Although the ability tends to wane as we get older, the human auditory system is pretty good at filtering out background noise and making a single voice able to be understood above the general hubbub of a crowded room. But electronic devices, such as smartphones, aren't quite as gifted, which is why getting Siri or Google Now to understand you in crowded environments can be an exercise in futility. But now researchers have developed a prototype sensor that’s not only able to figure out the direction of a particular sound, but can also extract it from background noise.
To create the sensor, scientists at Duke University in Durham, North Carolina used a class of materials known as metamaterials, which boast properties not found in nature, and a signal processing technique known as compressive sensing. The disk-shaped device is made of plastic and doesn't have any electronic or moving parts. Rather, it features a honeycomb-like structure and is split into dozens of slices which each feature a unique pattern of cavities of different depths. It is these cavities that distort the sound waves and give the sensor its unique capabilities.
"The cavities behave like sodabottles when you blow across their tops," says Steve Cummer, professor ofelectrical and computer engineering at Duke. "The amount of soda left in thebottle, or the depth of the cavities in our case, affects the pitch of thesound they make, and this changes the incoming sound in a subtle but detectableway."
The sound distortions have specific signatures that relate to thehoneycombed slice it passed over. When the resulting sounds are picked up by amicrophone and processed by a computer, the unique distortions make it possibleto separate noises from one other, even if they were all jumbled together. The sensor,the researchers claim, can even separate simultaneous sounds that originate fromdifferent directions, thanks to the way each sound is distorted.
In tests, three identical sounds were sent from three differentdirections to the sensor prototype. Results showed that it was able todistinguish between these noises with an accuracy of 96.7 percent. The team hopes toscale the 6 in (15 cm) -wide prototype down to a smaller size to allow it to be integrated into various devices. Aside from applications in consumer electronics, its creators say it could also find uses in other areas.
"I think it could be combined with any medical imaging device that useswaves, such as ultrasound, to not only improve current sensing methods, but tocreate entirely new ones," says AbelXie, the study’s lead author. "With the extra information, it should also be possible to improve the sound fidelity and increase functionalities for applications like hearing aids and cochlear implants. One obvious challenge is to make the system physically small. It is challenging, but not impossible, and we are working toward that goal."
The team's paper describing the research was recentlypublished in the Proceedings of the National Academy ofSciences.
Source: Duke University
