The parallel-plate resonator:An RF probe for MR and MRI studies over a wide frequency range

We explore the use of the parallel-plate resonator for the study of thin cuboid samples over a wide range of magnetic resonance frequencies.The parallel-plate resonator functions at frequencies from tens to hundreds of MHz.Seven parallel-plate resonators are presented and discussed in a frequency range from 8 to 500 MHz.Magnetic resonance experiments were performed on both horizontal and vertical bore magnet systems with lithium and hydrogen nuclei.Parallel-plate radiofrequency(RF)probes are easy to build and easy to optimize.Experiments and simulations showed good sensitivity of the parallel-plate RF probe geometry with a small decrease in sensitivity at higher frequencies.

OPTIMIZATION OF TRANSIENT FEEDING TO PARALLEL-PLATE TRANSMISSION LINES FROM COAXIAL LINE

The transient feeding to parallel-plate transmission lines from coaxial line is optimized by using the Finite-Difference Time-Domain (FDTD) method and a simple FDTD feed model. Observing the reflected voltages, this letter presents the optimal feeding position and ratio of width to height for a given input impedance of the coaxial line.

ON ANALYSIS OF THE STEADY FLOW IN AN IRRECTANGULARPARALLEL-PLATE FLOW CHAMBER

The parallel-plate flow chamber (PPFC), of which the height is far smaller than its own length and width, is one of the main apparatus for the in vitro study of the mechanical behaviors of cultured cells at the bottom of PPFC undergoing shear stress. The PPFC of which the upper and lower plates are rectangular is usually used by research workers, and the flow field in this kind of PPFC (except for the regions near the entrance and exit) is uniform([1]), so only the effect the shear stress with one value has on cultured cells can be observed during each experiment. A kind of PPFC of which the upper and lower plates are not rectangular is proposed in this paper. The distributions of the velocities inside and the shear stresses at the bottom of the chamber are given by analyzing the flow field of the steady flow in the PPFC. The results show that the mechanical behaviors of cultured cells undergoing the shear stresses with various values may be simultaneously observed by the use of this kind of irrectangular PPFC. The theoretical and experimental results obtained by Ultrasonic Doppler Technique show good agreement.

MULTI-MODE NETWORK ANALYSIS FOR DISCONTINUITIES IN PARALLEL-PLATE WAVEGUIDES PARTIALLY FILLED WITH MULTI CHIRAL RODS

The reflection and transmission characteristics of the guided modes in parallel-plate waveguides partially filled with one or multi chiral rods have been investigated by a method, which combines the multi- mode network theory with a rigorous mode matching procedure. The formulas of the reflection and transmis- sion coefficient matrix are derived. The numerical results for different cases are presented and have indicated that the chirality parameters and the geometrical dimensions of the chiral rods have significant influence on the reflection and transmission characteristics of the guided modes.

ANALYSIS OF PULSATILE FLOW IN THE PARALLEL-PLATE FLOW CHAMBER WITH SPATIAL SHEAR STRESS GRADIENT

The Parallel-Plate Flow Chamber （PPFC）, of which the height is far smaller than its own length and width, is one of the main apparatus for the in-vitro study of the mechanical behavior of cultured vascular Endothelical Cells （ECs） exposed to fluid shear stress. The steady flow in different kinds of PPFC has been extensively investigated, whereas, the pulsatile flow in the PPFC has received little attention. In consideration of the characteristics of geometrical size and pulsatile flow in the PPFC, the 3-D pulsatile flow was decomposed into a 2-D pulsatile flow in the vertical plane, and an incompressible plane potential flow in the horizontal plane. A simple method was then proposed to analyze the pulsatile flow in the PPFC with spatial shear stress gradient. On the basis of the method, the pulsatile fluid shear stresses in several reported PPFCs with spatial shear stress gradients were calculated. The results were theoretically meaningful for applying the PPFCs in-vitro, to simulate the pulsatile fluid shear stress environment, to which cultured ECs were exposed.

Removal of antibiotics in a parallel-plate thin-film-photocatalytic reactor: Process modeling and evolution of transformation by-products and toxicity

Photocatalytic degradation of sulfamethoxazole（SMX） antibiotic has been studied under recycling batch and homogeneous flow conditions in a thin-film coated immobilized system namely parallel-plate（PPL） reactor. Experimentally designed, statistically evaluated with a factorial design（FD） approach with intent to provide a mathematical model takes into account the parameters influencing process performance. Initial antibiotic concentration, UV energy level, irradiated surface area, water matrix（ultrapure and secondary treated wastewater） and time, were defined as model parameters. A full of 2~5 experimental design was consisted of 32 random experiments. PPL reactor test experiments were carried out in order to set boundary levels for hydraulic, volumetric and defined defined process parameters. TTIP based thin-film with polyethylene glycol ＋ TiO2 additives were fabricated according to pre-described methodology. Antibiotic degradation was monitored by High Performance Liquid Chromatography analysis while the degradation products were specified by LC–TOF-MS analysis. Acute toxicity of untreated and treated SMX solutions was tested by standard Daphnia magna method. Based on the obtained mathematical model, the response of the immobilized PC system is described with a polynomial equation. The statistically significant positive effects are initial SMX concentration,process time and the combined effect of both, while combined effect of water matrix and irradiated surface area displays an adverse effect on the rate of antibiotic degradation by photocatalytic oxidation. Process efficiency and the validity of the acquired mathematical model was also verified for levofloxacin and cefaclor antibiotics. Immobilized PC degradation in PPL reactor configuration was found capable of providing reduced effluent toxicity by simultaneous degradation of SMX parent compound and TBPs.

A portable and low-cost parallel-plate capacitor sensor for alkali and heavy metal ions detection

A portable and low-cost design of parallel-plate capacitor sensor is proposed and investigated for detection of heavy and alkali metal ions concentration in liquid solution.The application of a thin and long-sided parallel PCB plate allows one to measure the dielectric response of each sample through capacitive sensing technique.The measurements were based on the peak output voltage corresponding to the capacitance of the output measured by an oscilloscope with metal ions concentration of the solution varying from 0 to 10 ppm and input frequency ranging from 1 kHz to 10 MHz.The ICF of Li,Na and K in chloride solution was 2.4,2.1 and 1.9 MHz,respectively.The ICF of Na and K in hydroxide solution was 1.5 MHz and 1.1 MHz,respectively,while the ICF of Pb(NO_(3))_(2)was 490 kHz.The detected ICF was applied to further construct the portable sensor system,which is simple in design,low-cost in fabrication and easy to operate.The finding of ICF of each chemical element is necessary to solve the selectivity challenge of the capacitance-based sensor,which will be appropriate for chemical,environmental and engineering applications.

Multinuclear MR and MRI study of lithium-ion cells using a variable field magnet and a fixed frequency RF probe

An exploratory multinuclear magnetic resonance(MR)and magnetic resonance imaging(MRI)study was performed on lithium-ion battery cells with ^(7)Li,^(19)F,and ^(1)H measurements.A variable field superconducting magnet with a fixed frequency parallel-plate radiofrequency(RF)probe was employed in the study.The magnetic field was changed to set the resonance frequency of each nucleus to the fixed RF probe frequency of 33.7 MHz.Two cartridge-like lithium-ion cells,with graphite anodes and LiNi_(0.5)Mn_(0.3)Co_(0.2)O_(2)(NMC)cathodes,were interrogated.One cell was pristine,and one was charged to a cell voltage of 4.2 V.The results presented demonstrate the great potential of the variable field magnet approach in multinuclear measurement of lithium-ion batteries.These methods open the door for developing faster and simpler methods for detecting,quantifying,and interpreting MR and MRI data from lithium-ion and other batteries.

基于聚酰亚胺的柔性湿度传感器制备及研究

文中以聚酰胺酸(PAA)为前驱体,通过热处理工艺可得聚酰亚胺(PI)薄膜,添加氧化石墨烯(GO)合成PI/GO复合薄膜及后续电极制备得到基于聚酰亚胺的平行板电容式柔性湿度传感器。在此基础上深入研究了叉指电极式和平行板式构型、PAA旋涂转速、PAA酰亚胺化温度、GO喷涂量对湿度传感器性能的影响,最终得到的湿度传感器具有良好重复性、快速的响应恢复时间,最大湿滞仅为3.8%RH,且具有优异的柔性性能,在可穿戴柔性电子器件领域具有广泛的应用前景。

金属盖板镀层形貌对平行缝焊器件抗盐雾性能的影响

气密性封装是高可靠集成电路制造的关键技术。探讨了金属盖板表面镀层形貌对平行缝焊器件耐盐雾性能的影响。研究发现,平行缝焊后金属盖板表面出现的贯穿性裂纹是降低平行缝焊器件耐盐雾性能的关键因素。在相同封帽参数下,表面镀层为长条形晶胞的盖板封帽后出现多条贯穿性裂纹,无法通过24 h盐雾试验后气密性检测。而表面镀层为均匀大小的圆形晶胞的盖板具备更高的抗封帽裂纹能力,封帽后无贯穿性裂纹出现,且可通过48 h盐雾试验后气密性检测。

基于平行平板电极的非球面双液体透镜的仿真与实验分析

应用介电泳原理,设计了一种基于平行平板电极的非球面双液体透镜,具有结构简单和易于实现的优点.利用Comsol,Matlab和Zemax软件,建立了相应的非球面双液体透镜光学模型,仿真分析了其在不同电压下的焦距变化及成像特性,并与球面双液体透镜模型进行了比较分析.非球面双液体透镜的变焦范围大于球面的,前者的成像质量亦优于后者.而且,实验制备了该非球面双液体透镜器件,结果表明,在工作电压为0—280 V时,焦距变化为54.2391—34.5855 mm,与仿真结果基本相符,而且该器件的成像分辨率最大可达45.255 lp/mm.

并联气体开关导通分散性对平行板汇流装置放电电流的影响

为研究平行板汇流脉冲功率装置中并联开关导通分散性对装置放电电流的影响,依据实验结果,建立气体开关导通分散性模型和不同参数模块的电路仿真模型,分析放电电流随开关导通分散性大小和回路参数变化的规律。研究结果表明:开关导通分散性会引起回路出现过电流,降低回路电感和回路电容,增加负载电感和并联路数将导致过电流极值的进一步增加;过电压是开关延时数微秒依旧能够导通的必要条件,仅一台开关延迟导通时存在过电流幅值的最大值,模块1在70 kV工作电压时回路的最大过电流峰值607 kA,过电流倍数1.33;模块2在35 kV工作电压时回路的最大过电流峰值590 kA,过电流倍数15.6。随着延时导通开关数量和开关导通分散性的增加,负载电流峰值降低,电流上升时间增加,而各回路之间的电荷重新分布使负载电流受影响小于回路电流。负载电流的可用性和装置的安全运行允许负载电流峰值的波动≤5%,需要模块1分散性≤587.5ns,模块2分散性≤35.25μs,对应的过电流最大值分别为504 kA和135 kA。

基于非对称辐射单元的毫米波全金属漏波天线

周期漏波天线具备后向端射-前向端射的连续波束扫描能力。全金属周期漏波天线在毫米波雷达等系统中具有明确的应用前景,但普通方案受制于开放阻带效应,边射性能差、扫描性能受限。目前抑制开放阻带效应的方法主要包括加载四分之一波长变换器或匹配短截线、不对等双辐射元、短路过孔匹配等,适合于全金属周期漏波天线的解决方案尚待发掘。文中提出了一种采用非对称辐射单元抑制开放阻带效应的方法,并结合等效电路模型进行机理分析和方法验证。采用非对称辐射单元设计了毫米波全金属波纹平行板波导周期漏波天线。该天线在26.5~36 GHz频带内具有-47.5°~8.5°的连续波束扫描能力,且辐射效率高于78%。仿真和实验结果表明,该非对称辐射单元能够很好地抑制开放阻带效应,适用于宽角频扫全金属周期漏波天线设计。

静态气压下平行轨道加速器电流分布与等离子体速度特性

电磁等离子体加速器可产生高密度高速度等离子体射流而广泛应用于等离子体物理研究与应用领域.本文建立了平行轨道加速器电磁驱动等离子体实验平台,通过磁探头阵列和光电二极管阵列研究了静态气压下平行轨道加速器的电流分布和等离子体速度特性.平行轨道加速器驱动电源为正弦振荡衰减波电源,总电容为120μF,回路总电感约为400 nH,充电电压为13 kV时,放电电流为170 kA,脉宽为23.5μs.当放电电流较小、工作气压较高时,平行轨道加速器电流分布较集中,放电模式与雪犁模式相符.随着放电电流的增大或工作气压的降低,平行轨道加速器逐渐出现弥散的电流分布,形成等离子体前沿和等离子体拖尾两个区域.放电电流越大,工作气压越低,电流弥散分布越显著,等离子体前沿电流分布比例越低,等离子体前沿速度越高,但等离子体速度增大的比例远低于放电电流增大的比例或工作气压平方根的倒数增大的比例.

基于微流控芯片模型的渗流实验与数值模拟

基于微流控芯片加工技术,采用显微镜-微观模型实验装置,通过制作准二维微流控芯片模型来模拟多孔介质内部的骨架及孔隙结构,开展多孔介质渗流实验.通过测量芯片模型两端的压降并进行修正,计算芯片模型的渗透率.采用计算流体力学方法(CFD)对渗流过程进行数值模拟,并与实验结果进行对比分析.结果表明:在相同条件下,相对于微柱方形排列的芯片模型,微柱错开排列的芯片模型在微观上表现为迂曲度增大,增大的幅值为5.1%~7.9%;在宏观上表现为流阻和压降更大,渗透率更低,降低的幅值为4.5%~7.4%.芯片模型渗透率不仅与内部孔隙通道结构和孔隙率有关,还与颗粒直径和颗粒排列方式相关.当模型孔隙率为0.327~0.900时,数值模拟方法所得的微流控芯片模型的渗透率与实验所测结果接近,误差为9.78%~28.43%.Kozeny-Carman(KC)公式不能准确预测实验结果,并且最大误差为73.97%.提出修正平行板间导管流(平板流)渗流公式预测准二维微流控芯片模型渗透率,预测渗透率曲线与数值模拟和实验数据具有很好的一致性.

平行平板波导的导电型面板纸蜂窝夹层结构积水检测

针对传统的检测方法存在检测信号源功率高、检测速度慢等问题,且不适用于导电型面板纸蜂窝夹层结构,提出了基于平行平板波导理论的微波检测新方法,该方法具有非接触、对极性分子灵敏度高等综合优势,尤其适合导电型面板纸蜂窝夹层结构内积水的检测。首先,仿真分析了检测方法的可行性,并通过试验验证了仿真结果的正确性。试验结果表明:在8~12 GHz,随着碳纤维复合材料面板纸蜂窝夹层结构内积水量的增加,S21幅值不断减小,铝面板纸蜂窝夹层结构在低频段内满足该规律;然后,区分出铝面板纸蜂窝夹层结构内不同高度的积水积油缺陷;最后,讨论了波导的位置分布对积水缺陷检测的影响。本文为此类蜂窝板内其他缺陷类型的检测提供了新方法。

并联U型通道冷板冷却动力电池的换热特性

温度对锂离子动力电池性能有显著影响。本文提出的并联U型通道冷板,具有换热均匀性良好的特点,在动力电池等发热设备冷却方面具有优势。通过数值方法模拟了并联U型通道冷板的换热效果,结果表明,在不同流速下,并联U型通道冷板的温度标准差都小于1,证明其温度分布相当均匀;在较高和较宽的热流密度条件下,并联U型通道冷板保持了较好的换热特性一致性及换热均匀性。

三层多晶硅结构的挠曲式静电驱动MEMS微反射镜

将悬臂梁结构与平行平板型结构相结合,研发了一种挠曲式静电驱动微电子机械系统(MEMS)微反射镜。为了实现大扭转角度、小驱动电压的设计目标,通过仿真实验进行对比分析,确定了微反射镜的相关尺寸。采用低压化学气相沉积、光刻、反应离子刻蚀和溅射等工艺,成功制备出了一种具有三层多晶硅结构的微反射镜。在制备过程中得出氢氟酸去除牺牲层(磷硅玻璃)释放出微反射镜结构的最佳刻蚀时间为45 s。制作了开关频率为200 kHz的MOSFET高速驱动电路,电路中的栅极驱动电阻(R_(G))是影响输出的关键因素。实验结果表明,当R_(G)额定功率为300 W、电阻为47Ω时,微反射镜能够达到足够启动速度,实现高速开关的设计目标。最后,设计并搭建了微反射镜的测试系统,施加60 V的驱动电压进行测试,通过显微镜观察到微反射镜的明显动作变化以及屏幕上光斑的位移变化,表明制备的微反射镜可正常驱动。

基于静电驱动的平行平板型微反射镜的研制

设计了一种基于静电驱动的平行平板型微反射镜,主要由镜面、下电极、支柱和玻璃基板构成。通过有限元模拟分析得到的仿真结果表明,带孔结构的微镜模型模拟位移量是传统双横梁支撑结构微镜模型的1.5倍,确定了制备的微镜装置结构。在制备过程中只采用了溅射、光刻、机械切割及反应离子刻蚀等工艺,简化了工艺流程,降低了制备成本。使用反应离子刻蚀(RIE)去除牺牲层,为了克服光刻胶OFPR800灰化速度慢、灰化时间过长会损伤器件的问题,提出添加氟类气体的解决方法。实验结果表明,使用O_(2)和SF_(6)混合气体作为刻蚀气体刻蚀牺牲层后,射频(RF)溅射成的铝膜平均表面粗糙度为5.33 nm,均方根粗糙度为7.44 nm,在250~850 nm的波长范围内能够得到70%以上的反射率,并且无光刻胶的残留,刻蚀效果最理想,因此采用了O_(2)/SF_(6)RIE工艺去除牺牲层。针对仿真中出现镜面层厚度变化影响驱动位移的现象,制备了镜面层厚度分别为0.5和0.8μm两种微镜样品进行了测试。实验结果表明:0.5μm厚的样品不能承受自重而凹陷,0.8μm厚的样品镜面驱动位移接近0.1μm,符合设计要求。

基于裂缝平行板模拟实验体积压裂复杂裂缝理想支撑技术

采用可视化平行板裂缝物理模拟实验装置,开展了不同粒径支撑剂在不同黏度压裂液、变排量下的动态携砂实验,模拟现场施工排量下支撑剂铺置的规律与支撑剖面。利用API裂缝导流设备和岩心驱替装置,开展主裂缝和微裂缝支撑导流能力实验。研究表明,非剪切裂缝渗流能力在一定闭合压力下几乎全部散失,分支缝和远端微裂缝少量的支撑,会获得一定的渗流能力。滑溜水依靠其黏度基本不具备携砂能力,使用滑溜水进行体积压裂,更多依赖水动力携砂,而依靠黏度携砂更有利于将支撑剂输送到裂缝远端。在进行体积压裂时,段塞打磨建立好裂缝通道后,先期泵注一定量相对大粒径支撑剂,实现近井裂缝下部高导流支撑;然后泵注小粒径支撑剂,同时也可适当提高携砂液黏度,实现分支缝和裂缝远端支撑;最后高砂比尾追相对大粒径支撑剂,实现近井裂缝高导流支撑,从而保障和实现体积压裂裂缝的理想支撑,从根本上提高体积压裂效率与效果。