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881.
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. 相似文献
882.
水下信息实时传输的需求与日俱增,水声通信和光通信等传统通信手段在传输安全性与稳定性方面具有先天难以弥补的劣势,且在传输速率方面难以形成突破,因此亟待对新技术进行研究。为解决此问题,近年一些学者提出一种新机理、新材料和新工艺的小型化天线,有望实现低频天线在尺寸和性能上的跨越,实现水下通信技术的变革。该文对此类声波激励小型化天线进行研究。首先阐述并建立了天线辐射机理及理论模型,分析了不同材料参数对天线性能的影响;然后根据模型参数设计加工了基于铌酸锂(LiNbO3)晶体的压电型声波激励天线样机,实验结果表明在40.83 kHz谐振频率处,与同尺寸单极子天线相比,其接收电压峰值为后者的22倍,辐射效率为400多倍;最后对天线进行了方位测试和辐射效率计算。上述结果表明:基于压电晶体的声波激励天线技术在低频段小型化、机动化水下无线通信设备的应用中具有巨大潜力。 相似文献
883.
A permeable interface crack between elastic dielectric material and piezoelectric material is studied based on the extended
Stroh’s formalism. Motivated by strong engineering demands to design new composite materials, the authors perform numerical
analysis of interface crack tip singularities and the crack tip energy release rates for 35 types of dissimilar bimaterials,
respectively, which are constructed by five kinds of elastic dielectric materials: Epoxy, Polymer, Al2O3, SiC, and Si3N4 and seven kinds of practical piezoelectric ceramics: PZT-4, BaTiO3, PZT-5H, PZT-6B, PZT-7A, P-7, and PZT-PIC 151, respectively. The elastic dielectric material with much smaller permittivity
than commercial piezoelectric ceramics is treated as a special transversely isotropic piezoelectric material with extremely
small piezoelectricity. The present investigation shows that the structure of the singular field near the permeable interface
crack tip consists of three singularities: and , which is quite different from that in the impermeable interface crack. It can be concluded that different far field loading
cases have significant influence on the near-tip fracture behaviors of the permeable interface crack. Based on the present
theoretical treatment and numerical analysis, the electric field induced crack growth is well explained, which provides a
better understanding of the failure mechanism induced from interface crack growth in elastic dielectric/piezoelectric bimaterials.
The project supported by the National Natural Science Foundation of China (10572110), Doctor Foundation of the Chinese Education
Ministry and Doctorate Foundation of Xi’an Jiaotong University.
The English text was polished by Yunming Chen. 相似文献
884.
885.
We have investigated influence of ionic liquid concentration on the electromechanical response of ionic electroactive polymer actuators. Actuators were fabricated from ionomeric membrane and doped with different concentrations of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ionic liquid. Samples were investigated for their electromechanical and electrochemical characteristics; and it was observed that the maximum electromechanical strain of approximately 1.4% is achieved at 22 wt% ionic liquid content. Increasing ionic liquid concentration results in saturation of the electrode–ionomer interface and formation of ionic double/multi layers, which in turn result an inward accumulation of ions; hence, generate strain in an undesired direction that deteriorates the electromechanical response of the actuator. 相似文献
886.
887.
Negative thermal expansion of poly(vinylidene fluoride) and polyethylene tie molecules: A molecular dynamics study 下载免费PDF全文
The mechanism of thermal actuation for poly(vinylidene fluoride) (PVDF) and polyethylene (PE) tie molecules has been investigated using molecular dynamics simulations. Tie molecules are found in semicrystalline polymers and are polymer chains that link two (or more) crystalline lamellae, allowing for the transfer of force between these regions. A novel simulation technique has been developed to enable measurement of changes in the tie molecule length upon heating. We investigate the dependence of the percentage actuation observed upon heating, on the external applied force that stretches the tie molecules, the temperature range used for heating as well as the length and the number of tie molecules. Two molecular level mechanisms for actuation are identified. An entropically driven mechanism occurs at low applied forces and is applicable to all flexible polymers. A second mechanism due to conformational changes is observed for PVDF but not for PE at intermediate applied forces. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 2223–2232 相似文献
888.
In assistive technologies involving voice communication, an audio signal with specific shape is needed. In this regard, the design and fabrication of an electrostatic cantilever array is proposed. An array of four metallic micro-cantilevers with dimensions 650 μm × 200 μm × 0.3 μm is fabricated on the silicon substrate. The working principle is based on the electrostatic effect generated due to a conductive path applied between the electrodes. The results are taken from zinc oxide (ZnO) piezoelectric thin film that allows making contact with the vibrating cantilevers on a specified applied input impulse signals. The results demonstrated the switching action of the cantilevers that depends on the polarity of the input pulses. The results obtained are compared with the FEM based (COMSOL Multiphysics) model that is designed and analyzed prior to the experiment. Further, the experimental results showed a good agreement with the predicted values calculated by the simulated model for the input impulse signal applied synchronously to all the micro-cantilevers. However, for asynchronous actuation mode, the result of the as-fabricated device showed a variation than the simulated results. The vibrations are generated periodically from all the cantilevers and the output shows the resultant signals that are very much in the audible frequency range. 相似文献
889.
This paper represents the continuation of our research on built-in piezoelectric sensor for structural health monitoring of composite materials. Experimental research is focused on examining the effects of the embedded sensors on the structural integrity of composite laminates subjected to mechanical tests. A series of composite specimens with and without embedded sensor are tested in fatigue loading while constantly monitoring the response by acoustic emission technique. The acoustic signals are analysed using the classification k-means method in order to identify the different damage mechanisms and to follow the evolution of these mechanisms for both types of composite materials (with and without sensor). The mechanical behaviour of composites with and without embedded sensor shows no difference in the form. The incorporation of piezoelectric sensor causes low degradation of mechanical properties of composites. Comparing embedded sensor to sensor mounted on the surface, the embedded sensor showed a much higher sensitivity. It is thus verified that the embedded acoustic emission sensor had great potential for acoustic emission monitoring in fibre reinforced composite structures. 相似文献
890.
精密气动定位系统具有高精度、高速、大行程、传动平稳、使用费用低等优点,目前广泛地应用于光刻、数控机床等诸多精密工程领域.本文按照时间顺序介绍了精密气动定位系统的发展情况,总结了精密气动定位系统的应用特点,并指出当前精密气动定位系统一些有待改进的关键技术. 相似文献