A control model for hysteresis based on microscopic polarization mechanisms in piezoelectric actuator

Aiming at the limitation of control accuracy caused by hysteresis and creep for a piezoelectric actuator, the hysteresis phenomenon is explained based on the microscopic polarization mechanism and domain wall theory. Then a control model based on polarization is established, which can reduce the hysteresis and creep remarkablely. The experimental results show that the polarization control method is with more linearity and less hysteresis compared with the voltage control method.

The Infiltration Process and Texture Transition of 2D C/C Composites

2D needle-punched fiber felt was infiltrated by a kind of rapid isothermal chemical vapor infiltration technique. The infiltration process and texture transition of the infiltrated C/C composites were investigated. The porosity and the variations of the cumulative pore volume were determined by mercury porosimetry. The texture of matrix carbon was studied under a polarized light microscope. The results show that the relative mass gain of the sample increases directly as the infiltration time at the initial stage until 20 h, and subsequently the increasing rate of the relative mass gain decreases gradually with the prolonging of infiltration time. Three layers of pyrocarbon were formed around fibers. Low-textured pyrocarbon was obtained at the initial stage. With the densification going on, high-textured pyrocarbon was formed on the surface of low-textured pyrocarbon. Then, low-textured pyrocarbon was produced again during the final stage of densification. The texture transition is ascribed to the variation of the ratio of cumulative inner surface area to volume of pores and the gas partial pressure in pores.

Comparative Study on Mineral Medicine Os Draconis(Longgu)and Counterfeit Modern Animal Skeleton

[Objectives]To identify the authenticity of Longgu from the microscopic,infrared spectrum and chemical composition,and provide references for the quality control and evaluation methods of Longgu.[Methods]According to the mineral characteristics of Longgu,the identification research was carried out by microscope observation,near-infrared spectroscopy and X-ray fluorescence spectrometer.By comparing the single polarizing and orthogonal polarizing characteristics of genuine and fake Longgu,a qualitative identification model of genuine Longgu was established based on the near-infrared spectrum of genuine Longgu,and the detection results of elements in Longgu were analyzed.[Results]The genuine Longgu had apatite optical properties,and was quite different from the fake Longgu of animal bones.Compared with modern animal bones,genuine Longgus had relatively less P and Ca,but they were enriched in elements Sr and F.The correlation coefficient model with good predictive ability can be established by using the near-infrared characteristic spectrum.[Conclusions]Polarizing microscope,near-infrared spectroscopy and X-ray fluorescence spectroscopy can improve the identification results of Longgu.

Precise prediction of dielectric property for CaZrO_(3) ceramic

As for CaZrO_(3)(CZ)ceramic,the reported dielectric property values,especially dielectric constants,were much different from 23 to 32,which is reliable and credible?Without precise property data,CZ can’t be further developed and utilized accurately.Herein,CZ ceramic was fabricated by a traditional two-step sintering process,then simulated and calculated the dielectric properties precisely at a microscopic polarization angle using the lattice vibrational spectra and the Clausius-Mossotti(C-M)as well as damping equations.The Raman and Fourier transform far-infrared modes were analyzed and used to predict the intrinsic properties,which were consistent well with the values calculated from C-M and damping equations.The intrinsic permittivity,after precise prediction,is about 20,which is reliable and credible.As for the dielectric loss,the value of about 6
×10^(-4)was obtained after precise calculation,which is similar to other results.

Evaluation of the differential capacitance for ferroelectric materials using either charge-based or energy-based expressions

Differential capacitance is derived based upon energy,charge or current considerations,and determined when it may go negative or positive.These alternative views of differential capacitances are analyzed,and the relationships between them are shown.Because of recent interest in obtaining negative capacitance for reducing the subthreshold voltage swing in field effect type of devices,using ferroelectric materials characterized by permittivity,these concepts are now of paramount interest to the research community.For completeness,differential capacitance is related to the static capacitance,and conditions when the differential capacitance may go negative in relation to the static capacitance are shown.