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1.
Superconducting quantum interference devices with different damped junctions operated in directly coupled current-and voltage-bias modes 下载免费PDF全文
We investigate niobium thin film superconducting quantum interference devices (SQUIDs) with different Steward- McCumber parameters βc operated in both current- and voltage-bias modes. We experimentally prove that there is no difference between the two bias modes with respect to the SQUID intrinsic noise and the noise contribution from the preamplifier. Furthermore, the relationships of the SQUID dynamic parameters, (Rd)current bias ≈ (Rd)voltage bias and (σV/σФ)current bias ≈ [σi/σФ)Rd]voltage bias, are always satisfied. For a strongly damped SQUID withβc ≈ 0.25, addi- tional positive feedback (APF) and noise cancellation (NC) were employed to enhance σV/σФ, the former showing a degradation in the linear flux range but otherwise the same with NC. For a weakly damped SQUID with βc ≈ 3, it is di- rectly connected to the preamplifier without APF or NC, and a low SQUID system noise of about 4μФ0/x/Hz is measured, which is close to its intrinsic noise. 相似文献
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在多通道超导量子干涉器件(SQUID)磁探测系统中,磁场电压转换系数(∂ B/∂ V)是系统的一个重要参数由于SQUID器件和读出电路之间不可避免地存在差异性因此对传感器系统进行系统标定(每个通道的单独标定)显得十分重要本文采用(PCB) 板印制圆形线圈对36通道心磁系统进行标定,并与传统的亥姆霍兹方形线圈产生均匀场的标定方法进行比较结果显示PCB圆形线圈的标定结果 在1.46–1.73 pT·mV-1 之间,亥姆霍兹方形线圈标定的结果大都在1.56–1.64 pT·mV-1之间,结果基本一致.
关键词:
超导量子干涉器件
磁探测
磁场-电压转换系数
系统标定 相似文献
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本文利用磁屏蔽室和二阶轴向梯度计抑制环境磁场噪声, 建立了单通道脑磁探测系统, 并对不用声音频率下脑听觉激励磁场N100m响应进行了初步探测.结果显示, 1000 Hz音频和100 ms持续声音激励下, N100m峰值的典型强度约为0.4 pT.在低的声音频率激励下, N100m峰出现延时, 100 Hz 和1000 Hz之间的延时差别达到25 ms.相比于1 kHz特定频率的声音激励, 1—4 kHz 随机变频下的N100m峰幅度增强, 出现了数毫秒的延时.本研究为下一步利用软件梯度计进行多通道脑磁系统和听觉机理研究奠定了一定的基础. 相似文献
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A dual-washer superconducting quantum interference device(SQUID) with a loop inductance of 350 pH and two onwasher integrated input coils is designed according to conventional niobium technology. In order to obtain a large SQUID flux-to-voltage transfer coefficient, the junction shunt resistance is selected to be 33 ?. A vertical SQUID gradiometer module with a baseline of 100 mm is constructed by utilizing such a SQUID and a first-order niobium wire-wound antenna.The sensitivity of this module reaches about 0.2 fT/(cm·Hz1/2) in the white noise range using a direct readout scheme, i.e.,the SQUID is directly connected to an operational amplifier, in a magnetically shielded room. Some magnetocardiography(MCG) measurements with a sufficiently high signal-to-noise ratio(SNR) are demonstrated. 相似文献
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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. 相似文献
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SQUID gradiometer techniques are widely used in noise cancellation for biomagnetic measurements.An appropriate gradiometer baseline is very important for the biomagnetic detection with high performance.By placing several magnetometers at different heights along the vertical direction,we could simultaneously obtain the synthetic gradiometers with different baselines.By using the traditional signal-to-noise ratio(SNR) as a performance index,we successfully obtain an optimal baseline for the magnetocardiography(MCG) measurement in a magnetically shielded room(MSR).Finally,we obtain an optimal baseline of 7 cm and use it for the practical MCG measurement in our MSR.The SNR about 38 dB is obtained in the recorded MCG signal. 相似文献
7.
超导量子干涉器件(SQUID)是超导磁力仪的核心器件,应用于地球物理探测时,环境射频电磁场干扰SQUID工作,导致性能(噪声和工作稳定性等)全面下降,甚至无法正常工作.本文运用电磁场仿真技术和测试方法,对物探SQUID应用的射频干扰屏蔽方法与效果进行分析研究.模拟户外环境仿真,结果表明:随着屏蔽层数增加可屏蔽的射频场的频谱范围增大,8层时就可达到满意的屏蔽效果.测试与仿真结果的规律一致.基于室内和户外两种不同电磁环境开展了低温SQUID工作射频屏蔽对比验证.实验结果表明:不同应用环境对系统射频屏蔽的要求不同(室内:2层以上屏蔽,户外:8层以上屏蔽).本研究为定量分析并解决物探环境射频屏蔽的关键问题奠定了基础. 相似文献
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The performance of a superconducting quantum interference device(SQUID) gradiometer is always determined by its pick-up coil geometry, such as baseline and radius. In this paper, based on the expressions for the coupled flux threading a magnetometer obtained by Wikswo, we studied how the gradiometer performance parameters, including the current dipole sensitivity, spatial resolution and signal-to-noise ratio(SNR), are affected by its pick-up coil via Mat Lab simulation.Depending on the simulation results, the optimal pick-up coil design region for a certain gradiometer can be obtained.To verify the simulation results, we designed and fabricated several first-order gradiometers based on the weakly damped SQUID with different pick-up coils by applying superconducting connection. The experimental measurements were conducted on a simple current dipole in a magnetically shielding room. The measurement results are well in coincidence with the simulation ones, indicating that the simulation model is useful in specific pick-up coil design. 相似文献
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在三乙基苄基氯化铵和氢氧化钠溶液中,采用碘甲烷作为衍生剂进行衍生化反应,通过气相色谱法对氯苯酚类化合物的衍生物进行分离和测定,其4-氯苯酚、2,4-二氯苯酚、2,4,6-三氯苯酚衍生物的检出限分别为1.36,1.87,2.67mg·L^-1。用标准加入法对上述3种氯苯酚衍生物的峰面积测量的精密度进行试验,其相对标准偏差依次为4.2%,3.4%,5.1%。 相似文献