Multi-functional metamaterials for energy harvesting and vibration control

February 13, 2022

(News from Nanowerk) Metamaterials are artificially made composite materials that derive their properties from internal microstructures and nanostructures, rather than from the chemical composition of natural materials. Therefore, metamaterial structures enable properties and capabilities that are typically not possible to create using conventional materials discovery or chemical manufacturing technologies (read more in our introduction to metamaterials). .

Metamaterial architectures can be made with one or more materials for structural (eg, topological morphing, elastic wave, and vibration manipulation) and non-structural (eg, optical, acoustic, and electrical control) functions.

A combination of different types of functionality enables multifunctional metamaterials (MFMs) that can be used for a variety of applications where materials or structures need to perform two or more functions simultaneously.

A promising engineering application is a multifunctional metamaterial capable of effectively preventing unwanted noise and/or vibration in the low-frequency range and simultaneously harvesting trapped mechanical energy with nanogenerators.

In a recent article by Advanced functional materials (“Multifunctional Metamaterials for Energy Harvesting and Vibration Control”), researchers propose a novel multifunctional metamaterial capable of energy harvesting and vibration control based on triboelectric nanogenerator (TENG) technology.

This new type of TENG-based MFM has the potential to be used not only for energy harvesting and vibration isolation, but potentially also for autonomous sensing.

As shown in the figure below, the multifunctional metamaterial consists of a series of TENG-based unit cells and an acrylate support substrate. The unit cell (12 x 12 mm) is designed to be a chiral beam-like structure with a connected central mass (Figure 1b). The adoption of the chiral structure of the beams aims to maximize the effective contact area with the vibrating substrate. The central mass is 3D printed using nylon and coated with a thin layer of aluminum (Al) film/foil on its back to act as an electrode (Figure 1c).

Figure 1. Proposed triboelectric nanogenerator (TENG)-based multifunctional metamaterial (MFM). a) Schematic illustration of the TENG-MFM composed of a network of structural resonators based on TENG. An external vibration load or acoustic wave is applied to the center of the TENG-MFM plate. b) Geometry of the unit cell resonator which has a central mass and connected to the base using chiral shaped bundles. c) Schematic illustration of the layered structure of the unit cell. The resonator is 3D printed using nylon, then coated with a thin layer of aluminum (Al) as an electrode. The base is fabricated with an acrylate plate and covered with a thin layer of Al before depositing another thin film of PTFE on top. d) Schematic illustration of the operating mechanism of the TENG in separate contact mode. An electric field E(z) will be formed and will vary with charge volume and spacing distance d when induced charges appear on the surface of Al and PTFE. (Reproduced with permission from Wiley VCH Verlag)

Another thin layer of Al film is deposited on the upper surface of the acrylate plate, following a pattern defined according to the position and size of the central mass. After that, a polytetrafluoroethylene (PTFE) thin film is deposited on the Al film of the substrate surface (Figure 1c). A small gap between the ground resonator and the bottom substrate is designed to accommodate vibrational motions of the central ground when external excitation is applied.

Due to the different electron-attracting abilities of different triboelectric materials, the cyclic contact-separation interactions between the Al and PTFE layers will generate electric charges (Figure 1d) and also affect the central mass vibrations due to the force induced electrostatics.

Additionally, varying the vibration frequency and amplitude will cause the output voltage/current to change, allowing it to serve as a vibration sensor for external mechanical excitations near the TENG-MFM.

In their work, the researchers numerically and experimentally investigate the effects of key parameters – geometric dimension, structural configurations and material properties – on the performance of the MFM under different excitation frequencies.

They successfully demonstrate that their TENG-based MFM can efficiently harvest vibration energy, significantly suppress vibration and elastic wave attenuation, and even identify frequency.

The authors hope that their proposed advanced intelligent systems could be used for a variety of applications in automobiles, robotics, and implant devices.

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