Chinese researchers from the Beijing Institute of Technology have created a microphone that, unlike traditional ones, picks up light rather than air vibrations.
It is noted, that the innovative microphone captures light from barely noticeable surface vibrations. The technology of this so-called “visual microphone” is based on how surfaces respond to sound waves, using these subtle vibrations to produce sound.
The development makes it possible to listen in conditions, where conventional microphones are ineffective, such as when communicating through glass or when monitoring sound in isolated rooms, without the need for direct sound transmission.
“Our method makes it easier and cheaper to use light to capture sound, and allows it to be used when traditional microphones are ineffective. As long as light can be transmitted, direct sound transmission is not necessary”, — explains the lead researcher Xu-Zhi Yao.
Previous attempts to play sound, using light relied on sophisticated and expensive equipment, such as lasers or high-speed cameras. However, сhinese researchers decided to take a different approach. Their system uses a technology called single-pixel imaging, which eliminates the need for a camera with a sensor with millions of pixels. Instead, it uses a single photodetector and structured light patterns generated by a spatial light modulator.
The method is based on directing controlled light at an object and recording the smallest changes in reflected brightness, that occur as a result of the object’s vibrations in response to nearby sounds. These small changes in intensity are detected and converted into an audio signal using computational algorithms. This not only makes this technology easier and cheaper, but also widely available.
“Combining single-pixel imaging with Fourier-based localization techniques allowed us to achieve high-quality sound detection using simpler equipment and at a lower cost. Our system allows us to detect sounds using everyday objects, such as paper cards and leaves, in natural light and does not require the vibrating surface to reflect light in a certain way”, — he emphasized Xu-Zhi Yao.
To demonstrate the capabilities of the system, the researchers tested common materials, including a paper card and a piece of paper, by placing them half a meter away from the speakers that played a voice that voiced arrays of numbers and musical excerpts. The video microphone successfully recovered clear and intelligible audio, especially when using a paper card. Low-frequency sounds were recorded with noticeable accuracy, while higher frequencies showed some distortion — a limitation that the team was able to partially compensate for using signal processing techniques.
This device is also efficient in data processing. It operates at a speed of 4 MB per second, making it suitable for long or continuous recording and practical for storing or transferring data over the Internet.
According to the developers, their device can be used in a large number of professional fields. Potential applications: in environments with a large number of obstacles, for environmental monitoring, non-invasive medical monitoring, advanced industrial diagnostics.
However, as noted by Xu-Ji Yao, this technology currently exists only in the laboratory and can be used in special circumstances where conventional microphones are ineffective. The developers are currently working on increasing the sensitivity and creating a more portable version, as well as extending the range of the system to detect sound over long distances.
The researchers claim the potential of their microphone is far beyond laboratory research From detecting heartbeats and pulses at a distance to assisting in search and rescue operations where microphones cannot be used directly. At the moment, the system is a new way of “listening” with light, opening up opportunities for communication and monitoring in conditions previously inaccessible to conventional microphones.
Source: TechSpot
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