Ultrasonic hearing of bats mimicked by graphene-based technology

Graphene loudspeakers mimic communication of bats

American researchers have created graphene-based loudspeakers and microphones simulating the ultrasonic communication of bats and dolphins.

The device, developed by a team from University of California, Berkely, uses ultrasound pulses to transmit information and gauge distances and speeds of surrounding objects.

Compared to existing ultrasound - sonar - technology, the lightweight graphene-based system offers much better fidelity. Unlike standard radio waves technology, it could also communicate through objects, such as steel.

“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 Alex Zettl, physicist at UC. “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. The diaphragms in the new devices are made of one-atom thick graphene sheets offering 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 theoretically detect sound from 20 hertz up to 20,000 kilohertz, whereas bats hear only in the kilohertz range, from 9 to 200 kilohertz. The graphene loudspeakers and microphones operate from well below 20 hertz to over 500 kilohertz.

“There’s a lot of talk about using graphene in electronics and small nanoscale devices, but they’re all a ways away,” said Zettl. “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.”

The researchers said that graphene, thanks to its minimal thickness and weight, responds well to the different frequencies of an electronic pulse, unlike today’s piezoelectric microphones and speakers.

This comes in handy when using ultrasonic transmitters and receivers to transmit large amounts of information through many different frequency channels simultaneously, or to measure distance, as in sonar applications.

“Because our membrane is so light, it has an extremely wide frequency response and is able to generate sharp pulses and measure distance much more accurately than traditional methods,” Zhou said.

Graphene membranes are also more efficient, converting over 99 per cent of the energy driving the device into sound, whereas today’s conventional loudspeakers and headphones convert only eight per cent into sound.

Zettl anticipates that in the future, communications devices like mobile phones will utilise not only electromagnetic waves but also acoustic or ultrasonic sound, which can be highly directional and long-range.

“Graphene is a magical material; it hits all the sweet spots for a communications device,” he said.

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