Thermal Green's Functions for a Heat Source in a Piezoelectric Solid with a Parabolic Boundary

Using the Stroh formalism combined with the analytical continuation principle of Muskhelishvili, the Green's functions for a line heat source in a piezoelectric solid with a parabolic boundary are obtained in closed form. The obtained Green's functions not only satisfy all the given boundary conditions, but also ensure the displacement and electric potential to be single-valued. As special cases, the solutions for a piezoelectric half-plane are also presented, and they are shown to be consistent with previous works.     

Thermo-Elasticity Solution of Functionally Graded Plates Integrated with Piezoelectric Sensor and Actuator Layers

Based on theory of piezoelasticity, a functionally graded material (FGM) host plate under applied electric field and thermal or mechanical load is studied. The thermo-elastic constants of the plate vary continuously throughout the thickness direction in the form of an exponential function and the Poisson ratio is held constant. Analytical solutions for the temperature, stress and displacement fields for the plate with simply supported edges are derived by using the Fourier series expansions and state-space method. The theory is assessed by comparison with the previously published results. The effects of surface boundary conditions, gradient index, applied voltage, aspect ratio and length-to-thickness ratio on the behavior of the FGM plate are examined.     

Transient Thermoelectromechanical Response of a Piezoelectric Strip with Two Parallel Cracks of Different Lengths

This work is concerned with the thermoelectromechanical fracture behavior of two parallel cracks of different lengths in a piezoelectric material strip under thermal shock loading. The crack faces are supposed to be insulated thermally and electrically. By using both the Laplace transform and the Fourier transform, the thermal and electromechanical problems are reduced to two systems of singular integral equations, respectively, which are solved numerically. A numerical method is employed to obtain the time dependent solutions by way of a Laplace inversion technique. The intensity factors versus time for various geometric parameters are calculated and presented in graphical forms. Temperature change, the stress and electric displacement distributions in a transient state are also included.     

Phase structure and nano-domain in high performance of BaTiO3 piezoelectric ceramics

BaTiO₃ ceramics were prepared by conventional sintering technique with a special emphasis on the effects of sintering temperature (1100-1230 °C) on the crystalline structure and piezoelectric properties. XRD patterns indicated that the crystallographic structure changed from tetragonal phase to orthorhombic one with raising sintering temperature from 1160 °C to 1180 °C. Domains were shaped in a stripe and a herringbone in orthorhombic samples for BaTiO₃ ceramics. The domain width and domain density increased with raising sintering temperature. The BaTiO₃ ceramic sintered at 1190 °C showed the excellent electrical properties, d₃₃ = 355 pC/N, k_p = 40%, P_r = 10.2 μC/cm², respectively, which are originated to the contributions of both the crystallographic structure transition and nano-domain.     

High piezoelectric properties of BaTiO3-xLiF ceramics sintered at low temperatures

BaTiO₃-xLiF ceramics were prepared by a conventional sintering method using BaTiO₃ powder about 100 nm in diameter. The effects of LiF content (x) and sintering temperature on density, crystalline structure and electrical properties were investigated. A phase transition from tetragonal to orthorhombic symmetry appeared as sintering temperatures were raised from 1100 °C to 1200 °C or as LiF was added from 0 mol% to 3 mol%. BaTiO₃-6 mol% LiF ceramic sintered at 1000 °C exhibited a high relative density of 95.5%, which was comparable to that for pure BaTiO₃ sintered at 1250 °C. BaTiO₃-4 mol% LiF ceramic sintered at 1100 °C exhibited excellent properties with a piezoelectric constant d₃₃ = 270 pC/N and a planar electromechanical coupling coefficient k_p = 45%, because it is close to the phase transition point in addition to high density.     

Enhanced ferroelectric properties in (Ba1−xCax)(Ti0.94Sn0.06)O3 lead-free ceramics

Lead-free (Ba_1−xCa_x)(Ti_0.94Sn_0.06)O₃ (BCST) (x = 0.01-0.04) ceramics were prepared using a solid-state reaction technique. The effects of Ca content on the phase structure and electrical properties of the BCST ceramics were investigated. High piezoelectric coefficient of d₃₃ = 440 pC/N, planar electromechanical coupling factor of k_p = 45% and dielectric constant ?_r = 6900 were obtained for the samples at x = 0.03. At room temperature, a polymorphic phase transition (PPT) from orthorhombic phase to tetragonal phase was identified in the composition range of 0.02 < x < 0.04.     

单锥壳形阀压电泵阀体的设计与实验

为了更深入地了解单锥壳形阀压电泵阀体结构参数以及材料属性对泵工作输出的影响,并在此基础上探索通过改进阀体实现对泵工作输出调节的可行性,首先,对阀体受力情况进行了分析,建立了阀体的运动学模型,得到了阀体的弯曲变形量与其自身刚度、质量等参数的关系式;其次,定性分析了阀体自身刚度、质量等参数对工作频率的影响;最后,通过加工样机进行实验,实验结果证明了相关理论分析的正确性。实验中当阀体参数合适时,在工作电压为220V时,样机的工作频率为56 Hz,输出流量达190mL/min。     

Analysis of thermoelastic damping in microresonators by considering the stretching effect

In this paper, the previous theory for obtaining the quality factor of thermoelastic damping in microresonators has been modified. Here, the stretching term for the neutral axis of bending is considered, which has been neglected in previous work. The Taylor expansion of electric actuation has described the static position of microbeam, which is more accurate than previous work that extends it about the straight position of a microbeam. Also, the theory of this work may be used for two layered microresonators without this assumption that the length of two layered electrically actuated microresonators may be obtained, for the first time. To obtain this complete theory firstly the equations of motion coupled with thermal effects are obtained in a two layered microbeam where the second layer is deposited on a part of the first layer length. Then, the quality factor of thermoelastic damping of the system, i.e. the half of the ratio of the real part of the free vibration resonance frequency to its imaginary part, has been obtained by solving the free vibration equation using the strained parameter perturbation method. It has been shown that neglecting the stretching of neutral axis of bending and expanding the electrostatic actuation about the straight position of the microbeam considered in previous researches cause an error that is not negligible for the voltage larger than 30% of the pull-in voltage. Also, it is shown that the quality factor of thermoelastic damping in two layered microresonators depends on the value of length, thickness and the kind of material of the deposited layer.     

The effect of pre-milling/pre-synthesis process and excess Ba on the microstructure and dielectric/piezoelectric properties of nano-sized 0.94[(Bi0.5Na0.5)TiO3]–0.06[Ba(1+x)TiO3]

Lead-free piezoelectric ceramic specimens of 0.94[(Bi_0.5Na_0.5)TiO₃]–0.06[Ba_(1+x)TiO₃] (where 0 ≤ x ≤ 0.03) (abbreviated as nano-sized BNBT6(x)) compositions containing excess Ba were synthesized by a modified mixed oxide method. In this modified process (Bi_0.5Na_0.5)TiO₃ and Ba_(1+x)TiO₃ were separately prepared by pre-milling the starting powders in high energy mill (HEM) in order to obtain nano-particle size. BNBT6(x) specimens were also prepared by the conventional process to be compared with the former one. The pre-milling of the raw materials lowered the calcination temperatures of (Bi_0.5Na_0.5)TiO₃ and Ba_(1+x)TiO₃ by 110 and 200 °C, respectively, as compared with the conventional process. High energy milling improved the reaction activity and homogeneity of the materials used throughout the process, enhanced the sintering density and grain uniformity, and decreased the grain size. The effects of excess Ba on the characteristic of nano-sized BNBT6(x) specimens were systematically investigated. The piezoelectric and dielectric properties of BNBT6(x) specimens containing various amounts of excess Ba show maximum values of the planar electromechanical coupling factor (k_p) of 38% and the piezoelectric constant (d₃₃) of 198 pC/N with Ba excess amount of 0.02 mol [BNBT6(0.02)]. The d₃₃ then decreases with increasing excess Ba content to 0.03 mol, whereas the relative dielectric permittivity (K^T₃₃) steadily increases with increasing excess Ba and reaches the maximum value of 785 for this composition. Besides, the depolarization temperature (T_d) slightly decreased within the range of x = 0–0.01 mol and then tends to rapidly decrease with the excess Ba of 0.02 mol. In addition to this, the T_d remains unchanged with the higher excess Ba of 0.03 mol. The modified mixing and milling method were considered to be a new and promising process for lead-free piezoelectric ceramics owing to their excellent piezoelectric/dielectric properties.