This study performs the quantitative analysis and comparison to acoustic signal characteristics of Large yellow croaker （Pseudosciaena crocea） at two different ages. The sounds were recorded from the fishes in a net-cage. Two exponential oscillation functions are built to fit the acoustic signal of the fishes. The signal characteristic of the oscillation frequency and attenuation coefficient was described quantitatively. Simulation curves of the function could fit well acoustic signals. Both the average oscillation frequency and attenuation coefficient of the fitted signals from the 13-15-month-old fishes are lower than those from the 7-8-month-old fishes. The results suggest that the oscillation frdquency and attenuation coefficient of the acoustic signal flmction may be relevant to the physical process of sound production and age characteristics of Large yellow croaker. This study may be valuable for the acoustic application to the artificial culture of the species.
In this paper, a broadband unidirectional acoustic transmission based on inhomogeneous metamaterial shell with radial piecewise linear sound speed distribution is proposed. Acoustic rays in the case of external and internal incidences from the shell are deduced by geometric acoustic theory to show the unidirectional acoustic propagation in the polar coordinate system. Numerical full-wave simulations reveal that one way transmission has the intensity-independent unidirectional transmission feature over a wide frequency range. Finally, a scheme for realization of the proposed one way transmission model is designed and simulated by using multilayered materials, suggesting its potential applications in noise control, acoustic rectifiers,wave absorption and related fields.
In this paper, superwide-angle acoustic propagations above the critical angles of the Snell law in liquid–solid superlattice are investigated. Incident waves above the critical angles of the Snell law usually inevitably induce total reflection.However, incident waves with big oblique angles through the liquid–solid superlattice will produce a superwide angle transmission in a certain frequency range so that total reflection does not occur. Together with the simulation by finite element analysis, theoretical analysis by using transfer matrix method suggests the Bragg scattering of the Lamb waves as the physical mechanism of acoustic wave super-propagation far beyond the critical angle. Incident angle, filling fraction,and material thickness have significant influences on propagation. Superwide-angle propagation phenomenon may have potential applications in nondestructive evaluation of layered structures and controlling of energy flux.
