Underwater acoustic properties of a fluid-loaded and elastically coated plate with periodically attached distributed inhomogeneities

An analytical model is developed for evaluating the underwater acoustic radiation, reflection and absorption from an elastically coated plate with periodically attached distributed inhomogeneities under the excitation of a line force or a plane-harmonic wave. A typical example of the distributed inhomogeneity is a signal conditioning plate (SCP), which can be inserted between the coating and a hydrophone to raise the surface impedance and reduce signal degradation. Traditional way of fully attaching a signal conditioning plate (SCP) outside the coated plate has limited effect of reducing the signal degradation and also makes the structure unnecessarily heavy. In practice, the detection of incoming sound is usually carried out by an array of hydrophone sensors. One option to increase the SNR of the hydrophones is to place them in front of an array of SCPs. This work focuses on studying how the attached periodic SCPs will affect the aforementioned acoustical properties, in an effort to further enhance the local reflection/signal gain near each SCP without sacrificing the radiation and absorption performance of the structure heavily for stealth purposes, and meanwhile to reduce the weight of the structure. Through analytical modelling and numerical experiment, results show that the introduced periodically attached SCPs can greatly enhance the sound reflection near the SCPs at most frequencies, compared with the reflection from the coated plate without the SCPs. Meanwhile, the absorption coefficient and radiated sound power can be slightly affected by the SCPs depending on the properties of the selected coating and the SCPs. Recommendations are also given for the application of SCPs for underwater sensing purposes.