Envelope Correlation Parameter Measurements in a MIMO Antenna Array Configuration

In a 2 × 2 MIMO antenna array system envelope correlation coefficient “ρ” shows the influence of different propagation paths of the RF signals that reach the antenna elements. The approximated value of this coefficient is based on a simple closed-form equation and also varies from 0 to 1. Quite perfect performance for MIMO applications is achieved when this parameter approximates to zero. In this paper, we evaluate an antenna diversity MIMO system by measuring the envelope correlation coefficient. The corresponding results in our antenna array configurations show that the measured “ρ” has very small values and approximates to zero. This observation indicates quite perfect behavior and performance of our MIMO antenna array system.

AN EFFICIENT SIMULATION OF MULTIPLE CORRELATED RAYLEIGH FADING ENVELOPES

In order to better assess the performance of wireless communication systems,it is desirable to produce multiple Rayleigh fading envelopes with specified correlations.In this paper,we analyze theoretically a procedure which generates correlated Gaussian random variables from independent Gaussian random variables and give a physical explanation for the limitation of this procedure.Then,based on some uncorrelated Rayleigh fading envelopes,a simple but efficient procedure for generating an arbitrary number of cross-correlated Rayleigh fading envelopes is proposed.Simulation results and computational complexity analysis are presented,which show that the proposed method has some advantages,such as high accuracy,low computational complexity and easy implementation,over the conventional simulation method.

The Correlation of Hospital Operational Efficiency and Average Length of Stay in China: A Study Based on Provincial Level Data

Objective: To measure the hospital operation efficiency, study the correlation between average length of stay and hospital operation efficiency, analyze the importance of shortening average length of stay to the improvement of the hospital operation efficiency and put forward relevant policy suggestion. Methods: Based on China provincial panel data from 2003 to 2012, the hospital operation efficiencies are calculated using Super Efficiency Data Envelopment Analysis model, and the correlation between average length of stay and hospital operation efficiency is tested using Spearman rank correlation coefficient test. Results: From 2003 to 2012, the average of national hospital operation efficiency was increasing slowly and the hospital operations were inefficient in most of the areas. The national hospital operation efficiency is negatively correlated to the average length of stay. Conclusion: Measures should be taken to set average length of stay in a scientific and reasonable way, improve social and economic benefits based on the improvement of efficiency.

A Method for Incipient Fault Diagnosis of Roller Bearings Based on the Wavelet Transform Correlation Filter and Hilbert Transform

Noise is the biggest obstacle that makes the incipient fault diagnosis results of roller bearings uncorrected; a new method for diagnosing incipient fault of roller bearings based on the Wavelet Transform Correlation Filter and Hilbert Transform was proposed. First, the weak fault information features are picked up from the roller bearings fault vibration signals by use of a de-noising characteristic of the Wavelet Transform Correlation Filter as the preprocessing of the Hilbert Envelope Analysis. Then, in order to get fault features frequency, de-noised wavelet coefficients of high scales which represent high frequency signal were analyzed by Hilbert Envelope Spectrum Analysis. The simulation signals and diagnosing examples analysis results reveal that the proposed method is more effective than the method of direct wavelet coefficients-Hilbert Transform in de-noising and clarifying roller bearing incipient fault.

Three-Dimensional Sound Source Location Algorithm for Subsea Leakage Using Hydrophone

Leakages from subsea oil and gas equipment cause substantial economic losses and damage to marine ecosystem,so it is essential to locate the source of the leak.However,due to the complexity and variability of the marine environment,the signals collected by hydrophone contain a variety of noises,which makes it challenging to extract useful signals for localization.To solve this problem,a hydrophone denoising algorithm is proposed based on variational modal decomposition(VMD)with grey wolf optimization.First,the average envelope entropy is used as the fitness function of the grey wolf optimizer to find the optimal solution for the parameters K andα.Afterward,the VMD algorithm decomposes the original signal parameters to obtain the intrinsic mode functions(IMFs).Subsequently,the number of interrelationships between each IMF and the original signal was calculated,the threshold value was set,and the noise signal was removed to calculate the time difference using the valid signal obtained by reconstruction.Finally,the arrival time difference is used to locate the origin of the leak.The localization accuracy of the method in finding leaks is investigated experimentally by constructing a simulated leak test rig,and the effectiveness and feasibility of the method are verified.

VMD引导的轮对与轴承复合故障诊断方法

针对列车轮对轴承系统复合故障难以辨识与诊断问题,提出一种变分模态分解(variational mode decomposition,VMD)引导的多故障特征提取匹配方法.首先,为避免预定义模式数在运行过程中对先验知识依赖从而对诊断结果造成影响,对原始轴箱振动数据进行逐阶VMD分解,模式数为2~N;其次,对VMD分解获取的本征模态函数(VMD intrinsic mode functions,VIMF)进行相关峭度计算,提取相关峭度最大的VIMF;然后,将相关峭度最大的VIMF进行平方包络分析,提取故障特征频率;最后,将所提方法与快速峭度谱、相关峭度谱方法进行对比.仿真信号和试验数据分析表明:所提方法完全规避了VMD模型中关键参数K的选择问题,可以准确、有效地分别提取出轮对和轴承的故障特征;与快速谱峭度与相关谱峭度方法相比,获取的故障特征谐波分量在数量和信噪比上均具有明显优势.

超声穿透式测温传感器设计与系统实验研究

针对目前国内缺乏1200℃以上长时间超高温气体环境下有效的温度测试手段,基于超声脉冲穿透测温原理,通过设计均匀分布的平面八元圆环温度传感器阵列,成功研制出一种高效的温度场检测系统。依据波速V与气体温度T之间的经验函数,利用高温实验获得了各传感器性能数据。实验结果表明:该系统在1200℃高温环境下测量精度达到了97.98%,重复性95.52%以上,响应时间毫秒(ms)级别,符合设计要求。

基于FPGA的AES和ECC算法图像加密

随着数字图像的使用次数日益增多,保护机密图像数据免受未经授权的访问较为重要。针对数字图像在通信、存储和传输等领域存在的安全问题,文中基于对称算法模型和非对称算法模型的优点提出一种具有高安全性和高速度性的数字信封技术密码方案。该方案以AES(Advanced Encryption Standard)和ECC(Elliptic Curve Cryptography)为基础,经优化后用于对称密钥共享的ECC硬件架构来提高密钥的安全性。通过加入伪随机数、使用列移位替代列混淆运算以及三维S-box等方式对传统AES进行优化,在保持香农扩散和混淆原理的同时降低了时间复杂性。基于FPGA(Field Programmable Gate Array)实现AES算法的数字图像加密仿真以及性能测试。测试结果表明,所提密码方案具有快速性、高安全性和有效性等优点,能够有效地实现图像加密。

基于MCKD的海上风机齿轮箱轴承故障诊断方法

海上风机齿轮箱结构复杂、故障多发,同时受海上风机运行的强噪声干扰,轴承故障的特征信号提取较为困难。针对以上问题,提出了一种基于最大相关峭度解卷积(MCKD)的故障诊断方法,通过MCKD算法对振动信号进行降噪处理和特征增强,并利用增强包络谱对轴承的故障特征频率进行提取,从而实现对轴承的故障诊断。将该方法应用到海上风机齿轮箱轴承的模拟信号和实测信号中,研究结果表明:该方法对海上强噪声环境下齿轮箱轴承故障的特征提取和诊断具有良好的效果。

运载火箭测试数据分析与故障诊断方法

针对如何从运载火箭大量历史测试发射数据中发掘有用信息的问题,提出了一种基于数据挖掘的运载火箭数据分析与故障诊断方法,为火箭的故障诊断、产品设计、状态检测提供服务;针对火箭数据的特性和实际业务分析的需求,使用基于皮尔逊系数的相关性分析方法、基于希尔伯特变换的包络分析方法、基于窗口滑动函数的故障诊断方法组建火箭数据分析平台,对运载火箭的数据进行了深层次的挖掘和诊断;采用某型号火箭测试数据对火箭数据分析平台进行了验证,结果表明:以数据驱动的火箭数据分析平台相关性分析准确、参数包络线绘制精准、可有效识别异常数据,分析结果与理论知识相符,具有较高的实用价值,相比于传统数据分析方法更为精准、全面。

基于MOBWO-MCKD的风机滚动轴承故障特征提取方法

针对风力发电机轴承振动信号受强背景噪声及其他设备激励源影响,导致早期微弱故障特征不易提取这一问题,提出了一种基于多目标白鲸优化算法(MOBWO)优化的最大相关峰度反卷积(MCKD)风力发电机轴承故障特征提取方法。首先,采用MOBWO强大的全局及局部搜索能力优化了MCKD关键参数,获取了最佳参数组合;其次,利用优化后的MCKD对原始信号进行了解卷积运算,消除了背景噪声及其他设备激励源的影响,突出了轴承周期性脉冲信号;然后对解卷积信号进行了包络谱分析,提取了轴承故障特征频率,并将其与理论计算故障特征频率值进行了诊断结果对比;最后,采用实际工程中采集到的风力发电机轴承内圈和外圈的故障数据,对MOBWO-MCKD方法的有效性进行了试验验证。研究结果表明:基于MOBWO-MCKD的故障特征提取方法能够有效地消除背景噪声及其他设备激励源的干扰;由内圈信号包络谱可得到的内圈故障频率为f IR=125.87 Hz、2f IR=251.74 Hz;由外圈信号包络谱可得到的外圈故障频率为f OR=84.47 Hz、2f OR=168.94 Hz、3f OR=253.41 Hz。该特征提取方法可以为实际工程风力发电机轴承早期微弱故障特征提取研究提供一定的参考。

Temporal sequential correlation analysis on compoundaction potentials of the auditory nerve versus the stimulating AM-sound envelope

Compound action potentials of the auditory nerve in response to amplitude modulating tones were recorded in guinea pigs with electrode implanted to the exit of the internal auditory meatus and temporal sequential correlation between the responses and the modulators was studied in a paradigm of systematically changing acoustic parameters. Three kinds of modulators were used. continuous or burst sinusoids of fixed frequency (in the range of 40 Hz-5 kHz), short bursts of sinusoids with changing frequency and short segments of speech signal. Ranges of parametric variation were 500 Hz-20 kHz for carrier frequency, 5%-95% for modulation depth and 20 dB-90 dB SPL for intensity. For continuous or burst sinusoidal modulators of fixed frequencies, the correlation coefficient (r) remained quite high in most parametric conditions, ranging from 0.80 to 0.95. It became smaller mainly in instances of decreased response amplitude on account of unfavourable parameters. For burst modulators of changing frequency, r varied around 0.66-0.86. When segments of speech signal served as the modulators, significant correlation (r around 0.50 ) also existed, indicating the validity of the timing mode of information encoding for speech sound at the cochlear nerve level. Some theoretical and technical points in studying the timing mechanism of audition is discussed.

基于DDAE-GRA的滚动轴承早期故障诊断

提出一种将深度降噪自编码(DDAE)和灰色关联度分析(GRA)相结合的滚动轴承早期故障诊断方法。使用DDAE提取轴承振动信号的特征,以正常样本特征作为灰色关联分析的参考序列,计算滚动轴承全寿命周期数据样本特征与正常样本特征的关联程度作为轴承性能退化的指标,绘制性能退化曲线并使用3σ阈值判定轴承早期失效时间。对辛辛那提大学轴承数据集外圈故障轴承的分析结果表明:DDAE-GRA模型识别的轴承故障发生在第533个样本,该样本包络谱中出现了明显的外圈故障特征频率及其倍频;DDAE-GRA模型比小波包分解-GRA,DDAE-FCM,DDAE-SVDD具备更好的鲁棒性,更适用于滚动轴承早期故障监测。

具有大零相关区宽度的Ⅱ型偶长Z-互补对构造方法

利用交织技术提出了Ⅱ型偶长Z-互补对的构造方法,提出了以Golay互补对及其互补偶为基础序列的交织结构基本框架,并给出了该框架需要满足的必要条件,以使所得Z-互补对可以具有较大的零相关区宽度。所构造的Z-互补对的主要参数形式为((2k+1)N,(2k+1)N-k)-ZCP,其中N为所选Golay互补对的长度。所构造的Z-互补对虽然不能覆盖所有偶数长度,但其零相关区宽度可以达到或接近Ⅱ型偶长二进制Z-互补对的理论上界,且具有较小的峰均包络功率比,其值小于或等于4,应用到多载波扩频系统中可以消除更多的异步干扰和减小非线性失真。

基于WPT-ESCDE的电气设备运输车轮对轴承故障特征提取方法

变压器等电气设备的吊装、转运环节是疏于监控的薄弱环节,极易发生机械冲击引起的二次损伤,而轨道运输车的轮对承载特性及轮对轴承运行状态关乎运输安全。综合考虑轨道运输车轮对轴承运输环境,分析振动信号中存在的主要成分及特征,提出一种基于小波包-包络谱相关散布熵(WPT-ESCDE)的故障特征提取方法。首先,对振动信号的离散时间序列进行小波包分解,并对小波包子带系数进行重构;其次,对每个小波包子带计算平方包络谱,得到离散频率序列,将得到的小波包子带包络谱离散序列看作广义时间序列进行相关分析,得到包络谱相关函数;最后,计算包络谱相关函数的散布熵,筛选最优小波包子带序列进行特征提取。通过仿真分析和QPZZ-Ⅱ旋转机械故障模拟实验台实测信号验证了所提方法的有效性。

A Novel Compact Highly Isolated UWB MIMO Antenna with WLAN Notch

This paper presents a compact Multiple Input Multiple Output(MIMO)antenna with WLAN band notch for Ultra-Wideband(UWB)applications.The antenna is designed on 0.8mmthick low-cost FR-4 substrate having a compact size of 22mm×30 mm.The proposed antenna comprises of two monopole patches on the top layer of substrate while having a shared ground on its bottom layer.The mutual coupling between adjacent patches has been reduced by using a novel stub with shared ground structure.The stub consists of complementary rectangular slots that disturb the surface current direction and thus result in reducing mutual coupling between two ports.A slot is etched in the radiating patch for WLAN band notch.The slot is used to suppress frequencies ranging from 5.1 to 5.9 GHz.The results show that the proposed antenna has a very good impedance bandwidth of|S11|<−10 dB within the frequency band from 3.1–14 GHz.A low mutual coupling of less than−23 dB is achieved within the entire UWB band.Furthermore,the antenna has a peak gain of 5.8 dB,low ECC<0.002 and high Diversity Gain(DG>9.98).

基于VMD和窄带包络相关的船舶辐射噪声改进DEMON分析

船舶辐射噪声的包络谱中蕴含着轴频和桨叶数等船舶固有特征信息,对船舶目标识别具有重要意义。为了提高船舶辐射噪声包络谱解调性能,提出了基于变分模态分解(Variational Mode Decomposition,VMD)和窄带包络相关的改进DEMON分析方法。首先利用VMD算法代替传统带通滤波器,将船舶辐射噪声信号分解为若干个子带;然后对各子带进行希尔伯特(Hilbert)检波并计算平均窄带包络相关系数,用于衡量信号的包络调制在频域上的非均匀性;最后提取各子带信号包络谱并按照平均窄带包络相关系数进行加权融合,从而得出宽带噪声信号的包络谱。利用该方法对实测不同类型和不同航速船舶辐射噪声信号进行了处理,结果均表明所提方法能有效提高包络谱解调效果,较传统方法更为有效。

基于Fast-SC和EC的滚动轴承故障检测

解调分析的关键在于准确找到合适的解调频带,针对此问题,提出一种基于快速谱相关(fast spectral correlation,简称Fast-SC)和包络谱谱峰因子(crest of envelope spectrum,简称EC)的解调频带确定方法,应用于滚动轴承故障检测。首先,对信号进行Fast-SC计算,采用考虑滚动体滑移误差的故障频率区间作集成谱相关切片并将其作为目标谱相关曲线,根据其最大值确定解调频带的中心频率搜索中心;其次,用同时考虑冲击信号强度与周期性的EC进行频带优化选择,自适应获得优化的滤波参数组;最后,根据所得滤波参数组对信号进行带通滤波,并求其包络谱,实现轴承故障特征频率提取。仿真和实验表明,与Autogram解调算法相比,所提方法降噪能力更强,解调频带的选择更优。

基于CapSA-VMD的螺母质量判定方法

当数控伺服压力机压装定位螺母时,需要依据采集的数据信号对其进行质量判定,而数据信号极易受复合噪声的影响从而导致螺母误判。针对在复合噪声干扰下信号包络特征难以提取且VMD中参数难确定问题,提出一种结合卷尾猴搜索算法优化VMD参数,有效重构数据信号的方法。首先,选取MCCI为目标优化函数。其次,对复合信号进行自适应模态分解,借助排列熵算法和相关系数筛选出含噪低的分量进行信号重构。然后,以模拟和实测信号为样本,借助RMSE、SNR的具体数值做客观对比,分别经EMD、CEEMDAN、CapSA-VMD方法的重构信号做直观对比。结果表明,CapSA-VMD分解后不含虚假分量,去噪效果显著优于另外二者,螺母质量检测的准确率高达97.8%,研究结果可为压装定位螺母的复合信号去噪,提高包络线阈值判定准确率提供有益的参考。

Isolation Enhancement in a Compact Four-Element MIMO Antenna for Ultra-Wideband Applications

Mutual coupling reduction or isolation enhancement in antenna arrays is an important area of research as it severely affects the performance of an antenna.In this paper,a new type of compact and highly isolated Multiple-Input-Multiple-Output(MIMO)antenna for ultra-wideband(UWB)applications is presented.The design consists of four radiators that are orthogonally positioned and confined to a compact 40×40×0.8 mm3 space.The final antenna design uses an inverted L shape partial ground to produce an acceptable reflection coefficient(S11<−10 dB)in an entire UWB band(3.1–10.6)giga hertz(GHz).Moreover,the inter-element isolation has also been enhanced to>20 db for majority of the UWB band.The antenna was fabricated and tested with the vector network analyzer(VNA)and in an anechoic chamber for scattering parameters and radiation patterns.Furthermore,different MIMO diversity performance metrics are also measured to validate the proposed model.The simulation results and the experimental results from the constructed model agree quite well.The proposed antenna is compared with similar designs in recently published literature for various performance metrics.Because of its low envelope correlation coefficient(ECC<0.1),high diversity gain(DG>9.99 dB),peak gain of 4.6 dB,reduced channel capacity loss(CCL<0.4 b/s/Hz),and average radiation efficiency of over 85%,the proposed MIMO antenna is ideally suited for practical UWB applications.