philip lelyveld The world of entertainment technology

Amazing New Technology Can ‘Bend’ Sounds Into Your Ears Only

... We use two ultrasound beams at different frequencies that are completely silent on their own. But when they intersect in space, nonlinear effects cause them to generate a new sound wave at an audible frequency that would be heard only in that specific region. ...

Crucially, we designed ultrasonic beams that can bend on their own. Normally, sound waves travel in straight lines unless something blocks or reflects them. However, by using acoustic metasurfaces – specialized materials that manipulate sound waves – we can shape ultrasound beams to bend as they travel.

Similar to how an optical lens bends light, acoustic metasurfaces change the shape of the path of sound waves. By precisely controlling the phase of the ultrasound waves, we create curved sound paths that can navigate around obstacles and meet at a specific target location.

The key phenomenon at play is what's called difference frequency generation. When two ultrasonic beams of slightly different frequencies, such as 40 kHz and 39.5 kHz, overlap, they create a new sound wave at the difference between their frequencies – in this case 0.5 kHz, or 500 Hz, which is well within the human hearing range.

Sound can be heard only where the beams cross. Outside of that intersection, the ultrasound waves remain silent. ...

This isn't something that's going to be on the shelf in the immediate future. For instance, challenges remain for our technology. Nonlinear distortion can affect sound quality. And power efficiency is another issue  ...

See the full story here: https://www.sciencealert.com/amazing-new-technology-can-bend-sounds-into-your-ears-only?utm_source=substack&utm_medium=email