Breakthrough technology creates ‘audible enclaves’ that can be heard by one person in a crowd, allowing for targeted audio without disturbing others.
A team of researchers at Penn State has developed a technology that can create pockets of sound isolated from their surroundings, allowing for targeted audio without disturbing others. This innovation uses ‘ultrasound waves’ and acoustic metasurfaces to bend the sound waves around obstacles, creating ‘audible enclaves’ that can be heard by one person in a crowd.
The Challenge of Containing Sound Waves
Sound waves diffract or spread out as they travel, especially at lower frequencies, making it difficult to contain them. To address this issue, the researchers use two beams of ‘ultrasound waves,’ which vibrate at a frequency way above human hearing, serving as a ‘carrier for audible sound.’ This allows the sound waves to remain silent to human ears while traveling and only become audible when they reach their target.
Ultrasound waves are high-frequency sound waves with frequencies above human hearing, typically ranging from 20 kHz to several gigahertz.
They are used in medical imaging to create detailed images of internal organs and tissues without the need for surgery.
In medicine, ultrasound waves are employed for diagnostic purposes, such as detecting gallstones or monitoring fetal development during pregnancy.
The technology uses a transducer to convert electrical energy into sound waves that penetrate tissues and bounce back, providing real-time images.
Bending Sound Waves with Acoustic Metasurfaces
Another key innovation is transforming the ultrasound beams into something we can hear. By projecting each beam at slightly different frequencies, the researchers create a new sound wave equal to the difference between the beams, generating a sound wave at 500 Hz, which is comfortably in the midrange of human hearing.
Testing the System
To test the system, the researchers 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. They confirmed that sound was not audible except at the point of intersection, creating an ‘enclave.’ The current distance range for creating these enclaves is about three feet away at a moderate 60 decibels, roughly the volume of a conversation.
Potential Applications
The researchers envision various applications for this technology, including providing sound to certain groups without disturbing others in public spaces like libraries or museums. It could also be used for noise-cancellation in entire areas, offering peace and quiet in noise-polluted cities.
Noise cancellation technology uses destructive interference to reduce unwanted sound.
It works by inverting the noise signal and combining it with the original sound, resulting in a quieter environment.
This technology is commonly used in headphones, earbuds, and hearing aids.
Active noise control systems use microphones to detect ambient noise, which is then inverted and played back through speakers or drivers.
Noise cancellation has various applications, including reducing background 'noise' in recording studios and improving audio quality in public spaces.
