Comparison between AlN and Al_2O_3 ceramics applied to barrier dielectric of plasma actuator

This paper reports the material characterization and performance evaluation of an AlN ceramic based dielectric barrier discharge(DBD) plasma actuator. A conventional Al_2O_3 ceramic is also investigated as a control. The plasma images,thermal characteristics and electrical properties of the two actuators are compared and studied. Then, with the same electrical operating parameters(12-kV applied voltage and 11-kHz power frequency), variations of the surface morphologies,consumed power and induced velocities are recorded and analyzed. The experimental results show that the AlN actuator can produce a more uniform discharge while the discharge of the Al_2O_3 actuator is easier to become filamentary. The later condition leads to higher power consumption and earlier failure due to electrode oxidation. In the plasma process,the power increment of the AlN actuator is higher than that of the Al_2O_3 actuator. The induced velocity is also influenced by this process. Prior to aging, the maximum induced velocity of the AlN actuator is 4.2 m/s, which is about 40% higher than that of the Al_2O_3 actuator. After 120-min plasma aging, the maximum velocity of the aged AlN actuator decreases by 27.8% while the Al_2O_3 actuator registers a decrease of 25%.     

微秒脉冲电场下Pb_(0.99)(Zr_(0.95)Ti_(0.05))_(0.98)Nb_(0.02)O_3陶瓷击穿过程电阻变化规律

陶瓷作为应用非常广泛的一种材料,其电击穿问题一直是研究的重点和热点.由于击穿过程涉及热、光、电多场耦合效应,目前还没有一个普适的模型能够解释陶瓷击穿问题.针对此问题进行分析,实验中采用脉冲高压发生装置击穿陶瓷,通过对陶瓷击穿过程中等效电阻的研究,揭示了PZT95/5陶瓷样品体击穿和沿面闪络形成过程的异同.结果显示,在两种击穿模式下,陶瓷样品内部均会在40 ns左右形成导电通道,陶瓷等效电阻急剧下降至10~5?量级;然后体击穿与沿面闪络的导电通道以不同的速率继续扩展;电阻减小速率与导电通道上载流子的浓度有关,二者的等效电阻以不同速率减小,直至导电通道达到稳定.     

Magnetoresistance relaxation and flux creep in high-Tc superconductors

The appearance of hysteretic voltages on ceramic high temperature superconductors during the measurement of the mixed state resistance is now well known., While these voltages can be attributed to a field dependence of the critical current density, the primary phonomenon is the V—H—i characteristic which is representative of a magnetic field induced, dissipative process in the granular material.

Two mechanisms may be responsible for these effects; one is the well known flux-flow or flux-creep phenomenon where the electrical energy is used in changing the vortex system while the other is a more conventional thermal loss as the intergranular contacts are driven normal by the applied field.

The observation of a corresponding time dependent residual voltage which is associated with flux trapped in the superconductor is examined in terms of the two models, both of which are found to predict the observed time decay and also justify the derivation of the flux-trapping energies from the decay law. The differences between the models appear in the prefactors to the logarithmic decay term.     

The calibration of activated charcoal detectors in a small Rn exposure chamber

Passive methods for radon measurements, especially those based on radon adsorption, require observation of proper calibration methods.

The calibration method for diffusion-barrier charcoal detectors in a small (211 dm³) radon chamber has been proposed. The theoretical dependence of radon concentration vs. time inside the chamber during the exposure of charcoal detectors has been obtained and verified experimentally. For this purpose, the chamber volume as well as diffusion and adsorption parameters of the detector were taken into consideration.

For two types of detectors the conformity of calibration factors obtained in two ways: calculated from theoretical points (550 or 683 Bqm⁻³/cps depending on detector type) and from experimental points (553 or 691 Bqm⁻³/cps), was achieved.

The proposed method makes it possible to calibrate different kinds of radon-adsorbing detectors (not only charcoal canisters) in small chambers without the necessity of using any reference, active device.     

La0.5Ca0.5MnO3内禀与界面电脉冲诱导电阻转变效应的比较

一般地,钛矿结构锰氧化物的电脉冲诱导电阻转变(EPIR) 效应源于非内禀界面处的肖特基势垒. 本文采用固相烧结法制备了La_0.5Ca_0.5MnO₃ (LCMO)陶瓷样品, 用四线测量模式对样品电输运性质, 特别对其内禀EPIR效应和忆阻器行为进行了研究. 室温下, 尽管样品在四线测量模式下的I-V特性曲线呈欧姆线性规律, 但在适当的脉冲电压刺激下, 仍能诱导产生明显、稳定的EPIR效应. 通过与二线模式的界面EPIR比较, 发现LCMO内禀EPIR效应具有更小的脉冲临界电压、更好的稳定性和抗疲劳特性, 是稀土掺杂锰氧化物中观察到的一类新颖的EPIR效应. 关键词： 钙钛矿结构锰氧化物 电致电阻效应 电脉冲诱导电阻转变效应 肖特基势垒     

Sintering of glasses in the system RO–Al2O3–BaO–SiO2 (R=Ca, Mg, Zn) studied by hot-stage microscopy

Glass–ceramics for sealing solid oxide fuel cells (SOFCs) were developed by sintering and crystallization of the powdered glass seal. The non-isothermal sintering kinetics and crystallization kinetics were studied for four glasses in the system 50SiO₂·(45−x)BaO·xRO·5Al₂O₃ (R=Ca, Mg, Zn and x=0, 15) (mol%). Hot-stage microscopy (HSM) and differential thermal analysis (DTA) measurements demonstrated that it is possible to first sinter and then crystallize these glasses obtaining glass–ceramic seals with thermal expansion coefficients in the range 9–12×10⁻⁶ K⁻¹.

The non-isothermal sintering kinetics was analyzed by computer simulations using a previously reported model of sintering for polydispersed glass powders which takes into account the particle size distribution, surface energy and viscosity. Good agreement was found between the measured kinetics with HSM and the calculated kinetics for all glasses.     

直流老化对CaCu3Ti4O12陶瓷介电性能的影响

在电场为3.5 kV/cm的条件下, 对CaCu₃Ti₄O₁₂陶瓷进行了60 h的直流老化, 研究了老化过程对CaCu₃Ti₄O₁₂陶瓷介电性能和电气特性的影响. J-E特性测试结果表明, 直流老化导致CaCu₃Ti₄O₁₂陶瓷击穿场强、非线性系数和势垒高度明显降低. 介电性能测试结果表明, 低频介电常数和介电损耗明显增大, 并且介电损耗随频率的变化遵从Debye弛豫理论, 可分解为直流电导损耗和弛豫损耗, 直流老化主要导致了电导损耗的增加. 在低温233 K, 介电损耗谱中出现两个弛豫峰, 其活化能分别为0.10, 0.50 eV, 认为对应着晶粒和畴界的弛豫过程, 且不随直流老化而变化. 通过电模量谱对CaCu₃Ti₄O₁₂陶瓷的弛豫过程进行了表征, 发现直流老化导致的界面空间电荷在外施交变电场的作用下符合Maxwell-Wagner极化效应, 并在低频区形成新的弛豫峰. 在高温323-473 K的阻抗谱中, 晶界弛豫峰在直流老化后明显向高频移动, 其对应的活化能从1.23 eV 下降到0.72 eV, 晶界阻抗值下降了约两个数量级. 最后, 建立了CaCu₃Ti₄O₁₂陶瓷的阻容电路模型, 分析了介电弛豫过程与电性能之间的关联.     

A relation between the atomic charge of carbon and the C1s core electron binding energy estimated from a comparison of gas phase and solid state data and the molar polarizabilities of the investigated molecules

A method for internal calibration of ESCA (XPS ) spectra is described that permits the use of a simple relation between binding energy (E_b) and atomic charge (q) : E_b = kq + E_b0. This relation has been shown to hold for a large number of elements. So far the relation for carbon has, however, not been very well established. A method is now described that allows the use of carbon charges determined from E_b, vs. q correlations for other elements and has also made it possible to establish a linear relation for carbon. The method does not use carbon charges determined directly from quantum chemical calculations.

As an essential part of this procedure we investigated empirically the possible relation between the difference between the gas phase calibration standard and that for the same element in the solid state, “a”, and the molar polarizability of the substance, P. It was found that “a” decreases with increasing polarizability, tentatively as a=4.15+8.30 P^−1/3. Therefore, knowledge of the polarizability of carbon-containing molecules from the literature made it possible to determine “a” and then the charge of all other atoms in the molecule. In this way a set of E_b and qc date was obtained. These data were complemented by another set using theoretical q_c snd solid state E_b of phenyl compounds previously made.

The results of the investigation show a linear relation between E_b(Cls) and q_c valid for the solid state: E_b,(Cls) = 4.68 q_c + 286.2 eV with a correlation coefficient of 0.945. This brings the previously obtained k value for carbon, which seemed anomalously high, down to a value of similar magnitude as for other light elements.     

A novel drum piezoelectric-actuator

This paper presents a large displacement, piezoelectric-metal structure actuator, named the piezoelectric drum actuator. The drum actuator consists of a short, thick-walled steel cylinder sandwiched by two thin composite disks, which are fabricated from a brass disk bonded with a piezoceramic disk. The piezoceramic disk, which is polarized in its thickness direction, has a large diameter thickness ratio, producing a large radial displacement under an applied voltage in the thickness, leading to a large transverse deflection of the composite disks in the drum. The drum (outer diameter: 12.0 mm) has a displacement that is about eight times larger than that of a cymbal actuator made with the same ceramic material and comparable dimensions under the same dc driving voltage of 270 V. The drum actuator also showed a large resonance displacement of 56.7 μm under an ac voltage of 90 V. The effective piezoelectric charge coefficient d’₃₃ of the drum is about twice as large as that reported for the cymbal. PACS 77.65 -j; 85.50.+k; 43.38.fx     

Complete ultrasonic transducer characterization and its use for models and measurements

Transmitting and receiving properties of ultrasonic piezoelectric crystal transducers that directly affect the measured output voltage in an ultrasonic measurement system are described. These transducer properties are the transducer's electrical impedance and sensitivity, the transducer's radiation impedance, and the transducer's effective parameters (effective radius and focal length). It is shown that all these properties can be obtained with a series of calibration measurements, most of them purely electrical in nature. This series of measurements is described, including a newly developed method that makes the determination of the transducer sensitivity simpler than with previous methods. It is demonstrated that by combining these transducer properties with knowledge of the electrical properties of the pulser/receiver and cabling and the acoustic/elastic processes present in an ultrasonic measurement system, it is possible to accurately simulate the output voltage of the system.     

CuO added Pb_(0.92)Sr_(0.06)Ba_(0.02)(Mg_(1/3)Nb_(2/3))_(0.25)(Ti_(0.53)Zr_(0.47))_(0.75)O_3 ceramics sintered with Ag electrodes at 900℃ for multilayer piezoelectric actuator

CuO added Pb_(0.92)Sr_(0.06)Ba_(0.02)(Mg_(1/3)Nb_(2/3))_(0.25)(Ti_(0.53)Zr_(0.47))_(0.75)O_3 ceramics were studied to prepare high-quality multilayer piezoelectric actuators with pure Ag electrodes at 900℃. Cu O addition not only reduced the sintering temperature significantly from 1260℃ to 900℃ but also improved the ceramic density to 7.742 g/cm~3. The 0.7 wt.% Cu O added ceramic sintered at 900℃ shows the remnant polarization(P_r) of 40 μC/cm~2, 0.28% strain at 40 kV/cm, and the piezoelectric coefficient(d_(33)) of 630 pC/N. This ceramic shows a strong relaxor characteristic with a Curie temperature of 200℃. Furthermore, the 0.7 wt.% CuO added ceramic and pure Ag electrodes were co-fired at 900℃ to prepare a high-quality multilayer piezoelectric actuator with a d_(33) of over 450 pC/N per ceramic layer.     

Preparation and properties of polyurethane/MMT nanocomposite actuators

This study dealt with the electrostrictive response of a polyurethane (PU)/clay nanocomposite film, which was a promising candidate for a material to be used in polymer actuators. The nanocomposites were produced by using three types of montmorillonites (MMTs) such as natural MMT (Cloisite^®Na⁺), hydrophobic MMT (Cloisite^® 20A), and hydrophilic MMT (Cloisite^® 30B). The nanometer-scale silicate layers of organo-clay were completely exfoliated in PU for the cases of 1, 3 and 5 wt% PU/MMT nanocomposites as confirmed by wide X-ray diffraction (WAXD) profiles. Actuation tests indicated that the displacement of PU/MMT nanocomposite actuator was larger than pure PU actuator, caused by an increase in dielectric constant. Especially, PU/MMT nanocomposite actuator with Cloisite^® 30B had the largest displacement and it became possible to operate at low voltage.     

Effect of pressure on the performance of plasma synthetic jet actuator

The effects of the ambient air pressure level on the performance of plasma synthetic jet actuator have been investigated through electrical and optical diagnostics.Pressures from 1 atm down to 0.1 atm were tested with a 10 Hz excitation.The discharge measurement demonstrates that there is a voltage range to make the actuator work reliably.Higher pressure level needs a higher breakdown voltage,and a higher discharge current and energy deposition are produced.But when the actuator works with the maximum breakdown voltage,the fraction of the initial capacitor energy delivered to the arc is almost invariable.This preliminary study also confirms the effectiveness of the plasma synthetic jet at low pressure.Indeed,the maximum velocities of the precursor shock and the plasma jet induced by the actuator with maximum breakdown voltage are independent of the ambient pressure level;reach about 530 and 460 m/s respectively.The mass flux of the plasma jet increases with ambient pressure increasing,but the strength of the precursor shock presents a local maximum at 0.6 atm.     

A method of relaying the transverse profile of a laser beam and its application to holography

The holography of engineering plant where only restricted access is available requires a method of piping the pulsed laser beam to a compact, remote head. Because amplifier distortions which occur in pulsed lasers result in far field beam break-up, it is not possible to simply collimate the beam as normally possible with a continuous wave laser. A possible way to transmit the pulsed laser beam is by an optical relay which repeatedly images the output until the launching point is reached.

The use of a relay system to transmit the pulsed laser output 20 m has been demonstrated in the laboratory. Holograms taken at the output of the relay showed a resolution of 18l.p. mm^-1, the same as that achieved when a hologram was taken by expanding the beam immediately at the laser output.     

Comparison of electrical discharge techniques for nonthermal plasmaprocessing of NO in N2

This paper presents a comparative assessment of three types of electrical discharge reactors: 1) pulsed corona, 2) dielectric-barrier discharge, and 3) dielectric-pellet bed reactor. The emphasis is on the efficiency for electron-impact dissociation of N₂(e+N₂ →e+N+N) and the subsequent chemical reduction of NO by nitrogen atoms (N+NO→N₂+O). By measuring the concentration of NO as a function of input energy density in dilute mixtures of NO in N₂, it is possible to determine the specific energy cost for the dissociation of N₂. Our experimental results show that the specific energy consumption (eV per NO molecule reduced) of different types of electrical discharge reactors are all similar. These results imply that, during radical production in electrical discharge reactors, the electric field experienced by the plasma is space-charge shielded to approximately the same value. The specific energy consumption for the dissociation of N₂ using electrical discharge processing is measured to be around 240 eV per nitrogen atom produced. In the NO-N₂ mixture, this corresponds to a specific energy consumption of around 240 eV per NO molecule reduced     

变宽度分割电极片状压电致动器的位移特性

针对硬磁盘驱动器中磁头定位两级伺服系统设计了一种新型压电致动器——悬臂梁式变宽度分割电极片状压电致动器.沿厚度方向极化的PZT压电陶瓷薄长片，宽度沿长度方向变化且沿长轴对称，一端固定一端自由构成悬臂梁.其上下两表面的电极均沿长轴分割成对称的两部分.施加电场使其中一半在d₃₁模式作用下伸长，而与其对称的另一半缩短，则压电片沿宽度方向产生弯曲，自由端便可产生致动位移.对该致动器的驱动电压-端部致动位移特性进行了理论分析、有限元模拟及实验验证.致动器中的电场诱导应力远小于陶瓷的抗张强度.致动器端部位移的测试结果略大于理论计算值.与现有磁头悬浮臂尺寸相近的致动器，在20—50V的电压驱动下均可获得1—2μm的致动位移.对25kTPI(track per inch)的高道密度硬磁盘，该位移已能覆盖至少一个磁道宽度，满足磁头定位两级伺服系统对第二级致动器致动位移的基本要求. 关键词：     

电阻率与强度性能的关联及铜合金性能分区

铜合金以低电阻率为特征,由于电阻率与强度存在着共同的微观结构机理,两者往往协同变化,而导致难以对合金进行性能的全面评估和选材.本文以Cu-Ni-Mo合金作为研究对象,以团簇结构[Mo_1-Ni_(12)]构建固溶体的近程序结构模型,解析了电阻率和强度依赖于成分的定量变化规律,并定义了拉伸强度/电阻率的值为代表合金本质特性的"强阻比",得到了完全固溶态Cu-Ni-Mo合金的强阻比为7×10~8MPa/?·m,完全析出态的强阻比为(310—490)×10~8MPa/?·m.进而应用强阻比对常用铜合金进行了性能分区,给出铜合金材料选材的依据,得出了基于Cu-(Cr, Zr, Mg, Ag, Cd)等二元基础体系的铜合金适用于高强高导应用,而基于Cu-(Be, Ni, Sn, Fe, Zn, Ti, Al)等为基础二元体系的铜合金不能实现高强高导.该强阻比为310的特征性能分界线的发现为合金性能的全面评估提供了量化依据,可指导高强高导铜合金的选材和研发.     

The mapping of charges in carbonyl complexes of some transition elements from XPS data

A method for internal calibration of ESCA (XPS ) spectra is described that permits the use of a simple relation between binding energy (E_b) and atomic charge (q) : E_b = kq + E_b0. This relation has been shown to hold for a large number of elements. In order to test these relations, a procedure is suggested that allows the calculation of the atomic charges in carbonyl complexes of chromium, iron and nickel from gas-phase and solid-state ESCA data. The agreement with theoretically calculated charge values is good.

The charge distribution in carbon monoxide has been estimated in a similar manner and the result is discussed in relation to other investigations.     

Computer-assisted design of surface coils used in magnetic resonance imaging. II. Rotational discrimination nonlinear regression analysis and the design of surface coils

For a number of reasons, it is desirable to fabricate coils which, for a known current, shall produce predetermined values of the magnetic field intensity at a number of points within a nuclear magnetic resonance imager.

The calculation of the magnetic field intensity at a set of points involves the integration of the Biot-Savart equation for all components of the segments of conductor which make up the coil. This process in itself is a rather formidable task. When this process is parameterized in terms of coil diameter, coil spacing, etc. the problem is to determine the values of these parameters to match values of magnetic field intensities which are desired. The problem thereby increases in complexity to the point where, by ordinary methods, the problem becomes intractable.

A generalized solution technique has been developed on a digital computer to implement the rotational discrimination nonlinear regression techniques of Faris, Law and Letcher to find the best solution to this problem. The problem is posed by integrating the Biot-Savart equation. This produces algebraic expressions for incorporation into the optimization program which is executed on a computer in a conversational mode.

This technique was employed to specify the dimensions of a rectangular surface coil for the investigation of the whole human spine.     

基于内标法和CARS变量优选的倍硫磷含量LIBS检测

利用共线双脉冲激光诱导击穿光谱（LIBS）技术对溶液中的倍硫磷含量进行定量检测研究。采用石墨对倍硫磷溶液进行富集,利用双通道高精度光谱仪获取样品的LIBS光谱。以碳元素谱线（CⅠ247.856 nm）为内标对210~260 nm波段谱线进行校正,然后利用竞争性自适应重加权算法（CARS）筛选与倍硫磷相关的重要波长变量,最后应用最小二乘支持向量机（LSSVM）建立倍硫磷含量的定标模型,并与基本定标法及内标法建立的单变量定标模型进行比较。研究结果表明,共线双脉冲LIBS技术可以用于溶液中的倍硫磷含量检测。基本定标法建立的最优定标模型的拟合度R²为0.935 04,预测集样品的平均预测相对误差（PRE）为41.50%;内标法建立的最优单变量定标模型的拟合度R²为0.993 61,预测集样品的平均PRE为14.91%;内标-CARS-LSSVM定标模型的拟合度R²为0.998 6,预测集样品的平均PRE为8.06%。对比上述3类定标模型,内标-CARS-LSSVM定标模型性能最优,内标法建立的定标模型次之,而基本定标法建立的定标模型最差。由此可知,CARS方法可以有效筛选倍硫磷相关的重要变量,内标法结合CARS及LSSVM方法可以改善定标模型性能,提高预测精度。