Fabrication and sintering of Pt electrode deposited by screen printing method

采用单层和双层印刷法在氧化铝衬底上制备功能陶瓷厚膜用Pt电极, 研究了烧结温度、升温速率和电极厚度对Pt电极层的表面形貌、表面覆盖率和表面粗糙度的影响,以揭示晶粒长大、气孔生长及致密化机制. 结果表明, 在单层印刷Pt电极的烧结过程中,低温阶段残留的碳使不同温区Pt的主导扩散机制不同.双层印刷Pt电极中第一层在600℃下烧结后,印刷第二层再在1200℃下烧结具有最大表面覆盖率和最小平均粗糙度(其值约为0.82 um),同时具有最好的导电性能(方阻为0.044 Ω/□).     

A simultaneous approach for compliance minimization and piezoelectric actuator design considering the polarization profile

This article addresses the compliance problem along with the piezoelectric actuator design for active vibration control. The topology structural design is obtained by solving a compliance minimization problem with volume constraint, whereas the actuator design is carried out by the maximization of a control performance index written in terms of the controllability Gramian. This measure describes the ability of the actuator to move the structure from an initial condition to a desired final state, at rest for instance, in a finite time interval. The actuator design is also characterized by the polarization profile, which is defined according to the distribution of an additional design variable. Therefore, the actuators can yield both tensile and compressing fields at different points of the structure using the same applied control voltage. To achieve this goal, a material interpolation scheme based on the solid isotropic material with penalization and the piezoelectric material with penalization and polarization (PEMAP-P) models is employed, and both the optimum structure/actuator layout and polarization profile are obtained simultaneously. The sensitivities with respect to the polarization and design variables are calculated analytically. Numerical examples are presented considering the design and vibration control for a cantilever beam, a beam fixed at both ends, and an L-bracket structure to show the efficiency of the proposed formulation. The control performance of the designed structures are analyzed employing a linear-quadratic regulator simulation, and these results are compared to verify the influence of the optimized polarization profiles.     

Performance improvement of a piezoelectric bimorph actuator by tailoring geometry

This article illustrates performance improvement of a piezo-bimorph actuator by tailoring its geometry. We have analytically presented that a piezo-bimorph actuator with a tapered surface provides superior performance for out-of-plane bending compared to a rectangular surface while having equal mass and equal primary capacitance. Equal capacitance ensures equal input electrical energy and bandwidth for both the cases below its first resonant frequency. We have analytically derived performance measuring attributes of such an actuator considering high electric field, and shown the performance improvement quantitatively. We have also presented finite element solutions to compare with the analytical solutions. Some results are validated with the earlier published experimental results.     

Crack repair performance of piezoelectric actuator estimated by slope continuity and fracture mechanics

The active repair performance of the piezoelectric actuator for the cracked structure is studied in this paper. As an extension of the author’s previous study, this paper discusses a special repair case and new results by using two repair criteria: the slope continuity criterion and fracture mechanics criterion. Crack contact analyses and fracture mechanics in the crack tip field are considered in the plane strain finite element analyses. From numerical results, it is concluded that the fracture mechanics criterion is better for defining the repair voltage. The crack tip field and crack contact condition must be considered to obtain correct results. However, it is not a good idea for the active repair to use higher applied voltage on the piezoelectric actuator.     

Design and fabrication of functionally graded PZT/Pt piezoelectric bimorph actuator

A laminated piezoelectric bimorph actuator with a graded compositional distribution of PZT and Pt was fabricated, and its deflection characteristics were evaluated. Using experimentally determined compositional dependency of elastic and piezoelectric properties in the PZT/Pt composites, the modified classical lamination theory and the finite element method were applied to find the optimum compositional profile that will give a larger deflection and smaller stress, simultaneously. The miniature bimorph-type graded actuator that consists of a composite internal-electrode (PZT/30 vol% Pt) and three piezoelectric layers of different compositions (PZT/0–20 vol% Pt) were fabricated by powder stacking and sintering. The deflection of the actuator was measured using electric strain gages mounted on the top and bottom surfaces of the actuator. The deflection was found to strongly depend on the composition distribution profile. Under an applied electric field of 100 V m^–1, the actuator with an optimum composition profile exhibited a curvature of up to 0.03 m^–1, which is a satisfactory performance for this kind of actuators. The stress generated on actuation was estimated to be as low as 0.4 MPa, which is much smaller than those of conventional directly bonded actuators and will assure a long actuation life.     

Formulation and screen printing of water based conductive flake silver pastes onto green ceramic tapes for electronic applications

Environmentally friendly, water-based silver pastes, adapted for screen printing, were formulated with different silver contents (67–75%). These pastes allowed screen printing onto low temperature co-fired ceramic (LTCC) of narrow conductive tracks with a 60 μm line width and a 3 × 10⁻⁸ Ω m electrical resistivity. Inks were formulated with a mixture of spherical and flake shape silver particles with 2–4 μm mean diameter. Rheological behaviour of pastes was studied in order to determine its effect on printed lines properties. Prepared inks were then screen printed and sintered under normal atmosphere at 875 °C. As expected, electrical properties depended on silver content. Resistivity values varying from 1.6 × 10⁻⁸ to 3.3 × 10⁻⁸ Ω m were calculated over 36.3 cm line length. These values are very close to bulk silver resistivity (1.6 × 10⁻⁸ Ω m). Compared to previous research and commercial pastes, the newly formulated pastes reached equivalent or even better conductivities with lower silver content (70% by weight).     

丝网印版的分辨率特性研究

分析了丝网目数、丝径等几何参数及网版的厚度、粗糙度对丝网印刷精度的影响;对网版制作过程中的丝网选择,网版涂布曝光等注意事项做了研究,为获得高质量的网版提供了理论依据。对实际生产具有重要指导意义。     

Electromechanical analysis of piezoelectric bimorph actuator in static state considering the nonlinearity at high electric field

This article contains electromechanical analysis of a piezoelectric bimorph actuator at high electric field by incorporating second-order constitutive equations of piezoelectric material. Tip deflection, block force, block moment, block load, output strain energy, output energy density, input electrical energy, and energy efficiency are analytically derived for the actuator at high electric field. The analysis shows that output energy and energy density increase more rapidly at high electric field, compared to the prediction by the linear model. The analysis shows energy efficiency depends on electric field. Some analytical results are validated with the published experimental results.     

利用有机介质丝网印刷技术制备TiO2纳晶电极

在水热法制备TiO2胶体的基础上,加入松油醇、聚丙烯酸酯、Tx-100、乙基纤维素组成浆液,利用丝网印刷技术制备了染料敏化纳晶多孔TiO2薄膜电极.在光强为100mW/cm2的条件下,TiO2电极显示了良好的光电化学性能,由介孔TiO2电极组装的染料敏化太阳能电池的光电转换效率可达6.9%.     

利用丝网印刷技术制备纳晶多孔TiO2薄膜电极

在溶胶-凝胶法的基础之上,采用丝网印刷技术制备了性能稳定、高度多孔的纳晶TiO2薄膜电极,并采用不同的纤维素粘稠剂进行研究,发现采用乙基纤维素粘稠剂后,TiO2薄膜表面粗糙度较大,太阳能电池光电转换效率可以提高到5.27%.     

Mechanical,forming and biological properties of Ti-Fe-Zr-Y alloys prepared by 3D printing

Biomedical Ti-Fe-Zr-Y alloys were prepared by 3D printing on pure titanium substrate. The influences of Zr on mechanical, forming, and biological properties of the alloys were investigated in detail. The results showed that with increasing the Zr addition, the surface roughness, friction coefficient and worn volume decrease at first and then increase, the lowest values obtained at 5.86 at.% Zr addition. The ultimate compression stress and specific strength gradually decrease. The studied alloys have no cytotoxicity. They can promote the early adhesion and proliferation of cells. The eutectic alloy with 5.86 at.% Zr addition has the best ability of apatite deposition, it exhibits a better comprehensive performance among the studied alloys, which is superior to the Ti_70.5Fe_29.5 and Ti-6Al-4 V alloys.     

Developments of piezoelectric ultrasonic actuators operating under bending hybrid vibration modes

The exciting methods for the sandwich type piezoelectric ultrasonic actuators used bending hybrid modes are investigated. Five exciting methods are discussed and compared in detail, in which the polarizations and the partitions of the ceramic rings are different. Harmonic analyses are developed to obtain the effects of the exciting methods on the electromechanical coupling factors and the vibration amplitudes. At last, five prototypes are manufactured to verify their differences. Both the simulation and experiment results prove that the exciting method using ceramic rings with four separated partitions achieves great improvements on the efficiency, velocity and force, synchronously.     

Computational approach of piezoelectric shells by the GDQ method

A piezoelectric laminated cylindrical shell with shear rotations effect under the electromechanical loads and four sides simply supported boundary condition was studied by using the two-dimensional generalized differential quadrature (GDQ) computational method. The typical hybrid composite shells with 3-layered cross-ply [90°/0°/90°] graphite–epoxy laminate and bounded PVDF layers are considered under the sinusoidal pressure loads and electric potentials on the shell. The governing partial differential equation with first-order shear deformation theory in terms of mid-surface displacements and shear rotations can be expressed in series equations by the GDQ formulation. Thus we obtain the GDQ numerical solutions of non-dimensional displacement and stresses at center position of laminated piezoelectric shells. Displacement is generally affected by the thickness of laminated piezoelectric shells under the action of mechanical load. Stresses are generally affected by the thickness and the length of laminated piezoelectric shells under the actions of mechanical load and electric potential.     

压电驱动器可控预紧力主轴设计及性能分析

可控预紧力主轴能够满足高速主轴在整个切削转速范围内热、动特性兼优的要求,已逐步成为智能主轴的重要发展方向。为弥补压电驱动器（piezoelectric actuator, PEA）可控预紧力主轴设计及选型方面的不足,提出一种具有分辨率高、响应快、对切削刚度影响小及结构紧凑等优点的PEA可控预紧力主轴结构。建立了静止状态和运行状态下的角接触球轴承刚度模型,并以此为基础建立了PEA可控预紧力主轴的等效力学模型,得到了预紧机构负载刚度随预紧位移的变化规律。然后,分析了PEA的输出特性,建立了预紧机构的实际输入输出模型,并通过该模型分析了初始预紧力和PEA刚度对预紧力控制区间的影响规律,进而提出了预紧机构设计选型原则。最后,应用提出的主轴结构和预紧机构设计选型原则设计了PEA可控预紧力主轴试验台。试验结果表明预紧力控制分辨率为1.5 N,阶跃响应时间为300 ms,验证了所建预紧机构实际输入输出模型的准确性;温度控制试验结果表明该主轴试验台具有良好的温度调控能力。研究结果可为实际工程中PEA可控预紧力主轴的设计提供指导。     

Material properties of piezoelectric composites by BEM and homogenization method

Applications of boundary element method (BEM) to piezoelectric composites in conjunction with homogenization approach for determining their effective material properties are discussed in this paper. The composites considered here consist of inclusion and matrix phases. The homogenization model for composites with inhomogeneities is developed and introduced into a BE formulation to provide an effective means for estimating overall material constants of two-phase composites. In this model, a representative volume element (RVE) is used whose volume average stress and strain are calculated by the boundary tractions and displacements of the RVE. Thus BEM is suitable for performing calculations on average stress and strain fields of the composites. Numerical results for a piezoelectric plate with circular inclusions are presented to illustrate the application of the proposed micromechanics––BE formulation.     

Direct writing of semiconducting polythiophene and fullerene derivatives composite from bulk heterojunction solar cell by inkjet printing

The direct writing approach of poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) composite from bulk-heterojunction (BHJ) solar cell was efficiently addressed by inkjet printing technology using conventional chlorobenzene ink solution. The structure of inkjet-printed P3TH:PCBM BHJ film was fabricated by the repetitive direct writing of new line overlapped partially on former line. The best structure of P3HT:PCBM film for BHJ solar cell was observed from inkjet printing condition of around 50% of droplet overlaps with 2 wt.% BHJ ink at 25 °C of substrate temperature. The maximum power conversion efficiency reached 2.83% with an open circuit voltage of 0.62 V, a short circuit current density of 8.60 mA/cm², and a fill factor of 0.53 under air mass 1.5 G irradiation (100 mW/cm²).     

Analysis of laminated composite beams and plates with piezoelectric patches using the element-free Galerkin method

 An efficient meshfree formulation based on the first-order shear deformation theory (FSDT) is presented for the static analysis of laminated composite beams and plates with integrated piezoelectric layers. This meshfree model is constructed based on the element-free Galerkin (EFG) method. The formulation is derived from the variational principle and the piezoelectric stiffness is taken into account in the model. In numerical test problems, bending control of piezoelectric bimorph beams was shown to have the efficiency and accuracy of the present EFG formulation for this class of problems. It is demonstrated that the different boundary conditions and applied actuate voltages affects the shape control of piezolaminated composite beams. The meshfree model is further extended to study the shape control of piezo-laminated composite plates. From the investigation, it is found that actuator patches bonded on high strain regions are significant in deflection control of laminated composite plates. Received: 23 October 2001 / Accepted: 29 July 2002     

Detection of material interfaces using a regularized level set method in piezoelectric structures

An algorithm to solve the inverse problem of detecting inclusion interfaces in a piezoelectric structure is proposed. The material interfaces are implicitly represented by level sets which are identified by applying regularization using total variation penalty terms. The inverse problem is solved iteratively and the extended finite element method is used for the analysis of the structure in each iteration. The formulation is presented for three-dimensional structures and inclusions made of different materials are detected by using multiple level sets. The results obtained prove that the iterative procedure proposed can determine the location and approximate shape of material sub-domains in the presence of higher noise levels.     

Solving anti-plane problems of piezoelectric materials by the Trefftz finite element approach

Applications of the Trefftz finite element method to anti-plane electroelastic problems are presented in this paper. A dual variational functional is constructed and used to derive Trefftz finite element formulation. Special trial functions which satisfy boundary conditions are also used to develop a special purpose element with local defects. The performance of the proposed element model is assessed by an example and comparison is made with results obtained by other approaches. The Trefftz finite element approach is demonstrated to be ideally suited for the analysis of the anti-plane problem.The work was performed under the auspices of an Australian Professorial Fellowship Program with grant number DP0209487 and 21st Century Education Promotion Key project from Tianjin University.     

PZT系梯度功能压电驱动器的谐响应特性

研究了PZT系梯度功能压电驱动器谐振状态的机电响应特性，通过改变驱动电场和频率，研究其谐振频率和顶端位移的变化特性。结果表明：增加电场，谐振频率减小，谐振点位移增大，并逐渐趋向饱和。在谐振点附近，悬臂梁弯曲位移达到最大值。