基于亥姆霍兹共振的超薄弧形声学超表面地毯斗篷

Ultrathin acoustic metasurface carpet cloaking based on Helmholtz resonances

利用局部相位补偿调制的方式设计了一种超薄的弧形声学超表面地毯隐身斗篷.该斗篷由52个亥姆霍兹空腔共振结构单元组成,且结构单元厚度小于波长的0.2倍.数值模拟结果显示:文中所设计的隐身斗篷在深亚波长范围内隐身效果良好,其工作频宽为5850—7550 Hz.进一步探究声波斜入射时地毯斗篷的工作效果,发现在30°的入射角范围内都具有良好的隐身效果.此外,利用余弦相似度(cosine similarity,CSI)函数精确量化分析了该隐身斗篷的工作性能,计算结果展示,在斗篷工作的带宽范围内,覆盖斗篷后的CSI值趋近于无斗篷覆盖地面的CSI值,展示了其在的良好隐身性.本文所设计的斗篷均以超薄的亥姆霍兹共振结构为组成单元,结构简单,易于实现,有利于未来的实际应用.

With the development of metamaterials,the acoustic cloaking has attracted extensive attention due to its novel physics and potential applications.In recent years,based on the phase compensation modulation from Generalized Snell’s law and coordinate transformation,the acoustic cloakings in underwater and air have been widely and deeply studied.However,there is still an urgent need to design acoustic cloaks that are thinner and less affected by the incident angle of acoustic waves.Further,the designed cloaks should have a wider operating band and be more suitable for irregular objects.In this paper,an ultrathin curved acoustic metasurface carpet cloaking is studied by using of phase compensation modulation.The phase modulation is based on Helmholtz resonance(HR).The metasurface carpet is immersed in air,since the vibration mode of acoustic wave in the air is relatively single,thus the physical essence can be elucidated more clearly.The carpet cloak is composed of 52 Helmholtz resonant units,and the size of resonant unit is less than 0.2 of working wavelength.The phase change of HR unit is solved analytically by using the Generalized Snell’s law,and confirmed by the Multiphysics COMSOL software.The parameter effects of HR unit on the phase change are studied,demonstrating that the phase change of HR unit is sensitive to the change of height and radius of HR unit,while the change of width of HR cavity neck can make the phase of HR unit change smoothly.Therefore,when building 52 HR units,the width of the HR cavity neck is designed,and the height and radius of HR unit stay fixed.The simulating results demonstrate that the designed cloak works well in a frequency range from 5850 Hz to 7550 Hz.Also,we study the cloaking effect for oblique incidence,and the results show that the carpet cloak works well for incident angle less than 30°.To quantitatively analyze the bandwidth of the cloaking,we calculate the cosine similarity value.It elucidates that the value of the cloak is very close to that of the flat ground in a corresponding working frequency range.The cloak designed in this work is made of ultrathin Helmholtz Resonant structures.This cloak is simple and easy to realize and conducive to potential applications.