混凝土结构的压电声波检测分析

本文介绍了混凝土结构的压电体波和表面波检测的主要进展,对两种压电声波检测的优缺点进行了总结。体波检测设备一般埋入混凝土内部,需要选择合理的检测部位,检测结果较为精确;声表面波检测无需选择特定的部位,但是检测深度有限。在实际检测工作过程中,可以联合两种方法相互验证。     

High-performance Pb(Ni1/3Nb2/3)O3-PbZrO3-PbTiO3 ceramics with the triple point composition

Ternary 0.552Pb(Ni_1/3Nb_2/3)O₃-xPbZrO₃-(0.448-x)PbTiO₃ (PNN-PZ-PT) ceramics near the triple point compositions were fabricated by an improved two-step sintering method. The triple point composition 0.552PNN-0.135PZ-0.313PT ceramic has outstanding piezoelectric performance with piezoelectric coefficient d₃₃ = 1200 pC/N. Its easy fabrication and low cost make this piezoelectric material an excellent candidate for high sensitivity sensors and ultrasonic transducers. The evolution of domain structures for ceramics with composition near the triple point provides deeper insight into the mechanism of ultrahigh piezoelectric properties of PNN-PZ-PT ceramics.     

Surface structure and quenching effects in BiFeO3-BaTiO3 ceramics

The structure and properties of Mn-doped 0.67BiFeO₃-0.33BaTiO₃ ceramics are systematically investigated with respect to the effects of annealing prior to rapid cooling by quenching in air. Air-quenching induces a change in crystal structure from pseudo-cubic to rhombohedral, with higher quenching temperatures leading to an increased rhombohedral distortion. These structural changes are correlated with the appearance of more well-defined ferroelectric domain configurations. It is shown that the surface preparation procedures for XRD measurements can induce significant changes in the peak profiles, indicating differences in crystal structure between the surface and bulk regions. Frequency dispersion in the temperature-dependent relative permittivity for the as-sintered sample is significantly reduced after quenching, accompanied by enhancement of the Curie point and improved temperature-stability of piezoelectric properties. It is proposed that the formation of defect clusters by A-site cation diffusion during cooling is circumvented by quenching, leading to the observed modification of structural distortion and ferroelectric properties.     

Improved electric-field-induced strain and strong photoluminescence properties in novel Er3+-modified 0.93Bi0.5Na0.5TiO3-0.07BaTiO3 multifunctional ceramics

Recently, the progress of electronic devices toward miniaturization has strongly promoted development of multifunctional materials possessing multiple desirable properties. In this study, we develop and fabricate 0.93Bi_0.5Na_0.5TiO₃-0.07BaTiO₃-xEr multifunctional ceramics which show simultaneously considerable electric-field-induced strain and bright green light emission properties. With the introduction of Er³⁺, the ceramics gradually transform from non-ergodic relaxor phase to ergodic relaxor phase which could reversibly transform to ferroelectric phase under the electric field. As a result, with improving Er³⁺ content, the shape of the polarization-electric field loops of the ceramics become pinched, and it is obvious that the negative strain disappears while the positive strain gradually increases and reaches a maximum value 0.46% at x = 1.2 mol%. Besides, After the ceramics are poled, the light emission peak are greatly enhanced attributed to the decreased crystal symmetry and increased domain size, and is the strongest at x = 1.2 mol%. These results indicate that 0.93Bi_0.5Na_0.5TiO₃-0.07BaTiO₃-xEr ceramics are good candidates for developing multifunctional optoelectronic devices.     

一种压电半导体纳米线的热电耦合性能研究

采用有限元分析方法,研究了一种n型压电半导体纳米线(氧化锌)的电热耦合性能,分析了外部温度对氧化锌纳米线内部机械场、电场及电流场分布的影响,并讨论了本构方程线性化对电学参数的影响。研究结果表明,温度对氧化锌纳米线的电场、载流子浓度和电流密度影响很大,采用线性本构和非线性本构求得的电场、电子浓度和电流密度最大相差分别为24%,32%和68%,基于非线性本构分析压电半导体的电学性能会引起很大误差。该研究结果可为压电半导体器件利用温度调控电场、电流提供理论依据。     

预压力对压电驱动履带移动系统的性能影响

为了提高夹心式压电驱动移动系统的机械输出性能，提出了一种U型预压力调节机构，并开展了预压力对夹心式压电驱动履带移动系统输出性能影响关系的实验研究。首先，针对U型预压力调节机构的安装对夹心式压电振子的振动特性影响关系开展了有限元仿真分析，发现U型预压力调节机构始终处在夹心式压电振子的两相工作模态振动节点位置；其次，开展了夹心式压电驱动履带移动系统的原理样机的预压力调节测试实验，确定了系统的最大输出牵引力及其所对应的最佳预压力；最后，在最佳预压力工作状态下，开展了原理样机的牵引力特性、越障性能以及模拟月壤环境下的运动特性实验。研究结果表明，在最佳预压力工作状态下，夹心式压电驱动履带移动系统的机械输出性能最佳，为其进一步在月面巡视器上的应用提供了技术支持和试验基础。     

Electro-magneto temperature-dependent vibration analysis of functionally graded-carbon nanotube-reinforced piezoelectric Mindlin cylindrical shells resting on a temperature-dependent,orthotropic elastic medium

Vibration smart control analysis of a temperature-dependent functionally graded-carbon nanotube-reinforced piezoelectric cylindrical shell embedded in an orthotropic elastic medium is investigated. The mixture law is used for obtaining the material properties of the structure. The structure is subjected to a 2D magnetic field. Considering the first-order shear deformation theory, the motion equations are obtained. Based on an analytical method and differential quadrature method, the frequency is calculated. The effects of applied voltage, magnetic field, volume percent, and distribution type of carbon nanotubes, temperature, orthotropic elastic medium, and length to radius ratio of the shell are shown on system frequency.     

Wind turbine speed control of a contactless piezoelectric wind energy harvester

ABSTRACT

Wind turbine control is an important task to make the electricity generation secure in terms of energy demand and machine safety. It also yields to control the desired power level and optimized energy because of the assignment of turbine speed. The contactless piezoelectric wind energy harvester (CPWEH) used in this study has three piezoelectric layers located around the shaft with 120 degrees apart and they are buckled by the magnetic force without any physical contact. The superiority of this device is to generate energy for low wind speeds such as 1.5 m/s. However, for high speeds, high total harmonic distortions (THDs) govern the waveforms, thus controlling the turbine speed becomes necessary for optimizing the output power. Encouraged by this, a small low inertia dc generator is coupled with the wind turbine, and the generator terminals are connected to a resistor through a power switch to generate a braking torque that opposes to wind speed direction. By controlling the switch properly, turbine speed is ensured to remain within a certain band, which accordingly prevents the turbine from rotating very fast at damaging wind speeds. Several experiments are performed on the developed CPWEH with/without the presented control scheme which prove the existence of promising performance of our proposal.     

An effective method of bulk materials moisture measurement using capacitive sensors

When we speak about capacitance moisture meters for bulk materials we have to face with different values of dielectric permittivity for different bulk materials in dehydrated state, what causes a method error that can be named ‘type uncertainty’. Besides, different varieties of the same material have different values of dielectric permittivity, which depend from geographical origin, processing conditions etc. It can be hardly predicted automatically and type uncertainty can be compensated only in separate situations with the help of preliminary calibration. Main tasks of the research are to develop new comparison principle of moisture measurement with better accuracy due to effective compensation of physical, chemical and granulometric composition influence on the result of moisture measurement, develop new primary and secondary instrument transducers. Moisture sensor consists of four measuring capacitors. Two of them should be filled with a sample, which moisture content should be determined, and other pair of measuring capacitors should be filled with a same substance, but previously dehydrated. Mathematical models, developed to take into account granulometric composition of a bulk material were used to carry out a comparison analysis for three types of instrument measuring transducers. Obtained results proved that suggested principle of moisture measurement provides effective compensation of granulometric composition influence. Developed measuring principle had been experimentally tested what helped to confirm that it provides two times better compensation of different physical and chemical composition for different materials in comparison with the direct comparison method.     

Fabrication of 0.24Pb(In1/2Nb1/2)O3-0.42Pb(Mg1/3Nb2/3)O3-0.34PbTiO3 transparent ceramics by conventional sintering technique

0.24Pb(In_1/2Nb_1/2)O₃-0.42Pb(Mg_1/3Nb_2/3)O₃-0.34PbTiO₃ transparent ceramics were fabricated by a conventional sintering technique. Through optimization of sintering conditions of calcination and sintering temperatures and time, the obtained ceramics showed high optical transmittance of 53% and 71% at light wavelengths of 1300 and 2000 nm, respectively. The ceramics showed a rhombohedral to tetragonal phase transition at ~120°C and a tetragonal to cubic phase transition at 222°C. These transition temperatures were higher than those of 0.67Pb(Mg_1/3Nb_2/3)-0.33PbTiO₃ ceramics. In addition, the ceramics had a ferroelectric hysteresis loop, a large piezoelectric constant d₃₃ of 407 pC/N, and a planar electromechanical coupling factor k_p of 52%. These results suggest that the transparent ceramics may be used as a temperature-stable, linear electro-optic material.