New York: An ultrasonic microphone has been developed to help humans communicate in the manner bats and dolphins do through ultrasonic waves.

The microphone has been built by scientists of University of California Berkeley physicists, who used graphene to build lightweight ultrasonic loudspeakers and microphones, enabling people to mimic and gauge the distance and speed of objects around them.

"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 researcher Alex Zettl.

The study appears online in the Proceedings of the National Academy of Sciences. 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 nine to 200 kilohertz. The grapheme loudspeakers and microphones operate from well below 20 hertz to over 500 kilohertz.

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 more 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.

"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," Zettl said.