Broadband Negative Reflection of Underwater Acoustic Waves from a Simple Metagrating: Modeling and Experiment
Résumé
Metagratings are periodic arrays of subwavelength scatterers, or atoms, engineered to refract or reflect waves towards anomalous directions with unit efficiency. Here we design and build a metagrating to control the reflection direction of water-borne ultrasound waves impinging on rigid or free surface. The grating and its atoms are designed to cancel the specular reflection and to redirect acoustic power towards a negative reflection direction, through the first negative order Floquet mode. Despite a simple design, based on c-shaped brass particles acting as Helmoltz resonators, the grating is efficient (> 90%) over a relatively broad range of frequencies (74-103 kHz) for a broad range of incident angles (14 to 54 •). This good performance is obtained by tuning the distance between the atoms and the reflective surface. A multiple scattering analytical model is presented to explain the phenomenon, and a finite element model is developed to further investigate the performance of the proposed design. Predictions from the model are confirmed experimentally in a water tank. The simplicity, reconfigurability and scalability of the design, as well as its high efficiency, broadband behavior and robustness to incident angle are all features that make the grating potentially useful for various applications in underwater acoustic such as telemetry, communication, or noise mitigation.
Domaines
Acoustique [physics.class-ph]Origine | Fichiers produits par l'(les) auteur(s) |
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