EMD算法在低温超导瞬变电磁噪声抑制中的应用

瞬变电磁信号具有较宽的频谱,为使得超导瞬变电磁信号的接收不产生失真,要求接收信号的超导传感器具有足够高的带宽(100kHz以上),而接收高带宽信号会导致信号的噪声峰峰值变大,传统的滤波(模拟、数字)方法易造成衰减曲线畸变.基于数据驱动的经验模态分解(Empirical Mode Decomposition,EMD)算法能够根据信号本身特性对其进行信号分解和分量选择,具有自适应和不产生波形畸变的特点.本文采用EMD算法分别对数值模拟和野外实测的超导瞬变电磁信号进行EMD滤波处理和分析,结果表明,EMD可以显著压制瞬变电磁信号衰减曲线中的宽频带噪声且波形无畸变.经过EMD滤波的超导瞬变电磁与原始信号相比,信号衰减时间显著延长(从5ms延长至50ms),表明EMD算法能够极大提高瞬变电磁方法对地下深部信息的探测能力.     

高临界电流密度NbN约瑟夫森结的制备和特性表征

我们开展了高临界电流密度的NbN约瑟夫森结的制备和特性研究.利用直流磁控溅射方法在单晶MgO(100)衬底上外延生长NbN/AlN/NbN三层膜,并使用微加工工艺制备了NbN约瑟夫森隧道结,在液氦温度下对NbN约瑟夫森结的电流-电压特性进行了测量,实验结果表明,NbN约瑟夫森结具有良好的隧穿特性,其临界电流密度J_c为10 kA/cm^2,质量因子大于10,能隙是5.7 mV,这些实验结果为基于NbN结的超导数字电路研究奠定了坚实的基础.     

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.     

Research on high-T-c SQUID based non-destructive evaluation

A non-destructive evaluation system based on high-T_c dc-SQUID (superconducting quantum interference device) incorporating a gradient field excitation has been built. By using this system a 1mm-diameter hole at a depth of 2mm inside an aluminium plate at room temperature can be easily detected and imaged in an unshielded environment. The relation between the spatial resolution, or the smallest detectable flaw size, and experimental parameters is briefly analysed in terms of a simple metal ring model. The result shows that the spatial resolution depends strongly on the sensor-sample separation as well as on some other parameters, such as signal-to-noise ratio of excitation, excitation frequency and material conductivity.     

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.