We demonstrate the free rotation of an acoustic metasurface driven entirely by a nondissipative acoustic radiation torque, resulting from the transfer of orbital angular momentum from sound to matter. This direct observation of mechanical angular recoil establishes a quantitative link between the incident vortex field and the induced torque, with measured angular velocities, which are supported by analytical modeling. Recent advances in the design of arbitrary acoustic metasurfaces allow this rotational acoustomechanics to be extended to translational degrees of freedom, providing a simple and versatile route for noncontact acoustic actuation along multiple mechanical degrees of freedom. As such, this work contributes to the field of acoustic micromanipulation, fluid-structure interactions, and sound-driven mechanical systems.

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• Acoustic forces
• Acoustic metamaterials
• Metasurfaces