Resonating Drums Made Out of Graphene Could Lead to Better Sensors

A new type of electrically-controlled mechanical resonator could detect ultra-weak signals

2 min read
An illustration styled to look like a semiconductor micrograph. A sheet of hexagons with an electrode on either side is stretched over a circular depression.
Illustration: Roberto De Alba

Researchers at Cornell University have fabricated graphene membranes into micrometer-scale drums that can be stimulated by a voltage to transfer one type of mechanical vibration into another. The researchers believe this capability can lead to new applications in telecommunications where graphene-based mechanical resonators could be used as frequency mixers, which are often used, for example, to modulate carrier waves with signals.

In research described in the journal Nature Nanotechnology, the researchers found that graphene could produce three different frequencies of vibration in circular drums made of graphene. Each frequency, or mode, of vibration was coupled to the other and could exchange energy.

“We’ve shown that there is an effect that will convert energy from one mechanical mode to another mechanical mode,” said Roberto De Alba, a graduate student who led the research, in a press release. “It allows us to either damp out or amplify vibrations of one mode by activating the other mode.”

The graphene drums the Cornell researchers fabricated ranged in size from 5 to 20 micrometers and each drum could be triggered to begin vibrating by either an alternating electric field or by the thermal vibration of the atoms that made them up.

The researchers have decided to call these drums “phonon cavities” because they function like the optical cavities that are used to produce laser light and can also convert laser energy into mechanical energy. Phonons are vibrations in a crystal lattice that carry energy, so you could say that phonons are quasi-particles that make up vibrations just as photons are particles that make up light.

Four years ago, we saw how researchers the National Institute of Standards and Technology (NIST) and the University of Maryland were able to treat graphene like a drumhead and give it a band gap. Then two years later a team of scientists at the TU Delft’s Kavli Institute of Nanoscience in the Netherlands demonstrated that using this drumhead principal for graphene could lead to new types of sensors for mobile phones.

It is in this field of sensors that the Cornell researchers see an opportunity for their graphene-enabled phonon cavities.  When cooled to absolute zero these devices could be used to detect miniscule quantum signals.

De Alba added: “And because graphene is only a single atom thick, it has such a low mass that it makes a very good force sensor, gas sensor or pressure sensor. It could be used in research labs to study ultra-weak forces.”

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A Circuit to Boost Battery Life

Digital low-dropout voltage regulators will save time, money, and power

11 min read
Image of a battery held sideways by pliers on each side.
Edmon de Haro

YOU'VE PROBABLY PLAYED hundreds, maybe thousands, of videos on your smartphone. But have you ever thought about what happens when you press “play”?

The instant you touch that little triangle, many things happen at once. In microseconds, idle compute cores on your phone's processor spring to life. As they do so, their voltages and clock frequencies shoot up to ensure that the video decompresses and displays without delay. Meanwhile, other cores, running tasks in the background, throttle down. Charge surges into the active cores' millions of transistors and slows to a trickle in the newly idled ones.

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