Acoustic Macroscopic Rigid Body Levitation by Responsive Boundary Hologram

Abstract

Propagated acoustic waves, which generate radiation pressure, exert a non-contact force on a remote object. By suitably designing the wave field, remote tweezers are produced that stably levitate particles in the air without any mechanical contact forces. Recent works have revealed that holographic traps can levitate particles even with a single-sided wave source. However, the levitatable objects in the previous studies were limited to particles smaller than the wavelength, or flat parts placed near a rigid wall. Here, we achieve a stable levitation of a macroscopic rigid body by a holographic design of acoustic field without any dynamic control. The levitator models the acoustic radiation force and torque applied to a rigid body by discretising the body's surface, as well as the acoustic wave sources, and optimizes the acoustic field on the body surface to achieve the Lyapunov stability so that the field can properly respond to the fluctuation of the body position and rotation. In an experiment, a 40 kHz (8.5 mm wavelength) ultrasonic phased array levitated a polystyrene sphere and a regular octahedron with a size of ~50 mm located 200 mm away from acoustic elements in the air. This method not only expands the variety of levitatable objects but also contributes to microscopic contexts, such as in-vivo micromachines, since shorter-wavelength ultrasound than the size of target objects can be used to achieve higher controllability and stability.

17 pages, 4 figures

References in corpus (4)

• Global Optimization by Basin-Hopping and the Lowest Energy Structures of Lennard-Jones Clusters Containing up to 110 Atoms
• Observation of a single-beam gradient force acoustical trap for elastic particles: acoustical tweezers
• Metamaterial bricks and quantization of meta-surfaces
• Three-dimensional Mid-air Acoustic Manipulation by Ultrasonic Phased Arrays

Cited by in corpus (7)

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• Acoustic radiation torque on a particle in a fluid: an angular spectrum based compact expression
• OptiTrap: Optimal Trap Trajectories for Acoustic Levitation Displays
• Shaping contactless forces through anomalous acoustic scattering
• Dynamics of an acoustically trapped sphere in beating sound waves
• Airborne Ultrasound Focusing Aperture with Binary Amplitude Mask Over Planar Ultrasound Emissions
• Spatial Sound Modulation through Manual Reconfiguration of Phased Plate