Microstructural design studies for locally dissipative acoustic metamaterials

Abstract

Electronic, structural, and elastic properties of metal nitrides XN (X = Sc, Y): A first principle studyStress wave attenuation performance of locally dissipative acoustic metamaterials with various damped oscillator microstructures is studied using mechanical lattice models. The presence of damping is represented by a complex effective mass. Analytical solutions and numerical verifications of transmissibility are obtained for Kelvin-Voigt-type (KVO), Maxwell-type, and Zener-type (ZO) oscillators with viscous damping. Although peak attenuation at resonance is diminished, dissipative microstructures can provide broad spectrum attenuation without increasing mass ratio, obviating the bandgap width limitation of locally resonant microstructures. KVO gives the best broad spectrum performance akin to a low-pass filter for excitation frequencies above a cut-off value for a prescribed transmissibility criterion. For ZO, by tailoring the damping and stiffness, the frequency range of appreciable attenuation can at least span the bandgap widths of two limiting locally resonant cases. Static and frequency-dependent measures of optimal damping that maximize the attenuation characteristics are proposed. A transitional value for the excitation frequency is identified within the locally resonant bandgap, above which there always exists an optimal amount of damping that renders the attenuation for the dissipative metamaterial greater than that for the locally resonant case. Further microstructures with hysteretic damping depict a frequency-independent scaling in the effective mass and attenuation factor, but the bandgap width remains nearly the same as that for the corresponding viscously damped microstructures. This study demonstrates that dissipative microstructures, which are to some extent unavoidable in practical designs, when tuned, provide a means to substantially enhance the attenuation bandwidth of locally resonant acoustic metamaterials while also enabling the removal of the energy sequestered by the oscillators from the system. V C 2014 AIP Publishing LLC. [http://dx.FIG. 13. Real part of m eff for the LDAM with ZO microstructure for d 32 ¼ (a) 0.01, (b) 0.1, (c) 1, and (d) 10. 023518-8 J. M. Manimala and C. T. Sun J. Appl. Phys. 115, 023518 (2014) [This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to ] IP: 131.94.16.10 On: Mon, 22 Dec 2014 19:16:38 FIG. 14. Imaginary part of m eff for the LDAM with ZO microstructure for d 32 ¼ (a) 0.01, (b) 0.1, (c) 1, and (d) 10. 023518-9 J. M. Manimala and C. T. Sun FIG. 16. Imaginary part of non-dimensional wavenumber (qL ¼ a þ ib) for the LDAM with ZO microstructure for d 32 ¼ (a) 0.01, (b) 0.1, (c) 1 and (d) 10.

Wide band-gap seismic metastructures

“…This is in sharp contrast with the requirements in civil engineering application, where buildings must be protected from a rather broadband spectrum of a common earthquake. Several approaches have been proposed to widen the band gap of resonant metamaterials, ranging tuned damping 24 to geometries that enhance the effect of localized modes 25 . To attenuate waves in a broader frequency spectrum, we use arrays of resonators composed of units resonating at different frequencies.…”

Large scale mechanical metamaterials as seismic shields

“…The simulations are performed here for Lamb waves in the case of cross-like cavities with H=10 m (table 1). Material damping in the soil is presumed to increase linearly with frequency, as normally assumed when modelling wave propagation in viscoelastic metamaterials [41,46]. The shear modulus of the material G ( ve) therefore becomes complexvalued:…”

“…In the case of locally resonant inclusions, the viscoelastic behaviour of the matrix may lead to the decrease of the attenuation level inside the BG. However, the shielding performance of the whole structure can be improved by choosing for the soft coating a more viscous material than the matrix [46].…”

Dynamic load mitigation using negative effective mass structures

“…This mechanism of sequestration and rejection of energy achieved using resonators endows an apparent damping capability to such elastic structures that can exceed those achievable from dissipative mechanisms in structures with conventional damping. In addition, broadband attenuation performance is achievable using locally dissipative AM by tuning the dissipative and resonance mechanisms of local damped oscillator attachments [17]. Hence, AM-inspired NMS offers the prospect of achieving much higher simultaneous stiffness and damping-like behavior than conventionally damped structures.…”