Any phononic crystal is also a diffraction grating

What is it about?

Diffraction gratings are useful optical components that can disperse the colors of light. They are employed in spectrographs that measure the spectrum of light. The same can be performed with acoustic waves. We show here that a phononic crystal made of a periodic array of steel rods immersed in water acts as a diffraction grating. Because transmission can be canceled in frequency band gaps, diffraction efficiency can be optimized.

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Why is it important?

Diffraction gratings made by digging trenches in a plate can readily be made. Such periodic structures are, however, quite inefficient as the diffraction efficiency can hardly be optimized. Furthermore, there is always some transmission through the plate. Both disadvantages can be overcome with the phononic crystal grating.