Key Engineering Materials Vols. 562-565

Abstract: Low permeability reservoir is one of the most important petroleum reserve types in China. Therefore, some basic scientific problems about low permeability reservoir such as pore-throat size distribution, principle of porous flow should be deeply studied. Pore-throat size distribution, based on 69 cores from Changqing and Daqing oilfield of China, has been measured by comprehensive using Constant-Rate Mercury Injection and Nuclear Magnetic Resonance. It has been found that the Nano-pore-throat takes more than 60 percent of the total pore-throat of the low permeability reservoir and it is the key factor affecting the flow capacity when the permeability is less than 0.5×10-3μm2. The nano-pore-throat takes less than 40 percent of the total pore-throat and micron-pore-throat takes more than 45 percent when the permeability is larger than 5×10-3μm2. And Micron-pore-throat is the key factor affecting the flow capacity of low permeability reservoir. But when the reservoir permeability is between 0.5×10-3μm2 and 5×10-3μm2, its flow capacity is determined by the sub-micron-pore-throat and the amount of micron-pore-throat. Additionally, the key forces in micro-, sub-micro- and nanoscale pore-throat has been got by analyzing. The electrokinetic coupling matrix of mass transport has been gotten by analyzing the characteristics of the mass transport in small tube at different Debye ratio and pore-throat size distribution of ultra-low permeability.

Abstract: With the MEMS technology advancement, electronic devices are miniaturized at every development node. The surface roughness is affecting the detecting capacitance of MEMS device because surface to volume ratio is increasing rapidly. A novel model with one rough electrode is investigated in this paper. The impacts of surface roughness on detecting capacitance are analyzed. The image of height percentage is used to describe the surface roughness of electrode sample. The function of the surface roughness is obtained according the method of curve fitting. The effect of surface roughness on the capacitance is calculated. The results demonstrate the capacitance increases with the surface roughness.

Abstract: The effects of different relevant layers, especially the insertion layers (which are between Ta buffer layer and IrMn pinning layer) and free layers, on the magnetic properties of IrMn bottom-pinning spin valves are investigated. Spin valve with a NiFe insertion layer exhibits a higher GMR ratio of ~ 6.0% than that of 2.0% for the spin valve with a Cu insertion layer due to a better pinning strength. The spin valves with a CoFe/NiFe composite free layer have relatively better magnetic properties: a higher GMR ratio compared with the spin valve with a single NiFe free layer and a lower free layer coercivity compared with the spin valve with a single CoFe layer.

Abstract: Megasonic cleaning has been one of the most successful techniques for Cu/low-k interconnects post-CMP cleaning. The structural deformation and stress of Cu and low-k materials in megasonic cleaning are examined with finite element method (FEM). The maximum stress is concentrated in the binding area between Cu and low-k. With decrease of Cu line width, the maximum stress increases and the max value exceeds the yield strength of Cu which results in the plastic deformation. The increasing frequency will change the bubble collision times. Therefore the fatigue is potential. The maximum displacement moves from center to the sides of top surface with increase of line width. When the line width is 25nm, the deformation is the largest.

Abstract: MLUPS functions without contact or friction. With the large current power, mcu control core, laser interferometer position feedback, the stage meets the precision requirements hardware. The positioning system includes two-level positioning system—one-phase coarse positioning and two-phase fine positioning. Based on mathematical model, the immune PI controller is proposed in terms of magnetic edge effect, current harmonic and nonlinear characteristics of magnetic field. By designing target function, antigen affinity, antibodies affinity, mutation, immune algorithm optimizes parameters and memory cells. The stage working range is 10mm, the simulation result shows that the positioning precision is ±10 nm; the positioning time is 50 ms. The stage has a good performance in robustness

Abstract: The extinction ratio is the characteristic parameter of polarization-maintaining (PM) fiber couplers. The detection accuracy of polarization angle is related to the extinction ratio, and affects the thin-diameter PM fiber coupler performances greatly. A series of image processing steps including median filtering, adaptive image morphology, and maximum variance threshold segmentation method are used to get the outline of optical fibers. The minimum squares method is used to get the maximum intensity of the light. The experimental data is processed using the Fourier filtering method and influences of the manufacturing error and random errors of fibers are reduced. By fitting the experiment data with cubic spine method, and its mean square error of fitting is 0.05458, then the polarization angle of the PM fiber is determined. Experiments show that this method can precisely determine the fast axis position of PM fibers, and it can achieve the high precision alignment of 80 um PM fibers.

Abstract: For the existing symmetry Z-tooth MEMS delay mechanisms can not play sports in place under the influence of centrifugal force, this paper presents an asymmetric Z-tooth delay mechanism which can works reliably by weak environmental forces. Working principle and the stress condition of the mechanism are analyzed. Based on the dynamic model, this paper makes a computational analysis and simulation about the kinetic characteristics of the asymmetric Z-tooth delay mechanism, and the results show that the improved mechanism can works reliably and meets the requirements.

Abstract: Two one-dimensional, steady-state numerical models are presented to evaluate the performance of direct methanol fuel cells (DMFCs) in different aspects. One model is applied to simulate the double-layered catalyst structure, which reveals to greatly reduce both cathode and anode overpotential. Another model is created to simulate the effect of methanol and oxygen concentration on power density response in DMFC. In the numerical results, it was found that a DMFC consisting of double-catalyst layer electrodes exhibited many advantages over the traditional MEA, and the performances of the single cell are enhanced.

Abstract: This paper presents an analytical model based on the basis finite element analysis to solve the nonlinear behavior of double-cantilever structure. The structure beam is replaced with a series of beam elements by traditional finite element method. The deformation curve of the beam is calculated by gradually loading voltage in small increments, and pull-in behavior is identified when the convergence of the deflection iteration cannot be achieved after voltage increment. This method considers the effect of deformation on stiffness by establishing a new equivalent stiffness matrix for each voltage step on the basis of the results of previous steps. Through this approach, we prevent the approximate errors of the stiffness matrix from accumulating. The analytical results show good agreement with those obtained by using multiphysics coupling software.

Abstract: A neural network based approach for the identification of the rate-dependent hysteresis in the piezoelectric actuators is proposed in this article. In this method, a dynamic hysteresis operator for expanded input space is proposed to extract the change-tendency and rate-dependency of the dynamic hysteresis, the parameters of the hysteretic operator is identified using genetic algorithm. An expanded input space involving the original input variable and the new operator is constructed. Thus, based on the expanded input space, the neural networks can be utilized to approximate the behavior of the rate-dependent hysteresis. Furthermore, the dynamic performance of the model is improved because of the existence of dynamic operator. Finally, the method is used to the modeling of hysteresis in a piezoelectric actuator. The experimental results are presented to verify the effectiveness of the proposed approach.