Abstract
This study aims to investigate elastic wave localization that leverages defect band splitting in a phononic crystal with double defects through in-depth analysis of comparison of numerical and experimental results. When more than one defect is created inside a phononic crystal, these defects can interact with each other, resulting in a distinctive physical phenomenon from a single defect case: defect band splitting. For a phononic crystal consisting of circular-hole type unit cells in a thin aluminum plate, under A0 (the lowest antisymmetric) Lamb waves, both numerical simulations and experiments successfully confirm the defect band splitting phenomenon via frequency response functions for the out-of-plane displacement calculated/measured at the double defects within a finite distance. Furthermore, experimental visualization of in-phase and out-of-phase defect mode shapes at each frequency of the split defect bands is achieved and found to be in excellent agreement with the simulated results. Different inter-distance combinations of the double defects reveal that the degree of the defect band splitting decreases with the increasing distance due to weaker coupling between the defects. This work may shed light on engineering applications of a multiple-defect-introduced phononic crystal, including broadband energy harvesting, frequency detectors, and elastic wireless power transfer.
Highlights
Phononic crystals are artificial periodic structures that can efficiently tailor propagation of acoustic or elastic waves in solids [1, 2]
When elastic waves propagate through the phononic crystal with the single defect at one of the defect band frequencies, the single defect behaves as a single mechanical resonator, localizing the elastic waves inside the defect while exhibiting the corresponding characteristic defect mode shape (Additional file 1: Fig. S4)
It should be noted that the defect band splitting is the phononic crystal system’s characteristics not affected by the incident waves
Summary
Phononic crystals are artificial periodic structures that can efficiently tailor propagation of acoustic or elastic waves in solids [1, 2]. The first phononic crystal concept dates back to 1993 when Kyshwaha et al [3] presented the first acoustic band structure of periodic elastic composites, drawing the analogy to electromagnetic waves of the photonic crystal concept for light. The most common physical mechanism for phononic band gap formation is Bragg scattering [15, 16], whereas the existence of local resonance [17, 18] contributes to the band gap of acoustic or elastic metamaterials. Development of numerical methods for designing phononic band gaps
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