By Robert Sanders, UC Berkley Media Relations
UC Berkeley physicists have used super-thin sheets of graphene to build lightweight ultrasonic loudspeakers and microphones, enabling people to mimic bats or dolphins’ ability to use sound to communicate and gauge the distance and speed of objects around them.
More practically, the wireless ultrasound devices complement standard radio transmission using electromagnetic waves in areas where radio is impractical, such as underwater, but with far greater fidelity than current ultrasound or sonar devices. They can also be used to communicate through objects, such as steel, that electromagnetic waves can’t penetrate.
“Sea mammals and bats use high-frequency sound for echolocation and communication, but humans just haven’t fully exploited that before, in my opinion, because the technology has not been there,” said UC Berkeley physicist Alex Zettl. “Until now, we have not had good wideband ultrasound transmitters or receivers. These new devices are a technology opportunity.”
Speakers and microphones both use diaphragms, typically made of paper or plastic, that vibrate to produce or detect sound, respectively.
The diaphragms in the new devices are graphene sheets a mere one atom thick that have the right combination of stiffness, strength and light weight to respond to frequencies ranging from subsonic (below 20 hertz) to ultrasonic (above 20 kilohertz).
Humans can hear from 20 hertz up to 20,000 hertz, whereas bats hear only in the kilohertz range, from 9 to 200 kilohertz. The grapheme loudspeakers and microphones operate from well below 20 hertz to over 500 kilohertz.
Graphene consists of carbon atoms laid out in a hexagonal, chicken-wire arrangement, which creates a tough, lightweight sheet with unique electronic properties that have excited the physics world for the past 20 or more years.
“There’s a lot of talk about using graphene in electronics and small nanoscale devices, but they’re all a ways away,” said Zettl, who is a senior scientist at Lawrence Berkeley National Laboratory and a member of the Kavli Energy NanoSciences Institute, operated jointly by UC Berkeley and Berkeley Lab. “The microphone and loudspeaker are some of the closest devices to commercial viability, because we’ve worked out how to make the graphene and mount it, and it’s easy to scale up.”
“A recording of the pipistrelle bat’s ultrasonic chirps, slowed to one-eighth normal speed.” Recording by Qin Zhou/UC Berkeley.
Zettl, UC Berkeley postdoctoral fellow Qin Zhou and colleagues describe their graphene microphone and ultrasonic radio in a paper appearing online this week in the Proceedings of the National Academy of Sciences.
For more information, go to http://news.berkeley.edu/2015/07/06/bats-do-it-dolphins-do-it-now-humans-can-do-it-too/