A high sensitivity gradiometric magnetometer

We have investigated the possibility of raising the sensitivity of a magnetometer by using integrated microelectronic magnetic field sensor and gradiometric magnetic flux transforms, made from high temperature superconductors. A sensitivity of 10^–9 T has been achieved experimentally, on cooling the sensors to liquid nitrogen temperatures.Translated from Izmeritel'naya Tekhnika, No. 12, pp. 11–13, December, 1994.     

A vibrating coil magnetometer for quality control in relay manufacturing

Where relay performance is shown to depend on the coercive force of the material used in the cote, accurate but convenient measurement of this material property forms part of production quality control. A magnetometer for this purpose is described and some results presented to show the necessity for such measurements.     

G-M制冷机与振动样品磁强计的耦合试验

为了测量样品在低温(20 K)下的磁性材料的各个参数性能,实验台采用双级G-M制冷机直接冷却气氛室,利用氦气的自然对流传热来达到冷却样品的目的.振动样品磁强计(VSM)与G-M制冷机的耦合实验实现了低温条件下样品的磁性能的测定.介绍该实验台的设计过程和耦合实验结果.     

A superconducting vibrating reed applied to flux-line pinning. I. Theory

A theoretical treatment is given of a superconducting reed clamped at one end and performing flexural vibrations in a homogeneous longitudinal magnetic fieldB _a. When the flux lines are rigidly pinned the reed behaves like an ideal diamagnet whose bending distorts the external field. This generates a magnetic restoring force (line tension) B _a ² which is independent of the reed thicknessd, whereas the mechanical restoring force (stiffness) is d ³. Therefore, the resonance frequency /2 of a thin superconducting reed increases drastically when a fieldB _a is applied, or for a givenB _a, when the reed is cooled below its critical temperatureT _c. With decreasing pinning strength (characterized by Labusch's parameter ) the resonance frequency decreases, ²²– _pin ² where _pin ^{2 –1}, and an attenuation _v ^–2 occurs due to the viscous motion of flux lines. For larger vibration amplitudes an additional, amplitude-dependent damping _h ^–3 occurs due to the hysteretic losses caused by elastic instabilities during flux motion.On leave from Centro Atómico, Bariloche, Argentina.     

A superconducting vibrating reed applied to flux-line pinning. II. Experiment

Measurement has been made of the resonance frequency and amplitude of a superconducting reed performing flexural vibrations as a function of a longitudinal magnetic fieldB _a and temperatureT. Drastic increases in the resonance frequency and damping are found forB _a B _c2(T). The measured increase of the resonance frequency is in agreement with the theoretical results obtained in Part I for the diamagnetic behavior produced by rigidly pinned flux lines. The measured small deviations of the resonance frequency from the rigid-pinning field-dependence make it possible to obtain the elastic pinning force (Labusch's parameter ). For an amorphous Zr₇₀Pd₃₀ sample one obtains 2.8×10¹² B _c2(T)^3.5 N m^–4 T^–3.5 atB _a =0.4B _c2(T). Use of the theory developed in Part I leads to the conclusion that the measured damping is caused by hysteretic losses due to irreversible flux-line displacements rather than by viscous losses of vibrating flux lines.On leave from Centro Atómico, Bariloche, Argentina.     

Time-resolved strain and deformation measurement on the vibrating saxophone reed

Single-reed musical instruments, such as the saxophone, generate sound through a complex interplay between the mechanics of the reed and the hydrodynamic and acoustic pressure in the instrument mouthpiece. To understand this complex mechanism, experimental data are lacking. This paper presents full-field, time-resolved measurements of strain and displacement of a vibrating saxophone reed, measured under mimicked realistic playing conditions. It is found that strain along the length axis of the reed is mainly expansive, except in a small zone near the tip where it becomes compressive when the reed touches the front edge of the mouthpiece. At the instant in the vibration phase where the reed touches the mouthpiece, significant bending and compressive strain appear along the direction perpendicular to the reed axis. Strain magnitudes in both directions are similar, with absolute values of 0.1%. Full-field strain maps reveal subtle characteristics which are not revealed by displacement measurements. Bi-axial bending and strain may be an essential component in reed mechanics, which up till now has been fully neglected in modelling.     

A high field squid magnetometer for studying spin-polarized liquid3He

We present the SQUID magnetometer working in a field of 11T that we recently developed to study transiently polarized liquid³He. Emphasis is on the problems posed by the high magnetic field..     

Fully engineered high performance UHF SQUID magnetometer

A miniaturised UHF (430 MHz) ac-biased SQUID magnetometer operating at 4.2 K has been designed in which the first stage amplification is provided by a liquid helium cooled GaAs FET amplifier. The magnetometer, which uses in situ varactor tuning for the SQUID tank circuit and FETAmp has a signal energy sensitivity (figure of merit) ? 1.3 × 10^?3JHz^?1 ($\text{ 1 × 10}{}^{\mathrm{?5}}\text{Φ}{}_0\text{Hz}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}$ flux sensitivity) in flux lock. The system operates in full flux lock over a frequency range from dc to 5 MHz.     

A fluxgate magnetometer with a metallic glass core

A square-wave excited pulse-height fluxgate circuit is described, using a metallic glass core fluxgate and a minimum amount of active components. High reliability and linearity have been achieved.     

A simple low-frequency thin-film magnetometer

The usual way of plotting hysteresis curves involves the integration ofdB/dt, which has many disadvantages at low frequencies, and calls for complicated and expensive instrumentation. The instrument described here is not as accurate as a good vibrating sample magnetometer, but is very simple, inexpensive, and easy to construct and to use. It involves no integration and therefore its operation is independent of the frequency of the applied magnetic field, and can be readily applied for observing time effects. The magnetic inductionBis measured directly by a Hall probe placed in a 20-mil gap between two pieces of the same thin-film sample mounted in a 4-inch Varian magnet. A second Hall probe measures the applied fieldH, and by subtracting the voltages,B - His plotted vs.Hon anx-yrecorder. With commercial Hall probes, the voltage obtained is sufficient to apply directly to commercialx-yrecorders, without further amplification, even for rather thin films. At 100 mA through each of the probes, theHscale was 10μ V/Oe, while the M scale was 80μV/Mx.     

A gamma-level portable ring-core magnetometer

A four-transistor circuit is described for a battery operated magnetometer that has 0.1γ resolution using 1-in diameter 4-79 or 6-81 Mo-Permalloy tape cores of 20-40 Mx capacity. The center-tapped drive winding also serves as the sense winding, simplifying the sensor assembly. Some signal-to-noise results are presented to illustrate the fairly wide difference that may exist between cores of the same cross section and to demonstrate the advantage of reducing core area.     

大厚度翼型弹性振动中的分叉现象分析

基于SST两方程湍流模型,求解了雷诺平均Navier-Stokes方程获得非定常气动力,耦合翼型弹性振动方程,在时间域内模拟了大厚度对称翼型的振动过程,探讨了大迎角下大厚度翼型的流场和气动弹性的分叉现象。研究发现,在百万雷诺数条件下,厚度大于20%的对称翼型在一定大迎角范围内,会出现气动弹性振动过程的分叉现象,通过跟踪流场的变化发现,引起翼型振动分叉的原因在于翼型分离涡平衡态的转化。     

A magnetoelastic metallic glass low-frequency magnetometer

A complete theoretical analysis is presented of the operation of a magnetoelastic amorphous metal low-frequency magnetic field sensor. This directional magnetometer is a hybrid device consisting of a piezoelectric plate, a field-annealed amorphous metal ribbon, and a viscous fluid, and it exhibits a low-frequency magnetic field detection level of 8.0 pT/√Hz at 1.0 Hz. The sensor may also be configured as a first- and second-order gradiometer. The device analysis focuses on the influence of the constituent materials on the magnetometer performance, identifying potential noise sources and optimal design parameters. This analysis may be applied to a variety of magnetoelastic amorphous metal sensors, e.g. stress, strain, and torque sensors, and is also useful in research concerning fundamental aspects of magnetoelasticity. Experimental data are presented demonstrating the performance of magnetometers constructed with amorphous metal ribbons exhibiting striped and closure domain structures     

大功率纵-弯超声振动系统的研究

本文研究了一种大功率纵－弯昨合模式超声振动系统。该系统由两个纵向大功率夹心式压电超声换能器及一个均匀截面直棒组成。文中给出了该振动系统的具体结构及其共振频率设计方程。根据均匀直棒的纵向及弯曲振动理论，导出了振动系统中纵向及弯曲振动同频共振的条件。     

Magnetic measurements with the rotating-sample magnetometer

The general features common to all rotating-sample magnetic measurements are described, and the governing equations are given. A number of cases of special interest are discussed in some detail: these include the measurement of magnetization as a function of field and temperature and the measurement of rotational hysteresis, various kinds of anisotropy, and magnetostriction. The concept of the rotating sample magnetometer is not new, but the method has greatly increased in practical value because of the development of the lock-in amplifier. The rotating-sample magnetometer method has many points of similarity to the vibrating-sample magnetometer. It is superior to the vibrating-sample magnetometer for some purposes, notably for anisotropy and magnetostriction measurements, and is generally simpler to construct.