Large-scale airborne holographic acoustic tweezers for synthesizing acoustic fields and particle manipulation

The airborne holographic acoustic tweezers (AHAT) enable dynamic particle manipulation in three dimensions. One of the key technology is precise control of acoustic field over a large range. Traditional methods can only support limited array size which is a big obstacle in applications. This study proposes a large-scale and phase-precise AHAT system. The system is designed with four opposing arrays, comprising a total of 2304 transducer elements. Each element can be individually controlled by emitting a sinusoidal waveform, and the waveform can adjust the phase within the range of 0-360°, with a high phase resolution of 0.18° (π/1024). The operating frequency in air is set at 40 kHz, ensuring that the inter-channel synchronization error is within 45 ns and the phase error of <0.7°. This system enables the precise synthesis of various acoustic fields, including single-beam patterns such as focus, twin trap, and vortex, as well as complex patterns like letters, Chinese characters and butterfly contours. Expanded polystyrene particles with a diameter of approximately 1 mm can be accurately trapped, levitated, and moved along arbitrarily designed trajectories with an observable minimum translation resolution of 0.1 mm (approximately 1/85 wavelength in air) and a time interval of 1 ms between adjacent scanning beams for trapping. The proposed AHAT provides powerful performance for synthesizing acoustic fields and particle manipulation.