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Manipulating elastic waves of all polarizations is highly challenging due to the complex behavior of elastic waves. To achieve simultaneous broadband vibration attenuation and energy harvesting across all polarizations of elastic waves at low‐frequency ranges, a chiral mechanical metamaterial‐based energy harvester is proposed in this study. The systematic development of a complete bandgap and defect structure is achieved through theoretical eigenfrequency analysis and numerical simulations. The defect structure is incorporated to induce defect modes for all wave polarizations within the complete bandgap region, ensuring their compatibility with the overall shape of the structure. The proposed chiral mechanical metamaterial with defect (CMMD) demonstrated significant performance improvements, achieving electrical output power enhancements that are 20.5 times for flexural waves and 511.4 times for longitudinal‐torsional waves compared to the defectless chiral mechanical metamaterial. This study accentuates the thoughtful design and multifaceted utility of chiral mechanical metamaterials, paving the way for their application not only in energy harvesting but also in wave attenuation for various polarizations. [ABSTRACT FROM AUTHOR]

Chiral mechanical metamaterials with engineered asymmetric structures have garnered significant interest owing to their potential for manipulating mechanical waves and unconventional mechanical properties. Although several design methodologies have made significant strides in the design and discovery of chiral mechanical metamaterials, 3D designs that incorporate multiple mechanical characteristics remain largely unexplored and the static and dynamic properties of these structures have not received sufficient attention. Here, an innovative approach is introduced for the inverse design of 3D chiral mechanical metamaterials with desired static and dynamic properties, leveraging streamlined shapes to enable a versatile design. By employing conditional generative adversarial networks (c‐GANs), the desired mechanical properties are targeted by focusing on both wave attenuation and stress distribution under compression and shear loading. 3D chiral mechanical metamaterials with additive manufacturing are fabricated to demonstrate the performance of the proposed c‐GAN. Experimental investigations show that the generated structures exhibited a wide range of wave attenuation properties, low stress concentrations, and a variety of stress‐strain curve profiles including nonlinear stiffness, demonstrating their effectiveness in achieving the desired mechanical characteristics. This research offers significant advancements in the on‐demand design capabilities of metamaterials and their applications. [ABSTRACT FROM AUTHOR]

An elastic wave in a physical beam naturally possesses many wave modes, such as flexural, longitudinal, and torsional. Therefore, suppression of all possible vibration modes has been rarely achieved in beam-shaped periodic systems, especially at low frequencies. Here we present a low-frequency complete bandgap mechanism by overlapping the flexural bandgap with the longitudinal-torsional bandgap. To strengthen the general framework, we enforce an extra degree of freedom (rotational and torsional-spring) on the spring-mass system for the flexural and coupled (longitudinal-torsional) modes. The low rotational stiffness provides a low flexural bandgap, whereas the torsional stiffness yields a coupled-mode bandgap. To meet these prerequisites in physical modeling, a chiral trabeated metabeam is conceived, which allows all wave modes to be suppressed by a complete bandgap. Apart from single-mode mitigation, our work provides a route to implementing a low-frequency complete bandgap in a periodic fashion, potentially enabling the use of chirality in elastic structures. Engineering the mechanical response of metamaterials allows control of mechanical modes, with potential application to vibrational isolation. Here, a general framework for achieving a complete band-gap by combining orthogonal flexural and longitudinal-torsional band-gaps is demonstrated analytically and experimentally. [ABSTRACT FROM AUTHOR]

Mechanical metamaterials and phononic crystals enable localizing, focusing, and guiding of elastic or acoustic waves in various ways. Here, we describe the physical mechanisms underpinning wave manipulation and then review the most recent energy harvesting methods for converting localized mechanical wave energy to useable electrical energy. Due to the exceptional wave-matter interactions enabled by the man-made structures, energy is collected more efficiently than through conventional methods. Artificially designed mechanical structures are versatile, especially when used in renewable and ecologically-benign energy transformation, and have a wide array of potential applications. Judicious design of metamaterials and phononic crystals permits the realization of novel localization and wave-guiding properties. Here, recent developments and strategies for applying these structures to piezoelectric energy harvesting are reviewed. [ABSTRACT FROM AUTHOR]

• A trampoline metamaterial is designed for realizing multiband energy localization and harvesting. • Bragg-scattering and local resonance is exploited to control the bandgap at high and low frequencies. • Flexural wave energy is localized through defect modes by breaking the periodicity. • High-performance piezoelectric energy harvesting is achieved at multi-frequency range. In this study, we investigate high-performance piezoelectric energy harvesting at multiband frequencies. Previous harvesting platforms were limited to a high-frequency range and exhibited poor electrical performance. Our proposed piezoelectric energy-harvesting platform, which is based on a periodically arranged trampoline metamaterial, exhibits a remarkable electrical output at both low and high frequencies. The proposed harvesting platform broadens the bandgap induced by Bragg scattering in the high-frequency range, and the local resonance is critical in opening a wide bandgap in the low-frequency range. By breaking the periodicity, we generate multiband defect states for flexural wave trapping under fundamental physical phenomena. We experimentally demonstrate flexural wave localization in the defect cavity, while a confined wave is converted into high-performing electrical energy using a piezoelectric element. We measure 1.37 V and 4.05 V as output voltage, and 24.4 μ W and 1.28 m W as output power at the 1st and 2nd defect modes, respectively, which are 188% and 400% compared with the bare plate. Our high-power energy-harvesting platform has potential applications as a renewable and sustainable energy source in various fields, such as structural health monitoring, signal processing, and sensors. [ABSTRACT FROM AUTHOR]