Coupled Focused Acoustic Vortices Generated by Degenerated Artificial Plates for Acoustic Coded Communication

Acoustic vortices (AVs) show great significance in acoustic communication. However, the lack of confidentiality and the cross-talks in communications based on traditional AVs remain problems. Here, a degenerated centrosymmetric circular hole plate (DCHP) is designed to generate coupled focused acoustic vortices (CFAVs) with pure orbital angular momentums (OAMs) in both air and water. When an acoustic plane wave transmits through DCHP, two focused acoustic vortices (FAVs) with opposite topological charges are produced simultaneously, and the coupling between them results in a focused acoustic petal beam (FAPB). The OAM of the CFAV can be simply modulated by the angular interval of the adjacent holes on DCHP and the CFAV can be focused at any distances by adjusting the positions of holes. The DCHPs are demonstrated to be able to generate FAPBs numerically and experimentally. Furthermore, 8 FAPBs with different OAMs are set as 8 bases to represent 8 bits of ASCII binary code, and the information encoding and decoding for acoustic communication are realized in water using them. The proposed DCHP provides a convenient method to achieve CFAVs, which may be helpful to enhance the security, reduce the false information, and increase the information capacity in acoustic communication.