The short version
- A University of Pennsylvania team built a chip that forces sound waves vibrating about a billion times a second to travel along a single boundary.
- The waves turned 120-degree corners without scattering and, at a four-way junction, left only by the directions the pattern allowed.
- It is a physics demonstration, and the hoped-for uses in phones and quantum computers are the team’s projection, not a product.
Sound does not have to be audible to be useful. Phones already filter their radio signals with tiny vibrating crystals, and some quantum computers store information in sound near 1 GHz, about 50,000 times higher than human hearing reaches. In Physical Review Applied on November 2, Yue Jiang, A. T. Charlie Johnson and colleagues at the University of Pennsylvania, the University of Texas at Austin and Westlake University in China report a way to route that sound on a chip without losing it at bends.
The chip is a thin aluminum nitride membrane, a material already common in phone parts, etched with star-shaped holes arranged one way on one side of a boundary and another way on the other. The pattern forces the wave to run along the interface. The design adapts theory that Penn physicists Charles Kane and Eugene Mele developed for electrons about two decades ago. “The same ideas hold for light waves, and they also hold for sound waves,” Johnson said. Imaged with a microwave microscope, the waves turned 120-degree corners without scattering and split only where the pattern allowed at a four-way junction. Getting there took years and several failed designs.
The team’s next target is 6 to 10 GHz, the range phone makers are moving to.
