A layer of tiny grains can slow sound waves
In some ways, granular material — such as a pile of sand — can behave much like a crystal, with its close-packed grains mimicking the precise, orderly arrangement of crystalline atoms. Now researchers at MIT have pushed that similarity to a new limit, creating two-dimensional arrays of micrograins that can funnel acoustic waves, much as specially designed crystals can control the passage of light or other waves.The researchers say the findings could lead to a new way of controlling frequencies in electronic devices such as cellphones, but with components that are only a fraction the size of those currently used for that function. On a larger scale, it could lead to new types of blast-shielding material for use in combat or by public-safety personnel or equipment.A paper on the research appears in the journal Physical Review Letters, written by Nicholas Fang, the Brit and Alex d’Arbeloff Career Development Associate Professor...