Kinetic behavior of resistive oxygen sensor using cerium oxide

In order to decrease exhaust gas emissions, oxygen gas sensors with fast response are required. We evaluated two kinds of fast response time (<1 s) for two oxygen sensors with different cerium oxide particle sizes and crystallite sizes, using two methods: the commonly used jump method and the so-called dynamic method. The dynamic method consists of comparing the amplitude of oxygen partial pressure with that of the sensor output, following the changes in oxygen partial pressure produced by periodic modulation of the hydrostatic pressure with the composition of the atmosphere kept constant. The response times obtained with the jump method and dynamic method are defined as t₉₀ and t_b, respectively. Further, we evaluated the relationship between the amplitude magnitude of the oxygen sensor output (A_n) and the frequency of the oxygen partial pressure (f), using the dynamic method. The results obtained were as follows. The value of t_b for the oxygen sensor with a crystallite size and grain size of about 100 nm was 134 ms or less at 1173 K. The value of t₉₀ was 20 and 1 ms when the oxygen partial pressure changed from high to low and from low to high, respectively. From a plot of log A_n versus log f, it was concluded that the kinetics of a sensor using cerium oxide with crystallite and grain sizes from 100 to 300 nm were controlled by diffusion when the oxygen partial pressure was periodically changed in the shape of a sine wave. It was found that the newly developed equipment was able to evaluate two kinds of response times less than 50 ms.     

基于FLUENT的内啮合齿轮泵静压支撑研究

在分析内啮合齿轮泵胶合失效的基础上,设计了一种静压支撑方法。分析了内齿轮上液压力变化周期,创建了其网格模型,运用FLUENT仿真软件模拟出在一个周期内不同位置时内齿轮内壁所受油压分布以及液压力大小和方向。在此基础上,确定泵体内壁上静压支撑槽的角度范围,并比较了在开静压支撑槽前后的内齿轮受力大小。数值模拟和样机试验结果表明静压支撑方法可防止内啮合齿轮泵胶合失效。     

Study of human–seat interface pressure distribution under vertical vibration

The influence of whole-body vertical vibration on the dynamic human–seat interface pressure is investigated using a flexible grid of pressure sensors. The ischium pressure and the overall pressure distribution at the human–seat interface are evaluated as functions of the magnitude and frequency of vibration excitation, and seated posture and height. The dynamic pressure at the seat surface is measured under sinusoidal vertical vibration of different magnitudes in the 1–10 Hz frequency range. Two methods based on ischium pressure and ischium force are proposed to study the influence of seat height, posture and characteristics of vibration. The results of the study reveal that the amplitude of dynamic pressure component increases with an increase in the excitation amplitude in almost entire frequency range considered in this study. The dynamic components of both the ischium pressure and the ischium force reveal peaks in the 4 to 5 Hz frequency band, the range of primary resonant frequency of the seated human body in the vertical mode. The mean values of the dynamic ischium pressure and the ischium force remain constant, irrespective of the excitation frequency and amplitude. The magnitudes of mean pressure and force at the human–seat interface, however, are dependent upon the seat height and the subject's posture. The inter-subject variability of the static ischium pressure and effective contact area are presented as functions of the subject weight and subject weight-to-height ratio. It was found that heavy subjects tend to induce low ischium pressure as a result of increased effective contact area.

Relevance to industry

Pressure distribution at the human–seat interface has been found to be an important factor affecting the seating comfort and work efficiency of various workers. The study of human–seat interface pressure distribution under vibration is specifically critical to the comfort, work efficiency and health of vehicle drivers, who are regularly exposed to vibration. The results reported in this paper will be useful to study dynamic response of the interface pressure and design vehicle seats.     

压电传感器冲击滞后响应时间测量与分析

压电传感器作为机电换能器使用时响应迅速,使用冲击设备和测量系统对其进行了瞬态冲击滞后响应时间测量和分析.从传感器二阶系统的动态响应、应力波的传播角度出发,通过对滞后响应时间建模和分析,得到了影响该时间的因素,与传感器的结构参数、冲击激励的脉宽、是否有转接结构及安装力矩的大小有关.当传感器固有频率高、阻尼比小、激励脉宽窄、无转接结构和使用较大的安装力矩时,传感器具有更快的响应速度.     

水下传感器承压密封结构设计

设计了一种水下传感器承压密封结构,包括传感器外壳承压与整个机械结构的密封设计.承压外壳采用圆柱形设计,经耐压壳体理论计算能够承受最大10 MPa水压.通过O型圈与橡胶突起结构实现了静水压密封.与现有水下传感器硫化密封结构进行比较,所设计密封结构在保证测试需求的前提下具有可拆卸、易更换的优点.     

Computation of hydrostatic piezoelectric coefficients for 1–3 composites by the finite-element method

The hydrostatic piezoelectric charge coefficients (d_h) and hydrostatic piezoelectric voltage coefficients (g_h) of 1–3 PZT/polymer composites have been calculated by two equations containing the stress tensors of each element. A composite model is divided into 162 elements, and the stress distributions are computed under 0.7 MPa hydrostatic pressure using the finite-element method. The higher d_h value is found for the composite with 30.9% PZT and the higher g_h value for the composite with 19.8% PZT.     

Fabrication and characterization of low temperature sintering PMN–PZN–PZT step-down multilayer piezoelectric transformer

For the fabrication as step-down multilayer piezoelectric transformer, piezoelectric properties of Pb(Mg_1/3Nb_2/3)O₃–Pb(Zn_1/3Nb_2/3)O₃–Pb(Zr_0.52Ti_0.48)O₃ (PMN–PZN–PZT) ceramics were optimized by ZnO–Li₂CO₃ (ZL) and Pb₃O₄ content. Effects of the additions on the structure, bulk density and electrical properties of ceramics were investigated. The results revealed that the proper additions of ZL with Pb₃O₄ content could modify the electrical properties of the PMN–PZN–PZT ceramics. The composition sintered at 995 °C with 0. 01 wt.% ZL and 0.10 wt.% Pb₃O₄ content showed higher values, which were listed as follows: d₃₃ = 256 pC/N, K_p = 0.60, Q_m = 1910, _r = 1032, tan δ = 0.0070 and r = 2.09 Ω. In addition, the step-down piezoelectric transformers with optimized PMN–PZN–PZT composites were fabricated and the characteristics as the output power and resistance loads were measured. Meanwhile, the step-down piezoelectric transformers sintered at 995 °C showed the favorable characteristics with a higher gain G of 0.204 and a lower temperature rise of 6 °C when the output power was 5 W, and the driving frequency were approximately constant (≈126 kHz) when the output power was from 5 to 13 W. Moreover, the maximum efficiency (90.2%) was obtained at load resistance of 10 Ω.     

Millisecond-order response measurement for fast oxygen gas sensors

A novel method for the evaluation of fast response of oxygen gas sensors in terms of milliseconds is developed. Using the method of modulating oxygen partial pressure by changing the total pressure inside the test chamber, the millisecond-order measurement was succeeded. For the 100 Hz sign-wave operation, the measurement system generated the pressure changes from 180 to 220 kPa, corresponding to the change of oxygen partial pressure from 36 to 44 kPa. Using both jump-method and pressure modulation method, the response of the resistive oxygen sensors of cerium oxide thick films were evaluated at 1173 K and the kinetic mechanism of gas sensing was discussed. Their response times of t₉₀ obtained by square-wave change were measured to be 37 and 22 ms for high-to-low oxygen partial pressure and vice versa transition, respectively. The log–log plot of resistance of sensor and the frequency, pressure modulation spectra, was also evaluated at the same time and the kinetics of oxygen sensing was suggested to be diffusion-limited.     

基于ANSYS的埋入混凝土中压电陶瓷谐振频率分析

基于ANSYS研究压电陶瓷(PZT-5H)的振动模态,结合谐响应算法得出压电陶瓷3个不同区域的应变-频率曲线,并将压电陶瓷和混凝土单元耦合,实现了压电埋入式混凝土机敏模块的电-声系统声压云图仿真,得到了不同激励频率下的最大声压和声场分布。结果表明压电陶瓷在20 kHz~100 kHz频段内有4个振幅极大值频率点,随着谐振频率的增加,振幅逐渐增加,而振动分布呈先集中后分散的变化趋势;通过谐响应分析发现压电陶瓷声辐射面不同区域最大应变频率均在80kHz附近;由电-声系统的声场分析发现压电陶瓷的激励频率为79.666 kHz时声压最大、声场分布最优、声指向性集中。     

压力和温度对瓦斯扩散规律的影响研究

针对瓦斯吸附解吸法测定瓦斯扩散系数时局限于颗粒煤、无法施加围压且气体压力不能任意设定等问题,采用规则块煤结合气相色谱分析法测定瓦斯在块煤中的扩散系数,分析了不同气体压力、温度下块煤瓦斯扩散规律。实验结果表明,随着气体压力的增大,煤基质吸附气体增加且发生膨胀变形,从而孔隙减小,扩散阻力增大,扩散系数减小;随着温度的升高,气体分子运动速度增大,扩散动力增强,扩散系数变大。     

Evaluation of driver''s discomfort and postural change using dynamic body pressure distribution

The main objective of this study is the application of body pressure distribution measurements for the prediction of the driver's posture and its change. This requires quantitative analyses of dynamic body pressure distribution, which is the change of body pressure distribution with time. To investigate the relationship between dynamic body pressure data with driver's posture, 16 male subjects performed a simulated driving task for 45 min in a seating buck. During driving, the body posture and body-seat interface pressure were measured continuously, and the discomfort ratings were surveyed at the prescribed interval. For the statistical analyses, driving period, stature group, and lumbar support prominence were selected as independent variables, whereas subjective ratings of driver discomfort, driving posture, and body pressure values were selected as dependent variables. In this study, newly defined dynamic body pressure distribution variables were proposed, and the relationship between these pressure variables with subjective discomfort ratings were analyzed. The close correlations between the body pressure change variables and subjective discomfort ratings supported the possibility of using dynamic pressure data as a tool for the assessment of driver discomfort.

Relevance to industry

Since dynamic body pressure distribution data provide quantitative and objective indices in measuring driver's postural changes and discomfort while driving, the proposed method can be used for more effective automobile seat design and its evaluation.     

The Data Analyses of a Vertical Storage Tank Using Finite Element SOFT Computing

With the rapid development of the petrochemical industry, the number of largescale oil storage tanks has increased significantly, and many storage tanks are located in potential seismic regions. It is very necessary to analyze seismic response of oil storage tanks since their damage in an earthquake can lead to serious disasters and losses. In this paper, three models of vertical cylindrical oil storage tank in different sizes, which are commonly used in practical engineering are established. The dynamic characteristics, sloshing wave height and hydrodynamic pressure of the oil tank considering the liquid-structure coupling effect are analyzed by using ADINA finite element software, which are compared with the result of the standard method. The close numerical values of both results have verified the correctness and reliability of finite element model. The analytic results show that liquid sloshing wave height is basically in direct proportion to ground motion peak acceleration, the standard method of portion sloshing wave height calculation is not conservative. The hydrodynamic pressure generated by liquid sloshing caused by ground motion is not negligible compared with the hydrostatic pressure. The tank radius and oil height have a significant effect on the numerical value of hydrodynamic pressure. The ratio of the hydrodynamic pressure and hydrostatic pressure, which is named hydraulic pressure increase coefficients, is related to the height, which given by the GB 50341-2014 code in China have a high reliability. The seismic performances of tank wall near the bottom needs to be enhanced and improved in the seismic design of the oil tank.     

压电式压力测量系统准静态校准压力脉宽分析

压电式压力测量系统的低频(零频)特性不理想,静态校准时电荷会产生漂移,对灵敏度的获取产生影响.为准确获取测量系统的灵敏度,可采用准静态校准的方法,该方法存在如何选取校准压力脉宽的问题.根据压电式传感系统的等效电路,建立了在测量过程中电荷泄露的数学模型,分析了电荷漂移的主要原因;探讨了不同压力脉宽1 Hz内低频分量所占能量比;基于准静态校准实验,对典型压电式压力传感系统进行校准,获得了不同脉宽激励下测量系统的灵敏度,对灵敏度的差异进行分析,选取了合适的校准脉宽范围.     

Simulating adsorption of n-heptane in the Pt/Al2O3 model: influence of platinum

The molecular modeling method refered to in the literature as Grand Canonical Monte Carlo was used to analyze the phenomenon of n-heptane adsorption on the Pt/γ-Al₂O₃ catalyst. In order to describe relevant interactions, use was made of the forcefield methods (UFF and CVFF). With the conditions adopted for the purpose of the study, Pt was found to exert an advantageous effect on the adsorption of n-heptane. The number of adsorbed molecules was related to the content of the noble metal, and the relation was directly proportional, when temperature and pressure were constant. The contribution of Pt was most distinct at 573 K and 100 kPa.     

Dynamic analysis of thick laminated shell panel with piezoelectric layer based on three dimensional elasticity solution

Elasticity solution is presented for infinitely long, simply-supported, orthotropic, piezoelectric shell panel under dynamic pressure excitation. The direct and inverse piezoelectric effects are considered. The highly coupled partial differential equations (p.d.e.) are reduced to ordinary differential equations (o.d.e.) with variable coefficients by means of trigonometric function expansion in circumferential direction. The resulting ordinary differential equations are solved by the finite element method. Numerical examples are presented for [0/90/P] lamination, where P indicates the piezoelectric layer. Finally the results are compared with the published results.     

Microstructure, electrical and ethanol-sensing properties of perovskite-type SmFe0.7Co0.3O3

Ultrafine SmFe_0.7Co_0.3O₃ powder, prepared by a sol–gel method, shows a single-phase orthogonal perovskite structure. The influence of annealing temperature upon its crystal cell volume, microstructure, electrical and ethanol-sensing properties was investigated in detail. When the annealing temperature increases from 600 to 950 °C, the unit cell volume of the SmFe_0.7Co_0.3O₃ sample reduces, and its average grain size increases. When the annealing temperature increases from 600 to 850 °C, the optimal working temperature and response to ethanol of the SmFe_0.7Co_0.3O₃ sensor increase, and the response–recovery time shortens. But when the annealing temperature further increases from 850 to 950 °C, there are decreases of the optimal working temperature and sensor response, and the response–recovery time is prolonged. The results indicate that, as for sensor response, its optimal annealing temperature is about 850 °C, and the sensor based on SmFe_0.7Co_0.3O₃ annealed at 850 °C shows the highest response S = 80.8 to 300 ppm ethanol gas, and it has the best response–recovery and selectivity characteristics. When the ethanol concentration is as low as 500 ppm, the curve of its optimal response versus concentration is nearly linear. Meanwhile, the influence mechanisms of annealing temperature upon the conductance, the optimal working temperature and sensor response for SmFe_0.7Co_0.3O₃ were studied.     

Pulsed laser deposition of Y2O3 : Eu thin film phosphors

Thin films of Y₂O₃ : Eu cathodoluminescent (CL) phosphors were deposited using pulsed laser deposition using deposition temperature between 250°C and 800°C, O₂ pressures between residual vacuum (2×10⁻⁵ Torr) and 6 Torr, and post annealing up to 1200° for 1 h in air. The CL efficiency of the best thin film was about one third that of the starting powder. The brightness and efficiency of the thin films improved as the deposition temperature, O₂ pressure and post annealing temperature were increased, except that O₂ pressures above 600 mTorr did not significantly improve the CL properties. At deposition temperatures >600°C, the surface morphology changed from a smooth film to a nodular deposit for O₂ pressures >200 mTorr, with nodule dimensions ≈100 nm. Simultaneously, the CL properties improved dramatically because of enhanced optical scattering out of the thin film. Optical scattering was discussed in terms of anomalous diffraction. The CL properties also improved dramatically with high temperature post annealing. This effect was interpreted in terms of improved crystallinity and activation of the Eu. The low brightness and efficiency of thin films versus powder was affected by depletion of the Eu in the thin films owing to the deposition process.     

压电传感器测量路面动水压力研究

雨天动水压力的存在,不仅造成沥青路面易于出现水损害,加快路面使用性能衰减,而且影响到汽车行驶安全,准确测量动水压力数值的大小是研究其危害的有效途径。介绍压电传感器的基本原理。基于压电传感系统能够保证对结构动态压电数据的连续采集,通过自制的压电传感器和设计的标定与实验方案来分析实时采集的动态压电数据。研究结果表明:动水压力数值随着车速的增大而增加,车速为96 km/h时,动水压力达到0.35 MPa,压电传感器在测量动水压力中的应用将有助于解决或减轻沥青路面的水损害。     

高压传感器在高静压下的动态校准方法

提出了一种校准高压传感器频响特性的方法,动态校准系统主要由甘油油腔、霍普金森杆、气枪、应变片、电荷放大器、活塞式压力计和数据采集系统等组成.校准时先利用活塞式压力计在封闭式油腔中产生高静压,高静压作用于被校准的压力传感器.气枪发射子弹,子弹撞击霍普金森杆产生近似于冲激函数的窄脉冲应力波,应力波通过甘油传播并激励传感器,...     

Mechanical behavior of a circular micro plate subjected to uniform hydrostatic and non-uniform electrostatic pressure

Circular micro plates are used in the many Microelectromechanical devices as micropumps and micro pressure sensors. All such systems exhibit a static instability phenomenon (Divergence) which is known as the “pull-in” instability. In this paper a distributed model was used to investigate the pull-in instability of a circular micro plate subjected to non-uniform electrostatic pressure and uniform hydrostatic pressure. The non-linear governing equation was derived and in order to linearize the obtained governing equations, step by step linearization method was used, then the linear system of equation was solved by finite difference method. The obtained results for only electrostatic actuation were compared with the existing results and good agreement has been achieved. There are exist two method of actuation. The pull-in voltages for these two actuation mechanism were investigated and the obtained results exhibited different effects on each actuation mechanism.