MIT’s scientists have developed a laser system which resulted in them being able to transmit quiet audio messages into an individual’s ear from several feet away. The transmitted signal targeted toward one individual is designed in a way that it would be impossible for anyone else nearby to hear the transmission.
Using the photoacoustic effect, a condition in which water vapor in the air can absorb light and transfer it into sound waves, researchers were able to transmit quiet audio messages toward the ear of another person. They used a laser beam which transmitted the sound at 60 decibels, which is approximately equal to the volume of background music or the noise level of a restaurant conversation, MIT Technology Review described in a news release. With this technique, they managed to target a person and send quiet audio messages which traveled 2.5 meters (8.2 feet).
“We have demonstrated that an eye-safe laser will heat the water molecules in the air, via the well-known photoacoustic effect, to create a local sound,” Ryan Sullenberger, a researcher who worked on the project, told Digital Trends. “We have also leveraged the special behaviors that occur at the speed of sound to help us amplify and localize the sound.”
They also utilized a second technique which helped modulate the laser beam to encode a message and resulted in a clearer, whispering sound. The laser beam can be used for various purposes, including beam music, recorded speech and other tones which reach conversational volume heard only by one person. The study describing the system which can transmit quiet audio messages to individuals was published in the journal Optics Letters.
“This can work even in relatively dry conditions because there is almost always a little water in the air, especially around people,” team leader Charles M. Wynn said in a press release.
Future plans of the research team include increasing the range of the lasers which can transmit quiet audio messages directed toward a targeted person. More importantly, the communication transmission wouldn’t require additional equipment. That said, this technique could be used for various purposes, including spying and military purposes. Nevertheless, using it for spying purposes may raise questions about the security of the conversations.
“We are [next] hoping to make measurements at longer ranges [of around] 100 to 500 meters, outside, to better understand issues that might occur outside of a controlled laboratory setting,” Sullenberger told Digital Trends. “We are currently working on patenting the technology and would love to engage with interested parties.”