Diodes act as one-way filters for electric current, protecting delicate devices from sudden reversals in flow. Sound waves can also travel easily in both directions along a given path, like electricity does, so acoustic devices could block wrong-way reflections. Alas, acoustic diodes do not yet exist.
Jian-chun Cheng of Nanjing University in China and his colleagues have now described a possible way to build one consisting of a sandwich of acoustic layers. Key to the structure would be a layer of nonlinear material that, by changing the frequency spectrum of incoming sound waves, could act as a filter. The researchers suggest that acoustic diodes could be useful in improving ultrasound devices such as those used to break up kidney stones.
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Acoustic science: A sonic one-way street. Nature 461, 318 (2009). https://doi.org/10.1038/461318e
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DOI: https://doi.org/10.1038/461318e