Power-line interference suppression of MT data based on frequency domain sparse decomposition

Power-line interference is one of the most common noises in magnetotelluric(MT)data.It usually causes distortion at the fundamental frequency and its odd harmonics,and may also affect other frequency bands.Although trap circuits are designed to suppress such noise in most of the modern acquisition devices,strong interferences are still found in MT data,and the power-line interference will fluctuate with the changing of load current.The fixed trap circuits often fail to deal with it.This paper proposes an alternative scheme for power-line interference removal based on frequency-domain sparse decomposition.Firstly,the fast Fourier transform of the acquired MT signal is performed.Subsequently,a redundant dictionary is designed to match with the power-line interference which is insensitive to the useful signal.Power-line interference is separated by using the dictionary and a signal reconstruction algorithm of compressive sensing called improved orthogonal matching pursuit(IOMP).Finally,the frequency domain data are switched back to the time domain by the inverse fast Fourier transform.Simulation experiments and real data examples from Lu-Zong ore district illustrate that this scheme can effectively suppress the power-line interference and significantly improve data quality.Compared with time domain sparse decomposition,this scheme takes less time consumption and acquires better results.

Investigation and Reduction on Conducted Electromagnetic Interference Noise Mechanism for Complex Power Electronics Systems

针对复杂电子系统产生的传导EMI噪声,该文分别利用电偶极子模型、电路分析方法和散射参数方法提出了3种传导EMI噪声理论模型及其等效电路,包括因串扰引起的传导噪声模型,因接地不良引起的传导噪声模型,以及因PCB线缆阻抗失配引起的传导噪声模型。同时,还设计了一种串扰扼流圈以有效抑制因串扰引起的传导EMI噪声。实验结果表明,采用文中方法,某型商用车载导航和刷卡器能够通过GB 9254标准测试,噪声抑制效果分别可达44.8和29.28 dB V,从而验证了方法的有效性。

Signal-to-noise ratio of lensless ghost interference with thermal incoherent light

Factors influencing the signal-to-noise ratio （SNR） of lensless ghost interference with thermal incoherent light are investigated. Our result shows that the SNR of lensless ghost interference is related to the transverse length of the object, the position of the object in the imaging system and the transverse size of the light source. Furthermore, the effects of these factors on the SNR are discussed in detail by numerical simulations.

A novel approach to conductive EMI noise source modeling

A new approach to conductive electromagnetic interference （EMI） noise source modeling, i. e. the source internal impedance extraction, is presented. First, the impedance magnitude is achieved through an exciting probe and a detecting probe, or through calculations based on insertion loss measurement results when inserting a series nigh-value known impedance or a shunt low-value known impedance in the circuit. Then the impedance phase is extracted by the Hilbert transform （HT） of the logarithm of the obtained impedance magnitude. Performance studies show that the estimated phase error can increase greatly at a zero frequency in the Hilbert transform because of the existence of a singular point, and this effect can be eliminated by introducing a zero-point when the noise source does not include a series-connected capacitive component. It is also found that when the frequency is nigher than 150 kHz, the estimated phase error is not sensitive to the inductive source but sensitive to the capacitive source. Finally, under the conditions of the same measurement accuracies for impedance magnitude, the accuracy of complex impedance based on the HT can be improved about 10 times when compared with the accuracy of estimated parameters based on the impedance magnitude fitting method （IMFM）.

Low-T_c direct current superconducting quantum interference device magnetometer-based 36-channel magnetocardiography system in a magnetically shielded room

We constructed a 36-channel magnetocardiography（MCG） system based on low-Tc direct current（DC） superconducting quantum interference device（SQUID） magnetometers operated inside a magnetically shielded room（MSR）. Weakly damped SQUID magnetometers with large Steward–Mc Cumber parameter βc（βc≈ 5）, which could directly connect to the operational amplifier without any additional feedback circuit, were used to simplify the readout electronics. With a flux-to-voltage transfer coefficient V / Φ larger than 420 μV/Φ0, the SQUID magnetometers had a white noise level of about 5.5 f T·Hz-1/2when operated in MSR. 36 sensing magnetometers and 15 reference magnetometers were employed to realize software gradiometer configurations. The coverage area of the 36 sensing magnetometers is 210×210 mm2. MCG measurements with a high signal-to-noise ratio of 40 d B were done successfully using the developed system.

New Technique for Estimating and Suppressing Narrowband Interference in DSSS Systems

A generalized approach for narrowband interference （NBI） suppression in direct sequence spread spectrum （DSSS） communication systems using adaptive infinite impulse response （IIR） filter is presented. The excision filter coefficients depend on both the jammer power and its instantaneous frequency. The dependency of the filter construction on the jammer power is significant as it allows optimal tradeoff between interference removal and signal distortion by maximizing the receiver signal to noise ratio improvement（SNRI）. Instead of traditional adaptive line enhancer （ALE） estimator, a preferable NBI estimator-Fourier interpolation estimator （FIE） is proposed. Closed-form expressions of the SNR improvement and theoretical bit error rate （BER） based on the assumption that the output of the correlator is Gaussian distributed are both derived. Performance results obtained by numerical simulation are also presented and compared with theoretical results.

STUDY ON AMBIENT NOISE IN SAWMILL'S WORKSHOP

Ambient noise in 13 sawinill’s workshops was tested and analyzed to reveal its character and regularity. The situation of the ambient noise in sawimill s workshops was evaluated.

Interference Mitigation Techniques Using Receiver Processing and Resource Allocation

Heterogeneous network consists of the pico cells overlaid over the macro cell coverage area in a wireless cellular network. The pico cells are deployed to increase the capacity of the homogeneous network by reusing the spectrum further. However, more users will tend to be associated to the macro cell due to the fact that the transmit power of the pico cell is low. In order to increase the number of users associated to the pico cell, range extension techniques like biased association are used. This will cause severe interference to cell edge users of the pico cell from the macro cell causing degradation in throughput performance in the cell range extension area. In this paper, interference mitigation using receiver processing along with different scheduling techniques is proposed to improve the throughput, average delay, and the packet delivery ratio performance of the system. The performance comparison of the round robin, proportional fair and modified largest weighted delay first (MLWDF) algorithm for resource allocation using interference suppressing receiver is done, and analyzed. It is shown that the MLWDF algorithm achieves the highest throughput with minimum average delay of packets with the best delivery ratio.

Simplified iterative algorithm for OFDM phase noise mitigation

OFDM has been widely adopted in several communication systems. However, OFDM systems are very sensitive to the phase noise, which causes the CPE （common phase error） and ICI （inter-carrier interference）, and thus degrades the system performance significantly. Based on the IEEE 802.11a standard, a simplified iterative phase noise mitigation algorithm is proposed. The proposed algorithm has very low complexity, and requires no additional pilot information. The simulation result shows that good BER performance can be achieved through several few times of iteration.

Analysis Theory of Asymmetric dc SQUID Driven by Thermal Noises

An analysis expression for the stationary probability distribution of asymmetric superconducting quantum interference device with two Josephson junctions (dc SQUID) driven by thermal noise is derived from two-dimensional Fokker-Planck equation, where the potential condition is satisfied. Two of the three asymmetric parameters, inductance asymmetric parameter η and critical current asymmetric parameter α, can be changed in this condition, but resistance asymmetric parameter ρ cannot be changed. The 'ripple' phenomenon of circulating current can disappear with the change of coefficient α. The effects of asymmetric parameters on current-voltage relationship and transfer function of dc SQUID system are also represented.

Wavelet diagnosis of ECG signals with kaiser based noise diminution

The evaluation of distortion diagnosis using Wavelet function for Electrocardiogram (ECG), Electroencephalogram (EEG) and Phonocardiography (PCG) is not novel. However, some of the technological and economic issues remain challenging. The work in this paper is focusing on the reduction of the noise interferences and analyzes different kinds of ECG signals. Furthermore, a physiological monitoring system with a programming model for the filtration of ECG is presented. Kaiser based Finite Impulse Response (FIR) filter is used for noise reduction and identification of R peaks based on Peak Detection Algorithm (PDA). Two approaches are implemented for detecting the R peaks;Amplitude Threshold Value (ATV) and Peak Prediction Technique (PPT). Daubechies wavelet transform is applied to analyze the ECG of driver under stress, arrhythmia and sudden cardiac arrest signals. From the obtained results, it was found that the PPT is an effective and efficient technique in detecting the R peaks compared to ATV.

Moho反射波噪声干涉方法及其在青藏高原东北缘地壳结构成像的应用初探

基于南北地震带北段布设的密集流动地震台阵的连续波形记录,采用台阵噪声干涉技术获得了青藏高原东北缘Moho面PmP反射波,利用已有的区域三维地壳速度模型,采用沉积层校正方法建立研究区域的三维地壳初始模型,进而对噪声互相关函数进行基准面校正,然后采用共中心点叠加方法获得了研究区的地壳厚度分布.结果显示,青藏高原东北缘及周边不同块体地壳厚度差异显著,沿青藏高原北东向的扩展方向,地壳厚度逐渐变薄.祁连造山带中、西段地壳厚度约55~65 km,西秦岭造山带地壳厚度从西至东从53 km左右减小至42 km上下,阿拉善块体地壳厚度约50 km,鄂尔多斯块体西缘地壳厚度约40~45 km.六盘山断裂、海原断裂与天景山断裂附近呈现局部的地壳增厚,并且出现脉冲状Moho面反射震相,表明断裂带附近可能存在速度跃变较大的Moho面结构.祁连山北缘断裂出现叠置的反射震相,推测下地壳的逆冲形成了此类Moho结构.

基于遗传算法优化BP神经网络的GNSS干扰源定位技术

全球导航卫星系统(GNSS)应用已全面深入到国家安全和国民经济当中,但由于GNSS信号到达地面后信号强度很弱,极易受到无意或有意的人为干扰。当出现压制干扰时会影响接收机正常工作,从而导致某一区域导航定位效果受到影响,因此对干扰源的排查和消除十分重要。针对上述压制干扰,通过在监测区域分布一定数量低成本接收机,利用其接收的载噪比数据特征实现干扰源的位置估计。考虑到信号传播过程中的衰减模型是非线性的,提出了基于遗传算法(Genetic Algorithm,GA)优化反向传播(Back Propagation,BP)神经网络的干扰源定位方法,通过神经网络学习得到监测区域载噪比特征的复杂非线性关系,GA对神经网络的初始权值和阈值进行优化,最终在监测区域通过梯度下降法搜索出干扰源位置。结果表明,GA优化后的网络预测误差更小,能够初步定位干扰源位置且平均定位误差率(Average Localization Error Rate,ALER)约为0.23%,验证了模型的合理性和有效性。

基于样条插值的非线性自干扰对消技术

针对雷达干扰机收发天线之间存在的非线性自干扰耦合问题,研究一种基于样条插值的非线性自干扰对消方法。该方法将样条插值和自适应滤波相结合,分别建立样条哈默斯坦模型和样条维纳模型,通过引入鲁棒性较强的反正切(arctangent,ARC)函数作为代价函数,得到两种模型下样条控制点和滤波器系数的自适应学习规则,并分析样条控制点数量对自干扰对消性能的影响。仿真实验表明,对于带宽为60 MHz的信号,所提基于ARC参数学习方法与传统最小均方参数学习方法相比,对消比获得4 dB左右的提升,收敛速度提高1倍。另外,针对信道突变的场景,所提方法跟踪性能好且稳态误差低。当背景噪声中存在非高斯脉冲干扰时,所提方法能够有效应对脉冲噪声环境下的干扰。

基于遗传模糊PID算法的倒立摆稳摆抑噪抗扰实验与分析

倒立摆稳摆控制原理应用的实际工程需求牵引,使倒立摆成为检验各类控制算法的理想替代实验研究平台。因此,将倒立摆摆杆的姿态稳定控制和抑噪抗扰作为研究内容,以理论分析、编程实现、仿真实验和实物实验验证作为研究手段,聚焦控制器设计的优化。首先,引入模糊控制对PID参数调节进行优化,改固定参数调节为在线参数调节,旨在提高系统的鲁棒性与抗扰性;然后,运用遗传算法的量化因子和比例因子完成调节参数的在线寻优,通过设计适应度函数和选择算子,经过选择、交叉、变异不断演化迭代,最终获取最佳适应度个体、找到最优解,通过仿真验证遗传模糊PID算法突出的抑噪抗扰优势;最后,基于该控制策略进行倒立摆实物实验,验证了其指令跟踪有效性的结论。该研究表明:遗传模糊PID算法具有良好的指令跟踪和抑噪抗扰性能,具有一定的工程应用价值。

行星齿轮箱降噪能力A-CNN模型及其智能诊断

为了降低随机噪声对行星齿轮箱振动信号造成的干扰,设计了一种采用卷积神经网络(A-CNN)算法的行星齿轮箱故障诊断,可以实现对噪声的良好抗干扰性能,采用A-CNN进行处理时可以通过Dropout实现输入信号的随机干扰,再以多尺度卷积核模块完成干扰信号开展特征分析和多尺度特征学习的过程。研究结果表明:采用Dropout处理信号后能够大幅提升模型抗噪性能,当设置3dB强噪条件时提升近10%。当噪声强度低于6dB时,(15×15)卷积核获得比了比(7×7)卷积核更优的效果。当噪声水平上升后,测试模型准确率降低。与其它算法进行比较可知,设计的A-CNN算法在各噪声水平测试集都达到了最优性能。当受到3dB强噪干扰时,A-CNN可以获得比AlexNet提升20%准确率,并且与VGG相比也可以提升近10%准确率。

小型音乐厅减振隔声改造实践

为解决邻近交通线路带来的振动与噪声干扰问题,采用“房中房”方案,对首都师范大学音乐厅开展减振隔声改造工程。在改造实践中,克服构造改动限制多、减振隔声难度大等难点,系统地采用浮筑地面、隔声墙、减振吊顶、隔音门窗等全方位的隔声与减振改进措施。改造后经过测量,音乐厅的室内声环境已符合相关标准要求,预期目标得以实现。所提出的减振隔声措施可为类似体量中小型音乐厅的改造实践提供参考。

基于CEEMD和统计参数的斜拉桥损伤识别方法研究

为解决仅使用互补集成经验模态分解(complementary ensemble empirical mode decomposition,CEEMD)方法的斜拉桥信号分解存在含噪固有模态函数(intrinsic mode function,IMF)分量且不能进行损伤定量的问题,提出了一种基于CEEMD与统计参数方法相结合的斜拉桥损伤识别方法。该方法基于CEEMD方法对斜拉桥动力响应信号进行自适应性分解,确定适用的白噪声幅值标准差并推导CEEMD方法的集成次数,得到各阶IMF分量;采用欧氏距离对分解的IMF分量进行谱系聚类分析以避免模态混叠现象;采用峰度统计参数的有效权重峰度指标方法滤除含噪IMF分量,提取有效IMF分量并重构为有效IMF分量和;利用变异系数统计参数、二阶中心差分法和泰勒展开式推导损伤定位指标,根据四阶统计矩峰度统计参数推导损伤定量指标。用所提方法对某斜拉桥进行损伤识别研究,结果表明:仿真分析的损伤定位识别精度为100%,损伤定量最大误差为1.80%;在高斯白噪声干扰下,损伤定位不受影响,损伤定量最大误差为1.88%;进行实桥的损伤识别,结果表明实桥主梁无损伤。

一种基于改进NLMS的多雷达主瓣干扰抑制方法

远程探测场景下弹载主瓣干扰因与目标角度间隔小,单站抗干扰方法性能下降严重。多雷达通过合理布站可有效“分辨”目标和干扰,被认为是可有效抑制主瓣干扰的途径。针对当前多雷达抗主瓣干扰方法普遍存在收敛速度慢的问题,提出一种基于改进归一化最小均方(NLMS)的多雷达对消抗主瓣干扰方法,并通过理论推导给出了其应用条件。该方法通过定义消散因子实现对步长的自适应控制从而达到快速收敛的目的,仿真结果表明该方法在收敛速度及收敛后均方误差(MSE)上具有明显优势。最后通过外场试验进一步验证该方法的性能,在满足布站条件且干噪比≥30 dB的前提下,信噪比改善可达19 dB以上,具有较高的应用价值。

用于航空发动机振动监测的摩擦电传感器

航空发动机的振动监测对于飞行安全具有重要意义。航空发动机在发生机械故障时会产生异常低频振动信号,因此利用摩擦电传感器对低频信号的灵敏响应特性研究了一种摩擦电式振动传感器。同时针对摩擦电传感器在航空发动机振动监测中易受环境噪声干扰的问题,设计了一种具有隔声效果的声屏障结构。实验证明具有声屏障结构的摩擦电传感器可以减少20 dB以上的噪声干扰,并且在8 Hz振动频率以及25 m/s2振动加速度的环境下可产生1 V的输出电压以及60 nA的输出电流。此外,该摩擦电振动传感器在航空发动机试验平台上对于振动监测展现出很高的应用潜力,为航空发动机健康状态监测提供了重要的实用范例。