Добірка наукової літератури з теми "Piezoceramic layers"

In present study, the polymerization depths for the implementation of the laser stereolithography process in the system (oligomer - piezoceramics) on the wavelengths of 445-465 nm UV range were determined in the original BTO, KNN and NBT lead-free piezoceramic pastes. It was shown that powder pastes, which provide a polymerization depth more than 150 μm, are promising for using in 3D printing. Such depth was chosen to guarantee a sufficient overlap of neighboring layers during polymerization, at the laser beam velocity speed from 1 m/s and the distance between the laser paths of 50 μm. For NBT pastes, successful photo polymerization was carried out for the first time, and for KNN paste the process performance was significantly increased. Keywords: lead-free piezoceramics, stereolitography (SLA) - based ceramics 3D printing, UV- curing and bandwidths

Radially layered cylindrical piezoceramic/epoxy composite transducers have been designed by integrating the excellent performance of piezoelectric/polymer composites and the radial radiation ability of cylindrical configurations, which are promising in developing novel ultrasonic and underwater sound techniques. Our previous study has explored the effects of the external resistance on the electromechanical characteristics of the transducer, and obtained some valuable findings. To clearly understand the electromechanical characteristics of the transducer and to guide the device design, in this paper, parametric analysis was performed to reveal the effects of multiple key factors on the electromechanical characteristics. These factors include material parameters of epoxy layers, piezoceramic material types, and locations of piezoceramic rings. In order to better analyze the influence of these factors, a modified theoretical model, in which every layer has different geometric and material parameters, was developed based on the model given in the previous work. Furthermore, the reliability of the model was validated by the ANSYS simulation results and the experimental results. The present investigation provides some helpful guidelines to design and optimize the radially layered cylindrical piezoceramic/epoxy composite transducers.

In present study, the polymerization depths for the implementation of the laser stereolithography process in the system (oligomer - piezoceramics) on the wavelengths of 445–465 nm UV range were determined in the original BTO, KNN and NBT lead-free piezoceramic pastes. It was shown that powder pastes, which provide a polymerization depth more than 150 µm, are promising for using in 3D printing. Such depth was chosen to guarantee a sufficient overlap of neighboring layers during polymerization, at the laser beam velocity speed from 1 m/s and the distance between the laser paths of 50 µm. For NBT pastes, successful photo polymerization was carried out for the first time, and for KNN paste the process performance was significantly increased.

Magnetic field sensors using magnetoelectric (ME) effects in planar ferromagnetic-piezoelectric heterostructures convert a magnetic field into an output voltage. The parameters of ME sensors are determined by characteristics of the magnetic constituent. In this work, the low-frequency ME effects in heterostructures comprising a layer of antiferromagnetic hematite α-Fe2O3 crystal with easy-plane anisotropy and a piezoelectric layer are studied. The effects arise due to a combination of magnetostriction and piezoelectricity because of mechanical coupling of the layers. The field dependences of magnetization and magnetostriction of the hematite crystal are measured. The resonant ME effects in the hematite-piezopolymer and hematite-piezoceramic structures are studied. The strong coupling between magnetic and acoustic subsystems of hematite results in a tuning of the acoustic resonance frequency by the magnetic field. For the hematite layer, the frequency tuning was found to be ~37% with an increase in the bias field up to 600 Oe. For the hematite-PVDF heterostructure, the frequency tuning reached ~24% and the ME coefficient was 58 mV/(Oe∙cm). For the hematite-piezoceramic heterostructure, the frequency tuning was ~4.4% and the ME coefficient 4.8 V/(Oe∙cm). Efficient generation of the second voltage harmonic in the hematite-piezoceramic heterostructure was observed.

The work develops a generalized approach to the study of thickness (radial) vibrations arising in the piezoceramic plates, cylinders, spheres under electrical loads. The state of the problem and the main approaches, used in the problems of studying the oscillations of electroelastic bodies, are described. The use of multilayer elements with electroded interface surfaces and variable direction of polarization of the layers increases the conversion efficiency of electrical energy into mechanical energy, so multilayer piezoceramic plates, cylinders, spheres with changing polarization directions with electroded interfaces are considered. Because of piezoelectric elements are often embedded in the housing and supplemented with matching layers to protect against mechanical damage, it is necessary to study their effect on the oscillations of the element. The proposed approach makes it possible to study the vibrations of plane, cylindrical and spherical bodies with layers made of various electroelastic and elastic materials. Numerical implementation is carried out using finite differences. Nonstationary oscillations of PZT-4 ceramic elements at zero initial conditions are investigated. Oscillations of multilayer plates, cylinders and spheres with and without an external elastic or viscoelastic reinforcing layer under impulse and harmonic unsteady loads are investigated and compared. There are found own frequencies for 5-layer bodies of different geometry with and without an external layer. The first natural frequency for cylinder and sphere corresponds to the radial mode of oscillations, while the second natural frequency for cylinders and spheres and the first for flat bodies are almost equal and correspond to thickness mode. The transient processes in the elements under impulse loads and the influence of the outer elastic layer (housing or matching layer) are studied, taking into account the Rayleigh attenuation. It is established that for a flat layer the outer layer increases the amplitude and the period of free vibrations after removing the load, and for cylinders and spheres it decreases. The presence of an elastic layer enhances the third and dampens the fourth natural frequency of the transducer, thereby expanding the frequency range of its operation.

ABSTRACTThe nonlinear characteristics of a simply-supported three-layer circular piezoelectric plate-like power harvester near resonance are examined in the paper, where the energy-scavenging structure consists of two properly poled piezoceramic layers separated by a central metallic layer. The structure is subjected to a uniform harmonic pressure on the upper surface. Nonlinear effects of large deflection near resonance to induce the incidental in-plane extension are considered. Results on output powers are presented, which exhibit multi-valuedness and jump phenomena.

Modern low-voltage piezoelectric actuators consist of a stack of piezoceramic layers (PZT) with metallic electrodes in between. Due to the use of these parts in automotive applications, a big but sensitive market is opened. During application mechanical stresses are an inherent loading of these electro-mechanical converter components. Therefore some strength of the actuators is necessary to guarantee a demanded life time. Bending and tensile tests were performed on commercial components to measure the strength in axial direction. Fracture surfaces were investigated with the methods of fractography to get information about the weakest links in the microstructure.

We consider geometric and material nonlinearities when studying numerically, by the finite element method, transient three-dimensional electroelastic deformations of a graphite-epoxy square plate sandwiched between two piezoceramic (PZT) layers. Points on the four edges of the bottom surface of the plate are restrained from moving vertically. The two opposite edges of the plate are loaded by equal in-plane compressive loads that increase linearly with time and the other two edges are kept traction free. The plate material is modeled as orthotropic and neoHookean. For the transversely isotropic PZT the second Piola-Kirchhoff stress tensor and the electric displacement are expressed as second degree polynomials in the Green-St. Venant strain tensor and the electric field. Both direct and converse piezoelectric effects are accounted for in the PZT. The plate is taken to have buckled when its centroidal deflection equals three times the plate thickness. The dynamic buckling load for the plate is found to strongly depend upon the rate of rise of the applied tractions. With the maximum electric field limited to 1kV/mm, the buckling load is enhanced by 18.3$\%$ when the PZT elements are activated. For a peak electric field of 30kV/mm, the buckling load increased by 58.5$\%$. When more than 60$\%$ of the surface area of the top and the bottom surfaces of the plate are covered by the PZT layers, then square PZT elements placed symmetrically about the plate centroid provide a larger enhancement in the buckling load than rectangular shaped or cross-shaped PZT elements. An increase in the plate thickness relative to that of the PZT actuators decreases the effectiveness of the PZT in enhancing the buckling load for the plate. The finite element code was modified to also analyze, in time domain, transient deformations of a viscoelastic material for which the second Piola-Kirchhoff stress tensor is expressed as a linear functional of the strain history of the Green-St. Venant strain tensor. It was used to analyze three-dimensional deformations of a thick laminated plate with layers made of aluminum, a viscoelastic material and a PZT. The following two arrangements of layers are considered. In one case a central PZT layer is surrounded on both sides by viscoelastic layers and aluminum layers are on the outside surfaces. The PZT is poled in the longitudinal direction and an electric field is applied in the thickness direction. Thus shearing deformations of the PZT layer are dominant. In the second arrangement, the aluminum layer is in the middle and the PZT layers are on the outside. The poling direction and the electric field are in the thickness direction; thus its extensional deformations are predominant. Three indices are used to gauge the damping of motion of plate particles, and the effectiveness of PZT actuators in enhancing this damping. It is found that the optimum thickness of the viscoelastic layers for maximum total energy dissipation is the same for each set-up. Also, the total thickness of the PZT layers which results in the maximum value of one of these indices of energy dissipation is the same for the two set-ups. Both arrangements give the largest value of this index for a plate of aspect ratio 10. Buckling behavior of a sandwich plate containing a soft core is also studied. The effects of the ratio of the elastic moduli of the outer layers to those of the core, and of the core thickness on the buckling load are analyzed. The top and the bottom layers are connected by very stiff blocks on two opposite edges where in-plane compressive time-dependent tractions are applied.
Ph. D.

Unmanned Aerial Vehicles (UAV) are essentially automatic flight vehicles having dimensions, wingspan and airspeed, smaller than the conventional aerial vehicles. UAVs are employed widely in applications such as surveillance over a short distance, acquisition of a local target, detection of hazardous chemicals / biological agent, exploration of a harmful environment, search operations, etc. UAV can be classified into three main types depending on their method of propulsion and lift. These are fixed wing, rotary wing, and flapping wing. Flapping wing UAVs are more suitable for insect scale flights. Flapping mechanism requires actuators with large stroke periodic (reciprocal) motion at high speed (10-100s of Hz) with large output forces for overcoming the aerodynamic damping. There are several actuation mechanisms applicable to flapping-wing UAVs. The emphasis is on linear actuators, which simplify the mechanical transmission for flapping motions. Most of the prototypes developed so far have employed motor-driven mechanisms to achieve the flapping wing. Unconventional methods such as piezoelectric, thermal, electromagnetic, shape memory, electrostatic, etc. for actuation of flapping wings have also been used. Among the unconventional actuation methods, piezoelectric actuation is the most used mechanism because of its compact size and high-power density. However, the deflection generated by the piezoelectric actuator is intrinsically very small. Therefore, it is necessary to employ numerous types of motion amplification mechanisms to achieve large deflection. The development of an amplification mechanism is a complex procedure. Hence, several efforts have been made to evaluate different forms of piezoelectric actuators for flapping vehicle application. The in-situ piezoelectric actuator, employing piezoceramic coating directly on the structure by a simple method, looks promising for flapping wing application as it generates large displacement compared to the displacement produced by the bulk piezoelectric actuators. Piezoceramic coating is light in weight compared to the bulk piezoelectric actuator, as it is a composite material of highly dense piezoceramic material and less dense polymeric material. The current study evaluates the basic characteristics, performance and the aerodynamic behavior of the in-situ piezoceramic actuator for flapping wing applications. Initially, the basic characteristics of the in-situ piezoceramic actuator were evaluated. Its properties like density, elastic modulus and the transverse piezoelectric coefficient, d31, were evaluated. The density was measured to be 2300 kg/m3. Elastic modulus was measured as 3 GPa. The piezoelectric coefficient, d31 was measured by applying the coating on various substrates such as stainless steel, brass and polymer. Also, the in-situ piezoceramic actuator was applied with different thicknesses 30, 40 and 50 µm on the polymer substrate. The mean value of the measured d31 was found to be -26 pm/V. The performance of the piezoceramic coating (coated on a flexible substrate) was evaluated for flapping wing application using performance metrics from aerodynamic studies. The performance metrics are the tip velocity,, the dynamic electromechanical coupling factor (EMCF), k12, and the elastic energy per unit mass, . These metrics were obtained and verified using an analytical model. Based on these metrics, the performance of the developed flexible actuator was compared with conventional flexible piezoelectric polyvinylidene difluoride (PVDF) actuator. These metrics were found to be better for the developed actuators than PVDF. The best suitable wing configuration was selected using FE modelling based on the tip velocity ( ). It was found that the tip velocity depends on the thickness, length and shape of the flapping wing. Wing shapes of the dragonfly’s, tobacco hawkmoth’s and cicada’s forewings were considered. The thickness and length of the in-situ piezoceramic actuator were also varied. The results obtained through FE modelling were verified experimentally. Dragonfly wing was found to give maximum tip velocity ( ). The maximum value for υ of 114.7 mm/s was obtained for a dragonfly wing having in-situ piezoceramic actuator of 30 mm length from the root of the wing and a thickness of 30 µm. The lift force was measured using a load cell measurement set up in the clamped condition for the dragonfly wing. Insects use a variety of wingbeat kinematics to produce and control aerodynamic forces for their flight. For mimicking an insect flight, the selected actuator needs to be capable of producing insect flight kinematics. Therefore, twisting along with flapping motions of the wings by the in-situ piezoceramic actuators were attempted. Twisting motion of the wing was achieved by actuating two piezoceramic cantilevers type in-situ actuators applied over a wing with sinusoidal signals out of phase with each other by 180°. The fore wing and the hind wing were actuated by sinusoidal signals with a phase difference of 0°, 90°, 180° and 270°. Tip displacements of 4 mm for the fore wing and 3 mm for hind wing were measured. The kinematics of the flapping wing, which has been achieved by other actuators with complex mechanisms can thus be achieved by the simple in-situ piezoceramic actuators. The experiments on the measurement of the lift and kinematics of the flapping wing establishes that the in-situ piezoceramic actuator is a suitable candidate for flapping wing application. The improvement studies on tip velocity were carried out by implementing in-situ bimorph piezoceramic actuators. Dragonfly wings with the piezoceramic layer of thickness 30 µm were considered. As there was a implication of increase in the mass of the wing, selection of length of piezoceramic layers were carried out using FE modelling. The results obtained through FE modelling were verified experimentally. The maximum tip velocity of 245.1 mm/s is obtained for 25 mm length of both piezoceramic coating layers. Modified strip theory based on the blade elemental analysis has been used to study the aerodynamic performance of the three types of wing planforms. Lift, thrust and drag forces generated by the three wing forms have been calculated analytically by the model. As flapping wings are operated at the first mode resonance, the first mode resonant frequency, and the tip displacement at resonance from the experimental results were given as input to the aerodynamic model. The effect of variations in aerodynamic parameters such as incident angle, pitching angle and forward speed on the relevant forces were studied for the in-situ piezoceramic actuator actuated wings of three different wing planforms. For all the three wing planforms, it was observed that the lift increased with incident angle and forward speed and it was less affected by increasing the pitching angle. For the increasing forward speed, incident angle and pitching angle, thrust and drag also increased. The modelling results show that the wings produce positive mean lift and condition where the thrust is more than the drag for all the wing planforms. The overall results show that the in-situ piezoceramic actuator can be employed for flapping wing applications with further efforts.

The aim of the present study is to develop models of active laminated plates containing monolithic piezopolymer sensor layers and a new type of actuator layers made of Piezoelectric Functionally Graded (PFG) material, which is a mixture of piezoceramics and polymer or epoxy matrix. The electromechanical properties of the PFG layers can be tailored varying continuously the piezoceramic volume fraction across the thickness during the manufacturing process. The analysis and numerical simulations are focused on the relationship between the material compositional gradient and electromechanical properties and also dynamic responses of the structure obtained. Three types of functions, which describe the volume fraction distribution of constituents, are considered: exponential, parabolic and sigmoid. The effective properties of the PFG material, i.e. the Young’s modulus and piezoelectric coefficient gradations, are determined using to the rule of mixtures. A constant velocity feedback algorithm is used for the active damping of transverse plate vibration. The dynamic analysis concerns steady-state behavior of rectangular symmetrically laminated plates and is based on hypothesis of the classical plate theory. The numerical simulations are performed to recognize the influence of the applied pattern of the piezoceramic fraction distribution and its parameters on the gradient of elastic and piezoelectric properties within the PFG actuators and, as the final result, the active plate structural response presented in terms of amplitude-frequency characteristics. The changes in both the natural frequencies and resonant amplitudes are compared and the influence of the piezoceramic gradation on the control system operational effectiveness is also indicated and discussed.

Abstract The use of piezoelectric sensor and/or actuator layers in engineering structures provides smart sandwich structures with adaptive responses. Moreover, due to the brittle behavior of piezoceramic materials, inserting nanocomposite and porous layers between piezoelectric layers offers more flexible and lighter structures along with maintaining the advantages of nanocomposite materials. Therefore, in this paper, we have proposed smart sandwich plates consisting of a porous polymeric core and two graphene-reinforced composite (GRC) layers integrated with two piezoceramic layers. The distributions of porosities and randomly oriented graphene particles are assumed to be functionally graded (FG) along the thickness of core and nanocomposite layers, respectively. For the static behavior of the proposed sandwich plates, the coupled electro-mechanical governing equation has been extracted by minimizing potential energy equation with respect to displacement and electrical potential. The governing equation has been discretized by adopting a higher order shear deformation theory (HSDT) of plates and a developed mesh-free method. Using the developed solution framework, the effects of porosity and graphene characteristics, electromechanical loads, and layer thicknesses on the deflection behavior of the proposed FG piezoelectric porous nanocomposite sandwich plates (FG-PPNSPs) have been studied.

It is common practice to reduce the voltage level within piezoelectric actuators by utilizing multiple layers, typically bonded together. Unfortunately, this has a tendency to result in device failure due to delamination. For example, with benders the typical lifetime is 105 to 106 cycles, limiting its use in practical applications. This poses an interesting design tradeoff: the stroke is increased due to sharper gradients between material layers; however, the higher gradients lead to high stress concentrations at those interfaces. One approach to reducing these stresses is to grade the material properties through a monolithic piece of piezoceramic so that no interfaces or bonding elements exist, but this comes at the cost of stroke. This paper explores the design tradeoff inherent to monolithic functionally graded piezoelectrics. An analytical free-displacement model for a monolithic piezoceramic beam with a generic gradient is derived. Key to this is the inclusion of the complex electric field distribution which rises from the non-homogeneous material properties. This model is used along with finite element models to examine the effect of continuous linear and stepwise material gradients on the displacement performance as well as the stress levels. The study shows that using monolithic functionally graded piezocermics can significantly reduce the stresses with only a minor impact on the device stroke.

This paper presents the investigation of a novel concept involving the combination of piezoelectrics and new thin-film battery technology to form multifunctional self-charging, load-bearing energy harvesting devices. The proposed self-charging structures contain both power generation and energy storage capabilities in a multilayered, composite platform consisting of active piezoceramic layers for scavenging energy, thin-film battery layers for storing scavenged energy, and a central metallic substrate layer. Several aspects of the design, modeling, fabrication, and evaluation of the self-charging structures are reviewed. A focus is placed on the evaluation of the load-bearing capabilities of the fabricated self-charging structures through both classical static failure testing as well as dynamic vibration failure testing.

Piezoceramic Patches are commonly used as actuator devices in smart structures if the induced forces are sufficient for the application. To model these devices in a structural dynamics simulation, a finite element model can be augmented by active layers. This needs a suitable element meshing, taking care of the actual shapes and positions of the active patches in use. If many different setups have to be evaluated, which is naturally the case for placement strategies for suitable actuator positions, this approach is quite cumbersome. To ease and speed up the augmentation of fixed finite element models with piezoceramic patches, so called modal correction methods have been successfully used in this context. These approximative methods avoid the remeshing and the reassembling of the underlying finite element model by adapting the modal description of the structural model with the mass, stiffness and electrical coupling effects of the applied patches. In this paper different aspects of this modelling approach are discussed especially for a tool chain to optimize patch locations in an ASAC simulation environment.

Abstract An electromechanical model for a circular piezoelectric actuator is developed. A critical challenge in certain applications employing piezoceramic actuators is to maximize the displacement provided by the actuator while minimizing it power consumption. This problem is addressed here by developing an electromechanical model which can be used to optimize the volume displacement to admittance ratio for various circular actuator designs. The model includes multiple layers with independent radii which can be varied to optimize performance. The piezoceramic, bonding, plating, and mounting materials can be varied to accommodate various design criteria. An advantage of the model lies in the property that for a variety of material configurations, analytic solutions can be obtained. Numerical examples demonstrating the properties of the model are presented.

Abstract. Annotation. Rubber products are widely used in the construction of vehicles, for example, as sealing and protective devices, suspension joints and are the basis of automobile tires. Modern trends related to increasing the level of vehicle safety require the use of innovative approaches in the design and use of new materials with unique properties. This article proposes an approach to create a rubber with sensory properties that can be used in various automotive products and prevent situations that can harm both human health and lead to serious damage to the structure of the vehicle itself. We have developed an intelligent vehicle door seal to prevent injury to a person when the door is closed carelessly. The sealant, which reacts to deformation when a foreign body enters the seal site, consists of rubber with the addition of piezoceramic powder and two electrode layers. Each electrode layer has several parallel strip-like electrodes positioned along the perimeter of the seal. This document describes possible applications for rubber products with sensory properties and an additive method for making such rubber with the addition of piezoceramic powder.

Vibration-to-electricity conversion using piezoelectric transduction has been studied by several researchers over the last decade. PZT (lead zirconate titanate) - based piezoelectric ceramics such as PZT-5A and PZT-5H have been very frequently employed in design of piezoelectric energy harvester beams. Recently, the single-crystal piezoceramics PMN-PT (lead magnesium niobate – lead titanate) and PMN-PZT (lead magnesium niobate – lead zirconate titanate) have also been investigated for electrical power generation due to their large piezoelectric constants (particularly the d31 constant for the bending mode). Piezoelectric, elastic and dielectric properties of these piezoceramics differ from each other considerably. Even though the d31 constants of two piezoceramics might differ by an order of magnitude (e.g. PZT-5A and PMN-PZT), this large difference is not necessarily the case for their power outputs. It is theoretically discussed and experimentally demonstrated in this paper that the d31 piezoelectric constant alone is an insufficient parameter for selecting the best piezoelectric material to design a power generator for vibration-based energy harvesting. Elastic compliance of a piezoceramic has a strong effect on its electrical power output. In addition, since these devices are usually designed for resonance excitation, mechanical damping constitutes another parameter that might change the entire picture regarding the power generation performance. The last one is particularly critical considering the fact that it is difficult to control mechanical damping due to clamped interfaces and adhesive layers in practice. Theoretical comparisons are given for geometrically identical bimorphs with PZT-5A, PZT-5H, PMN-PT (with 30% PT), PMN-PT (with 33% PT) and PMN-PZT layers using an experimentally validated distributed-parameter electromechanical model. Two experimental demonstrations are presented. The first case compares two geometrically identical bimorphs (using PZT-5A and PZT-5H piezoceramics) and shows that the bimorph with PZT-5A can generate larger power than the one with PZT-5H in spite of the larger d31 constant of the latter. The second experimental case compares the power generation performances of a PZT-5H unimorph and a PMN-PZT unimorph. In agreement with the theory, considerably large damping identified for the PMN-PZT unimorph results in much lower power output compared to that of the PZT-5H unimorph.

Vibration-based energy harvesting has attracted interest of researchers from various disciplines over the past decade. In the literature of piezoelectric energy harvesting, the typical configuration is a unimorph or a bimorph cantilevered piezoelectric beam located on a vibrating host structure subjected to base excitations. As an alternative to cantilevered piezoelectric beams, piezoelectric layers structurally integrated on thin plates can be used as vibration-based energy harvesters since plates and plate-type structures are commonly used in aerospace, automotive and marine applications. The aim of this paper is to present experiments and electroelastic finite element simulations of a piezoelectric energy harvester structurally integrated on a thin plate. The finite element model of the piezoceramic patch and the all-edges-clamped plate are built. In parallel, an experimental setup is constructed using a thin PZT-5A piezoceramic patch attached on the surface of all-edges-clamped rectangular aluminum plate. The electroelastic frequency response functions relating voltage output and vibration response to forcing input are validated using the experimentally obtained results. Finally, electrical power generation of the piezoceramic patch is investigated using the experimental set-up for a set of resistive loads. The numerical predictions and experimental results show that the use of all-edge-clamped flexible plate as host structure for piezoelectric energy harvester leads to multimodal vibration-to-electricity conversion.