Abstract
Elastic guided wave focusing is of great interest for applications such as vibroacoustic control, energy harvesting, or Structural Health Monitoring. Different strategies allow generation of this effect, GRadient-INdex devices in particular exploit medium with varying properties such as thickness to reproduce an adequate refractive index profile as in optics. The resulting continuous profiles have a curved geometry that can be hard to manufacture, and be difficult to integrate in a given design. The purpose of this paper is to propose a discrete design for a GRIN lens. It is composed of segments selected in number and thickness to give similar focusing effects as a continuous lens profile. The identified configuration is manufactured and bounded on an aluminium plate to evaluate the effective focusing performances. Numerical and experimental vibrometry results confirm that the proposed lens exhibits a fixed focal point over a broad frequency range. The discrete design overcomes fabrication issues encountered in continuous design, allowing for an easier integration in devices for elastic wave control.
Highlights
Focusing of elastic waves is of high interest for applications such as energy harvesting (Carrara et al 2012; Tol et al 2016; Hyun et al 2019), Structural Health Monitoring (Kudela et al 2018), or acoustic imaging (Davis et al 2007; Deng et al 2009; Peng et al 2010)
The paper proposes a design for a passive discrete GRadient-INdex devices (GRIN) lens to focus elastic waves
The discrete configuration consists in a set of segments with varying thicknesses in order to generate a refractive index for wave focusing
Summary
Focusing of elastic waves is of high interest for applications such as energy harvesting (Carrara et al 2012; Tol et al 2016; Hyun et al 2019), Structural Health Monitoring (Kudela et al 2018), or acoustic imaging (Davis et al 2007; Deng et al 2009; Peng et al 2010). Different strategies have emerged to achieve wave control such as Phononic Crystals (PC) consisting in periodic structures exhibiting phononic bandgaps (Timorian et al 2020), Elastic MetaMaterials (EMMs) that exploit local resonances (Campana et al 2020), acoustic mirrors based on specific parabolic or elliptic shapes to generate curved trajectories and localize elastic waves (Carrara et al 2012), or continuous profile (Krylov and Tilman 2004) All these solutions can be used to give rise to GRadient-INdex devices (GRIN): their purpose is to reproduce the inhomogeneous behavior of materials in which propagating waves follow curved trajectories under adequate refractive properties as observed in optics (Gomez-Reino et al 2002). Elastic Metamaterials (EMMs) exploit local resonances in periodic structures instead of multiple scattering, the GRIN-lens consists, in this case, of a set of solid
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