Steerable Radiation Forces with Frequency-Detuned Acoustic Metasurfaces

Abstract: We demonstrate that acoustic waves can induce controlled translation and rotation of macroscopic objects through small, but deliberate, detuning of the driving wave frequency. When an object is patterned with a suitably designed acoustic metasurface, small changes in the incident frequency $ω\pm δω$ are converted into directional radiation forces and torques, enabling steerable motion even for objects much larger than the acoustic wavelength. We present the concept of a force-optimal metasurface topology and show that it enables fully reversible forces in real time: the object is moved in one direction for positively detuned incident frequency $ω+δω$ and in the opposite direction for negatively detuned frequency $ω-δω$, where $ω=22.5 \textrm{ kHz}$ and $δω=2.5 \textrm{ kHz}$ for a proof of concept at inaudible frequencies. This mechanism is demonstrated experimentally at ultrasonic frequencies with 3D-printed metasurfaces. The proposed concept is scalable across frequencies and materials, offering a building block for realizing complex, remote-controlled, dynamical behaviors that can be programmed by reconfiguring material surface patterns.