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《物理学报》2019,(13)
超导量子干涉器件(superconducting quantum interference device, SQUID)作为一种极灵敏的磁通传感器,在生物磁探测、低场核磁共振、地球物理等领域得到广泛应用.本文介绍了一种基于SQUID的高灵敏度磁强计,由SQUID和一组磁通变压器组成. SQUID采用一阶梯度构型,增强其抗干扰性.磁通变压器由多匝螺旋的输入线圈和大尺寸单匝探测线圈组成,其中输入线圈与SQUID通过互感进行磁通耦合.利用自主工艺平台,在4英寸硅衬底上完成了基于Nb/Al-AlO_x/Nb约瑟夫森隧道结的SQUID磁强计制备.低温测试结果显示,该磁强计磁场灵敏度为0.36 nT/Φ_0,白噪声段磁通噪声为8μΦ_0/√Hz,等效磁场噪声为2.88 fT/√Hz. 相似文献
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超导纳米量子干涉器件是近年来发展起来的一种新型超导器件, 通过现代微纳加工技术将其超导环缩小到纳米尺寸, 构成高度灵敏的微观自旋探测器, 理论上可以达到测量单电子自旋的灵敏度. 同时, 高温超导由于具有较高的临界温度和上临界场也备受关注. 然而, 相比于低温超导量子干涉器件, 高温超导量子干涉器件的1/f 噪声更加显著, 这限制了其在低频下的应用. 本文基于双晶衬底技术, 通过聚焦离子束加工制备高温超导纳米量子干涉仪, 并对其在液氦和液氮温区下的电学性能、4.2 K 下的磁通噪声进行表征. 实验发现, 通过预先退火处理钛酸锶双晶衬底, 可以有效改善衬底表面的粗糙度, 进而优化高温超导纳米量子干涉仪的1/f 磁通噪声. 最终得到低频下(1 Hz)的磁通噪声灵敏度为4.9 μΦ0/Hz1/2 , 比未事先预处理的小一到两个数量级, 这对于推进高温超导纳米量子干涉器件在低频下的应用意义重大. 相似文献
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针对低信噪比下利用单水听器估计辐射噪声功率谱密度精度较差的问题,提出一种基于多途信道传输函数估计的垂直阵测量估计1 m处舰船辐射噪声功率谱密度的方法。该方法将信道传输函数表示为多途路径近场阵列流形向量的叠加,较快地估计了信道传输函数,将其用于舰船辐射噪声功率谱密度估计,可较简便地估计距声中心1 m处辐射噪声的功率谱密度,即谱源级。分析了产生功率谱密度估计误差的原因,包括信道估计误差和环境噪声引起的误差,为降低估计误差提供了理论依据。仿真结果表明,该方法估计1 m处辐射噪声功率谱密度的性能良好。 相似文献
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用有限温度下的分子动力学方法模拟二维无序钉扎磁通系统的低频宽带电压噪声.计算了磁通运动的电压噪声谱密度,研究了宽带噪声(BBN)随驱动电流、钉扎强度和温度的变化规律.BBN随钉扎强度的增加而增大,反映了BBN是磁通运动受体钉扎阻碍而产生的内部耗散. BBN随温度的升高而减小,表明热运动部分抵消了体钉扎以及磁通之间相互作用,软化了磁通线格子,使磁通运动BBN减小.以上结论与实验相符,并能解释磁通运动的微观图像.
关键词:
第Ⅱ类超导体
电压噪声
动力学模拟 相似文献
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Takao Itoh 《Journal of Molecular Spectroscopy》2008,252(2):115-120
Fluorescence and excitation spectra of coronene vapor have been measured under different conditions. Weak emission which can be regarded as the fluorescence from the third excited singlet state, S3(1E1u), was observed in addition to the S1(1B2u) and S2(1B1u) fluorescence. The observed S2 and S3 fluorescence are substantially different from those reported previously for coronene vapor. Addition of oxygen resulted in significant decrease of the S1 fluorescence intensity, but did not affect the S2 fluorescence intensity, indicating the faster decay rate of the S2 state than that of S1. Excitation energy dependence of the S1, S2 and S3 fluorescence quantum yields (ΦF(S1), ΦF(S2) and ΦF(S3), respectively) revealed that ΦF(S1) decreases with increasing excitation energy, while ΦF(S2) and ΦF(S3) increase significantly. The quantum yield ratios, ΦF(S2)/ΦF(S1) and ΦF(S3)/ΦF(S2), obtained as a function of excitation energy are correlated with the ratios of the relative internal conversion rates. 相似文献
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We have developed a very large magnetic shielding vessel made from high-Tc Bi-Pb-Sr-Ca-Cu-O superconductor and have experimentally confirmed that this vessel can reduce a weak magnetic field to -100 dB or 1/105. The size of this vessel is 32 cm in diameter, 64 cm in depth and 2.5 cm in thickness. The shielding effect of the vessel does not decrease even at a low frequency like 0.2 Hz. The high attenuation ratio in the low frequency range indicates that magnetic shielding using a high-Tc superconductor is promising for neuromagnetic measurements with SQUID. 相似文献
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S. Büttgenbach M. Herschel G. Meisel E. Schrödl W. Witte W. J. Childs 《Zeitschrift für Physik A Hadrons and Nuclei》1974,266(4):271-274
The hyperfine structure of the ground state 4d 5 5s 7 S 3 of95Mo and97Mo has been measured by the atomic beam magnetic resonance technique with the following results:95Mo:A=?208.582060(10)MHz,B=37.050 (100) kHzC=?30 (10) Hz,D=?3 (3) Hz97Mo:A=? 212.980930 (10) MHz,B?69.990(140)kHzC=?5 (10) Hz,D=0 (3) Hz. After application of corrections calculated according to second order perturbation theory, the hyperfine structure constants became:95Mo: Ac=?208.582560(290)MHz,B c =16.920(4300)kHzC c=?30(270) Hz,D c =? 3 (50) Hz97Mo: Ac=212.981450(300) MHz,B c =?90.780(4400)kHzC c=?6(270) Hz,D c =0 (50) Hz. With the known ratio ofg I(95Mo)/g I(97Mo) [1] a calculation of the hyperfine anomaly yields:95 Δ 97=?0.01009(17)%. The ratio of the uncorrectedB factors isB(97Mo)/B(95Mo)=?1.8890(47). Because of the relatively large effects of second order hyperfine structure, the ratio of the correctedBfactors differs considerably from the ratio of the uncorrectedB factors. From the correctedB factors the electric quadrupole moments may be evaluated by means of calculated radial integrals [2]. The results are:Q (95Mo)=?0.019(12)barns,Q(97Mo)=0.102(39)barns. 相似文献
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At an extremely low temperature of 20 mK, we measured loop current in a tunable rf superconducting quantum interference device (SQUID) with a dc-SQUID. By adjusting the magnetic flux applied to the rf-SQUID loop (Φf) and the small dc-SQUID (Φfcjj), respectively, the potential shape of the system can be fully controlled in situ. Variations of transition step and overlap size in switching current with the barrier flux bias are analyzed, from which we can obtain some relevant device parameters and built up a model to explain the experimental phenomenon. 相似文献
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Nanoparticles (NPs) were produced by ablating tungsten and boron-carbide (B4C) target materials in atmospheric pressure nitrogen ambient using ArF excimer laser pulses. The size distributions of the NPs formed during the ablation were monitored—within a 7-133 nm size window—by a condensation particle counter connected to a differential mobility analyzer. The laser repetition rate was varied between 1-50 Hz, and the fluence was systematically changed in the range of 0.5-15 J/cm2, for both materials, allowing a comparative study in an extended laser parameter regime. The multishot ablation threshold (Φth) of B4C was determined to be ∼1.9 J/cm2 for the laser used (ArF excimer, λ = 193 nm). Similarly to earlier studies, it was shown that the size distributions consist of mainly small nanoparticles (<∼20 nm) attributed to a non-thermal ablation mechanism below Φth. An additional broad peak appears (between 20 and 40 nm) above Φth as a consequence of the thermally induced macroscopic ablation. Chemical composition of deposited polydisperse nanoparticles was studied by X-ray photoelectron spectroscopy showing nitrogen incorporation into the boron-carbide. 相似文献
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E. B. Alexandrov M. V. Balabas A. K. Vershovski A. S. Pazgalev 《Technical Physics》2004,49(6):779-783
The sensitivity σ of an optically pumped quantum magnetometer is measured directly by comparing the output frequencies of
85Rb and 87Rb magnetometers integrated in a single two-isotope cell. The result σ87=59.6±6 fT Hz−1/2 agrees well with the value σ
87
light
=53.7±2 fT Hz−1/2 obtained indirectly by measuring 87 the ratio of the resonance steepness to the shot noise of light. 相似文献
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Jian‐Li Guo Chong Liu Bin‐Bin Xie Yan‐Ying Zhao Ke‐Mei Pei Hui‐Gang Wang Xuming Zheng Yue‐Jie Ai Xue‐Bo Chen Wei‐Hai Fang Chi Shun Yeung 《Journal of Raman spectroscopy : JRS》2012,43(10):1477-1486
The photophysics and photochemistry of pyrazine (C4H4N2, D2h) after excitation to the S2 (1 1B2u, 1ππ*) electronic state were studied by using the resonance Raman spectroscopy and complete active space self‐consistent field method calculations. The B‐band resonance Raman spectra in cyclohexane solvent were obtained at 266.0, 252.7, and 245.9 nm excitation wavelengths to probe the structural dynamics of pyrazine in the S2 (1 1B2u, 1ππ*) state. Three electronic states 1 1B3u, 1 1B1g, and 1 1B2g were found to couple with the S2 (1 1B2u, 1ππ*) state. Two conical intersection (CI) points CI[S2(B2u)/S1(B3u)] and CI[S1/S0] and one transition state of the isomerization between pyrazine and pyrimidine were predicted to play important roles in the photochemistry of pyrazine. On the basis of the calculations, the mechanism of the photoisomerization reaction between pyrazine and pyrimidine has been proposed. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
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Exclusive Bc-meson decays accompanied by the production of vector or pseudoscalar heavy quarkonia (η c , η c (2S), J/φ, φ(2S), and B s (*) ) and an nπ light-meson system, where 1 ≤ n ≤ 5, are considered. 相似文献