航空超导全张量磁梯度仪的串扰研究

航空超导全张量磁梯度仪是使用飞行平台搭载的磁法测量设备,因其磁场灵敏度高、采集信息丰富、体积小等特点,被认为是第三代航磁探测的发展方向.本文构建了六棱锥构型的全张量梯度模块,由一个三轴超导量子干涉器(SQUID)磁强计和6个低温超导平面一阶SQUID梯度计组成.测试结果表明,在该多通道系统中,SQUID之间的串扰明显,对测量结果造成影响.本文对该超导全张量磁梯度仪的串扰进行了分析,并测量了串扰数据.分析了影响串扰的因素后,通过增加SQUID间的间距和改变接线方式等措施,对全张量模块结构进行了优化.实验结果表明,新构型模块对串扰改善在一个数量级以上,极大地提高了超导全张量磁梯度仪的精度和实用性.     

低噪声超导量子干涉器件磁强计设计与制备

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.     

高温超导技术在微磁传感器中的应用与发展

磁传感器在诸多领域有着广泛的应用,而随着高温超导技术的快速发展,将高温超导材料应用于磁信号测量成为超导材料应用的一个重要领域。文章探讨了高温超导材料在微弱磁场测量方面的主要应用,介绍了三种在微弱磁场测量方面能达到或有希望达到f T量级的传感器。其中包括:基于约瑟夫森结效应的超导量子干涉器(SQUID),基于超导零电阻效应的巨磁电阻(GMR)磁传感器和由文章作者所在的实验室提出的巨磁阻抗(GMI)/超导复合磁传感器。文章重点介绍了GMI/超导复合磁传感器,并对此传感器在结构和应用方面的最新进展进行了说明。     

低温超导全张量磁梯度计不平衡度补偿研究

超导全张量磁梯度仪因其信息量丰富、磁场灵敏度高、体积小等特点,被认为是第三代航磁探测的发展方向.全张量梯度仪可由多个不共面的平面一阶超导量子干涉器件(SQUID)梯度计构成.目前,采用微纳加工工艺制备的超导平面梯度计能获得最好的平衡度,其共模抑制比可达103~104,但仍然不能满足运动条件下的应用需求.在实际应用中,可采用三轴SQUID磁强计对梯度计进行补偿,达到抑制运动噪声的目的.本文基于最小二乘(LMS)自适应滤波算法,通过数值仿真分析了平面梯度计的不平衡度、环境磁场大小以及环境剩余磁梯度对补偿效果的影响.同时,我们构建了六棱锥构型的全张量超导梯度仪,并采用三轴磁强计作为补偿通道,在野外均匀地球磁场下进行了测试.结果表明,该补偿方法能够大幅减小均匀磁场下的梯度计的不平衡输出,可以将梯度值补偿约2个数量级,极大提高了超导全张量磁梯度仪在运动状态下的实用性.     

高阶高温超导量子干涉器件平面式梯度计的设计

设计了一种高温超导平面式梯度计的探测线圈，利用这种探测线圈与超导量子干涉器件(SQ UID)耦合，可以制成二阶或更高阶的高温超导SQUID平面式磁场梯度计.设计的探测线 圈由两个闭合环路组成，每个闭合环路是由若干个环路通过细小的连接通道连接而成.两个 闭合环路由一条超导窄带分割，将SQUID与这条超导窄带耦合可以测出超导窄带上的电流大 小.通过调整各个环路的形状、面积和位置，可以使超导窄带上的电流与磁场的高阶梯度成 正比，从而测得磁场的高阶梯度. 通过计算，得到了各个环路的面积、电感以及位置的关 系，在理 关键词： 高阶平面式磁场梯度计 高温超导薄膜     

超导磁梯度张量探头结构优化方法研究

针对传统超导磁梯度张量探头中多个磁梯度计间的噪声互扰会降低系统灵敏度的问题，本文提出了一种基于二维傅里叶变换的磁梯度张量探头结构优化方法。通过二维傅里叶变换及逆变换将磁场矢量Z分量沿着Z轴方向的二阶空间导数B_zzz转换为磁场矢量的3个分量以及一阶磁梯度张量的5个独立元素，把通常至少需要6个SQUID一阶平面磁梯度计的探头结构简化为只需要1个二阶SQUID磁梯度计的探头结构，消除了磁梯度计之间的噪声干扰，系统灵敏度提高了1个数量级。实验结果表明该探头具有良好的探测能力，证明了这种优化方法的可行性。     

多通道心磁系统标定方法研究

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     

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.     

四面体磁梯度张量系统的载体磁干扰补偿方法

针对搭载于水下无人航行器(UUV)的四面体磁梯度张量系统易受载体磁场干扰的问题,提出了一种载体磁干扰补偿方法.该方法在载体磁干扰产生机理的基础上,利用磁梯度张量差分测量算法融合四面体磁梯度张量系统中四个矢量磁力仪的载体磁干扰,建立了磁梯度张量系统载体磁干扰数学模型;然后在此数学模型的基础上提出了磁干扰补偿方法,并根据磁梯度张量9分量的数学关系提出了补偿参数辨识方法;最后通过仿真实验对方法进行了验证,结果表明该补偿方法可以有效补偿磁梯度张量系统95.9%的载体磁干扰.该方法利用补偿参数对磁梯度张量系统的输出值直接进行磁干扰补偿,从理论上解决了磁梯度张量系统中各个矢量磁力仪载体磁干扰的统一补偿问题.     

适用于超高灵敏磁测量的新型高效磁屏蔽研究

高效磁屏蔽对于超高精度超导量子干涉仪(SQUID)等超高灵敏器件可靠稳定工作至关重要。实践中一般采用多层的高磁导率笨重复合磁屏蔽,或者用小型的轻量屏蔽桶配合差分式平面梯度计完成超高灵敏信号测量。文章作者提出并实现了一种新型的高性能磁屏蔽装置,采用实时的动态磁补偿与高温超导线圈相结合就可以实现。对该装置磁屏蔽效果进行了数值仿真计算,并实际测量了该屏蔽装置的轴向和横向磁场,装置屏蔽因数最高可达80 dB;实验测量发现,新型装置可以同时有效地屏蔽轴向与纵向磁场干扰。     

HT_c rf SQUID用于磁异常移动测量的初步研究

高温超导量子干涉器(HTcSQUID)磁强计的基本特点是噪声低、低频响应好、工作带宽大,在需要微弱磁场测量的许多技术领域发挥着重要作用,将其用于磁异常探测(MAD)是搜索地下/水下磁性目标物的有效技术。本文采用国产射频高温超导量子干涉器(HTcrf SQUID)磁强计,在非磁屏蔽环境中开展了移动状态下的磁异常探测实验,初步结果表明,基于HTcrf SQUID磁强计的MAD技术是一项具有研究和使用价值的新技术。     

Residual field suppression for magnetocardiography measurement inside a thin magnetically shielded room using bi-planar coil

For a magnetocardiography (MCG) system inside a magnetically shielded room (MSR), the residual field should be further suppressed to obtain high-quality MCG signals. In this paper, a compensation system has been developed based on the bi-planar coil and the proportional-integral-derivative (PID) controller. The bi-planar coil, derived from the target-field theory and the Tikhonov regularization method, is utilized to generate magnetic field with high uniformity in the pre-defined target region. And the PID controller is introduced to provide dynamic compensation current for the coil, according to the residual field change monitored by a reference SQUID magnetometer. The measurement results show that the noise suppression ratio (NSR) can reach above 20 dB in the low-frequency range from 0.1 Hz to 50 Hz. The DC component and the fluctuation of the residual field in time-domain can be respectively suppressed to 0 pT and 4 pT, indicating that this proposed compensation method is useful for the MCG measurement.     

A scanning superconducting quantum interference device microscope for room temperature samples

We have constructed a scanning low-T_c superconducting quantum interference device (SQUID) microscope, in which the SQUID is mounted on the lower end of a copper rod and cooled to liquid helium temperature. There is a 65μm thick sapphire window under the SQUID. The sample at room temperature underneath the window can be scanned to produce magnetic images. The microscope has a spatial resolution of 100－150μm and a magnetic field sensitivity of 3－60pT/$\sqrt{Hz}$ in a magnetically unshielded environment. We have used this scanning SQUID microscope to measure various room temperature samples.     

Stabilization of the Polarity of (NdSmDy)(FeCo)B Permanent Magnets for Application in Magnetic Undulators

The temperature dependences of the magnetization of polycrystalline samples of (NdSmDy)(FeCo)B sintered permanent magnets are measured in various magnetic fields by a SQUID magnetometer. Near T = 110 K, the spin-reorientation transition occurs. Bistable magnetic states with two equally possible orientations of the magnetization vector corresponding to different polarities of the permanent magnet are formed in the samples near the spin-reorientation transition. The polarity of the sintered magnets can be stabilized by a small external magnetic field of ～250 Oe. It provides new possibilities for the application of these magnets in cryomagnetic systems such as magnetic undulators.     

基于磁通门和时域数字鉴频的磁场锁定系统

永磁型磁共振仪器的磁体易受温度和其他环境磁场干扰,造成主磁场波动,进而影响仪器测量的重复性和准确性.本文讨论了两种解决磁场波动的锁定方法：一方面,通过磁通门传感器对环境波动引起的瞬态磁场进行高灵敏探测,然后采用现场可编程门阵列进行实时处理并计算磁场补偿量;另一方面,针对环境温度变化引起的缓慢磁场偏移,则采用时域数字鉴频锁场方法,在对锁样品进行射频激发后,将磁共振信号通过混频变换到较低的频率范围,再转换为方波,然后直接送入现场可编程门阵列进行周期测量,并计算磁场补偿量.将两种方法获得的磁场补偿量叠加后,再转换为电流信号驱动安装在磁体上的B₀补偿线圈,并研制了一套磁场锁定系统,以实现对磁场的锁定. 在0.5 T食品快检磁共振分析仪上进行测试验证,结果显示当受到瞬态干扰时,可将磁场稳定在±4 Hz（对应磁场为±0.093 9 μT）范围内,同时也可以精准测量温度造成的磁场偏移,该结果验证了本文磁场锁定方法的可行性.     

An efficient calibration method for SQUID measurement system using three orthogonal Helmholtz coils

For a practical superconducting quantum interference device(SQUID) based measurement system,the Tesla/volt coefficient must be accurately calibrated.In this paper,we propose a highly efficient method of calibrating a SQUID magnetometer system using three orthogonal Helmholtz coils.The Tesla/volt coefficient is regarded as the magnitude of a vector pointing to the normal direction of the pickup coil.By applying magnetic fields through a three-dimensional Helmholtz coil,the Tesla/volt coefficient can be directly calculated from magnetometer responses to the three orthogonally applied magnetic fields.Calibration with alternating current(AC) field is normally used for better signal-to-noise ratio in noisy urban environments and the results are compared with the direct current(DC) calibration to avoid possible effects due to eddy current.In our experiment,a calibration relative error of about 6.89 × 10-4is obtained,and the error is mainly caused by the non-orthogonality of three axes of the Helmholtz coils.The method does not need precise alignment of the magnetometer inside the Helmholtz coil.It can be used for the multichannel magnetometer system calibration effectively and accurately.     

Hall传感器的标定装置及相关标定实验研究

Hall传感器是加速器磁铁磁场测量必不可少的工具之一。为保证Hall传感器能够完成高精度的测量,在实际使用过程中,需要对其进行周期性标定。除此以外,当前加速器磁体的测试任务对Hall传感器的测量范围及工作温度提出了新的需求,因此建立一套标准的大跨度磁场及温度范围的Hall传感器标定系统具有非常重要的现实意义。基于此,搭建了一套完整的高精度Hall传感器标定系统并着重论述了其中的数据采集部分。目前基于该系统开展了一系列0~2.0 T磁场区(HHP-NP、HPCS、DTM151、HE244T等Hall传感器)下的标定尝试,标定曲线采用线性、多项式等不同方式拟合,结果表明拟合结果良好,线性偏离程度(测试结果线性偏离程度越小,精度越好)最优情况下好于0.01%。     

Calculation and error analysis for magnetic field parameters of a standard saddle coil

The calculation and measurement of field parameters and their derivatives play a very important role in designing and constructing saddle-shaped bipolar-magnetic coils [1]. In this article, new distribution function F_n and its derivatives along z-axis are defined, formularized and presented. Calculation and error analysis for the magnetic field parameters of a standard saddle coil are conducted and presented using the formulas. It is shown that the method and formulas can be used in calculating the field parameters, derivatives and the magnetic vector H for the bipolar-magnetic coils.     

SQUID sensor application for small metallic particle detection

High-Tc superconducting quantum interference device (SQUID) is an ultra-sensitive magnetic sensor. Since the performance of the SQUID is improved and stabilized, now it is ready for application. One strong candidate for application is a detection system of magnetic foreign matters in industrial products or beverages. There is a possibility that ultra-small metallic foreign matter has been accidentally mixed with industrial products such as lithium ion batteries. If this happens, the manufacturer of the product suffers a great loss recalling products. The outer dimension of metallic particles less than 100 μm cannot be detected by an X-ray imaging, which is commonly used for the inspection. Ionization of the material is also a big issue for beverages in the case of the X-ray imaging. Therefore a highly sensitive and safety detection system for small foreign matters is required. We developed detection systems based on high-Tc SQUID with a high-performance magnetic shield. We could successfully measure small iron particles of 100 μm on a belt conveyer and stainless steel balls of 300 μm in water. These detection levels were hard to be achieved by a conventional X-ray detection or other methods.