EIT信号对CPT磁力仪弱磁测量性能的影响

针对现有磁力仪测量数百纳特斯拉弱磁场存在精度低和便携性差等问题,提出一种通过压窄CPT磁力仪EIT信号线宽来实现弱磁场测量的方法.该方法是根据EIT信号磁场测量仿真模型,采用相敏检波二阶微分信号获得磁力仪灵敏度系数,并根据最佳灵敏度系数分析得出EIT信号分离条件及其线宽对弱磁场测量性能的影响.仿真和试验结果表明:具有窄...     

可实现三维位置检测的球型电机磁场分析

本文提出了一种直流永磁球型电机整体结构的设计理念.为了减小球型电机运动环节产生的摩擦力,针对球型电机结构特点,设计了基于十字轴结构的运动装置,并结合编码器以及倾角传感器提出了在球型电机内部可实现三位置检测的设计思路.为了得到球型电机的力矩输出与线圈激励的关系,对球型电机进行了磁场分析,利用麦克斯韦定律建立标量磁位的拉普拉斯方程,求解方程并利用边界条件得到空间磁场分布表达式,其结果可为进一步的研究和实验方案设计提供借鉴和参考.     

High-sensitivity giant magneto-inductive magnetometer characterization implemented with a low-frequency magnetic noise-reduction technique

The Giant Magneto-Inductive (GMI) effect in amorphous magnetic and conducting wires is analyzed using the concepts and words of electronics engineering to show the way high-sensitivity GMI magnetometers may be designed. Starting from a simple modeling of the magneto-impedance, direct and field-locked loop magnetometers are discussed, together with the implementation of a low-frequency noise-reduction technique that makes good use of a basic modulating method. It allows the removal of a part of the 1/f noise in the magnetometer. The unmodulated magnetometer characteristics are the following: bandwidth higher than 100 kHz and white noise level lower than 7 pT//spl radic/Hz above 40 KHz. Similarly, the main auxiliary modulated magnetometer characteristics are as follows: bandwidth of 4.8 kHz and white noise level lower than 60 pT//spl radic/Hz above 3 Hz. The slew rate in both cases is limited by the electronics to 5 mT/s. The dynamic of these magnetometers is about /spl plusmn/25 /spl mu/T, which corresponds to more than 120 dB in 1 Hz bandwidth above 1 Hz.     

A two-axis magnetometer using a single magnetic tunnel junction

Based on a qualitative study of the Stoner-Wohlfarth model, we point out that driving a magnetic tunnel junction (MTJ) with an alternative two-dimensional magnetic field allows to measure simultaneously two components of an external magnetic field. Only one single MTJ without a pinning layer is needed to measure both components of a magnetic field parallel to the junction plane. The response of the magnetometer does not depend on the resistance of the junction or the amplitude of its variations. A prototype has been manufactured and encouraging experimental results are presented. Sensitivities higher than 500 V/T and a noise level of 2 /spl mu/T//spl radic/Hz are reported.     

Low temperature growth of carbon nanotubes in a magnetic field

We report on the growth of carbon nanotubes on a glass substrate at a low temperature of 450 °C by plasma-enhanced chemical vapor deposition in the presence of a magnetic field. The growth of carbon nanotubes can be realized at 450 °C only when a magnetic field is applied to the substrate. Carbon nanotubes cannot be grown in the absence of a magnetic field at the same temperature. An NH₃ plasma pretreatment significantly improved the uniformity of the grain size of the Ni catalyst under the magnetic field. The enhancement in the growth of CNTs at low temperature can be attributed to the magnetic moment pre-alignment of the ferromagnetic catalyst film under high magnetic field. A high emission current density of 20 mA/cm² was obtained at 6 V/μm and a stable emission current was observed. This method permits the growth of carbon nanotubes directly on glass substrate at much more reliable low temperatures for the fabrication of high-density field emitter arrays.     

Three-dimensional magnetic field measurement of a modifiedthin-film magnetic head for vertical recording by means ofLorentz-tomography

The method of Lorentz tomography with an electron beam as a microprobe, combined with an analytical reconstruction procedure, has been successfully adapted to thin-film heads for vertical recording. It is noted that the measured results can be used as a basis for adjusting the magnetic parameters of the thin-film head to achieve good agreement with corresponding FEM or BEM (finite element or boundary element method) calculations. It is concluded that Lorentz tomography can be used as an important tool in the design of thin-film magnetic heads     

Transient magnetic field of a strip line with a magnetic keeper

The transient magnetic field of a strip line in a memory device with a finite conductivity ground plane and a finite permeability magnetic keeper is studied. The driving source consists of a line current or a uniform current sheet. The waveform of the current is assumed to be piecewise linear. Laplace and Fourier transform methods are used to obtain the field.     

Overhauser磁力仪低噪声信号处理技术

针对磁力仪输出信号信噪比低的问题,同时为给Overhauser磁力仪的研制提供参考依据,提出一种低噪声信号处理技术。首先根据质子旋进信号(FID)特点,建立系统噪声模型,分析探头电阻热噪声和放大器等效输入噪声对测量造成的影响,提出LC谐振方案和低噪声放大电路以提高系统信噪比并通过实验测试仪器噪声水平。最后,将所研制的磁力仪与商用磁力仪进行对比测试,实验表明:提出的信号处理技术能有效降低系统噪声,FID信号信噪比36 d B,研制的Overhauser磁力仪磁场测量精度0.2 n T,性能接近商用仪器水平,证明其在磁场测量中的有效性。     

An undulator with a composite magnetic field

A new type of undulator greatly improved in tunability as compared with a usual undulator, is proposed. The undulator has a composite magnetic field which is a linear superposition of two sinusoidally varying fields with different spatial periods. The wavelength can be changed by varying the field strength of the longer-period component while keeping that of the shorter-period component at the highest possible value. Numerical calculations of the spectral brightness were carried out. The proper ratios between the two spatial periods were found to be 3:1, 5:1 and 7:1.     

Application of zeeman modulation faraday spectroscopy to the measurement of a magnetic field

We report what is to our knowledge the first possibility of a NO(2) molecular magnetometer based on the Zeeman modulation magnetic rotation spectroscopic (ZM MRS) technique and the magneto-optic activity of NO(2). The linear dependence of the ZM MRS signal intensity on the modulating magnetic field is theoretically analyzed and experimentally measured. The design concept of the magnetometer and its main features are discussed.     

Force model identification for magnetic suspension systems viamagnetic field measurement

In magnetic suspension analysis, a simplified model of the current-to-distance relationship is not sufficient to design an optimal control. Due to the nonlinearity of the magnetic field, an accurate model, which is a function of the suspended object, suspension distance, core material, and operation conditions, is difficult to obtain. An improved force-model-identification method for magnetic suspension systems establishes reliable parameters for describing the magnetic field characteristics. The parameter for each test sample can be calculated under the specified operating conditions after some magnetic field measurements. The results lead to effective controller design for magnetic suspension systems     

Spin-glass with short-range interaction in a magnetic field

The properties of spin-glasses with nonmagnetic defects are considered in the vicinity of the transition point in a finite magnetic field, by means of a percolational approach. It is shown that the dependence of the magnetic specific heat C(h) = C(h)–C(o) or of the magnetic susceptibility M(h)/h on field and temperature allows us to define the distribution function of finite clusters with respect to their size. In addition to general formulas resulting from the scaling laws, more detailed formulas are obtained for two model distributions: (a) the Bethe lattice distribution, (b) a special model distribution with arbitrary indices.     

Quantum magnetometer for stabilization of the neutron magnetic resonance

The design of a quantum magnetometer on cesium vapor is described. The device is intended for stabilization of the neutron resonance in experiments devoted to the search for the electric dipole moment (EDM) of neutron. The choice of this magnetometer type is justified and its potential sensitivity is estimated.     

Increasing the accuracy of measurement of magnetic field intensity in permeameters

Conclusion If the extrapolative transducer is well designed, the amplitude error can be reduced to 2–3% and the angular error to 30–40. The extrapolative transducer can be constructed without difficulty; it may be used both in the laboratory and in industry.Some difficulty in designing the extrapolative transducer arises from the need for experimental H(l) curves. For permeameters with the sample inside the magnetizing coil, however, the method of automatic linear extrapolation can be used even without these curves; as a result, measurement errors will be substantially decreased.If especially high accuracy is required, the method of nonlinear automatic extrapolation with three transducers can be used. In this case, it is absolutely necessary to have a large number of experimental H(l) curves.Translated from Izmeritel'naya Tekhnika, No. 9, pp. 64–66, September, 1968.