Global Sensitivity Analysis of (a)Symmetric Energy Harvesters

Parametric variability is inevitable in actual energy harvesters and can define crucial aspects of the system performance, especially in susceptible systems to small perturbations. In this way, this work aims to identify the most critical parameters in the dynamics of (a)symmetric bistable energy harvesters with nonlinear piezoelectric coupling, considering the variability of their physical and excitation parameters. For this purpose, a global sensitivity analysis based on the Sobol' indices is performed by an orthogonal decomposition in terms of conditional variances to access the dependence of the recovered power concerning the harvester parameters. This technique quantifies the variance concerning each parameter individually and jointly regarding the total variation of the model. The results indicate that the frequency and amplitude of excitation, asymmetric bias angle, and piezoelectric coupling at the electrical domain are the most influential parameters that affect the mean power harvested. It has also been shown that the order of importance of the parameters can change from stable conditions. In possession of this, a better understanding of the system under analysis is obtained, identifying vital parameters that rule the change of dynamic behavior and constituting a powerful tool in the robust design and prediction of nonlinear harvesters.

Longitudinal and Transverse Electrocaloric Effects in Glycinium Phosphite Ferroelectric

A modified proton ordering model of glycinium phosphite ferroelectric, which involves the piezoelectric coupling of the proton and lattice subsystems, is used for the investigation of the electrocaloric effect. The model also accounts for the dependence of the effective dipole moment on a hydrogen bond on an order parameter, as well as a splitting of parameters of the interaction between pseudospins in the presence of shear stresses. In the two-particle cluster approximation, the influence of longitudinal and transverse electric fields on components of the polarization vector and the dielectric permittivity tensor, as well as on thermal characteristics of the crystal, is calculated. Longitudinal and transverse electrocaloric effects are studied. The calculated electrocaloric temperature change is quite small, about 1K; however, it can change its sign under the influence of a transverse field.

Electromechanical modelling of piezoelectrically actuated MEMS tunable lenses with geometric nonlinearity

This article presents a variational model for the geometrically nonlinear behaviour of the piezoelectrically actuated MEMS tunable lenses. Residual stresses during fabrication and larger actuation voltages cause large deflections such that a linear model would provide less accurate approximation. This presses the need for a nonlinear model that can explain the softening and hardening effects exhibited by the lens during its operation and affect its optical performance. Thus, in the view of von Kármán’s plate theory, the presented nonlinear model predicts the lens displacement after solving a cubic nonlinear system of equations. The chosen displacement ansatz fits the problem under study by satisfying the mechanical boundary conditions, and simplifying calculation of the variational integrals and optical representation of the lens’ sag. The model also shows good agreement with FEM simulations over various combinations of tensile and compressive residual stresses. Moreover, it succeeds in fitting measurements when used in a constrained optimization scheme in which the layers’ residual stresses and the e-form piezoelectric coupling coefficient are the fitting parameters.

Dispersion Diagram of Trigonal Piezoelectric Phononic Structures with Langasite Inclusions

The dispersion relation of elastic Bloch waves in 1-3 piezoelectric phononic structures (PPnSs) with Langasite (La3Ga5SiO14) inclusions in a polymeric matrix is reported. Langasite presents promising material properties, for instance good temperature behaviour, high piezoelectric coupling, low acoustic loss and high quality factor. Furthermore, Langasite belongs to the point group 32 and has a trigonal structure. Thus, the 2-D bulk wave propagation in periodic systems with Langasite inclusions cannot be decoupled into XY and Z modes. The improved plane wave expansion (IPWE) is used to obtain the dispersion diagram of the bulk Bloch waves in 1-3 PPnSs considering the classical elasticity theory and D3 symmetry. Full band gaps are obtained for a broad range of frequency. The piezoelectricity enhances significantly the band gap widths and opens up a narrow band gap in lower frequencies for a filling fraction of 0.5. This study should be useful for surface acoustic wave (SAW) filter and 1-3 piezocomposite transducer design using PPnSs with Langasite.

Quantitative probe for in-plane piezoelectric coupling in 2D materials

Piezoelectric response in two-dimensional (2D) materials has evoked immense interest in using them for various applications involving electromechanical coupling. In most of the 2D materials, piezoelectricity is coupled along the in-plane direction. Here, we propose a technique to probe the in-plane piezoelectric coupling strength in layered nanomaterials quantitively. The method involves a novel approach for in-plane field excitation in lateral Piezoresponse force microscopy (PFM) for 2D materials. Operating near contact resonance has enabled the measurement of the piezoelectric coupling coefficients in the sub pm/V range. Detailed methodology for the signal calibration and the background subtraction when PFM is operated near the contact resonance of the cantilever is also provided. The technique is verified by estimating the in-plane piezoelectric coupling coefficients (d11) for freely suspended MoS2 of one to five atomic layers. For 2D-MoS2 with the odd number of atomic layers, which are non-centrosymmetric, finite d11 is measured. The measurements also indicate that the coupling strength decreases with an increase in the number of layers. The techniques presented would be an effective tool to study the in-plane piezoelectricity quantitatively in various materials along with emerging 2D-materials.

Design and Analysis of a While-Drilling Energy-Harvesting Device Based on Piezoelectric Effect

A while-drilling energy harvesting device is designed in this paper to recovery energy along with the longitudinal vibration of the drill pipes, aiming to serve as a continuous power supply for downhole instruments during the drilling procedure. Radial size of the energy harvesting device is determined through the drilling engineering field experience and geological survey reports. A piezoelectric coupling model based on the selected piezoelectric material was established via COMSOL Multiphysics numerical simulation. The forced vibration was analyzed to determine the piezoelectric patch length range and their best installation positions. Modal analysis and frequency response research indicate that the natural frequency of the piezoelectric cantilever beam increased monotonously with the increase of the piezoelectric patch’ thickness before reaching an inflection point. Moreover, the simulation results imply that the peak voltage of the harvested energy varied in a regional manner with the increase of the piezoelectric patches. When the thickness of the piezoelectric patches was 1.2–1.4 mm, the designed device gained the best energy harvest performance with a peak voltage of 15–40 V. Works in this paper provide theoretical support and design reference for the application of the piezoelectric material in the drilling field.

Influence of the uniaxial stress $p_2$ and transverse fields $E_1$ and $E_3$ on the phase transitions and thermodynamic characteristics of GPI ferroelectric materials

A modified GPI model that accounts for the piezoelectric coupling between the ordered structural elements and the strains $\varepsilon_j$ has been used for studing of effects arising in GPI ferroelectrics under the action of the uniaxial stress $p_{2}$ and electric fields $E_1$ and $E_3$. The polarization vectors and components of static dielectric permittivity are calcucated in the two-particle cluster approximation for mechanically clamped crystal, and piezoelectric and thermal parameters are also determined. The influence of the simultaneous action of the stress $p_{2}$ and fields $E_1$ and $E_3$ on the phase transition and physical characteristics of GPI crystal has been studied.

The C-eigenvalue of third order tensors and its application in crystals

<p style='text-indent:20px;'>In crystallography, piezoelectric tensors of various crystals play a crucial role in piezoelectric effect and converse piezoelectric effect. Generally, a third order real tensor is called a piezoelectric-type tensor if it is partially symmetric with respect to its last two indices. The piezoelectric tensor is a piezoelectric-type tensor of dimension three. We introduce C-eigenvalues and C-eigenvectors for piezoelectric-type tensors. Here, "C'' names after Curie brothers, who first discovered the piezoelectric effect. We show that C-eigenvalues always exist, they are invariant under orthogonal transformations, and for a piezoelectric-type tensor, the largest C-eigenvalue and its C-eigenvectors form the best rank-one piezoelectric-type approximation of that tensor. This means that for the piezoelectric tensor, its largest C-eigenvalue determines the highest piezoelectric coupling constant. We further show that for the piezoelectric tensor, the largest C-eigenvalue corresponds to the electric displacement vector with the largest 2-norm in the piezoelectric effect under unit uniaxial stress, and the strain tensor with the largest 2-norm in the converse piezoelectric effect under unit electric field vector. Thus, C-eigenvalues and C-eigenvectors have concrete physical meanings in piezoelectric effect and converse piezoelectric effect. Finally, by numerical experiments, we report C-eigenvalues and associated C-eigenvectors for piezoelectric tensors corresponding to several piezoelectric crystals.</p>

POTÊNCIA GERADA EM UM SISTEMA DINÂMICO DECAPTAÇÃO DE ENERGIA CONTROLADO VIA MÉTODO LQR: COMPARAÇÃO ENTRE EXCITAÇÃO PERIÓDICA E NÃO-IDEAL

Most of active control in vibrational dynamic systems is used to reduce vibrations. However,the aim of this research is specifically the use of vibrations to generate electrical energy, in such a way that the vibration becomes a desired phenomenon. In this way, the intention is to use the Optimal Control via Linear Quadratic Regulator (LQR), resulting in greater transduction of vibrational energy to electric power, varying the excitation type and performing an analysis of the stabilityand the effects of control to the dynamic system.The analyzed system is a bimodal mass-spring-damper with piezoelectric coupling-mechanic who suffers excitations periodic and non-ideal. This work intends to determine which system generates more electric power.