New Device Offers Elevated Cat-Like 'Hearing'

A nano-sized "drumhead" can receive and transmit signals across radio frequency at a range the human ear cannot naturally hear.

Cats are widely regarded to have some of the best hearing abilities in all the animal kingdom. Cats' hearing range can often surpass those of dogs, and felines can typically determine pitch and tones much better than their human counterparts -- especially the 'big cats'. A team of researchers have engineered a new hearing device inspired by cats that can greatly improve what the human ear can hear. 

The atomically thin "drumhead" comes in at just tens of trillions of times smaller in volume and 100,000 times thinner than the human eardrum. The researchers at Case Western Reserve University hope to one day use the devices to create the next generation of low-power communications with a significantly improved range. 

"Sensing and communication are keys to a connected world," said associate professor of electrical engineering and computer science Philip Feng. Feng served as the corresponding author on a paper about the work published on March 30 in the journal Science Advances. "In recent decades, we have been connected with highly miniaturized devices and systems, and we have been pursuing ever-shrinking sizes for those devices."

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The biggest struggle for the team, according to Feng, was getting a broader range of signal on an incredibly small device. 

"In the end, we need transducers that can handle signals without losing or compromising information at both the 'signal ceiling' (the highest level of an undistorted signal) and the 'noise floor' (the lowest detectable level)," Feng said.

The human eardrum can typically pick up anything between 60 to 100dB in a range from 10Hz to 10kHz. Once outside of this range, the human ears quickly stop picking up the sound. However, the common house cat can pick up even higher ranges. 

In order to duplicate this effect, the researchers needed to construct the 'eardrums' on an atomic level. They used a combination of nanofabrication and micromanipulation to suspend atomic layers over a silicon wafer. The team then made electrical contacts to the devices. Even for all its tiny size, the resonators show frequency "tunability," according to the researchers," which means that tones can be manipulated by stretching the drumhead membranes through electrostatic forces. It would be similar to tuning a kettle drum in an orchestra, Feng noted. 

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"Not only having a surprisingly large dynamic range with such tiny volume and mass, but they are also energy-efficient and very 'quiet' devices," Feng said, "We 'listen' to them very carefully and 'talk' to them very gently."

At this time, the project wasn't tailored to a specific device or usage in mind on the current market. The team wanted to test exactly how far down they could minimize the technology while simultaneously improving the quality. The improved transducers might be developed more over time, but for now, Feng said he's pleased with crafting one of the world's smallest scale audio device.

"What we've done here is to show that some ultimately miniaturized, atomically thin electromechanical drumhead resonators can offer remarkably broad dynamic range, up to ~110dB, at radio frequencies (RF) up to over 120MHz," Feng said. "These dynamic ranges at RF are comparable to the broad dynamic range of human hearing capability in the audio bands."

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