压电曲梁单元及其形状控制

航空航天等领域对结构形状要求非常严格,利用压电材料的逆压电效应控制结构变形是现代空间结构形状控制中一个很好的选择。本文基于一般曲梁单元,推导了空间压电曲梁单元的方程表达式,主体壳结构与压电单元之间利用约束方程连接。在此基础上进一步采用最小二乘法得到了压电控制单元上的最优电压,实现了压电曲梁单元的变形控制。数值算例表明了...     

Polyfluoroalkylated tripyrazolylmethane ligands: Synthesis and complexes

Tripyrazolylmethanes represent a novel class of uncharged ligands analogous to charged tripyrazolylborates (scorpionates), which are isoelectronic and isolobal with cyclopentadienides. We report here a straightforward synthesis of the first polyfluoroalkylated tripyrazolylmethane ligands bearing C₄F₉-C₁₂F₂₅ ponytails, based on allylation/perfluoroalkylation/reduction sequence of transformations of 2,2,2-tripyrazol-1-ylethanol. Model complexation reactions of these ligands gave sandwich complexes of copper(II), nickel(II), cobalt(II) and iron(II), the structure of which was confirmed by detailed MS analysis, as well as by NMR spectroscopy for the fourth diamagnetic complex. Fluorophilicity of the ligands and their complexes peaks for C₁₀F₂₁ ponytail but lies below zero.     

Associative combination of lone pair-π, π-π and anion-π interactions observed in a ternary system comprising Mg(II)-malonate-2-aminopyridine-hexafluoridophosphate

One Mg(II) malonate complex with protonated 2-aminopyridine and hexafluoridophosphate as counterions, (C₅H₇N₂)₄[Mg(C₃H₂O₄)₂(H₂O)₂](PF₆)₂ (1) [C₅H₇N₂ = protonated 2-aminopyridine, C₃H₄O₄ = malonic acid] has been synthesized from purely aqueous media just by mixing the reactants in their stoichiometric proportion and its crystal structure has been determined by single-crystal X-ray diffraction. The role of weak forces like lone pair?π and anion?π interactions in influencing the self-assembly process appears to be of importance. A rare combination of lone pair?π and anion?π interactions in 1, of the type lone pair?π/π?π/π?anion, is observed, and this unusual supramolecular network is fully described here.     

Estimation of frequency characteristics of the Tonpilz piezoelectric transducer with a bending piezoelectric disk

A Tonpilz piezoelectric transducer which has a bending piezoelectric disk on the radiation surface for widening the frequency band to improve sonar detection performance in shallow water has been proposed. Variance of transmitting voltage response of this transducer depend on the phase difference between signals which applies to the ring-stack and the bending-disk piezoelectric resonators. Thus, an estimation of an optimal phase difference, which can be applied for obtaining the maximum value of transmitting voltage response, is important factor to assemble sonar array with sonar transducers. In this paper, we applied three methods to estimate transmitting voltage response at an arbitrary phase difference from a few measurements, and the estimation errors of those methods affected by internal impedances of power sources and/or noise are investigated to select the best method. The effectiveness of the best method was verified by water-pool experiments.     

High-frequency ultrasonic transducer based on lead-free BSZT piezoceramics

This paper describes the fabrication and evaluation of a high-frequency (40 MHz) transducer based on lead-free piezoceramics for ultrasonic imaging. The transducer with an aperture size of 0.9 mm has been fabricated using barium strontium zirconate titanate ((Ba_0.95Sr_0.05)(Zr_0.05Ti_0.95)O₃, abbreviated as BSZT) ceramics. The lead-free BSZT has a piezoelectric d₃₃ coefficient of 300 pC/N and an electromechanical coupling factor k_t of 0.45. High-frequency ultrasound transducers were fabricated and a bandwidth of 76.4% has been achieved with an insertion loss of −26 dB. Applications in high resolution biological and medical imaging could be possible with this lead-free material.     

Love waves in functionally graded piezoelectric materials by stiffness matrix method

A numerical matrix method relative to the propagation of ultrasonic guided waves in functionally graded piezoelectric heterostructure is given in order to make a comparative study with the respective performances of analytical methods proposed in literature. The preliminary obtained results show a good agreement, however numerical approach has the advantage of conceptual simplicity and flexibility brought about by the stiffness matrix method. The propagation behaviour of Love waves in a functionally graded piezoelectric material (FGPM) is investigated in this article. It involves a thin FGPM layer bonded perfectly to an elastic substrate. The inhomogeneous FGPM heterostructure has been stratified along the depth direction, hence each state can be considered as homogeneous and the ordinary differential equation method is applied. The obtained solutions are used to study the effect of an exponential gradient applied to physical properties. Such numerical approach allows applying different gradient variation for mechanical and electrical properties. For this case, the obtained results reveal opposite effects. The dispersive curves and phase velocities of the Love wave propagation in the layered piezoelectric film are obtained for electrical open and short cases on the free surface, respectively. The effect of gradient coefficients on coupled electromechanical factor, on the stress fields, the electrical potential and the mechanical displacement are discussed, respectively. Illustration is achieved on the well known heterostructure PZT-5H/SiO₂, the obtained results are especially useful in the design of high-performance acoustic surface devices and accurately prediction of the Love wave propagation behaviour.     

A cylindrical standing wave ultrasonic motor using bending vibration transducer

A cylindrical standing wave ultrasonic motor using bending vibration transducer was proposed in this paper. The proposed stator contains a cylinder and a bending vibration transducer. The two combining sites between the cylinder and the transducer locate at the adjacent wave loops of bending vibration of the transducer and have a distance that equal to the half wave length of bending standing wave excited in the cylinder. Thus, the bending mode of the cylinder can be excited by the bending vibration of the transducer. Two circular cone type rotors are pressed in contact to the end rims of the teeth, and the preload between the rotors and stator is accomplished by a spring and nut system. The working principle of the proposed motor was analyzed. The motion trajectories of teeth were deduced. The stator was designed and analyzed with FEM. A prototype motor was fabricated and measured. Typical output of the prototype is no-load speed of 165 rpm and maximum torque of 0.45 N m at an exciting voltage of 200 V_rms.     

利用共焦球面扫描干涉仪测量压电陶瓷伸长灵敏度

提出了一种测量压电陶瓷伸长灵敏度的新颖方法,此方法利用He-Ne激光器的模式分析实验装置,通过测量相邻两激光干涉序中各对应谱线的电压增量,计算出压电陶瓷的伸长灵敏度.测量过程避免了专用仪器的制造,利用实验室基本设备实现了对压电陶瓷灵敏度的便捷精确测量.     

基于压电探测判定激光支持燃烧波和爆轰波的点燃阈值

为了获得激光支持燃烧波和爆轰波的点燃阈值,采用压电探测器检测波长为1 064nm的Nd:YAG激光作用在铝靶表面所产生的应变和冲压。从实验结果观察到压电信号的变化分为3个阶段,分别为光热弹性应变阶段、等离子体增强耦合阶段和激光支持爆轰波对靶表面的压力阶段,并从理论上研究了这3个阶段的激光与靶材料相互作用的机理,从而可以从压电信号是否发生跃变判断出激光支持燃烧波和激光支持爆轰波的点燃阈值,与其它方法所得到结果基本吻合。     

压电振子阵列型超声喷丸强化*

为了提高超声喷丸强化加工的面积、效率及加工质量,对传统单振子超声喷丸强化技术进行了改进,提出了压电振子阵列型超声喷丸强化加工方法。分析了超声喷丸强化的机理,进行了压电振子的优化设计,分析了激振片的谐振响应,实验测试了系统样机在不同超声电源功率下弹丸撞击工件的区域分布;探究了超声电源功率、喷丸距离、弹丸直径和喷丸时间对加工样件显微硬度的影响,结果表明：以超声电源功率作为唯一变量,弹丸冲击工件表面的区域面积随超声电源功率增大而增大;7075铝合金样件的表面显微硬度及其提高率,随超声电源功率的增大、喷丸时间的增加、喷丸距离的减小及弹丸直径的增大而增大;超声电源功率为50W、喷丸时间为20min、喷丸距离为5mm、弹丸直径为1.5mm时喷丸效果最好,此时工件表面显微硬度增加量为65.1HV,表面显微硬度提高率为36.7%。压电振子阵列型超声喷丸强化技术可以有效增加喷丸冲击工件的面积,提高工件的表面显微硬度和加工效率。