Decoupled Beamforming and Noise Cancellation

The enhancement of noise-corrupted speech acquired by microphones is indispensable to the functioning of a wide variety of digital signal processing algorithms. Many existing products are equipped with steerable, stand-alone fixed beamformers which provide moderate levels of directivity. Moreover, many applications have long employed the classical adaptive noise canceller configuration with a reference sensor near the noise source to cancel unwanted noise. In this paper, the cascading of stand-alone beamformers with back-end adaptive noise cancellers is studied. A decoupled model for signal enhancement using front-end beamformers and cascaded noise cancellers is presented. The inter-operation of the beamforming and noise canceling units is studied by defining the signal-to-interference ratio (SIR) gain, directivity index, and white noise gain offered by the beamforming and noise cancelling components. The performance of decoupled beamformer-noise canceller structures is evaluated using experimental measurements. An experimental procedure for evaluating output SIR is presented. Results reveal SIR improvements of up to 27 dB, and are compared to those stemming from conventional adaptive beamformers     

Research of Modified LMS Adaptive Noise Cancellation

Noise cancellation is very important in the field of signal processing. In this paper, the designation of a modified LMS Adaptive Noise Cancellation is demonstrated in detail; the model is simulated. We have compared the performance of the new model with the old model. The result of the experiments shows that this designation improves the noise cancellation′s performance greatly.     

进化论自适应滤波算法及降噪特性研究

基于生物进化论策略的自适应滤波算法，利用其有性繁殖和无性繁殖的随机搜索能力实现全局最优搜索，可克服最小均方法（Least Mean Square，简称：LMS）对于多峰特性问题有可能收敛于某一局部最小值，无法实现全局最优的缺点。提出峰值系数指标PR（Peak Ratio）概念解决进化论自适应滤波器的性能评估问题，提出收敛速度CS（Converge Speed）指标和峰值系数指标PR高度的方法解决最优滤波参数的选取问题，并列进化论自适应滤波器的降噪进行模拟仿真，讨论了滤波长度和进化系数对进化论自适应算法消噪效果的影响及最优滤波参数。     

空间有源消声控制器的优化设计

本文根据声源辐射理论和线性声场迭加原理,提出了一种三维空间有源消声的数值优化方法。通过最小化适当曲面上由初级声源和次级声源产生的合成声压的平方和,可以求得自由声场中给定区域或全空间声功率最小意义下次级声源的优化幅值和优化相位。这种方法可适用于单极子源和多极子源的情况。如考虑实际次级声源的特性,特别是其相位延迟特性,用本方法所求得的优化频响特性往往比有源消声中常用的“幅频平直、相位相反”的频响特性能更好地用实际模拟电路逼近,因此优化结果具有实用意义。实验表明,由本方法设计出的系统具有较好的消声效果。     

一种应用于自适应降噪的变步长LMS算法

通过建立步长因子μ与误差信号е之间的非线性关系,提出一种改进的变步长LMS算法,并将其应用于通信降噪.该算法除了具有传统固定步长LMS算法计算量小、稳定性好、简单、易于实时处理等优点外,理论分析及计算机仿真结果表明,其收敛速度及稳定性优于SVSLMS算法,且不需要进行指数运算,计算复杂度低于SVSLMS算法,用于通信降噪取得了较好的效果.     

石油管道超声检测信号的两级自适应噪声消除算法

针对石油管道缺陷超声检测信号的噪声消除问题, 研究了一种两级自适应噪声消除算法. 第一级自适应滤波器作为预处理级, 使信号获得较好的相关性和信噪比, 确保第二级自适应滤波器获得更优的性能. 实测超声信号两级自适应滤波结果表明: 两级自适应滤波算法能有效增强超声检测信号中的缺陷信号成分, 显著提高信噪比.     

应用频域ICA对参考输入进行预处理的ANC系统

传统有源降噪(ANC)理论和系统希望将声场能量全部抵消,不能适用于存在信号情况下的ANC应用,为尝试解决这一问题,本文提出了一种新的将频域独立成分分析(ICA)技术用于频域ANC系统,对系统参考输入进行预处理的方法.ICA的分离作用可以减少参考输入和信号的相关性,显著降低信号对ANc控制滤波器的干扰,减少了信号的失真,提高了系统收敛前后的声场信噪比.理论分析和仿真实验表明:该系统具有传统ANC系统所不具备的信号背景下降低噪声的能力.     

探测系统噪声对激光束束宽测量的影响

讨论了由于探测系统噪声原存在,对目前广泛采用的二阶矩束宽定义的激光束空域参数测量系统的影响,并给出实际测量系统设计时减少噪声影响的方法。     

Protection of a Ballistic Laser Gravimeter against the Effects of Inertial Noise

An efficient method of filtration of the vertical component of inertial noise acting on a ballistic laser gravimeter based on the use of a two-channel vibration-shielded interferometer is considered.     

Frequency-Impulse Modulation as a Means of Attaining Accuracy in Cesium Atomic Clocks

An electronic system has been developed which corrects for cavity-detuning errors in cesium atomic-beam frequency standards. The RF signal applied to the beam tube is square-wave phase modulated, i.e., frequency-impulse modulated. The transient response of the beam tube to these phase steps is used as a control signal. When the positive and negative transients are both equal in area and identical in shape, it will be shown that the applied RF signal must be exactly at cesium frequency (for the given magnetic field) and the RF cavities must be exactly in tune. Two feedback loops are needed; one for correcting the crystal oscillator, the other for adjusting the relative phase of the RF cavities. With cavity detuning error greatly reduced by this system, the remaining source of inaccuracy is the uncertainty of the magnetic field in the drift region of the beam tube. An experiment is described which may permit setting a given cesium-beam standard to a frequency that differs by a precisely known amount from the zero-field cesium-resonance frequency.     

Investigating mechanism of inclined CPT in granular ground using DEM

This paper presents an investigation on mechanism of the inclined cone penetration test using the numerical discrete element method (DEM). A series of penetration tests with the penetrometer inclined at different angles (i.e., \(0^{\circ },\,15^{\circ },\,30^{\circ },\,45^{\circ }\) and \(60^{\circ }\) ) were numerically performed under \(\mu =0.0\) and \(\mu =0.5\) , where \(\mu \) is the frictional coefficient between the penetrometer and the soil. The deformation patterns, displacements of soil particles adjacent to the cone tip, velocity fields, rotations of the principal stresses and the averaged pure rotation rate were analyzed. Special focus was placed on the effect of friction. The DEM results showed that soils around the cone tip experienced complex displacement paths at different positions as the inclined penetration proceeded, and the friction only had significant effects on the soils adjacent to the penetrometer side and tip. Soils exhibited characteristic velocity fields corresponding to three different failure mechanisms and the right side was easier to be disturbed by friction. Friction started to play its role when the tip approached the observation points, while it had little influence on rotation rate. The normalized tip resistance \((q_{c}=f/\sigma _{v0})\) increased with friction as well as inclination angle. The relationship between \(q_{c}\) and relative depth \((y/R)\) can be described as \(q_{c}=a\times (y/R)^{-b}\) , with parameters \(a\) and \(b\) dependent on penetration direction. The normalized resistance perpendicular to the penetrometer axis \(q_{p}\) increases with the inclination angle, thus the inclination angle should be carefully selected to ensure the penetrometer not to deviate from its original direction or even be broken in real tests.     

Flicker Noise and Telegraph Noise in High-Temperature Superconductors

The mechanism capable to explain the peculiarities of both the telegraph noise and flicker noise in high-temperature superconductors (HTS)—in particular, their common behavior—is proposed. It bases on the impurity mechanism of high-temperature superconductivity and the suggestion that an origin of the flicker noise in most cases is a process that can be described by the equation of diffusion type, with a medium discreteness taken into account. In the transition region, the flicker noise and telegraph noise are explained by fluctuations of the concentration (x _ef ) of the two-level systems each having a localized electron pair. These fluctuations disappear according to the diffusion equation. The telegraph noise is considered as a result of opening and closing superconducting and nonsuperconducting channels due to the x _ef fluctuations. In the normal state, the flicker noise is explained by concentration fluctuations of different impurities that change the charge carrier mobility.     

Cancellation of coherent artifacts in optical coherence tomography imaging

Coherent artifacts in optical coherence tomography (OCT) images can severely degrade image quality by introducing false targets if no targets are present at the artifact locations. Coherent artifacts can also add constructively or destructively to the targets that are present at the artifact locations. This constructive or destructive interference will result in cancellation of the true targets or in display of incorrect echo amplitudes of the targets. We introduce the use of a nonlinear deconvolution algorithm, CLEAN, to cancel coherent artifacts in OCT images of extracted human teeth. The results show that CLEAN can reduce the coherent artifacts to the noise background, sharpen the air-enamel and enamel-dentin interfaces, and improve the image contrast.     

自适应消噪技术在旋光准直仪中的应用研究

通过对自适应消噪技术理论分析和实验研究，成功地将其应用于旋光准直仪中，用自适应消噪技术对远近距离多种不同准直测量的实验结果进行处理。结果表明：在不同实验条件下，消噪后补偿度达30%-80%。     

CPT原子钟系统的数字正交解调算法及实现

介绍了将数字正交解调算法应用于CPT原子钟系统的锁相环路,通过FPGA硬件结构实现解调功能所开展的研究.经MATLAB和QUARTUS2的联合仿真表明,该算法抗噪声能力强,解调结果可靠性高,是应用于高性能CPT原子钟的理想算法.实际应用于CPT原子钟的实验结果与理论预期和实验仿真结果相一致.该方案有利于原子频标的工作状态调整和保持产品性能一致性.     

纺织厂噪声及其控制技术研究

对纺织厂织布车间,细纱车间的噪声情况做了调研与测试。分析纺织厂的噪声现状。整群抽样选取对比组,通过问卷调查和实地测试相结合方法,探讨噪声对生产和工人身心健康的影响,提出降噪综合控制方法,并通过实验测试得以验证。     

Noise in Silicon Nanowires

The current–voltage and noise characteristics of bridging silicon wires have been measured at room temperature. From the linear current–voltage characteristics the bulk and contact resistance contributions are extracted and modeled. The excess noise observed at low frequencies is interpreted in terms of bulk and contact noise contributions, with the former comparable, in terms of Hooge parameter values, to the low noise levels observed in high-quality silicon devices. The contact noise is significant in some devices and is attributed to the impinging end of the bridging nanowires.     

船厂高噪声涂装车间噪声评价及降噪设计

船厂涂装车间作业噪声和设备噪声高达100dB(A),对内对外均有影响.对广州某船厂新建涂装车间的噪声进行分析、评价和预测,同时提供达标降噪设计,可供同类工程参考.     

Cancellation of bending-induced birefringence in single-mode fibers: application to faraday sensors

We demonstrate that one can cancel the bending-induced linear birefringence in single-mode fibers by inducing a controlled anisotropy in a direction orthogonal to the bending plane. In particular, the controlled anisotropy can be generated by application of a lateral compressive stress on the fiber. This effect can be applied for the construction of birefringence-free fiber coils in Faraday sensor heads (e.g., in current sensors) to improve their sensitivity.