Design of a resonant Luneburg lens for surface acoustic waves

被引:37
作者
Fuentes-Dominguez, Rafael [1 ]
Yao, Mengting [1 ]
Colombi, Andrea [2 ]
Dryburgh, Paul [1 ]
Pieris, Don [1 ]
Jackson-Crisp, Alexander [3 ]
Colquitt, Daniel [4 ]
Clare, Adam [3 ]
Smith, Richard J. [1 ]
Clark, Matt [1 ]
机构
[1] Univ Nottingham, Fac Engn, Opt & Photon Grp, Nottingham NG7 2RD, England
[2] ETH, Dept Civil Environm & Geomat Engn, Stefano Franscini Pl 5, CH-8093 Zurich, Switzerland
[3] Univ Nottingham, Fac Engn, Adv Component Engn Lab ACEL, Nottingham NG7 2RD, England
[4] Univ Liverpool, Dept Math Sci, Liverpool, Merseyside, England
基金
瑞士国家科学基金会; 英国工程与自然科学研究理事会;
关键词
Metamaterial; Luneburg lens; SAW; Additive manufacturing;
D O I
10.1016/j.ultras.2020.106306
中图分类号
O42 [声学];
学科分类号
070206 ; 082403 ;
摘要
In this work we employ additive manufacturing to print a circular array of micropillars on an aluminium slab turning its top surface into a graded index metasurface for surface acoustic waves (SAW). The graded metasurface reproduces a Luneburg lens capable of focusing plane SAWs to a point. The graded index profile is obtained by exploiting the dispersion properties of the metasurface arising from the well-known resonant coupling between the micropillars (0.5 mm diameter and variable length similar to 3 mm) and the surface waves propagating in the substrate. From the analytical formulation of the metasurface's dispersion curves, a slow phase velocity mode is shown to arise from the hybridisation of the surface wave with the pillar resonance. This is used to compute the radial height profile corresponding to the refractive index given by Luneburg's equation. An initial validation of the lens design, achieved through ray theory, shows that ray trajectories have a strong frequency dependence, meaning that the lens will only work on a narrow band. An ultrasonic experiment at 500 kHz where plane SAWs are generated with a piezoelectric transducer and a laser scanner measures the out of plane displacement on the metasurface, validates the actual lens performance and the manufacturing technique. Finally, comparison between the ray analysis and experimental results offers insight into the behaviour of this type of metasurface especially in the proximity of the acoustic bandgaps and highlights the possibility for acoustic shielding.
引用
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页数:6
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