Ultrathin acoustic metasurface carpet cloaking based on Helmholtz resonances

Abstract

<sec>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.</sec><sec>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.</sec><sec>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.</sec><sec>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.</sec>