We are discussing a device for transmitting directional sound. It uses special "acoustic lenses", and the principle of its operation resembles the optical system of a camera.
On the Diversity of Acoustic Metamaterials
With different , whose acoustic properties depend on the internal structure, engineers and scientists have been working for a long time. For example, in 2015, physicists managed to on a 3D printer, an "acoustic diode" - it is a cylindrical channel that allows air to pass through, but completely reflects sound coming from only one direction.
Also this year, American engineers have developed a special ring that blocks up to 94% of noise. Its working principle is based on when the energy of two interfering waves is distributed asymmetrically. We talked about this device in more detail in one of our .
In early August, it became known about another audio development. Engineers from the University of Sussex a prototype of a device that, using two metamaterials (βacoustic lensesβ) and a video camera, allows you to focus sound on a specific person. The device was called the "sound projector".
How it works
There are two "acoustic lenses" in front of the sound source (audio speaker). These lenses are a 3D printed plastic plate with a large number of holes. What these "lenses" look like can be seen in on the first page (you need to open the full text of the document).
Each aperture of the "audio lens" has a unique shape - for example, bumps on the inner walls. When sound passes through these holes, it changes its phase. Since the distance between the two "acoustic lenses" can be varied using electric motors, it becomes possible to direct the sound to one point. The process is similar to focusing the optics of a camera.
Focusing is automatic. For this, a video camera (approximately $12) and a special software algorithm are used. It remembers the person's face in the video and tracks its movement in the frame. Next, the system calculates the relative distance and changes the focal length of the projector accordingly.
Where will they be used
Developers that in the future the system may replace headphones - devices will broadcast sound from a distance directly into the ears of users. Another potential area of ββapplication is museums and exhibitions. Visitors will be able to listen to the lectures of electronic guides and not disturb others. Of course, it is impossible not to mention the advertising sphere - it will be possible to inform store visitors about the conditions of personal promotions.
But engineers still have to solve a number of problems - so far, the audio projector is only capable of operating in a limited frequency range. In particular, it only plays notes from G (G) to D (D) in the third and seventh octaves.
Residents of Hacker News also potential problems in the legal field. In particular, it will be necessary to regulate who and under what conditions can receive personalized advertising messages. Otherwise, chaos will begin in the premises of shopping centers. As the developers of the βaudio projectorβ say, this issue will be partially solved by the face recognition system. It will determine whether the person has given their consent to receive such advertisements or not.
In any case, the practical implementation of the technology "in the field" is out of the question.
Other Ways to Transmit Directional Sound
At the beginning of the year, engineers from MIT developed a technology for transmitting directional sound using a laser with a wavelength of 1900 nm. It is harmless to the human retina. The sound is transmitted using the so-called when water vapor in the atmosphere absorbs light energy. As a result, a local increase in pressure occurs at a point in space. A person is able to perceive the arising air vibrations with the βnaked earβ.
Similar technology is being developed by specialists from the US Department of Defense. Using a femtosecond laser, they create a ball of plasma in the air, and cause sound vibrations in it using another nanolaser. True, in this way you can only generate a roar and an unpleasant noise, similar to the howl of a siren.
So far, these technologies have not gone beyond the laboratories, but their counterparts are beginning to "penetrate" into user devices. Last year, Noveto already an audio speaker that creates "virtual headphones" on a person's head using ultrasonic waves. Therefore, the mass distribution of directional sound technology is only a matter of time.
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Source: habr.com