years away from Earth …

Team develops compact, high-power terahertz source at room temperature

Terahertz (THz) radiation—radiation in the wavelength range of 30 to 300 microns—is gaining attention due to its applications in security screening, medical and industrial imaging, agricultural inspection, astronomical …

Spinning-disk microscope offers window into the center of a cell

A new method of imaging cells is allowing scientists to see tiny structures inside the ‘control centre’ of the cell for the first time.

Single gene mutation linked to diverse neurological disorders

A research team, headed by Theodore Friedmann, MD, professor of pediatrics at the University of California, San Diego School of Medicine, says a gene mutation that causes a rare but devastating neurological disorder known …

NASA spacecraft zips by Earth en route to Jupiter

NASA’s Jupiter-bound spacecraft has swung by Earth in a flyby designed to boost its speed for the long trip toward the outer solar system.