A virtual lock-in amplifier,spectrum analyzer,impedance meter and semiconductor analyzer implemented on an SR7265 hardware target

Lock-in amplifiers are used to detect and measure very small alternating current(AC)signals down to the range of nVs.Accurate measurements can be made even when the small signals are buried by noise thousands of times larger.With the digital signal processing(DSP)technology involved in modern instrumentation,a lock-in amplifier is more versatile in sensing and recovering small signals.Combining the virtual instrumentation technology,we reorganize the functional blocks of a programmable lock-in amplifier and build it as a virtual spectrum analyzer,virtual impedance meter,virtual network analyzer,virtual semiconductor parameter analyzer,signal generator,etc.A 4 layer model is used to implement these virtual instruments.The same virtual instrument can also be implemented on a general purpose FPGA developing board.

Investigation on experimental method of low-impedance materials using modified Hopkinson pressure bar

To increase the detectability of split Hopkinson pressure bar （SHPB） of low-impedance materials, modifications were conducted on traditional SHPB apparatus with a PMMA tube to output transmitted signal, and weak signals were further amplified by semiconductor strain gauges. Experiments on soft rubbers and cushioning foam materials were carried out. In order to analyze the accuracy of the experimental results, the stress equilibrium issues involved in the assumptions of SHPB were investigated. First, by way of re-constructing loading process of incident wave, the stress- strain curve was obtained, along with the stress equilibrium ratio of specimen. Secondly, the influences on the accuracy of stress-strain curves were investigated through the elastic modulus comparisons. And the results illustrate that the bilinear incident wave from experiments can ensure the stress equilibrium deformation of specimen after 2 normalized times, much sooner than ramp incident waves. Moreover, it even facilitates specimen deformation with a constant strain rate. The results confirm that the detectability of the modified SHPB can be down to tens kPa with enough accuracy level.

Hydration Process of Cement-Based Materials by AC Impedance Method

AC impedance is a new method to study the changes of pore structure and the hydration degree during the hydration and hardening process of cement paste by the change of the electrochemical parameters. Employing AC impedance method, we studied the hydration and hardening process of cement paste with fly ash and slag, and analyzed the influence of different hydration age, water-binder ratio and mineral admixture on the impedance parameters. Moreover, we compared the results with those by the conventional porosity testing method and X-ray diffraction method. The results showed that AC impedance could be taken as a new technology in cement and concrete research.

A Flier-plate Material with Graded Impedance Used in Dynamic High-pressure Physics

By using such flier-plate material,quasi-isentropic compression can be realized.Based on it,hypervelocity launching is further accomplished.As a result,an extremely high dynamic pressure can be obtained in laboratory,offering a practical method for the comprehensive determination of materials behavior,response,equation-of-state and properties in dynamic loading process.

Mechanical Impedance of Cerebral Material

The tentative variation of the mechanical impedance, of a cylindrical sample of cerebral material, has been achieved by Vibrometer Laser according to the frequency. The studied matter is supposed homogeneous, isotropic and stationary. A multilayered mechanical model has been associated to the studied sample to simulate its vibration. The theoretical expression of mechanical impedance has been determined while taking the mechanical/electric analogy as a basis. A good adjustment of theoretical model parameters permitted us to have a good agreement theory/experience of the mechanical impedance variation according to the sample vibration frequency.

LiMn_2O_4 thin films derived by rapid thermal annealing and their performance as cathode materials for Li ion battery

The LiMn2O4 thin film as a cathode material was prepared through solution deposition followed by rapid thermal annealing （RTA）. The phase identification and the study of surface morphology were carried out by X-my diffraction and scanning electron microscopy. Electrochemical properties were examined by cyclic voltammetry, galvanostatic charge-discharge experiments, and electrochemical impedance spectroscopy. The results show that the film prepared by this method is homogeneous, dense, and crack-free. The thin film has a capacity of 38 μtAh/（cm^2·μm） with the capacity loss of 0.037% per cycle after being cycled for 100 times. The average diffusion coefficient for lithium ions in the RTA-derived LiMn2O4 thin film is 1×10 ^-10 cm^2·s^-1.

Electrochemical characterization of MnO_2 as electrocatalytic energy material for fuel cell electrode

Development of inexpensive non Pt based high electrocatalytic energy materials is the need of the hour for fuel cell electrode to produce clean alternative green energy from synthesized bio alcohol using biomass. MnO 2,electro synthesized at different current density is found to be well performed electrocatalytic material,comparable to Pt,with higher current density,very lowovervoltage for the electrochemical oxidation of methanol. From EIS study,the polarization resistance of the coated MnO 2is found to be much lowand electrical double layer capacitance is high,the effect increases with increase in current density of electro deposition. XRD,EDX and AAS analysis confirm the M nO 2deposition. The morphology of SEM images exhibits an enhanced 3D effective substrate area,for electro oxidation of the fuel. A fewnano structured grains of the deposited M nO 2is also observed at higher current density. The fact supports that a high energetic inexpensive electro catalytic material has been found for fuel cell electrode to synthesis renewable energy from methanol fuel.

Ionic Conductivity of Nano-LaF_3 Bulk Material at Room Temperature

Nanocrystalline powder of LaF3 was synthesized by a method of direct precipitation from water solution. Particle size and shape of LaF3 nanocrystalline powder was analysed with TEM. Particles were mainly spherical with narrow particle size distribution （10 20 nm）. The average particle size analysed with XRD is 16.7 nm. Nano-LaF3 bulk material was prepared by compacting the powder to 1 GPa at room temperature and a vacuum of 10^-4 Pa. The ionic conductivity of nano-LaF3 bulk material was studied with complex impedance spectra at room temperature. The ionic conductivity of nano-LaF3 bulk material （1 × 10^-5 S·cm^-1 ） at room temperature is significantly increased compared to that of single crystal LaF3 （1 × 10^-6 S·cm^-1）. A special phenomenon was observed firstly time that the ionic conductivity increased gradually with multiple testing in result of relaxation.

Impedance Characteristics of MgO-ZrO_2 Ceramics Doped with CeO_2

The ultrafine CexMg0.06Zr1-xO1.94 （ x = 0 16% ） powders were synthesized by a chemical co-precipitated method. The pressed compacts were sintered in air at 1300, 1400, 1500, 1600℃ for 3 h, respectively. The phase of the ceramics was characterized by the X-ray diffraction （XRD） method. The conductivity of the ceramics was measured by the AC complex impedance technique at 700- 1200 ℃. The ratio of the cubic phase in the ceramics improves with increasing CeO2 content, leading to a enlargement of the oxygen ionic migration channel. The contact resistance between conductive phase particles decreases with increasing CeO2 content, leading to a lower migration hindrance of the oxygen ionic. Consequently, the ionic conductivity of the ceramics improves with increas- ing CeO2 content. Additionally, an analysis for this phenomenon was also presented.

Synthesis and room temperature ionic conductivity of nano-LaF_3 bulk material

The ionic conductivity (at room temperature) of nano-LaF3 bulk material and a new discovered phenomenon of increasing ionic conductivity caused by grain boundary relaxation activated by AC (alternating current) shocking were reported. Nano-crystalline powder of LaF3 with average grain size of 16.7 nm was synthesized with a method of direct precipitation from aqueous solution. Particle size and shape of LaF3 nano-crystalline powder were analyzed by XRD and TEM. Nano-LaF3 bulk material was prepared by compacting the powder to 1 GPa at room temperature and vacuum of 10?4 Pa. The ionic conductivity of nano-LaF3 bulk material was studied with complex impedance spectra at room temperature. The ionic conductivity of nano-LaF3 bulk material (10?5 S/cm) at room temperature is significantly increased compared with that of single crystal LaF3 (10?6 S/cm). A special phenomenon is observed for the first time that the ionic conductivity increases gradually with AC scanning times.

Improvement of giant magneto impedance of Co-rich melt extraction wires by stress-current annealing

In order to improve the giant magneto impedance （GMI） of Co-rich wires for high sensitive sensor applications, Co6sFe4.sSilsBlz5 wires were prepared by melt an extraction technique and subjected to Joule stress-current anneal treatments with different tensile slresses applied. And then their GMI response was investigated at a frequency range from 0.1 to 13 MHz. It was found through the comparison of results that the GMI effect of these wires had been improved through stress-current anneal treatments, because the tensile stress applied on these Co-rich wires introduced magnetoelastic energy and increased anisotropy, which improved the circular permeability and GMI effect. Their impedance ratio AZ/Z increased from 244% to 480.9% at 7 MHz and the field sensitivity increased to 0.83%/（A/m） at 5 MHz, when a tensile stress of 244 MPa was applied at an anneal current of 100 mA for 10 min. It was therefore concluded that these annealed wires were suitable for high sensitive sensor applications.

Understanding the Thermal Impedance of Silicone Rubber/Hexagonal Boron Nitride Composites as Thermal Interface Materials

Silicone rubber(SR) composites are most widely used as thermal interface materials(TIMs) for electronics heat dissipation. Thermal impedance as the main bottleneck limiting the performance of TIMs is usually neglected. Herein, the thermal impedance of SR composites loaded with different levels of hexagonal boron nitride(h-BN) as TIMs was elaborated for the first time by the ASTM D 5470 standard test and finite element analysis. It was found that elastic modulus and surface roughness of SR composites increased with the increase of h-BN content, indicating that the conformity was reduced. When the assembly pressure was 0.69 MPa, there existed an optimal h-BN content at which the contact resistance was minimum(0.39 K·cm^(2)·W^(-1)). Although the decreased bond line thickness(BLT) by increasing the assembly pressure was beneficial to reduce the thermal impedance, the proper assembly pressure should be selected to prevent the warpage of the contact surfaces and the increase in contact resistance, according to the compression properties of the SR composites. This study provides valuable insights into fabrication of high-performance TIMs for modern electronic device applications.

贴合材料硬度对PVDF薄膜传感器冲击波测量的影响研究

在人员毁伤效能评估中,体感冲击波值为重要的毁伤判据之一。为提高人员体表冲击波测试的准确性,同时保证传感器阻抗匹配的优势,提出了一种柔性膜片阻抗匹配下的冲击波测试技术,并对不同硬度的贴合材料对冲击波超压测量的影响展开了实验研究。首先在刚性表面对聚偏二氟乙烯薄膜(PVDF)传感器进行了冲击波标定实验,得到了PVDF传感器力电响应关系;在此基础上,对4种硬度的聚氨酯橡胶作为贴合材料的PVDF传感器加载不同强度冲击波,实验结果表明,与PVDF直接贴合在类生物组织上相比,硬度为50A的贴合材料能够改善横向效应的影响使得传感器灵敏度系数基本保持为常数,但贴合材料硬度增加为70A和90A时测量非线性度分别增加了22.6%与30.2%。

引气剂调节水泥基微膨胀材料波阻抗的研究

为满足施工要求制备与各类较硬岩石波阻抗匹配的水泥基微膨胀回填材料,采用普通硅酸盐水泥、矿粉、中级砂等为原料,引气剂为密度和波速调节材料,通过改变水胶比、砂胶比与引气剂质量分数,探究其对水泥基微膨胀材料抗压强度、密度、波速和波阻抗的影响规律;测量各组材料的流动度和竖向膨胀率是否满足回填施工要求;通过微观测试,探究引气剂质量分数对水泥基微膨胀材料内部孔隙结构与孔隙率的影响规律。结果表明:引气剂的加入在水泥基微膨胀材料内部引入气泡,随引气剂质量分数增加,水泥基微膨胀材料内部孔隙率逐渐增大,抗压强度、密度、波速与波阻抗均下降;所制备出的水泥基微膨胀材料可满足的波阻抗范围为4.67~10.3 kt·m^(-2)·s^(-1),能够匹配各类常见较硬岩石波阻抗;对水泥基微膨胀材料28 d波阻抗进行多元线性回归分析,得到精度较高的回归模型,实际应用时注浆效果较好,可用于岩石波阻抗匹配材料的快速制备。

新型多层复合结构雷达吸波材料的研制及其性能研究

通过阻抗匹配原理将玻璃纤维增强复合材料、聚甲基丙烯酰亚胺泡沫、炭黑浸渍板进行多层结构复合,层板间使用环氧树脂胶粘,制备了一种具有宽带吸波效果的雷达吸波材料。通过弓形法反射率测试装置与矢量网络分析仪测试吸波材料在1~18GHz的吸波性能。结果表明:吸波材料在L波段、C波段、X波段、Ku波段具有优异的吸波性能,在L波段平均反射率为-12.9dB,在C波段平均反射率为-15.21dB,在X波段平均反射率为-19.25dB,在Ku波段平均反射率为-28.06dB,吸波材料在减轻重量的同时有效减少了阻抗突变和雷达散射截面积,具有较好的工业应用价值。

羰基铁基复合材料的高效吸波-防腐双功能特性研究

随着5G先进通信技术和雷达探测技术的快速发展,电磁污染问题和特种装备的隐身突防问题日益突出。铁磁性吸波材料凭借高饱和磁化强度和优异的电磁波衰减能力已发展为应用较为广泛的隐身材料,然而,由于应用环境的多元化,铁磁性吸波材料的腐蚀问题严重制约其实际应用。本文采用多步液相反应,成功制备出具备优异吸波-防腐双功能的多级结构羰基铁基复合材料。该材料最低反射损耗高达-48.3 dB,有效吸收带宽达7.0 GHz。同时,其抗腐蚀性能也得到大幅改善,自腐蚀电压Ecorr显著右移至-0.22 V,自腐蚀电流密度Icorr下降至1.21×10^(-7)A/cm^(2)。为新型高性能铁磁性吸波材料的设计和工程应用提供了有力支撑,对于解决电磁污染和装备隐身问题具有重要意义。

PUF/PANI-CO双壁微胶囊的制备及改性水性环氧涂层的防腐性能

以蓖麻油(CO)为芯材、脲醛树脂(PUF)和聚苯胺(PANI)为壁材,采用原位聚合法和物理沉积法制备了双壁微胶囊PUF/PANI-CO,将其添加到水性环氧涂层(WEC)中制备了复合涂层PUF/PANI-CO/WEC。通过FTIR、XRD和SEM对PUF/PANI-CO进行了表征,采用电化学阻抗谱(EIS)和盐雾实验考察了PUF/PANI-CO/WEC的防腐性能。结果表明,PUF/PANI-CO是以CO为芯材,PANI相互交叉沉积在内壁PUF外而形成的致密外壁的双壁微胶囊,粒径3~4μm;PUF/PANI-CO/WEC在质量分数为3.5%的NaCl水溶液中浸泡30 d后,涂层的低频阻抗为7.600×10^(8)Ω·cm^(2);PUF/PANI-CO/WEC与金属基体之间的附着力为15.64 MPa。PUF/PANI-CO/WEC的防腐性能源于三方面:PANI/PUF-CO较好的分散性和稳定性能够有效提高水性环氧涂层的阻隔性;壁材破裂时释放的芯材能够填补涂层中的缺陷,从而阻断腐蚀介质的传输路径;PANI不仅可以提高微胶囊的稳定性,而且能够促进金属基体表面钝化膜的形成,延缓腐蚀介质的渗入,进而对基体起到良好的保护作用。

基于虚拟材料法的金属膜片联轴器振动传递特性分析

在对大型船舶金属联轴器进行振动性能试验时由于试验台架体积大、成本高,导致进行试验十分困难,因此研究高效率和高精度的仿真计算方法具有重要意义。传统精确的数值仿真网格多、效率低,为此采用虚拟材料法对船舶金属联轴器进行数值仿真并进行试验验证。首先通过计算和试验得到螺栓的虚拟材料层各参数,然后对大型金属联轴器的所有螺栓连接部位进行简化建模。其次通过该方法得到金属膜片联轴器的刚度特性、模态特性、阻抗特性和振动传递特性,并与传统建模方法的计算效率进行对比。最后搭建联轴器振动性能实验台架进行验证。研究结果表明:采用虚拟材料法的联轴器振动性能仿真效率提高73.9%;四组采用虚拟材料法的联轴器膜片组件刚度与实验测得的联轴器刚度的平均误差为2.61%,与带螺栓模型测得的刚度平均误差为1.15%。金属膜片联轴器前5阶模态频率仿真与试验的平均误差为9.91%,在10~2000 Hz频带,金属膜片联轴器轴向和径向阻抗的仿真与试验的误差分别为1.9和2.8 dB,金属联轴器轴向和径向的振级落差仿真与试验的误差分别为4.69和3.41 dB。试验与仿真结果误差较小,符合工程精度要求,该方法的计算效率和准确性得到验证。

人工神经网络和电阻抗谱法压电材料快速表征

压电材料作为重要的功能材料,广泛应用于社会的各领域,但其弹性常数的偏差会导致应用过程中出现错误的设计,弹性常数的正确表征对压电器件的正确设计尤为重要。与其他测量方法相比,电阻抗谱仅需要阻抗分析仪即可实现测量,通过测量阻抗谱反演获得压电材料的弹性常数。传统电阻抗谱法通过不断修正材料参数,使得测量阻抗谱和计算阻抗谱最大程度吻合,该过程需要多次迭代,计算量大,耗时较长。该文提出采用神经网络建立阻抗谱到弹性常数的正向模型,测量得到阻抗谱后仅需一次正向计算即可得到弹性常数。使用Comsol和Matlab联合仿真建立数据集,引入丢弃法避免模型过拟合,利用Pytorch建立模型,经过训练后,最大谐振频率偏差从初始2.8%降至0.8%。该技术为压电材料弹性常数精密测量提供可靠的理论与实践途径。