Bats use ultrasonic sounds to navigate for a reason. These very high frequency sounds are more long-range and easier to focus in one direction than those audible to humans — qualities that are useful for both bats and communication technology.

Developing microphones and speakers that can process ultrasound has been a challenge in the field of communication technology research, but a new graphene-based design allows them to do so extremely efficiently, according to a paper published in the journal Proceedings of the National Academy of Sciences. This advance represents one of the early steps toward commercially-viable graphene-based devices.

"There's a lot of talk about using graphene in electronics and small nanoscale devices, but they're all a ways away," the study's senior author, Alex Zettl of the University of California, Berkeley said in a statement. "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."

Both speakers and microphones use a vibrating layer of material called a diaphragm to produce or detect sound. Usually, the diaphragm is made of paper or plastic, but researchers tested out a new design that uses the one-atom thick material known as graphene as the diaphragm. 

They found that using graphene as the diaphragm material made it possible for the speakers and microphones to operate across an incredibly broad range of frequencies, including ultrasound. The benefits of using graphene are in part due to the fact that it is extremely thin and lightweight.

"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," lead study author Qin Zhou of the University of California, Berkeley said in a statement.

Graphene also dramatically improves the efficiency of the devices. Diaphragms made of graphene are able to convert more that 99 percent of the energy used to drive the device into sound. Conventional speakers, for comparison, convert only about eight percent of the energy they use into sound.

In addition to its potential to create higher quality and more efficient speakers and microphones, this design for a graphene-based diaphragm could allow communications devices such as cell phones to become more bat-like by utilizing ultrasound.

"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," Zettl said in a statement. "Until now, we have not had good wideband ultrasound transmitters or receivers. These new devices are a technology opportunity."


Photo: Bill Tyne | Flickr

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