The 0.95MgTiO3-0.05CaTiO3 (95MCT) powders and ceramics were prepared by a sol-gel method by using Mg(NO3)2•6H2O, Ca(NO3)2•4H2O and Ti(C4H9O)4 as the starting materials. The effects of calcination temperature on phase formation, morphology and particle size distribution of the proposed powders were examined, and the microwave dielectric properties of 95MCT ceramics made from different size particles were investigated. The dried gels were calcined at 600 °C, 700 °C, 800 °C and 900 °C, and the derived particle sizes of powders were 10-20 nm, 50-100 nm, 60-120 nm and 120-150 nm, respectively. The proper sizes, which range from 50-150 nm, lowered the sintering temperature of 95MCT ceramics effectively from 1400 °C to 1175 °C due to the high surface energy. Sintered at 1175 °C, the 95MCT ceramic prepared from 50-100 nm size particles had compact structure and exhibited good microwave dielectric properties: εr = 21.33 and Q×f = 36,315 GHz.
In our work, we aimed to improve the interfacial properties of the Polyetheretherketone (PEEK) polymer/carbon fiber (CF) by treating the fibers with wet chemical method, a higly oxidative chemical solutions called piranha solution and chromate solution. The changes of the surface funtional groups, chemical compositions and structures of the carbon fibers were characterized by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR),surface morphology was studied by scanning electron microscopy (SEM), mechanical interfacial properties of the composites was evaluated by means of interlaminar shear strength (ILSS) tests. The results indicated that graphitic carbon was the major carbon functional component on the carbon fiber surfaces and other functional groups were also presented, such as C–O, C-OH, C = O. Consequently, these introductions of oxygen functional groups onto the carbon fiber surfaces led to an improvement of the ILSS of the composites.
Acoustic focusing has been widely applied in biological and industrial fields. In this work, a coding acoustic metasurface consisting of two kinds of hexagonal coding bits is designed. Using the metasurface, acoustic focusing can be implemented in three-dimensional space. Besides, by altering the coding sequence, the focal length can be manipulated flexibly to satisfy the practical demands. Furthermore, bifocal focusing, which has a great potential in multiplane imaging, can be realized by properly arranging the coding sequence. Our works broaden the prospects of the coding metasurfaces and have promising applications in the areas of biomedical therapy and imaging.
Polymer-based piezoelectric motors have excellent properties, such as lightweight and corrosion resistance. In addition, 3D printing and customized additive manufacturing of polymers provide new opportunities for the development of piezoelectric motors with complex or special structures. In this paper, a 3D printed polymer-based sandwich-type piezoelectric motor operating in a single longitudinal mode is developed. A vibration decomposition model of the motor and an analytical model considering polymer viscoelasticity are established to analyze the dynamic characteristics and to determine the geometric structure of the motor. To increase the coefficient of friction, a polymer surface texture is utilized on the contacts. The experimental results show that the friction coefficient of the contact tip with surface texture is about 0.16, which increased by 45.5% compared to a smooth surface. The resonance frequency is 28.648 kHz, and the maximum no-load speed under 300 Vp-p is 54 r/min. Our study shows the promise of polymer-based materials in the development of the piezoelectric motor.
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