Scattering from Multiple Compliant Tube Gratings in a Viscoelastic Layer

摘要

From previous studies of scattering from multiple gratings of resonant compliant tubes in water the excitation of noncompliant, antisymmetric structural modes by nearfield evanescent waves was found to severely degrade the reflectivity of closely packed gratings in the bandwidth of excitation of the compliant symmetric modes. Also, transmission resonances due to the spring mass spring configuration of the two gratings separated by a fluid mass diminished low frequency performance. In this paper, encapsulating the gratings in a low stiffness elastomer is shown experimentally to have a minimum effect on single and widely separated gratings with respect to fluid but enhances the performance of closely packed gratings. Comparison of insertion loss performance with a high stiffness encapsulant indicates dramatic differences in bandwidth and frequency response. A mathematical model will be discussed and compared with the experimental data.