干涉相消降低水下目标的背向散射

Researchers have a growing interest in the reduction of acoustic scattering cross-section, which may find its special application in military. The absorbing material is usually adopted to attenuate the sound energy, resulting the reduction of scattering cross-section of the targets. However, in the low-frequency range, the thickness of the absorbing material should be largely increased to attain a relatively high absorption. Because the backward scattered waves are always used to detect the targets, we first propose a mechanism of the coupling among multiple local resonances to control the phase of reflected waves, which exhibits a nearly linear dependence on frequency over a wide band, and then the reduction of the scattering cross-section of underwater targets is achieved through the destructive interference of scattered waves. Our proposed mechanism of the coupling among multiple local resonances overcomes the limits of the current mechanism for acoustic wavefront manipulation in air, which cannot be easily extended from the background medium air to water. In addition, the corresponding size of local resonance is far smaller than the wavelength, which means our proposed method may find some applications in the reduction of the scattering cross-section of underwater targets in the low-frequency range.

声散射截面的降低因其在军事上有着特殊的应用得到了研究者们的广泛关注。常规方式是通过吸收声波的能量达到降低目标散射截面的目的，但在低频段却需要极厚的吸收层。考虑到声学探测绝大部分是基于回波检测的方式，本项目提出了一种多局域共振耦合的物理机制调控反射波的相位，使之在宽带范围内线性依赖于频率, 并在此基础上利用干涉相消的声波阵面操控方式宽带实现水下目标声散射截面的降低。本项目中多局域共振耦合的物理机制克服了目前声波阵面操控方式难以在水中应用的缺点。 此外，所设计的局域共振结构的尺寸远小于声波的波长，这使得我们所提的这种方法在低频段降低水下目标声散射截面方面有着重要的应用前景。

声散射截面的降低因其在军事上有着特殊的应用得到了研究者们的广泛关注。常规方式是通过吸收声波的能量达到降低目标散射截面的目的，但在低频段却需要极厚的吸收层，并且存在耐压问题。考虑到声学探测绝大部分是基于回波检测的方式，本项目提出了一种多局域共振耦合的物理机制调控反射波的相位，使之在宽带范围内线性依赖于频率, 并在此基础上利用干涉相消的声波阵面操控方式宽带实现水下目标声散射截面的降低。 该项目的研究表明利用多个小孔之间的耦合，可以实现反共振，其可以作为一个调控反射相位的新的自由度。利用该特性，我们设计水下宽带的2bit 编码的超表面。 理论、仿真以及实验这三方面的研究表明在14.3kHz~40.5kHz频率范围内超表面的使用会使声散射截面减小10dB以上，该研究有望用于鱼雷隐身。