Researchers from South Korea’s POSTECH University have developed a speaker, which they call “MiPAL”, to direct sound to a specific person without it reaching their neighbor.
It's worth noting that a regular loudspeaker emits sound in all directions. MiPAL, however, works differently. Its front features a metasurface lens that focuses ultrasonic waves into a narrow beam. The audible sound is then incorporated into this beam and transformed into a directed signal in the air.
At the end of the device are ultra-flexible elements that absorb structural vibrations and prevent lateral sound leakage.
The fundamental problem engineers address is the natural propagation of sound in all directions. Unlike light, which travels in a straight line, sound waves scatter and leak into surrounding spaces. It's worth noting that classic parametric arrays with hundreds of emitters (inducers) are expensive and complex, while simpler designs suffer from parasitic vibrations that cause lateral sound leakage.
However, POSTECH's innovation transcends these limitations. On the front surface of the transducer, a metasurface acts as a lens, converting ultrasonic waves into a narrow, audible beam. On the back, flexible meta elements suppress parasitic vibrations, preventing sound leakage to the sides. All these components are integrated into a single unit that can be manufactured using 3D printing technology.
The device operates in a frequency range of 500 Hz to 10 kHz. Testing was conducted in conditions mimicking an airplane cabin, where one "passenger" could clearly hear music and speech, while their neighbor could barely hear anything. All components are 3D printed and can be easily adapted to the required task.
Professor Chunsuk Ro said, "We have combined supermaterials and ultrasound into one system."
This technology could be used in airplanes, trains, and museums, where sound is audible only in the desired area. The innovation is still undergoing further testing.
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