高Tcrf SQUID梯度计及其在心磁图测量中的应用

我们用两套ＨＴｃｒｆＳＱＵＩＤ组成一阶梯度计,在无屏蔽条件下,进行了心磁图测量。实验结果表明,在利用了梯度计消除环境噪声,再通过平均、数字滤波等方法进一步提高信噪比后,我们测得的心磁图中,可以清楚地看到Ｐ、Ｑ、Ｒ、Ｓ、Ｔ等各个波,其信噪比达到１２０,已可满足实用的要求。     

在SQUID心磁测量中基于奇异值分解和自适应滤波的噪声消除法

采用矩阵奇异值分解(singular value decomposition, SVD)的方法，对高温射频超导量子干涉仪(HTc rf-SQUID)采集到的单通道心磁信号进行处理.证明了对于近似周期性的心磁信号，在无参考噪声的情况下矩阵奇异值分解的方法与自适应窄带陷波相结合有较好的消除广谱噪声的效果. 关键词： 高温射频超导量子干涉仪 心磁信号 奇异值分解 噪声消除     

互补型自适应滤波器在心磁信号处理中的应用

将心磁信号从干扰噪声中加以提取并有效地消除噪声干扰是心磁信号处理中尤为重要的环节 .从改进算法的角度出发，提出互补型自适应滤波器结构以实现心磁信号的消噪处理.该滤波器针对心磁这类非平稳信号进行设计，有效地解决了常规自适应滤波器应用于心磁信号处理时收敛速度和稳态误差的矛盾.通过仿真实验和心磁实验结果表明，该算法能有效地消除心磁信号的背景噪声和工频干扰噪声.同时该算法也可用于其他非平稳信号的消噪处理. 关键词： 自适应滤波 心磁图 最小均方误差     

HT_c SQUID工作环境低频磁干扰消除研究

针对高温超导量子干涉器(HT_c SQUID)磁强计技术在非磁屏蔽环境中受到的极低频干扰,实验研究了主动补偿方法消除这种干扰的可行性和有效性。实验由高精度程控电流源提供电流,通过亥姆赫兹线圈产生用于抵消极低频干扰的补偿磁场,使用两套HT_c SQUID磁强计搭建了测试系统,其中一套用于低频磁干扰背景的探测,另一套用于磁干扰补偿消除效果的甄别。结果表明,这种动态补偿消除方法可以达到比较好的效果。     

一种互补型自适应滤波最小均方法在SQUID测量的心磁信号中的应用

提出了一种互补型自适应滤波最小均方算法在SQUID测量的心磁信号中的应用，快的收敛速度和很好的跟踪能力通过根据最小均方原则在两个滤波器之间来回转换加权参量来实现     

全张量SQUID磁梯度计在航空磁测方面的应用研究

航空磁测在矿产资源勘探、地球物理、科学研究以及军事应用等方面应用甚广。文中对超导量子磁力仪在航空磁测的应用研究情况进行了综述,简要介绍了SQUID磁强计与梯度计的差别。最后介绍了构成全张量超导磁探仪的两种方法,分析了两种方法的磁梯度不平衡度以提高航空磁测的实用性。     

自适应统计滤波的单幅干涉条纹图相位解调研究

基于统计信号处理技术的最大后验估计原理 ,提出一种新的自适应滤波方法。该方法能有效减少干涉条纹图中的噪声 ,仅估计一幅非载波条纹图上每一点的空间频率向量的幅值和方向 ,通过解系数阵为正定阵的方程组 ,就能获得准确的条纹相位分布。通过实例说明了此方法的处理过程。     

心磁信号广义S变换域奇异值分解滤波方法

针对心磁信号工频及背景噪声干扰问题, 提出了广义S变换奇异值分解(singular value decomposition, SVD)滤波方法.在离散S变换基础上, 导出了广义矩阵S变换和逆变换公式. 通过对采样信号进行广义S变换, 调节时频分辨率, 利用SVD分解方法确定有效心磁信 号区域, 实现自适应时频滤波. 实验结果表明, 该方法能有效滤除工频及背景噪声干 扰, 且在较少奇异值个数情况下可获得更好的滤波性能. 关键词： 心磁信号 S变换 奇异值分解 时频滤波     

数字滤波在心磁噪声抑制中的应用

提出了一种基于数据重置最小均方算法的自适应数字滤波器, 并将其应用于抑制心磁信号的背景噪声. 数值模拟结果表明该滤波器对于相关噪声,尤其是有幅值变化和时间延迟的情况, 有很强的抑制效果. 该滤波器有很宽的带宽.利用它可以使心磁信号的信噪比提高到器件的本征噪声水平. 利用周期平均的方法进一步提高信噪比, 对滤波前后心磁信号的频谱进行了分析.     

扫描SQUID显微镜的研制及其在磁成像和无损检测中的应用

研制了两种用于检测室温样品的超导量子干涉器(SQUID)扫描磁场显微镜(以下简称扫描SQUID显微镜),一种使用常规低Tc(Nb)SQUID器件,另一种使用高温(YBCO)SQUID器件.SQUID安装在内杜瓦底部的冷指底端,外杜瓦底部有60～75微米厚的白宝石窗口,被测样品处于室温状态位于窗口下,SQUID与被测样品之间的间距通过波纹管的伸缩进行调节.常规低Tc(Nb)器件系统的空间分辨率优于140μm,磁场灵敏度优于3pT/Hz1/2,高温(YBCO)器件系统的空间分辨率～500μm,磁场灵敏度～46pT/Hz1/2.两者均能长时间稳定地工作在无屏蔽环境中.利用两台扫描SQUID显微镜,进行了多种有应用价值的磁成像实验和无损检测研究.     

An adaptive speech enhancement method for siren noise cancellation

Siren noises usually severely disturb the intelligibility of voice communication inside the cabs of police, paramedic and fire vehicles. It is often desired that such unwanted noise can be removed from the speech signal. In this paper, a new method is proposed to adaptively cancel siren noises and enhance speech signals. Based on the characteristics of siren noises, an anti-speech filter and a time delayer are employed in the single and dual channel noise cancellation systems to reduce the siren noises. Experiment results demonstrate that the effectiveness of the proposed method for canceling the siren noises and the performance of the enhanced speech signal is satisfying.     

Enhancing optomechanical force sensing via precooling and quantum noise cancellation

We theoretically investigate optomechanical force sensing via precooling and quantum noise cancellation in two coupled cavity optomechanical systems.We show that force sensing based on the reduction of noise can be used to dramatically enhance the force sensing and that the precooling process can eifectively improve the quantum noise cancellation.Specifically,we examine the effect of optomechanical cooling and noise reduction on the spectral density of the noise of the force measurement;these processes can significantly enhance the performance of optomechanical force sensing,and setting up the system in the resolved sideband regime can lead to an optimization of the cooling processes in a hybrid system.Such a scheme serves as a promising platform for quantum back-action-evading measurements of the motion and a framework for an optomechanical force sensor.     

应用于助听器反馈抑制的信噪比自适应滤波算法

针对基于自适应滤波器的助听器反馈抑制系统,该文提出了一种基于信噪比的归一化最小均方误差算法,采用最小值统计法估计误差信号的噪声分量,从而计算出误差信号的信噪比来计算自适应滤波系数的更新步长。当误差信号信噪比越高,语声占主要成分,信号的相关性越强,此时将滤波器的更新步长控制在较小值,减小滤波器的失调量;当信噪比越低时,噪声占主要成分,信号的相关性相对较弱,更新步长取较大值,加快滤波器的收敛速度。在仿真实验中,该文提出的基于信噪比的归一化最小均方误差算法相较于传统算法在平均稳态失调量和稳态失调范围上分别低1 dB和2 dB,其最大稳态增益提高了4 dB,同时具有更快的稳态收敛速度,验证了该文提出算法的有效性。     

基于近场聚焦逆波束形成的UUV平台噪声自适应抵消

UUV平台自噪声会对舷侧阵产生干扰,从而影响其探测性能,本文针对平台尾部自噪声源的直达噪声和海面反射噪声,提出了基于近场聚焦逆波束形成的平台噪声自适应抵消方法。文中利用UUV平台设计参数、深度以及运动姿态信息对尾部自噪声传播到舷侧阵的路径建立几何模型,并分析了影响该路径的因素;通过该模型,平台尾部自噪声能够实时自适应地通过聚焦波束形成被估计出来,从而在舷侧阵的接收信号中实现干扰抵消。仿真结果与海试实验数据处理结果表明,该方法能够有效抑制尾部自噪声干扰,显著提高UUV探测弱目标的能力。     

Design and analysis of a BLPC vocoder-based adaptive feedback cancellation with probe noise

The band-limited linear predictive coding (BLPC) vocoder-based adaptive feedback cancellation (AFC) removes the high-frequency bias, while the low frequency bias persists between the desired input signal and the loudspeaker signal in the estimate of the feedback path. In this paper, we present a BLPC vocoder-based adaptive feedback canceller with probe noise with an objective of reducing the low-frequency bias in digital hearing-aids. A step-wise mathematical analysis of the proposed feedback canceller is presented employing the recursive least square and normalized least mean square adaptive algorithms. It is observed that the optimal solution of the feedback path is unbiased for an unshaped probe noise, but is biased for a shaped probe signal; the bias term does not consist of correlation between the desired input and the loudspeaker output. The identifiability conditions are analysed and it is shown that a delay, greater than or equal to the length of the adaptive filter, must be introduced in the forward path to achieve an unbiased feedback path estimate. Algorithm analysis and computer simulations presented in this paper justify the reason for selecting the proposed design over the existing BLPC vocoder-based feedback cancellation algorithm.     

机车驾驶室中自适应有源降噪系统的研究

根据机车驾驶室中噪声特征的分析结果，提出了采用FIR滤波器的自适应有源降噪(ANNC)系统。为消除机车驾驶室中严重的背景噪声干扰影响，应用伪随机相关法对驾驶室中的噪声脉冲响应进行测量。通过数字仿真研究，对基于IMS算法的ANNC系统的关键参数进行了寻优。最后，在实际声场中建立了实时双通道ANNC系统并进行了相关的实验验证。仿真与实验的结果证明了本文提出的AANC系统的可行性和有效性。     

A normalized data-reusing least-mean-square algorithm of noise cancellation for magnetocardiography

An adaptive filter based on Data-Reusing Least-Mean-Square algorithm has been proposed and applied in magnetocardiography (MCG) to suppress ambient noise, Numerical simulation studies indicate that the adaptive filter is a powerful noise suppresser for correlated interferences, especially for those with amplitude changing and time delay.Also the filter has a wide frequency bandwidth. With this filter, the signal-to-noise ratio of an MCG is improved to the intrinsic noise level, The periodic average method for further improvement of the noise level in MCG is also discussed.     

Adaptive noise cancellation in neuromagnetic measurement systems

Summary The noise spectrum of a superconducting second-derivative gradiometer has been investigated in an urban environment. Data have been acquired from the gradiometer with three orthogonal accelerometers and a triaxial fluxgate magnetometer attached to the dewar. These data have been analyzed by using signal processing techniques, primarily an adaptive noise canceller, to reduce noise in the gradiometer data. Results shown here indicate that the environmental noise and/or the dewar motion noise can be reduced as much as 40 dB in noise power. It is also shown, in the case of poor signal-to-noise ratio (S/N∼1), that a 10 Hz sine wave can be extracted. This technique not only shows promise for noise reduction, but also aids in the identification of noise signals which might be misconstrued as part of the evoked response. Analysis of data containing evoked response is now underway. Paper presented at the ?IV International Workshop on Biomagnetism?, held in Rome, September 14–16, 1982.     

基于模式搜索的自适应干扰抵消器算法的研究

为了减小同址干扰对接收机性能的影响,设计了一种基于正交矢量合成的自适应干扰抵消器;根据其中控制单元提取出的数据的特点,提出了将模式搜索算法(PSA)作为控制器算法,并对其进行了改进;利用实际测量的数据进行了仿真分析,结果表明,相比于PSA算法、模拟退火算法、遗传算法,改进后的PSA算法具有更快的收敛速度,同时收敛精度相差无几;最终的实现结果也证明了该方法可满足性能要求。