Why traction-free? Piezoelectric crack and Coulombic traction

The non-zero traction condition is introduced in piezoelectric crack problems with the unknown Coulombic traction acting on the crack surfaces. An analytical solution under this condition is obtained by means of the generalized Stroh formalism and by accounting for the permittivity of medium inside the crack gap. As the crack in such materials can be thought of as a low-capacitance medium carrying a potential drop, the Coulombic traction always pulls the two opposite surfaces of the crack together. It is proved that under relatively larger mechanical loading and relatively smaller electrical field, the Coulombic traction may be negligible and the previous investigations under the traction-free crack condition may be accepted in a tolerant way, otherwise the Coulombic traction may lead to some erroneous results with over 10% relative errors. It is also shown that, unlike the traction-free crack condition, the applied electric field does change the Mode I stress intensity factor (SIF) for a central crack in an infinite plane piezoelectric material, and in this way may significantly influence piezoelectric fracture. It is also concluded that the variable tendencies of the normalized SIF and the ERR against the applied electric field depend on the mechanical loading levels. This load-dependence feature may lead to a transformation of the normalized SIF and the ERR from an even functional dependence to an odd functional dependence on the applied electric field.     

压电阻尼主动控制中局部应变的电路补偿及其参数识别

论文［１］提出了在压电阻尼主动控制中用压电基片来补偿局部激励拉压应变增进阻尼控制的方法。本文则进一步提出用简单的电路来等效替代压电基片及相应的电路参数识别算法，从而使补偿变得更为简便。实验证明了两者的补偿效果相同。     

Control of stress response in a rotating infinite hollow multilayered piezoelectric cylinder

The theoretical study of the control of stress is developed for a rotating infinite hollow multilayered radially polarized piezoelectric cylinder. The exact solution is obtained by means of the state-space method. As an illustrative example, the distribution of the radial and tangential stresses in a rotating hollow internally pressurized five-layered piezoelectric cylinder subjected to different electric potential at the internal and external surfaces are performed. Numerical results show that the distribution of the stress can be controlled by applying appropriate electric potentials at the correct surfaces.     

Dynamic properties of an omni-directional piezoelectric motor for precision position control

A piezoelectric motor capable of omni-directional movements has been developed to apply for robot joints, eyes, and precision positioning stage. The piezoelectric actuator has a simple structure of a cone type consisting of two piezoelectric ring-typed ceramics with electrodes divided into four segments and stainless steel elastic bodies. Before manufacturing the piezoelectric motor, the admittance characteristics and displacements of the actuator as a function of frequency were simulated. Elliptical motions of the actuator were created at several frequencies between the longitudinal and transverse resonance frequencies. The actual motor with alumina ball exhibited nice performance using a driving circuit with two rotary encoders and a PID controller. The moving element was omni-directionally operated at a driving frequency of 53.8 kHz and an output voltage of 280 V_p-p. The developed motor enables the moving element to move to a desired position with a resolution of 1.2°/pulse, an angular velocity of 4 rad/s, and a thrust force of 200 g.     

SH surface acoustic wave propagation in a cylindrically layered piezomagnetic/piezoelectric structure

SH surface acoustic wave (SH-SAW) propagation in a cylindrically layered magneto-electro-elastic structure is investigated analytically, where a piezomagnetic (or piezoelectric) material layer is bonded to a piezoelectric (or piezomagnetic) substrate. By means of transformation, the governing equations of the coupled waves are reduced to Bessel equation and Laplace equation. The boundary conditions imply that the displacements, shear stresses, electric potential, and electric displacements are continuous across the interface between the layer and the substrate together with the traction free at the surface of the layer. The magneto-electrically open and shorted conditions at cylindrical surface are taken to solve the problem. The phase velocity is numerically calculated for different thickness of the layer and wavenumber for piezomagnetic ceramics CoFe₂O₄ and piezoelectric ceramics BaTiO₃. The effects of magnetic permeability on propagation properties of SH-SAW are discussed in detail. The distributions of displacement, magnetic potential and magneto-electromechanical coupling factor are also figured and discussed.     

Effect of carbon black on properties of 0–3 piezoelectric ceramic/cement composites

0–3 cement-based piezoelectric composites were fabricated using sulphoaluminate cement and piezoelectric ceramic [0.08Pb(Li_1/4Nb_3/4)O₃ · 0.47PbTiO₃ · 0.45PbZrO₃] [P(LN)ZT] as raw materials by compressing technique. The influences of carbon black content on the piezoelectric and dielectric properties, electric conductivity and impedance were investigated. The results indicate that the piezoelectric strain constant d₃₃ and piezoelectric voltage constant g₃₃ of the composites increase gradually with a suitable carbon black addition. When the carbon black content is 0.3 wt%, both of the piezoelectric strain constant d₃₃ and piezoelectric voltage constant g₃₃ of the composite exist the maximum value, which are 17.45 pC N⁻¹ and 36.3 mV m N⁻¹, respectively. As the carbon black content increases, the dielectric constant ε_r, dielectric loss tanδ and electric conductivity σ of the composites all increase, while the impedance decreases. In the frequency range tested, the more the carbon black content, the higher the ε_r value. The planar electromechanical coupling coefficient K_p, the thickness electromechanical coupling coefficient K_t and the mechanical quality factor Q_m are almost unaffected by the carbon black content.     

压电免疫传感器用于乙肝表面抗原的测定

乙肝表面抗原 ( HBs Ag)的检测是临床诊断乙型肝炎的一项重要指标 .目前常用酶联免疫法和放射免疫法检测 [1] ,但酶本身性质不稳定且价格昂贵、操作繁琐 ;而放射免疫法存在放射性废物难处理的局限性 .压电免疫传感器具有装置简单、价格便宜、灵敏度高、实时快速和无需标记等优点 ,广泛应用于环境监测、药物分析及微生物检测等多个领域 [2～ 4 ] .本文应用自组装单分子膜技术 ,在压电石英晶体表面形成致密有序的半胱胺单分子膜 ,通过戊二醛共价交联 ,将乙肝表面抗原单克隆抗体分子固定于晶体电极表面 ,研制成 HBs Ag压电免疫传感器 ,用于…     

Theoretical analysis of the electronic structure of truncated-pyramidal GaN/AlN quantum dots

We present a theoretical analysis of the electronic structure of GaN/AlN quantum dots (QD) with a hexagonal, truncated-pyramidal shape. We use a Fourier-transform technique that we had previously developed to calculate the 3D strain and built-in electric fields due to the QD structure. The electron and hole energy levels and wavefunctions are then calculated in the framework of an 8-band k·P model (with zero spin–orbit splitting), using an efficient plane-wave expansion method. We show that because of the large built-in piezoelectric and spontaneous polarization fields, the calculated transition energy is sensitive to variations in the wetting layer width, pyramid top diameter and also to the values chosen for the piezo-electric constants and spontaneous polarization values of bulk GaN and AlN. Numerical results are presented for a set of GaN/AlN QD structures that have been studied experimentally and described in the literature. We find that the calculated value of the ground-state optical transition energy for these structures is in good agreement with experiment.     

Studies on Non－potentiometric Piezoelectric Sensor System for Determination of Vitamin B1

A piezoelectric sensor responsive to vitamin B1 was fabricated based on the vitamin B1-tetraphenylborate ion pair. The general performance characteristics of the sensor are presented here. The proposed sensor showed a wide working pH range, a good sensitivity and selectivity. The response range is between 1.0×10-7-4.9×10-5 mol/L with a detection limit of 8×10-8 mol/L at pH 4.0. The selectivity should be attributed to the preferential adsorption of the component ion on the membrane/solution interface. The adsorption behavior of vitamin B1 on the crystal surface was investigated with a quartz crystal impedance(QCI) system.