Ultrasonic metamaterial at MHz frequencies using microstructured glass.

Acoustic metamaterials enhance traditional material properties, providing opportunities to shape sound fields in applications ranging from biomedical imaging and clinical therapy to nondestructive testing. However, at the megahertz frequency range, only a few metamaterial architectures exist. They are often highly attenuating or difficult to manufacture and generally provide limited control. Here, we introduce a megahertz-frequency ultrasonic metamaterial based on laser-engraved glass. By structuring metavoxels with different engraving patterns, we define an anisotropic metamaterial exhibiting local variations in the sound speed of up to 20% compared to unstructured glass and losses 100× lower than in comparable three-dimensional-printed metamaterials. We use this metamaterial to define a library of standard elements that can be modularly combined to 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.