It involves exciting the moisture in the air around a listener’s ear using a laser from several meters away.
In a phenomenon known as the photoacoustic effect, the excited water vapor absorbs the light and vibrates into an audible frequency. Yes, sounds like something from a spy movie. But, it’s real and works too.
If you’re worried about how safe it is to send a laser beam into someone’s ear, it’s perfectly safe.
According to the MIT team, the system is quite safe. “It’s the first system that uses lasers that are fully safe for the eyes and skin to localize an audible signal to a particular person in any setting.”
Channeling sound into a narrow field is not a new technology. While some of them use speakers to intensify the sound waves, others depend on channeling ultrasound within a small area. The downside of this method is the listener must be close to the source to hear the message.
With the high frequencies associated with this laser technology, you can reduce loss over long distances and carry a message much further.
The research team experimented with two methods of sound transmission with the laser. With the first, they varied the laser’s amplitude through a modulator in a continuous wave.
Rather than use a modulator for the second method, the researchers used a mirror to create a dynamic photoacoustic spectroscopy. Simply put, it involves sweeping the laser back and forth over the speed of sound with the mirror. This enabled the researchers to jiggle more water particles, which leads to a louder wave.
According to optomechanical engineer Ryan M. Sullenberger, there are trade-offs between the two methods. “The traditional photoacoustics method provides sound with higher fidelity, whereas the laser sweeping provides sound with louder audio,” said the onto-mechanical engineer.
The potential applications of this technology are endless. Aside from the obvious military use (of warning spies of impending dangers), the tech is also useful for advertising. Ultimately, this laser beam technology is suitable for anywhere ambient noise is an issue.
Although the laser tech is still at an early developmental stage, we hope it’ll be available commercially soon.
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