Engineers Create Smallest FM Radio Transmitter Using Graphene

Ranjini Raghunath for – Your Universe Online

A team of engineers at Columbia University have created the smallest ever FM radio transmitter using a form of carbon known as graphene. The paper describing the device and its potential was published online on Nov. 17 in the journal Nature Nanotechnology.

Like diamond or graphite, graphene is made up of carbon atoms that are laid out in hexagonal patterns in a layer a million times thinner than a sheet of paper.

The team used graphene to build a key component used in radio broadcasting called voltage controlled oscillator (VCO), which generates frequency-modulated (FM) radio waves.

In typical radio broadcasts, a transmitter generates an alternating current that is converted into radio waves by an antenna or aerial. Information, such as music or speech, is carried by these invisible radio waves. Using an external source of voltage, these waves can be “tuned,” or in other words, their frequency can be tweaked in different ways to carry different types of information.

The Columbia team used the graphene VCO to send and receive audio signals at a frequency of 100 MHz, which falls within the FM radio bandwidth (87.7 to 108 MHz). Both simple and complex music signals (“Gangnam Style!”) were used to tune the VCO’s output. The team also recovered the audio signal using an ordinary FM radio receiver, and found that it “faithfully reproduced” the original signal.

“This device is by far the smallest system that can create such FM signals,” said James Hone, professor of Mechanical Engineering and senior author of the study.

Graphene’s exceptional strength, heat and electrical conductivity and flexibility combined with its tiny size make it the ideal material for making nano-electromechanical systems (NEMS) — like the FM transmitter. NEMS are electronic devices that integrate multiple properties on a single, tiny chip. NEMS are scaled-down versions of micro-electromechanical systems (MEMS) commonly used in sensors, such as ones that detect tilting of the tablet screen, Hone pointed out.

With electronic devices becoming smaller each day, it is becoming increasingly difficult to “miniaturize” components for these devices without taking up a lot of space and electrical power, explained Kenneth Shepherd, Columbia University electrical engineering professor and co-author of the paper.

Previous MEMS-based transmitters made using quartz crystals had bulky sizes which made tuning the frequency difficult. Graphene NEMS, however, can be tuned to very high frequencies without showing mechanical strain on the material structure. They also take up a very small on-chip area.

“It’s an important first step in advancing wireless signal processing and designing ultrathin, efficient cell phones,” Hone said in a statement.

Hone and his colleagues previously demonstrated that graphene is the strongest material known to man – about 200 times stronger than structural steel. Graphene is so strong that “it would take an elephant, balanced on a pencil, to break through a sheet of graphene the thickness of Saran Wrap,” Hone said, in an earlier study.

Graphene is already being touted as the next silicon, with potential applications in creating flexible smartphones, boosting Internet speeds and delivering drugs inside the human body.

While demonstrating the promise of graphene-based NEMS, the current work “opens up new regimes for miniature NEMS-based, large scale electronic circuitry,” the researchers wrote.