Italian scientists Giulio Casati and Stefano Lepri think they’ve found the mathematical principles required for a sonic one-way mirror. Though purely theoretical, the pair’s work predicts that it is possible to construct a material that would prevent sound from passing through on one side, but allow it from the other. The practical upshot is that were you to sit in a room with walls made of this material, you could hear everything outside the room but no one could hear you.
Lepri and Casait uses “nonlinear properties” to achieve this feat. Looking at previous research done with diodes that distribute heat asymmetrically, the pair found that it is possible to apply similar principles to sound. Discovery News writes:
To direct sound waves, the researchers propose alternating layers of linear and strongly nonlinear materials asymmetrically. With the right formation, when a sound wave enters from one side, it will essentially get caught in the material and then be redirected. This is because the frequency is shifting in two different directions, Casati explained.
Though they believe that such material is physically possible, that does not mean that constructing such a material is feasible. But even if their work is never functionally realized, Casati and Lepri have shown that the math, at least, can make sound do amazing things.
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