Design and Fabrication of Negative-Refractive-Index Metamaterial Unit Cells for Near-Megahertz Enhanced Acoustic Transmission in Biomedical Ultrasound Applications

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Acoustic metamaterials with negative index of refraction offer great potential for improving resolution and signal transmission in biomedical ultrasound. Their potential has remained unrealized, however, for the lack of a fabrication technology that can create metamaterials compatible with biomedical imaging and operating at frequencies near 1 MHz. The authors report the simulation, fabrication, and characterization of integrated Helmholtz and membrane resonators with characteristic lengths less than 1 mm, produced by silicon-based clean-room microfabrication. Their work finally realizes a negative-index acoustic metamaterial that can be applied in ultrasound imaging and therapeutics.