Imagine being able to listen to music or other audio that no one else can hear, without having to wear headphones. Doing so is now possible via so-called “audible enclaves,” which already exist in functional prototype form.
The technology is being developed at The Pennsylvania State University, by a team led by professor of acoustics Yun Jing.
Putting it simply, the system allows projected sound to only be heard by someone standing or sitting in a specific location. People located beside, behind or even in front of that person won’t be able to hear it, unless they trade places with the individual.
Here’s how the setup works …
The sound is emitted in the form of ultrasound waves by two ultrasound transducers, which emit the waves at slightly different frequencies. Positioned directly in front of each transducer is an “acoustic lens” known as a metasurface, which utilizes microstructures to bend the direction of the ultrasound waves passing through them.
As a result, the waves from each transducer follow a curved path, bending outward to either side before bending back in and ultimately intersecting. Each of the waves is inaudible to the human ear if encountered on its own. If someone is located right at the point where the waves intersect, however, their combined signals produce audible sound.
Heyonu Heo
“To test the system, we used a simulated head and torso dummy with microphones inside its ears to mimic what a human being hears at points along the ultrasonic beam trajectory, as well as a third microphone to scan the area of intersection,” says postdoctoral scholar Jia-Xin “Jay” Zhong, first author of the study. “We confirmed that sound was not audible except at the point of intersection, which creates what we call an enclave.”
In its current form, the technology is limited to a transmission distance of about 1 meter (3.3 ft) and a sound level of around 60 decibels, which is normal speaking volume. It is believed that both of those figures could be increased, however, simply by boosting the intensity of the ultrasound waves.
The scientists hope that the system could ultimately find use in settings such as classrooms, vehicle interiors, or virtual/augmented reality setups. A paper on the research was recently published in the journal Proceedings of the National Academy of Sciences.
Source: Penn State