Forward-looking: Researchers at the Beijing Institute of Technology have developed a microphone that doesn’t detect air vibrations like traditional models. Instead, it captures light reflected from subtle surface movements. This new device – a so-called “visual microphone” – relies on how surfaces respond to sound waves, using those tiny vibrations to reconstruct audible information.
The advance opens up possibilities for listening in environments where conventional microphones struggle – such as communicating through a glass window or monitoring sound in isolated spaces – without the need for direct transmission of sound.
“Our method simplifies and reduces the cost of using light to capture sound while also enabling applications in scenarios where traditional microphones are ineffective, such as conversing through a glass window,” explained Xu-Ri Yao, the lead researcher on the project. “As long as there is a way for light to pass through, sound transmission isn’t necessary.”
Previous attempts to capture sound using light have relied on complicated and expensive equipment, such as lasers or high-speed cameras. The Beijing team took a different approach. Their system uses a technique called single-pixel imaging, which eliminates the need for a camera sensor packed with millions of pixels. Instead, it leverages a single light detector and structured light patterns projected by a spatial light modulator.
In essence, the technique works by projecting manipulated light onto a target and capturing minute shifts in reflected brightness as the object vibrates in response to nearby sounds. These tiny intensity changes are detected and, through computational algorithms, converted back into a sound signal. This approach not only reduces cost and complexity but also makes the technology more accessible.
“Combining single-pixel imaging with Fourier-based localization methods allowed us to achieve high-quality sound detection using simpler equipment and at a lower cost,” Yao said. “Our system enables sound detection using everyday items like paper cards and leaves, under natural lighting conditions, and doesn’t require the vibrating surface to reflect light in a certain way.”
To demonstrate the system’s capabilities, the researchers tested common materials such as a paper card and a leaf, positioning them roughly half a meter from audio sources like speakers playing spoken numbers and musical excerpts. The visual microphone successfully reconstructed clear and intelligible audio, particularly when using the paper card. Lower-frequency sounds were captured with notable accuracy, while higher tones exhibited some distortion – a limitation the team partially mitigated using signal-processing techniques.
The setup is also data-efficient, producing a modest stream of about 4 MB per second, which makes it suitable for long-term or continuous recording and practical for storage or internet transfer.
The researchers envision applications across a wide range of industries. Potential use cases include communication through solid barriers, remote environmental monitoring, non-intrusive medical observation, and advanced industrial diagnostics.
“Currently, this technology still only exists in the laboratory and can be used in special scenarios where traditional microphones fail to work,” noted Yao. The team is now working to improve sensitivity and accuracy, as well as developing a more portable version of the system and extending its range for longer-distance sound detection.
Looking ahead, the researchers see potential well beyond the lab – from detecting heartbeats and pulses at a distance to aiding search-and-rescue operations where microphones cannot be directly deployed. For now, the system represents a new way to “listen” using light, opening possibilities for communication and monitoring in environments previously inaccessible to conventional microphones.