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Abstract Similar to optical spin-orbit interactions (SOIs), acoustic SOIs are anticipated to offer fresh perspectives and capabilities for acoustic manipulation beyond conventional scalar degrees of freedom. However, the acoustic extrinsic SOIs caused by particular properties of the medium were seldom explored. Here, the acoustic extrinsic SOI is observed in a double spiral acoustic beam (DSAB), as evidenced by the rotation of the spatial intensity pattern along the propagation axis. The interaction of the acoustic plane wave with the well-designed artificial flat structure generates two non-paraxial focused acoustic vortices (NFAVs) with different spin angular momentums. The coaxial coupling between them leads to acoustic spin-controlled orbital rotation (SOR). Theoretical formulations, supported by numerical simulations and experimental results, are provided to demonstrate the validity of acoustic SOR. Our work provides new perspectives and capabilities for understanding sound processing, and may open an avenue for the development of spin-orbit acoustics.

Radially self-accelerating acoustic beams (RSABs) with rotating field distributions enable three-dimensional manipulation of particles. Nevertheless, the generation of desired RSABs is always a challenge. In this study, we derive a general form for the RSABs with a rotating acoustic field. We investigate the correlation between acoustic intensity and phase distribution of the RSAB in-depth via theoretical calculations. Artificial structure plates carved with Archimedean spiral slits are designed to produce two-component RSABs (TRSABs). It is found that the number of main lobes, rotational speed, and initial position of the TRSAB can be modulated by simply changing the number of arms, initial radius, and relative angle of the two sets of spirals. The experimental and numerical demonstrations confirm the ability of artificial structure plates to generate TRSABs. Finally, simulations are performed to calculate the acoustic radiation force on Rayleigh polydimethylsiloxane particles in a TRSAB. The work presented here could greatly benefit acoustic particle three-dimensional trapping and manipulation.

We design an asymmetric transmission system (ATS) with two flat acoustic metasurfaces (AMs) to yield bidirectional asymmetric acoustic focusing (BAAF). The acoustic waves could be focused on both sides of the ATS with different focal lengths and intensities. To achieve high intensity energy concentration, the accelerating acoustic beams are selected to realize the BAAF. The working bandwidth of the BAAF based on our ATS could reach ∼ 0.4 kHz. It is found that by adjusting the distance between two flat AMs, the focal length and intensity of the bidirectional focusing could easily be modulated. Because the distance between two flat AMs is large enough, the BAAF even could be converted into a unidirectional acoustic focusing. The proposed BAAF may find applications in non-destructive evaluation, biomedical imaging and medical diagnosis. [ABSTRACT FROM AUTHOR]