A layered co-focal elliptical-cylindrical acoustic cloak is designed based on the effective medium theory. The distribution of acoustic field is simulated using the finite element method. The cloak possesses the properties of low-reflection outside and wavefront-bending in the cloak shell. The relationship between the cloaking effect and the number of discrete layers, the direction of incident wave are also investigated. The effective working frequency band can be broadened by using more layers. As the cloak is of a line-transformed type, its properties are associated with the direction of incident wave. Only when the incident wave is parallel to the major axis of the ellipse, can the cloak have the best performance. In addition, the cloak is of a cylindrical structure as the focus of the ellipse-cylinder is small enough. This work is expected to be helpful for realizing acoustic cloaks with complex shapes.
In this paper, a local resonant phononic crystal is designed and fabricated based on Helmholtz resonators. Experiment is carried out to study the defect mode of the structure, in which a point defect is introduced. Due to the coupling of the defect cell and perfect cells, a narrow pass band appears in the local resonant forbidden band. Meanwhile, acoustic energy localization effect is observed around the defect resonator at the frequency of defect mode which changes with the defect parameter. However, the defect mode is close to the edge of the forbidden band, the localized energy is high. In addition, if the resonant frequency of the defect unit is smaller than that of the perfect unit, the localized energy is mostly distributed in the waveguide. In contrast, the energy is mostly localized in the resonators when the defect unit frequency is larger than that of the perfect unit. This work will be of help for designing new acoustic functional devices of filters and concentrators.
An approximation approach is proposed for realizing an arbitrarily shaped acoustic cloak. Based on the effective medium theory, the designed cloak is a discrete layered structure using homogeneous isotropic materials. The performance of the cloak is simulated, and the results demonstrate that the cloak possesses properties of lowreflection outside the cloak and wavefront-bending in the cloak shell. This work proves the feasibility of realizing an arbitrarily shaped acoustic cloak using normal materials.
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