Ultrasonic metamaterial at MHz frequencies using microstructured glass

Acoustic metamaterials enhance traditional material properties through microstructure engineering, providing new opportunities to shape sound fields in applications ranging from biomedical imaging, clinical therapy to non-destructive testing. However, at the MHz frequency ranges, only a few metamaterial architectures exist. They are often highly attenuating or difficult to manufacture, and generally provide limited 3D control over sound propagation. Here, we introduce a MHz-frequency ultrasonic metamaterial based on laser-engraved glass. By structuring meta-voxels with different engraving patterns, we define a fully-3D, anisotropic metamaterial exhibiting local variations in the sound speed of up to 20% compared to unstructured glass, and losses 100x lower than in comparable 3D printed metamaterials. We use this metamaterial to define a library of standard elements that can be modularly combined to create and shape complex-patterned ultrasonic fields. Our experiments are supported by a theoretical model, which provides additional insights into the microstructural origin of the metamaterial behavior and opens the door to designing tailored ultrasound fields and responses.