4. Outlook

The metafluids whose specific engineering we have just presented have unique properties in terms of acoustic refractive index. The latter can be controlled and modulated over a wide range, from positive to negative, including zero values.

However, the direct application of these materials is not immediate. On the one hand, they are soft solids, easily deformable and subject to fluidification under relatively low mechanical stress, which makes them difficult to shape; on the other, they are extraordinarily absorbent. Perhaps this aspect is both the most limiting for making them into components, but the most interesting in the short term, not really for a negative index, but because they are more effective than traditional absorbent materials for thicknesses typically ten times smaller (patent presented in the documentation section of this article).

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