| Feb 13, 2022 |
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(Nanowerk News) Metamaterials are artificially engineered composite materials derive their properties from internal micro- and nanostructures, rather than the chemical composition found in natural materials. As a result, metamaterial structures enable properties and capabilities, which are generally not possible to create using conventional material discovery or chemical manufacturing technologies (read more in our metamaterials primer).
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Metamaterial architectures can be made with one or several materials for structural (e.g., topological morphing, elastic wave, and vibration manipulation) and nonstructural functions (e.g., optical, acoustic, and electric control).
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A combination of diffident kinds of functionality enables multifunctional metamaterials (MFMs) that can be used for a variety of applications in which the materials or structures need to simultaneously perform two or more functions.
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One promising engineering application is a multifunctional metamaterial that is capable of effectively preventing unwanted noises and/or vibrations in the low-frequency range and simultaneously harvesting the trapped mechanical energy with nanogenerators.
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In a recent paper in Advanced Functional Materials (“Multifunctional Metamaterials for Energy Harvesting and Vibration Control”), researchers propose a new multifunctional metamaterial capable of energy harvesting and vibration control based on triboelectric nanogenerator (TENG) technology.
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This new type of MFM based on TENGs has the potential to be used for not only for energy harvesting and vibration isolation, but potentially also for self-powered sensing.
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As illustrated in the figure below, the multifunctional metamaterial consists of a series of unit cells based on TENGs and a supporting substrate made of acrylate. The unit cell (12 x 12 mm) is designed to be a chiral beam-like structure with a central mass connected (Figure 1b). The adoption of the chiral structure of beams is to maximize the effective contact area with the substrate in vibration. The central mass is 3D printed using nylon and coated a thin layer of aluminum (Al) film/foil on its back to serve as the electrode (Figure 1c).
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| Figure 1. Proposed triboelectric nanogenerator (TENG) based multifunctional metamaterial (MFM). a) Schematic illustration of the TENG-MFM consisting of an array of structural TENG-based resonators. An external vibration load or acoustic wave is applied at the center of the TENG-MFM plate. b) Geometry of the unit cell resonator which has a central mass and connected with the base using chiral shape beams. c) Schematic illustration of the layered structure for the unit cell. The resonator is 3D printed using nylon, and then coated a thin layer of aluminum (Al) as electrode. The base is fabricated with acrylate plate and coated with a thin layer of Al before depositing another thin PTFE film on top of it. d) Schematic illustration of the working mechanism of the contact-separate mode TENG. An electric field E(z) will be formed and varying with the charge volume and gap distance d when indued charges appear on the Al and PTFE surface. (Reprinted with permission by Wiley VCH Verlag)
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Another thin layer of Al film is coated on the top surface of the acrylate plate, following a pattern defined based on the position and size of the central mass. After that, a thin polytetrafluoroethylene (PTFE) film is deposited onto the Al film of the substrate surface (Figure 1c). A small gap between the mass resonator and the bottom substrate is designed to allow the vibration motions of the central mass when an external excitation is applied.
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Owing to the different attraction abilities to electrons by different triboelectric materials, the cyclic contact-separation interactions between the Al and PTFE layers will generate electrical charges (Figure 1d) and will also affect the vibrations of the central mass due to the induced electrostatic force.
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In addition, the variation of the vibration frequency and amplitude will result in the change of the output voltage/current, making it possible to serve as a vibration sensor for external mechanical excitations nearby the TENG-MFM.
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In their work, the researchers numerically and experimentally investigate the effects of the key parameters – geometric dimension, structural configurations, and material properties – on the performance of the MFM under different excitation frequencies.
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They successfully demonstrate that their TENG-based MFM can effectively harvest vibration energy, significantly suppress the vibration and elastic wave mitigation, and even identify the frequency.
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The authors are hopeful that their proposed advanced smart systems could be used for a variety of applications in automobiles, robotics, and implant devices.
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