Papers by Keyword: Piezoelectricity

Abstract: Amongst current aircraft research topics, morphing wing is of great interest for improving the aerodynamic performance. A morphing wing prototype has been designed for wind tunnel experiments. The rear part of the wing - corresponding to the retracted flap - is actuated via a hybrid actuation system using both low frequency camber control and a high frequency vibrating trailing edge. The camber is modified via surface embedded shape memory alloys. The trailing edge vibrates thanks to piezoelectric macro-fiber composites. The actuated camber, amplitude and frequency ranges are characterized. To accurately control the camber, six independent shape memory alloy wires are controlled through nested closed-loops. A significant reduction in power consumption is possible via this control strategy. The effects on flow via morphing have been measured during wind tunnel experiments. This low scale mock-up aims to demonstrate the hybrid morphing concept, according to actuator capabilities point of view as well as aerodynamic performance.

Abstract: (Na_0.5Bi_0.5)_0.94Ba_0.06TiO₃ (NBBT) ceramics doped with 0.1∼2.0 mol.% Ba (Zr_0.05Ti_0.95)O₃ were investigated in terms of the sintering, microstructure, phase transition, and piezoelectric properties. BZT doping has no remarkable effect on the microstructure and densification within the studied doping content. Up to 2 mol.% BZT can dissolve into the lattice of NBBT ceramics, and the structure symmetry is not changed. However, a significant change in the piezoelectric properties took place. The piezoelectric coefficient d₃₃ for the 0.1 wt.% BZT-doped NBBT ceramics sintered at 1150 °C was found to be 120 pC/N and the electromechanical coupling factor k_p = 0.24.

Abstract: Current work is devoted to the problems of mathematical modeling of electrically polarized nanomaterials using LAMMPS software. There are next methods in this software for modeling of such kind: the fluctuating charge method; the adiabatic core-shell method; the thermalized Drude dipole method. This work provides information on advantages and disadvantages of each method; well-structured scripts for LAMMPS software. As our primary research is devoted to the crystalline elastic materials, much attention is given to the 1st and 2nd methods. Main purpose of research is to build models for zinc oxide (ZnO) for identification of elastic and piezoelectric constants and behavior of nanostructures in different fields. Results for analysis are given in figures and tables.

Abstract: Crystals of the 422 symmetry class exhibit interesting piezoelectric behavior, as their piezoelectric tensor has only a single non-zero coefficient, d₁₂₃ = d₁₄: such unique behavior has the potential to enable novel gyroscopic sensors and high-precision torsional MEMS actuators. Although alpha-phase tellurium dioxide (paratellurite, alpha-TeO₂) is one of the few materials belonging to this symmetry class, this material has been primarily studied for its interesting optical properties. Indeed, a large uncertainty in the piezoelectric coefficient of paratellurite exists, with d₁₂₃ measurements on single crystals ranging from 8.13 pC/N to 14.58 pC/N; this large uncertainty results from the difficulty in using conventional piezoelectric characterization techniques on paratellurite, and impedes adoption of this extraordinary material. The present study characterizes the piezoelectric behavior of this interesting material using two independent techniques, (1) a three dimensional laser Doppler interferometer system, and (2) electrochemical impedance spectroscopy (EIS). The experimental results are analyzed using numerical simulations for dynamic excitation conditions over a frequency range of 20 Hz to 200 kHz.

Abstract: High temperature piezoelectric materials have numerous potential applications, including high temperature ultrasound NDT, MEMS, sensors, or actuators. However, conventional piezoelectric materials are unsuitable for operation above 400°C. Lithium niobate (LiNbO₃) is a promising candidate because of its very high Curie temperature (approximately 1210°C) and reasonable piezoelectric coefficients. However, the piezoelectric properties are not sufficiently understood, partly due to the difficulties in characterizing this behavior at high temperature. Degradation mechanisms well below the Curie temperature, suspected to include phase transformations, oxygen loss, and excessive ionic conductivity, further deteriorate this property. In order to better understand these physical mechanisms, electrochemical impedance spectroscopy (EIS) is used to characterize monocrystalline LiNbO₃ from room temperature to 500°C, with excitations from 20 Hz to 20 MHz. An equivalent circuit model analysis, including resonant frequencies, is developed to investigate the temperature dependence of the piezoelectric behavior, as well as the mechanical elasticity and damping. Numerical values extracted from this analysis allows for numerical simulations to model device behavior.

Abstract: This article will present a morphing wing actuated using both surface embedded Shape memory alloys (SMAs) and trailing edge Macro-fiber composites (MFCs). This combination enables the airfoil to simultaneously achieve large scale deformations at low frequencies as well as rapid actuation with a limited amount of displacement. Thereby not only can the shape of the airfoil be optimized in function of the current mission profile but also the shear layer can be influenced. Each actuator is modelled using both a finite element and/or an analytical model and the results will be verified experimentally.

Abstract: Lead zirconate titanate (PZT)-based nanocomposites embedded with ZrO₂ nanoparticles were fabricated by citrate precursor route from metastable phases in situ. The effect of ZrO₂ content on mechanical and piezoelectric properties of composites was investigated. m-ZrO₂ particles covering 30-70 nm are dispersed homogenously inside the PZT matrix grain with stress strips around m-ZrO₂ nanoparticles. The fracture mode changes from intergranular to intragranular with increasing the amount of ZrO₂. Transformation toughening and nanoparticle dispersion toughening of ZrO₂ contributed to the reinforcement of the PZT/ZrO₂ nanocomposites. It is exciting to found that the mechanical properties as well as the piezoelectric properties were both increased compared with those of monolithic PZT when add a certain amount of ZrO₂.

Abstract: We confirm piezoelectric performance of bottom electrospun PVDF-TrFE mat is higher than that of top mat and report the mechanism of additional poling process of electrospun nanofibers by local electric field which is originating from residual charges in far-field electrospinning process. Piezoelectric output measurement of poly (vinylidene fluoride-co-trifluoroethylene) electrospun nanofibers was performed by push test and output signals of bottom and top were compared. The local electric field strength calculated by simulation was higher than reported electric field strength of near-field electrospinning (10 MV/m). It can be concluded that the piezoelectric outputs of electrospun nanofibers tend to be improved by residual charge density and electrospinning condition.

Abstract: Piezoelectric properties of ZnO nanowires orientated along [0001] are investigated via density functional theory (DFT). A new method to calculate the volume of nanowires was proposed, which is crucial to the value of piezoelectric coefficients. Results show that the axial effective piezoelectric coefficients are 29.99 Cm^-2, 25.93 Cm^-2, 22.82 Cm^-2 for ZnO nanowires with diameters of about 0.6 nm, 1.2 nm, 1.8 nm, which are considerably larger than that of the bulk (20.19Cm^-2). It is found that the change in volume during the strain played a dominated role in size effects. This work helps to gain a deeper understanding of the piezoelectric size effects in ZnO nanowires.

Abstract: At the moment a problem of fracture and lifetime estimation for piezoelectric materials is not completely solved. The paper considers fundamentals of linear fracture electromechanics, fracture parameters and fracture criteria. The main difference from linear mechanics is crack face boundary conditions taking into account relative permeability of media inside the crack gap and coulomb traction. Different types of crack face boundary conditions and their numerical implementation are described. The paper presents results of finite element modeling of fracture toughness experiments on the compact tension specimens under combined electromechanical loading. Different types of crack face boundary conditions were tested and comparison of fracture parameters and fracture criteria was carried out.