Acoustic scattering of underwater targets has great prospects for detection, recognition and identification of various underwater targets, which is of great significance in ocean and sea navigation and exploration. In recent years, underwater acoustic scattering research has largely focused on shifting from static to dynamic modeling to improve the detection and identification of complex and special targets. This has helped lay a firm foundation for the practical application of the unique features of acoustic scattering. Various elastic waves and geometric echoes in shells and plates produce a number of interesting sound-scattering features that have been explored for underwater applications, such as underwater metasurface.
Different structures in different forms and states have been used to control elastic/sound waves. For example, the propagation of sound waves has been controlled using different methods like acoustic switcher and high-transmission metasurface. Recently, designing acoustic barcodes using unique acoustic scattering features have attracted significant research attention for applications deemed of great importance for underwater positioning and navigation, such as passive acoustic identification tags.
To date, significant research efforts have been devoted to constructive acoustic barcodes for different underwater acoustic scattering applications using different approaches. For example, underwater structures exhibiting sound-scattering characteristics have been designed for acoustic marking based on path differences. This includes those generated by periodic structures distributed on flat plates and radially layered polymethyl methacrylate materials. With the advances in fabrication technologies, other methods like optical-based methods have been developed for fabricating underwater markers.
Inspired by the previous findings and research progress, Assistant Professor Fulin Zhou, Professor Jun Fan, Professor Bin Wang, Dr. Yanling Zhou and Ms. Jinfeng Huang from Shanghai Jiao Tong University developed a new design for different acoustic structures, such as discontinuous ribbed structures, for polydirectional time-domain acoustic coding. The design of these structures was based on the echo sound path difference as well as the use of elastic and geometric features in the frequency and time domain. The corresponding and effective coding methods for these structures was also proposed and verified. Their research work is currently published in the journal, Applied Acoustics.
The authors reported the effectiveness of the echo sound path differences of the discontinuous ribbed structures in facilitating the time-domain coding. A frequency-domain technique based on azimuthal transformation was proposed for geometric Bragg scattering characteristics. The transformation of the Bragg fringes into vertical lines and the relationship between their abscissas and the Bragg scattering characteristics were observed. This coding method was used to design spiral grooved and periodically ribbed structures in the middle- and high-frequency bands.
Low-frequency coding was achieved by exploiting the resonance characteristics of subsonic Rayleigh waves. It was applied to elastic polymer spheres, allowing the combination of single and multiple spheres for acoustic coding in the low-frequency band by reducing their mutual scattering strength. The decoding process was mainly influenced by the physical formulation of the Bragg scattering.
In summary, a new method for performing acoustic coding in the frequency and time domains using underwater target acoustic scattering characteristics was reported. This method allowed acoustic coding of the frequency and time domain in both low- and high-frequency bands. The advantages of the proposed coding method include its flexibility, low cost, and feasibility. In a statement to Advances in Engineering, the authors explained that their findings provided useful insights that would expand the practical application scope of underwater acoustics by contributing to designing advanced coding methods for different structures.
Zhou, F., Fan, J., Wang, B., Zhou, Y., & Huang, J. (2022). Acoustic barcode based on the acoustic scattering characteristics of underwater targets. Applied Acoustics, 189, 108607.