Search Results (6)

Piezoceramic products are actively used in modern technical devices and appliances. Disk piezoelectric devices are widely used in elements of information systems: in wireless communication, elements of satellite communication, global positioning systems. Among such devices, microwave piezo motors on traveling waves of various types are distinguished, including a motor built on an electromechanical disk converter, which performs non-axisymmetric oscillations under the action of a harmonic electric load. In this study, we perform separation of the electrode coating of the plate with thin diametrical dielectric sections and introduce a time-varying electric potential difference of different amplitude or phase to individual parts of the plate. We study the problem of non-axisymmetric planar oscillations of a piezoceramic disk with thickness polarization and the problem of optimization of the electromechanical coupling coefficient (EMCO) value as a function of an infinite number of parameters in space $l_2$ of square summable sequences. Full article

To significantly reduce the amplitude of longitudinal vibrations of the beam in the vicinity of its natural frequencies, a fundamentally new method of damping vibrations is used. For this purpose, the beam surfaces are covered with layers of polarized piezoceramics with a strong piezoelectric effect. We will use two types of electrical conditions on the electrodes of the piezoelectric layers: short-circuited electrodes and disconnected electrodes. On short-circuited electrodes, the electric potential is zero. As a result of the piezoelectric effect, an electric charge appears on the disconnected electrodes when the beam is deformed. The electroelastic state of a beam with different electrical conditions is described by different boundary value problems. A new approach to damping vibrations in the vicinity of natural frequencies is based on the following rule for controlling the dynamic characteristics of a structure: when the beam vibration frequency approaches its natural vibration frequency, we change the electrical conditions on the electrodes of the piezoelectric layers, thereby changing the spectrum of its natural frequencies. Let, for example, the vibration frequency of a beam with short-circuited electrodes approach its natural frequency. In this case, the amplitudes of the sought quantities grow without limit. The natural frequency spectrum of a beam with disconnected electrodes will differ from the spectrum of a beam with short-circuited electrodes. As a result, the amplitudes of the sought quantities will decrease. It is shown that the efficiency of vibration damping can be significantly increased by choosing the direction of the preliminary polarization of the piezoelectric material and the location of its electrodes. Numerical examples are given that demonstrate the effectiveness of the proposed method. The advantage of the method lies in its simplicity and the low cost of the piezoelectric material, which serves as a non-inertial damper. Full article

The manipulator is the key component of the micromanipulator. Using the axial expansion and contraction properties, the piezoelectric tube can drive the manipulator to achieve micro-motion positioning. It is widely used in scanning probe microscopy, fiber stretching and beam scanning. The piezoceramic tube actuator used to have continuous electrodes inside and outside. It is polarized along the radial direction. There are relatively high polarization voltages, but poor axial mechanical properties. A new tubular actuator is presented in this paper by combining interdigitated electrodes and piezoceramic tubes. The preparation, polarization and mesoscopic mechanical properties were investigated. Using Lead Zirconate Titanate (PZT-52) as a substrate, the preparation process of interdigitated electrodes by screen printing was studied. For initial polarization voltage determination, the local characteristic model of the actuator was extracted and the electric field was analyzed by a finite element method. By measuring the actuator’s axial displacement, we measured the actuator’s polarization effect. Various voltages, times and temperatures were evaluated to determine how polarization affects the actuator’s displacement. Optimal polarization conditions are 800 V, 60 min and 150 °C, with a maximum displacement of 0.88 μm generated by a PZT-52 tube actuator with interdigitated electrodes. PZT-52 tube actuators with a continuous electrode cannot be polarized under these conditions. The maximum displacement is 0.47 μm after polarization at 4 kV. Based on the results, the new actuator has a more convenient polarization process and a greater axial displacement from an application standpoint. It provides technical guidance for the preparation and polarization of the piezoceramic tube actuator. There is potential for piezoelectric tubular actuators to be used in a broader range of applications. Full article

Ferro-piezoceramic materials (FPCM) with different degrees of ferrohardness were fabricated by double solid-phase synthesis followed by the sintering technique using hot pressing method. The X-ray studies carried out in a wide temperature range showed that with increasing temperature, each of the studied FPCM undergoes a series of phase transformations, accompanied by a change in the symmetry of the unit cell. In this case, near the phase transition to the nonpolar cubic phase, in each of the FPCM, the formation of a fuzzy symmetry region is observed, which is characterized by weak distortions and temperature–time instability of the crystal structure. The study of the piezoelectric modulus d₃₃ in the quasi-static regime as a function of temperature made it possible to reveal the different nature of its behavior in materials of various degrees of ferrohardness. It was shown that the conservation of the state in ferrosoft materials above the Curie temperature is associated with the relaxation nature of the change in their properties, the existence of a region of fuzzy symmetry (noncubic phase) in them above the Curie temperature, and increased inertia of the system. The expediency of taking into account the presented results in the development of electromechanical converters based on FPCM of various degrees of ferrohardness, operated under temperature effects, including cyclic ones, was shown. Full article

Synchronized-switching techniques have significantly enhanced the harvested energy from semipassive and active surrounding ambient mechanical vibration harvesters. They have allowed a large improvement of vibration-control efficiency using piezoelectric devices. Unfortunately, for such techniques, dielectric limitations appear as soon as the piezoceramic operates under external solicitation of higher amplitudes and frequencies. Under extreme conditions, active materials exhibit nonlinear behavior related to dielectric hysteresis that significantly reduces their performance. In this work, we focus on this nonlinear behavior and its consequences in terms of system efficiency. We apply a realistic model including accurate material laws. In such models, a constant piezoelectric coupling $d_{31}$ is not suitable as a coefficient anymore and it should be replaced by a function depending on the polarization level through the active material. The response of more realistic systems including hysteresis was taken into account and compared with the basic model, where a constant $d_{31}$ was considered. Full article

According to the EU-Directives 2002/95/EC, 2002/96/EC, lead-based piezoceramics must be substituted in the future with more environmentally friendly alternatives, only when a reliable alternative is found. This is why an increasing interest has grown in the research community to find lead free piezoelectric materials that fulfil the requirements for this substitution. Different families of compounds have been shown to be possible candidates for this use, such as bismuth and niobates based perovskites, pyrochlores, etc. However, a material with piezoelectric coefficients similar to those of PZT (lead zirconate titanate, Pb[Zr_xTi_1-x]O₃) has not been yet found. Besides, each of these families has its specific characteristics in terms of remnant polarization, coercive field or application temperature. Thus, the choice of each material should be made according to the specific needs of the application. In this sense, Aurivillius-type structure materials (also known as Bismuth Layered Structure Ferroelectrics, BLSF) can take advantage of their specific properties for uses as Lead Free Piezoelectric systems. Some of them have a high Curie temperature, which make them good candidates to be used as high temperature piezoelectrics; high coercive fields, which facilitates their use as actuators; or a high switching fatigue resistance, which can be useful for future applications as Ferroelectric Random Access Memories (FERAM). Full article