Now physicists at Nanjing University in China have come up with a method to clean up pictures made from high-pitched acoustic waves. Think of a one-way mirror—but for sound. Their system would let the pressure waves that carry sound pass through if they come from the left. But it reflects waves hitting it from the right.
No known natural material can do this. But a metamaterial—a clever arrangement of thin brass plates bent into tiny maze-like shapes—has just the right properties.
The metamaterial can even be tailored to steer the outgoing sound and to filter out all sounds except those of a particular frequency. That’s just what you want for a sharp ultrasound picture. The work appears in Applied Physics Letters. [Yong Li et al., Unidirectional acoustic transmission through a prism with near-zero refractive index]
The researchers are now building a prototype of their design. Maybe one day, the only thing fuzzy about those first fetal photos will be the way they make you feel inside.
—Wayt Gibbs
