Credit: Xu-Ri Yao, Beijing Institute of Technology
Physicists have developed a cheap and simple device which can transform ordinary objects into microphones.
The technology uses light to detect minute vibrations caused by sound waves on the surfaces of objects and decodes this visual information into audible signals.
Before now, these “visual microphones” have relied on expensive lasers or high-speed cameras. They also required the vibrating surface to be made of mirrors and materials called “retroreflectors”, which reflect light back to where it came from with minimal scattering. These materials are often used on high-visibility clothing, street signs and bicycles.
The simpler and less expensive new approach can pick up and decode sound from the surfaces of leaves and pieces of paper.
“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,” says lead researcher Xu-Ri Yao from Beijing Institute of Technology in China. “As long as there is a way for light to pass through, sound transmission isn’t necessary.”
While the technology only exists in the laboratory at the moment, Yao says it could be used in special scenarios where traditional microphones fail to work.
“The new technology could potentially change the way we record and monitor sound, bringing new opportunities to many fields, such as environmental monitoring, security and industrial diagnostics,” says Yao.
“For example, it could make it possible to talk to someone stuck in a closed-off space like a room or a vehicle.”
Laboratory tests revealed the visual microphone can reconstruct clear and intelligible audio, including Chinese and English pronunciations of the numbers “1, 2, 3, 4” and a segment from Für Elise by Ludwig van Beethoven.
The technology relies on a computational imaging approach known as “single-pixel imaging”. It captures images using a single light detector, or pixel, rather than the millions used in a traditional camera sensor.
Sound waves cause tiny vibrations on the surface of the object, which in turn triggers subtle changes in the light intensity captured by the single-pixel detector.
Algorithms then use these optical intensity measurements to reconstruct how the object is moving. They then decode this information into audible sound.
“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,” says Yao.
Conveniently, it also generates a volume of data small enough to be easily downloaded to storage devices or uploaded to the internet.
“We aim to expand the system into other vibration measurement applications, including human pulse and heart rate detection, leveraging its multifunctional information sensing capabilities,” says Yao.
The technology is presented in a study in the journal Optics Express.