Arbitrary In-plane Directions Research Articles

Analysis of Floquet Waves in Periodic Multilayered Isotropic Media with the Method of Reverberation-Ray Matrix

The in-plane elastic waves in periodically multilayered isotropic structures, which are decoupled from the out-of-plane waves, are represented mainly by the frequency–wavenumber spectra and occasionally by the frequency–phase velocity spectra as well as being studied predominantly for periodic bi-layered media along and perpendicular to the thickness direction in the existing research. This paper investigates their comprehensive dispersion characteristics along arbitrary in-plane directions and in entire (low and high) frequency ranges, including the frequency–wavelength, wavenumber–phase velocity, wavelength–phase velocity spectra, the dispersion surfaces and the slowness curves with fixed frequencies, as well as the frequency–wavenumber and frequency–phase velocity spectra. Specially, the dispersion surfaces and the slowness curves completely reflect the propagation characteristics of in-plane waves along all directions. First, the method of reverberation-ray matrix (MRRM) combined with the Floquet theorem is extended to derive the dispersion equation of in-plane elastic waves in general periodic multilayered isotropic structures by means of the elastodynamic theory of isotropic materials and the state space formalism of layers. The correctness of the derivation and the numerical stability of the method in both low and high frequency ranges, particularly its superiority over the method of the transfer matrix (MTM) within the ranges near the cutoff frequencies, are verified by several numerical examples. From these demonstrations for periodic octal- and bi-layered media, the comprehensive dispersion curves are provided and their general characteristics are summarized. It is found that although the frequencies associated with the dimensionless wavenumber along thickness ql=nπ (n is an integer) are always the demarcation between pass and stop bands in the case of perpendicular incident wave, but this is not always exist in the case of the oblique incident wave due to the coupling between the two modes of in-plane elastic waves. The slowness curves with fixed frequencies of Floquet waves in periodically multilayered isotropic structures, as compared to their counterpart of body waves in infinite isotropic media obtained from the Christoffel equation now have periodicity along the thickness direction, which is consistent to the configuration of the structures. The slowness curves associated with higher frequencies have a smaller minimum positive period and have more propagation modes due to the cutoff properties of these additional modes.

A two-dimensional energy harvester with radially distributed piezoelectric array for vibration with arbitrary in-plane directions

Piezoelectric vibration energy harvesters have attracted much attention in the last decades due to their great potential application in powering various ultra-low-power sensors/actuators in the ambient environment. Many works have been presented to improve the energy conversion efficiency and broaden the operating bandwidth. One purpose of these studies is to harvest vibration energy with a specific excitation direction. However, a vibration source in a practical environment may from different directions. In this article, a piezoelectric vibration energy harvester with the radially distributed piezoelectric array is proposed to scavenge two-dimensional vibration energy. Meanwhile, we introduce a new concept, named angle bandwidth, to describe the ability of harvesting two-dimensional vibration energy. The theoretical analysis and the simulation results indicate that this harvester can scavenge vibration energy with arbitrary in-plane directions using the arc-shaped radially distributed piezoelectric array on a flexible cylinder. The experimental results show that this new design has large angle bandwidth, and the angle bandwidth increases from 87.5° to 106.3° when increasing the number of polyvinylidene fluoride elements from one to four. Also, the angle bandwidth of piezoelectric array in series is always larger than that in parallel. Overall, the present two-dimensional piezoelectric vibration energy harvester has the potential for a higher multi-directional vibration energy harvesting efficiency than a traditional cantilever-shaped piezoelectric vibration energy harvester. It also can be used as a self-powered vibration direction sensor.

Thermal conductivity of graphene grain boundaries along arbitrary in-plane directions: A comprehensive molecular dynamics study

The thermal conductivity of polycrystalline graphene is expected to be lower than that of pristine graphene, due to the existence of defects, such as grain boundaries (GBs). To study the thermal transport behavior in polycrystalline graphene, it is crucial to understand the thermal conductivity of graphene GBs as a function of the tilt GB misorientation angle and in-plane thermal loading angle. However, existing studies of thermal conductivity of graphene GBs only consider the case where the thermal flux is perpendicular or parallel to the graphene GB. To address this issue, here we perform systematic non-equilibrium molecular dynamics simulations and investigate the thermal conductivity of graphene GBs for all possible tilt GB misorientation angles (23 cases) under arbitrary in-plane thermal loading directions. The findings from the present study can offer quantitative guidance for using polycrystalline graphene in thermal devices and flexible electronics applications.

Hybrid generator based on freestanding magnet as all-direction in-plane energy harvester and vibration sensor

Vibration is a widely existing mechanical phenomenon containing enormous energy that can be transformed into electricity without polluting the environment. However, most current mechanical energy harvesters only can scavenge energy from a specific direction, resulting in the waste of energy from other directions. Here, we propose a triboelectric-electromagnetic hybrid generator built on freestanding magnet (FMHG), which is able to harvest low-frequency vibration energy from arbitrary in-plane directions. Besides, it can detect vibration direction from periodical or pulse movement. Under the excitation of shaker, maximum power of 85.7 µW and 3.29 mW are obtained by one electrode pair of the TENG and EMG respectively, which can charge a capacitor of 20 µF to 7 V rapidly benefiting from the hybrid configuration. The hybrid generator can light up commercial LEDs driven by human running and bicycle braking, as well as distinguish leg movement in eight directions, proving its application potential in building up self-powered sensing systems such as alarms, environmental monitor and human-machine interface.

Hysteresis modelling of GO laminations for arbitrary in-plane directions taking into account the dynamics of orthogonal domain walls

The anisotropy of magnetic properties in grain-oriented steels is related to their microstructure. It results from the anisotropy of the single crystal properties combined to crystallographic texture. The magnetization process along arbitrary directions can be explained using phase equilibrium for domain patterns, which can be described using Neel's phase theory. According to the theory the fractions of 180° and 90° domain walls depend on the direction of magnetization. This paper presents an approach to model hysteresis loops of grain-oriented steels along arbitrary in-plane directions. The considered description is based on a modification of the Jiles–Atherton model. It includes a modified expression for the anhysteretic magnetization which takes into account contributions of two types of domain walls. The computed hysteresis curves for different directions are in good agreement with experimental results.

Wideband and 2D vibration energy harvester using multiple magnetoelectric transducers

This paper investigates a magnetoelectric (ME) vibration energy harvester that can scavenge energy in arbitrary directions in a plane as well as wide working bandwidth. In this harvester, a circular cross-section cantilever rod is adopted to extract the external vibration energy due to the capability of it\'s free end oscillating in arbitrary in-plane directions. And permanent magnets are fixed to the free end of the cantilever rod, causing it to experience a non-linear force as it moves with respect to stationary ME transducers and magnets. The magnetically coupled cantilever rod exhibits a nonlinear and two-mode motion, and responds to vibration over a much broader frequency range than a standard cantilever. The effects of the magnetic field distribution and the magnetic force on the harvester\'s voltage response are investigated with the aim to obtain the optimal vibration energy harvesting performances. A prototype harvester was fabricated and experimentally tested, and the experimental results verified that the harvester can extract energy from arbitrary in-plane directions, and had maximum bandwidth of 5.5 Hz, and output power of 0.13 mW at an acceleration of 0.6 g (with g=9.8 ms-2).

Sandwich-structured two-dimensional MEMS electret power generator for low-level ambient vibrational energy harvesting

This paper presents a novel sandwich-structured electret-based power generator (SEPG) for two-dimensional (2D) low-level ambient kinetic energy harvesting. The generator is based on a symmetrical resonator that consists of a double-sided electrode-patterned seismic mass suspended by four-folded parallel beam flexures. The experimental analysis shows that it is able to scavenge kinetic energy from arbitrary in-plane directions by combining its two primary vibration modes at the frequencies of 121Hz and 125Hz. Sandwich structure is adopted in the proposed device that has two separate capacitive circuits 180° out-of-phase with each other to be integrated into a single seismic mass system. This configuration has its merits in that both the vertical pull-in electrostatic force as well as the horizontal damping force can be reduced. With the present prototype, an overall output power of 0.12μW is obtained for the two capacitive parts at an acceleration of 0.2g at 125Hz, corresponding to a normalized power density of 5.56μWcm−3g−2. The results show that the generator can potentially offer an intriguing alternative for scavenging low-level ambient energy from 2D vibration sources.

Design and optimization of a bi-axial vibration-driven electromagnetic generator

To scavenge energy from ambient vibrations with arbitrary in-plane motion directions and over a wide frequency range, a novel electromagnetic vibration energy harvester is designed and optimized. In the harvester, a circular cross-section elastic rod, not a traditional thin cantilever beam, is used to extract ambient vibration energy because of its capability to collect vibration from arbitrary in-plane motion directions. The magnetic interaction between magnets and the iron core contributes to a nonlinear oscillation of the rod with increased frequency bandwidth. The influences of the structure configurations on the electrical output and the working bandwidth of the harvester are investigated using Ansoft's Maxwell 3D to achieve optimal performance. The experimental results show that the harvester is sensitive to vibrations from arbitrary in-plane directions and it exhibits a bandwidth of 5.7 Hz and a maximum power of 13.4 mW at an acceleration of 0.6 g (with g = 9.8 ms−2).

Energy Harvesting from Ambient Vibrations with Arbitrary In-Plane Motion Directions Using a Magnetostrictive/Piezoelectric Laminate Composite Transducer

A magnetoelectric (ME) vibration energy harvester has been designed to scavenge sufficient energy from ambient vibration with arbitrary motion directions in a plane and over a range of frequencies. In the harvester, a circular-cross-section cantilever rod is adopted to extract the vibration energy due to its ability to host accelerations in arbitrary in-plane motion directions. The magnetic coupling between the magnet and the ME transducer results in nonlinear oscillation of the cantilever rod with increased frequency bandwidth. To achieve optimal vibration energy harvesting performance, the effects of the nonlinear vibration and the harvester parameters including the magnetic circuit and the separation distance on the electrical output and the␣working bandwidth are analyzed. The experimental results show that the harvester can scavenge vibration energy in arbitrary in-plane directions, exhibiting a bandwidth of 4.0 Hz and maximum power of 0.22 mW at acceleration of 0.6g (with g = 9.8 m s−2).

Design and analysis of a 2D broadband vibration energy harvester for wireless sensors

This paper presents a design for a novel vibration energy harvester using a magnetoelectric (ME) transducer, which is efficiently applicable in two-dimensional (2D) motion and over a range of vibration frequencies. This harvester adopts a circular cross-section cantilever rod to extract the ambient vibration energy because of its ability to host accelerations in arbitrary motion directions. Moreover, the magnetic interactions between the magnets and the ME transducer will lead to the nonlinear oscillation of the rod with increased frequency bandwidth. The influences of the nonlinear vibration factor and magnetic field distribution on the electrical output and bandwidth of the harvester are investigated to achieve optimal vibration energy harvesting performances. The experimental results showed that, the harvester was sensitive to the vibration with arbitrary in-plane directions. With an acceleration of 0.6g (where g=9.8ms−2), it had the working bandwidths of 4.2Hz, 2.6Hz, 2.3Hz, 2.5Hz and 3.2Hz, and the output powers of 0.6mW, 0.49mW, 0.33mW, 0.5mW and 0.56mW at the in-plane excitation angles of−90°, −45°, 0°, 45° and 90°, respectively.