基于迈斯纳效应的二阶梯度计不平衡度调节方法

基于超导量子干涉器的磁场梯度计可在无磁屏蔽的噪声环境中测得高信噪比信号,可检测pT量级的心脏磁场。通过推导超导环与二阶梯度计天线的互感耦合关系,建立三维静磁场仿真模型,模拟得出超导环对梯度计不平衡度的调节范围为-0.73～0.78。平衡后的梯度计可有效抑制0.031 Hz～10 Hz频率范围内环境噪声的谐波分量。梯度计在无磁屏蔽环境中测量得到42.64 dB高信噪比的心磁信号,验证了超导环平衡方法的可靠性。     

新型自动化磁灵敏度检测系统硬件设计的研究

目前由福建省计量科学研究主导编写的国际标准"ISO16063-33"振动与冲击传感器的性能评定中已经正式发布,它解决振动冲击传感器的磁灵敏度的测量方法。本文根据新国际标准ISO16063-33《振动与冲击传感器校准方法—磁灵敏度的测试》的要求,介绍一种新型自动化磁灵敏度检定系统的硬件设计。其采用亥姆霍兹线圈作为系统磁场发生器,用步进电机驱动线圈旋转,以预应力阻尼弹簧减振器作为整个装置的减振器。最后通过实验与数据分析,系统可满足振动与冲击传感器的磁灵敏度检定的要求。     

电磁兼容试验中亥姆霍兹线圈的设计及验证

主要研究电磁兼容中亥姆霍兹线圈低频磁场抗扰度试验技术,给出了亥姆霍兹线圈的设计研制思路。根据国际标准和实际使用情况的要求,对其结构、性能及均匀性等分别进行分析、研究和验证,并对实际使用的磁场强度根据具体标准进行了举例验证。研究成果能为电磁兼容低频磁场的测试方法与测试线圈的研制提供技术指导。     

非零横截面亥姆霍兹线圈的中心轴向磁场

以圆形亥姆霍兹线圈为例,通过数学建模将线圈横截面分割成微单元网格,分析了亥姆霍兹线圈横截面宽度和厚度对中心轴向磁场的不同影响,研究结论对线圈的绕制方式具有指导作用。     

超磁致伸缩微位移致动器的研究

 基于超磁致伸缩材料的磁致伸缩特性设计了一种用于微位移驱动的致动器．分析了致动器工作磁场的组成，计算了线圈的工作电流，并以此为依据设计了稳流电源．分析结果表明，设计的稳流电源满足工作要求；线圈提供的工作磁场能够保证超磁致伸缩棒工作在线性区域。     

载流圆线圈平面内任意一点磁场的测试与理论分析

借助于DH4501B型亥姆霍兹线圈磁场实验仪对载流园线圈平面内任意一点的磁场进行测试;并在球坐标系下,利用磁感应强度的计算公式毕奥-萨伐尔定律结合园电流磁场的对称性推导出全空间磁感应强度的计算公式,给出载流园线圈平面内任意一点的数值解;所得数值解与实验测定的结果相比较,二者吻合的相当理想,验证了实验的正确性。     

载流圆线圈平面内任意一点磁场的测试与理论分析

借助于DH4501B型亥姆霍兹线圈磁场实验仪对载流园线圈平面内任意一点的磁场进行测试;并在球坐标系下,利用磁感应强度的计算公式毕奥-萨伐尔定律结合园电流磁场的对称性推导出全空间磁感应强度的计算公式,给出载流园线圈平面内任意一点的数值解;所得数值解与实验测定的结果相比较,二者吻合的相当理想,验证了实验的正确性.     

一种高准确度的标准磁场装置

采用宽频比较仪的电流检测技术,设计了高稳定度和高准确度的电流源,与亥姆霍兹线圈组成了高准确度标准磁场装置,从而实现对磁强计的校准。标准磁场经标定后,上位机软件能自动显示磁通密度,作为标准磁场使用。     

磁灵敏度测试装置的电机驱动技术的研究

在新的国际标准ISO/16063-33"振动与冲击传感器磁灵感度测试方法"中,要求测试装置中的传感器静止,磁场旋转。测试装置用电机带动磁线圈使磁场旋转,而传统的步进电机驱动技术由于运转噪音大,会使传感器的测量的不确定度增加。本文介绍一种恒频斩波恒总流尖峰的五相混合式步进电机驱动技术,通过软硬件设计使磁场旋转更加平稳,提高传感器磁灵敏度的测量精度。     

M型电磁传感器检测裂纹的仿真分析及参数优化

传统的脉冲涡流传感器采用圆柱式结构,其磁场大部分在空气中传播,造成能量的损失,因此该文设计M型电磁传感器在单线圈传感器上增加一个U型磁轭来提高磁场的利用率。通过ANSYS仿真软件对M型传感器与单线圈传感器检测不同深度的裂纹进行仿真对比,结果证明M型传感器的灵敏度高,信号强,同时对于传感器激励源参数进行优化。     

A high homogeneous field superconducting magnet for Argonne polarized proton target

We have designed and built a superconducting magnet for a large polarized proton target. The magnet consists of a pair of thick Helmholtz coils. Each Helmholtz coil consists of 9 step-subcoils balancing the ampere-turns around the Helmholtz line, thus providing an optimum for field uniformity without the help of Correction coils. This magnet generates 25 kilogausses with field uniformity one part in 10,000 over more than 5 cm diameter spherical target volume. It was designed to allow a large warm bore of 34.5 cm with axial aperture of 96° and between the Helmholtz pair, a wide warm separation of 12.7 cm with transverse aperture of 23°, thus allowing large accessibility to the proton target and for the scattering detectors in high energy scattering experiments.     

A transducer made up of fluxgate sensors for testing wire ropedefects

Based on analyzing the magnetic leakage feature of wire rope defects, the longitudinal resolved vector B_ot of the defect leakage field is taken for the object to be tested. In order to detect the weak magnetic leakage field, a fluxgate sensor of single core and single winding is developed. Using the fluxgate, a new kind of transducer for testing defects of wire rope has been designed. The structure and interface circuit of the transducer are studied. The experimental results of detecting the LF and LMA defects of the wire rope are presented     

多相绕组电子束偏转扫描装置仿真分析

为了提高带电粒子束通道内磁感应强度均匀度,分析了磁偏转扫描装置的线圈匝数密度分布对磁场的影响,表明扫描绕组的匝数密度沿横截面圆周按正弦规律分布,那么横截面内磁感应强度呈均匀分布。工程实际中绕组分布不可能严格按照正弦分布,为弱化绕组量化分布效应,从而提出了采用大于两相的多相绕组结构,建立了几何模型和有限元模型,并利用Maxwell软件对不同绕组相数的磁偏转扫描装置进行电磁场仿真,并制作实物进行测量,测量结果与仿真结果基本一致,表明相数越多偏转扫描装置通道内的磁场强度均匀度越高。     

动态脑电地形图调节的经穴磁刺激系统设计

针对现有电、磁刺激系统参数调节存在的不足,设计了一种利用动态脑电地形图反馈调节的经穴磁刺激系统．该系统磁刺激发生模块基于DDS技术,利用单片机编程产生刺激波形、幅度、频率可调的刺激信号,功率放大后,经喇叭状刺激线圈产生磁场,作用于人体穴位．脑电仪在线检测大脑的脑电信号,经计算机数据处理,实时显示大脑a波动态脑电地形图,并反馈调节磁刺激强度、刺激频率和刺激波形．结果表明,该系统可以优化经穴磁刺激的输入方式,改善大脑a波能量,促进脑瘫病人神经系统恢复和康复训练．     

Pulsed Eddy Current Testing of Carbon Steel Pipes’ Wall-thinning Through Insulation and Cladding

Pulsed eddy current testing of wall-thinning through cladding and insulation was studied from both theoretical and experimental aspects. The analytical solution was derived for a simplified four-layered structure and was used to conduct simulations to ascertain the feasibility of this method. A pulsed eddy current testing probe consisting of a circular excitation coil and an AMR-sensor-embedded differential detector was fabricated to measure the time-varying magnetic field signals on the axisymmetric excitation coil??s axis. The measurement system was able to measure magnetic field down to a few hundred micro-Gausses in an unshielded environment. Simulation and test results showed that over a certain time after turning off the excitation current the magnetic field signal??s decay behavior is almost merely relevant to the pipe??s wall thickness. Future development of a carbon steel pipe??s wall-thinning can be evaluated by using decay coefficients estimated from previously obtained test data.     

Advances of Barkhausen Emission Measurement

Barkhausen emission (BE) is a well-known phenomenon used in nondestructive testing techniques of ferromagnetic materials. The weaknesses of methods based on BE are related to the difficulties of ensuring measurement reproducibility because of the influence of the specimen on the measurement channel. In this paper, we propose a method of sensor calibration prior to measurement. To implement the calibration, a BE sensor is equipped with an additional calibration coil. The electrical pulse induced in the calibration coil is then used to reconstruct measured magnetic field pulses at the specimen surface.     

Characterization of a magnetic field sensor based on torquemeasuring [for fusion diagnostics application]

A sensor for low-frequency measurements of the magnetic field is presented in the paper. It is based on measurements of an electromagnetic torque. An output directly proportional to the unknown magnetic field is produced. This method has the main advantage of avoiding the drift present in the integration of signals from inductive sensors. The design and construction criteria, aiming at an uncertainty of a few milliteslas in field measuring, are described. The analysis of the sensor linearity is presented in the paper together with the test rig, able to guarantee reproducible conditions. The dynamic behavior of the torque-based sensor is considered. It is studied either on the basis of the coil and load cell characteristics or analyzing the response to an applied known electromagnetic torque     

A Remote Query Pressure Sensor Based on Magnetic Higher Order Harmonic Fields

The design and fabrication of a wireless, passive pressure sensor based on the change in magnetic higher order harmonic fields is described. The sensor was made of an airtight pressure chamber with two opposite membranes: a rigid membrane attached to a magnetically soft ferromagnetic strip (sensing element) and a flexible membrane attached to a permanent magnetic strip (biasing element). The flexible membrane of the chamber deflected with changing pressure, thus varying the separation distance between the sensing and biasing elements. The change in separation distance in turn altered the biasing field experienced by the sensing element, varying the pattern of its magnetic higher order harmonic fields allowing remote pressure monitoring through a magnetic coil. In this work, different materials were used to fabricate the flexible membranes for sensors of different dynamic ranges. Experimental results showed the shifts in magnetic higher order harmonic fields were linear for all sensors, but with different sensitivity depending on the elasticity of the flexible membrane. The novelty of this sensor is its wireless, passive nature, which is ideal for applications where wire connections are prohibited. In addition, the simple sensor design reduces cost, allowing disposable use. Potential applications of such a sensor technology include long-term structural monitoring (concrete, asphalt) and in vivo pressure monitoring inside the human body.      

CNG储气井井筒腐蚀的漏磁检测探索

为了对CNG储气井安全隐患进行有效检测,根据漏磁检测原理,应用ANSYS对CNG储气井井筒漏磁磁场分布进行模拟.仿真结果表明,在合适的磁化参数下可以有效地检测出腐蚀状况.在此基础上,采用交变磁化方式,以锰锌铁氧体作为磁化材料,用霍尔元件阵列检测漏磁信号,加以计算机组成漏磁检测系统.实验结果表明.该系统能够检测出井筒的缺陷,但是精度还需进一步提高.