DeviceGuru

A University of California Berkeley research team claims to have created the world’s smallest radio, a fully functional radio receiver built from a single carbon nanotube one ten-thousandth the diameter of a human hair.

The “nanotube radio” implements all of the key components of a radio — antenna, tuner, amplifier, and demodulator — within the single microscopic carbon nanotube. Consequently, the radio is many orders of magnitude smaller than conventional radio receivers.

Evolution of the radio, from 1930s furniture to microscopic nanotube
(Click to enlarge)

Thanks to their micro-miniaturization, nanotube radios could facilitate the insertion of tiny radio-controlled devices into the human bloodstream, or could enable the design of “smaller, cheaper, and more efficient wireless devices such as cellular phones,” according to the team.

At the moment, they’re being used to listen to popular music, though. “We have already used the nanotube radio to receive and play music from FM radio transmissions such as Layla [play clip] by Eric Clapton (Derek and the Dominos) and the Beach Boy’s Good Vibrations [play clip],” the team says.

Technical bits

The Berkeley team’s experimental nanotube radio receives signals in the 40-400 MHz range, using both frequency and amplitude modulation. Unusually, the device’s antenna and tuner receive radio signals via high frequency mechanical vibrations of the nanotube, rather than through traditional electrical means.

Traditional radio receivers consist of four functional elements, as illustrated in the following diagram:

Traditional radio receivers consist of four key components

In contrast, the nanotube radio provides all four key radio receiver components via a single carbon nanotube, according to the project team, as indicated in the diagram below:

The nanotube radio combines all four key receiver components in one carbon nanotube

The team explains, “The entire radio consists of an individual carbon nanotube mounted to an electrode in close proximity to a counter electrode. A direct current (dc) voltage source, such as from a battery, is connected to the electrodes and powers the radio. Important for the radio’s operation, the applied dc bias negatively charges the tip of the nanotube, sensitizing it to oscillating electric fields. Also, both electrodes and nanotube are contained in vacuum, typically below 10-7 Torr.

“Interestingly,” the team adds, “this geometrical configuration is reminiscent of a conventional vacuum tube, and indeed there are some key functional similarities between the two.”

In the case of the nanotube radio, electromagnetic waves cause the carbon nanotube to physically vibrate through their interaction with the tube’s charged tip, according to the project team. Only incoming waves whose frequency matches the nanotube’s “flexural resonance” frequency produce significant mechanical vibration intensity, however. In this manner, specific radio signals can be selected from among the multitude of electromagnetic waves that are continually bombarding us.

In the nanotube radio prototype, the device is “tuned” by applying an electrostatic field to the carbon nanotube, a process that affects the resonant frequency in a manner analogous to tuning a guitar string by adjusting the tension applied to it.

Nanotube radio videos

Here are two videos that offer a glimpse of the nanotube radio in operation, and how it works:

Video showing the nanotube radio in action, taken using a high resolution transmission electron microscope
(Click image to play video)

Simulation showing the electric field surrounding the nanotube radio during radio operation
(Click image to play video)

Further information

Further information is available on the nanotube radio project’s website. A detailed technical paper is available here (PDF download).

[Above images and videos are reproduced courtesy Zettl Research Group, Lawrence Berkeley National Laboratory and University of California at Berkeley.]