Scientists Create Invisible Headphones: Ultrasound-Based Audio Enclave Technology Unveiled

Researchers at the University of Pennsylvania and Lawrence Livermore National Laboratory have developed a technology called audio enclaves — personal, eavesdropping-proof sound areas. No headphones are needed to listen to individual messages. The technology creates local audibility zones that follow a specific person and are intended exclusively for that person.

Image source: University of Pennsylvania

The idea of ​​the development is based on the use of ultrasound as a carrier of sound in the audible range. Ultrasound itself with a frequency above 20 kHz is not perceived by the human ear. However, according to the laws of physics of wave propagation, when two waves with different frequencies intersect, a new wave is formed with a frequency equal to the difference in the original frequencies. This allows the signal frequency to be reduced to the level of audible sound.

The researchers used two ultrasound emitters: one operating at 40 kHz and the other at 39.5 kHz. Where they intersected, a region with a frequency of 500 Hz arose, which is easily discernible by the human ear.

The emitters themselves also had unique properties. Their surface had a lens effect for sound waves, which allowed ultrasound to be directed and bent in space. Thanks to this, the researchers were able to precisely form a personal audio enclave around a person.

Scientists caution that audio enclave technology is still in its early stages of development and will take several years to commercialize. If successful, personal audio addressing could improve security in businesses and law enforcement agencies, and open up new possibilities for consumer applications.

For example, car passengers will be able to listen to different music without headphones, without disturbing the driver. In public places, the technology will allow paying attention to important sounds without increasing the overall level of noise pollution.