Vibro-acoustic topology optimization for improving the acoustic insulation and mechanical stiffness performance of periodic sandwich structure.

The traditional parameter adjustment design makes it difficult to effectively regulate the acoustic insulation performance of periodic sandwich structures while meeting the lightweight and mechanical stiffness requirements. A dynamic three-field floating projection topology optimization (FPTO) method for periodic structures is proposed to meet the optimization requirements of low-noise and high-stiffness performance of lightweight periodic sandwich structures. The sound transmission loss is taken as the optimization objective, and the lightweight volume and mechanical stiffness performance are taken as the multiple constraints. The results show that a smooth topology configuration with superior sound insulation performance, high stiffness, and a freely customizable number of periodic cores can be obtained via the proposed method. The accuracy and effectiveness of the presented method are verified via 3D printing technology and impedance tube sound insulation experiments, providing an important reference for the optimal design of lightweight composite structures for vibration and noise reduction in transportation equipment.

Reflection phase dispersion editing generates wideband invisible acoustic Huygens's metasurface.

Acoustic metasurfaces show non-traditional abilities in wave manipulation and provide alternate mechanisms for information communication and invisibility technology. However, most of the mechanisms remain narrow band (relative bandwidth ∼5%), and a wideband trait is essential for engineering applications. For example, controllable effective material properties-reflection or transmission phase-has barely been realized in wideband because the intrinsic dispersion relation is not always editable. In this paper, wideband reflection phase editing is realized, and wideband invisibility of a phase preserved Huygens's metasurface on a flat background is achieved with anomalous reflection. This metasurface is built with proposed unsymmetrical twin Helmholtz resonators which reach a predefined dispersion relation target value. The total instantaneous acoustic fields show nearly identical carpeting effects in a consecutive band with relative bandwidth 52.1% (from 5400 to 9200 Hz) in simulation and experiment.

Asymmetric transmission of acoustic waves in a waveguide via gradient index metamaterials.

We demonstrate that asymmetric acoustic wave transmission in a waveguide can be achieved via gradient index metamaterials (GIMs). We theoretically prove that the acoustic wave can be efficiently converted to surface waves (SWs) via GIMs. The GIMs in a waveguide can allow the transmission of acoustic waves in one direction but block them in the other direction. This theory is validated by experiments. Our findings may provide new applications in various scenarios such as high-efficiency acoustic couplers and noise control.