(July 8, 2015) University
of California, Berkeley, physicists have used 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.