Tag Archives: acoustics

Acoustics and carbon nanotubes

Mikhail Koslov from the University of Texas at Dallas has written a Dec. 18, 2014 Nanowerk Spotlight article about his research into carbon nanotubes and their acoustic properties,

Carbon nanotube assemblies enabled design of a hybrid thermo-electromagnetic sound transducer with unique sound generation features that are not available from conventional diaphragm and thermo-acoustic speakers.

EM image of multi-walled carbon nanotube sheet used for thermo-electromagnetic sound transducer. (Image: Mikhail Kozlov, University of Texas at Dallas)

EM image of multi-walled carbon nanotube sheet used for thermo-electromagnetic sound transducer. (Image: Mikhail Kozlov, University of Texas at Dallas)

Kozlov goes on to explain his work in more detail,

… a hybrid thermo-electromagnetic sound transducer (TEMST) [was] fabricated using highly porous multi-walled carbon nanotube sheet that was placed in the proximity of a permanent magnet. Upon electrical AC excitation, thermal response of the material is combined with diaphragm-like sheet oscillations induced by the electromagnetic action of the Lorentz force.

Unlike conventional diaphragm loudspeaker, acoustic spectrum of the TEMST device consists of a superposition of TA and EM responses that can be altered by applied bias voltage. Variation of bias voltage changes spectral intensity and spatial distribution of generated sound.

In particular, propagation direction of the sound can be reversed by switching bias polarity that somewhat resembles voltage-controlled acoustic reflection. Such uncommon behavior was explained by interference of the two contributions being beneficial for diverse sound management applications.

It was found also that amplitude of first TEMST harmonic changes a lot with applied magnetic field, while the second one remains almost field independent. This unusual feature is convenient for magnetic sensing similar to that enabled by Lorentz force magnetometers. The magnetic field detection in the TEMST device is facilitated by the audio sensing system.

Here’s a link to and a citation for the paper,

Thermo-electromagnetic sound transducer based on carbon nanotube sheet by Mikhail Kozlov and Jiyoung Oh. J. Appl. Phys. 116, 094301 (2014); http://dx.doi.org/10.1063/1.4894143 Published online Sept. 2, 2014

This paper is behind a paywall.

Nano oscillation and music

It’s one of those breakthroughs that sounds exciting but is a little hard to understand if you’re not working in that field … still … Scientists at the National Institute of Nanotechnology in Canada have solved a problem that was preventing more widespread application of nano-electro-mechanical systems (NEMS). They’ve developed a technique to control vibration/oscillation that could be compared to ‘unringing a bell’. The ability to stop the vibration of a nano cantilever in less than a nanosecond opens up new possibilities in information and communications technology (ICT) and other fields.  There’s a more detailed article about the work here at Nanotech Wire or here at Nanowerk. The research is described in the Nov. 2, 2008 online Nature Nanotechnology article, “Time-domain control of ultrahigh-frequency nanomechanical systems,” the abstract is here. The article itself is behind a paywall.

Chinese researchers are investigating ways to exploit the acoustic properties of carbon nanotubes which are usually lauded for their strength and their electrical properties. Shoushan Fan and colleagues from Tsinghua University in Beijing and Beijing Normal University created sheets of carbon nanotubes and sent audio frequency currents through them as if they were music speakers. However, unlike a standard speaker which creates sound by emitting a vibration, the scientists did not detect any vibrations from the ‘carbon nanotube’ speakers. The researchers believe that the carbon nanotube speakers work as thermoacoustic devices using temperature and pressure oscillation in the surrounding air to emit sound. For more including a video clip of the carbon nanotube speakers in action and a brief mention of 19th century thermoacoustic devices, go here.

One more reminder about Visible Verse, the video poetry event on November 6, 2008 at Pacific Cinematheque (1131 Howe St., Vancouver) at 7:30 pm. Tickets and more info. here.