World’s Smallest Acoustic Speaker Demonstrated at Aerospace

Diagram of a field effect transistor with a single suspended carbon nanotube. (Illustration: Reprinted with permission from ACS Nano. Full citation at end of article.)

Scientists at Aerospace and USC have demonstrated the world’s smallest speaker, consisting of an individual suspended carbon nanotube. The speaker is approximately 2 microns long and has a diameter of only 0.001 microns. For comparison, the average human hair has a diameter of about 70 microns. According to Dr. Adam Bushmaker, a senior member of the technical staff at Aerospace, “This is 10 billion times smaller than any previous electroacoustic system studied.”

Bushmaker is leading an Aerospace Independent Research and Development project studying carbon nanotube field effect transistors (FETs), and had the assistance of intern Blake Mason last summer.

Currently, silicon FETs are used in many different digital electronic devices, but carbon nanotubes are being considered as a possible replacement for the silicon, and could provide a number of improvements, such as better switching speed and efficiency. Aerospace collaborates with professor Stephen Cronin’s research group in the electrical engineering department at USC, which fabricates the devices and sends them to Aerospace to study.

While studying the FETs, the team realized that by applying an acoustic frequency AC voltage to the single suspended nanotube, the nanotube and surrounding air molecules heat up, creating a sound wave that can be detected with a commercial microphone.

These findings give important insight into thermal properties of nanoelectronic devices, and heat transport at the nanoscale in general. This research was published in a paper in American Chemical Society Nano in May 2015.


Illustration reprinted with permission:
Thermoacoustic Transduction in Individual Suspended Carbon Nanotubes
Blake J. Mason, Shun-Wen Chang, Jihan Chen, Stephen B. Cronin, and Adam W. Bushmaker
ACS Nano 2015 9 (5), 5372-5376
DOI: 10.1021/acsnano.5b01119
Copyright 2015 American Chemical Society