Factors affecting the sensitivity of gamma-level ring-core magnetometers

A theoretical and experimental analysis has been made of the geometrical and magnetic factors affecting the sensitivity of the ring-core magnetometer first introduced by Geyger in 1961. Using a drive-to-pickup transfer function derived from an assumed dynamic hysteresis loop and a given dc input signal, the second-harmonic output voltage was derived for both current-source and voltage-source driving conditions. Results of the analysis, which were confirmed by experiment, show the following. 1) When a single, diametrically wound (solenoid-type) pickup winding is used with a ring-core sensor, simultaneous minimization of both fundamental and second-harmonic feedthrough can be achieved by a simple rotational adjustment. This optimization is possible only with a circular core. 2) Sensitivity can be increased by increasing frequency, number of pickup turns, dynamic differential permeability, cross-sectional area, and effective sensor length, and by decreasing the dc initial permeability (μ0). 3) The dominant factor affecting the sensitivity is the demagnetizing termmu_{0}K = mu_{0}l^{-1.72} (4A/pi)^{0.86}, which determines the entrance attenuation of the dc signal to be measured. Highest sensitivity is obtained whenmu_{0}Kis small, which requires a low initial permeability, since a large dimensional ratiol/A^{1/2}is usually not attainable. When the demagnetizing term is not small, the sensitivity advantages of the other factors are negated by the input signal attenuation. Power considerations show that increasing sensitivity by raising area, length, or frequency results in increased power consumption. However, increasing sensitivity by using a pickup coil with a larger number of turns or by a sensor core with lower initial permeability can be achieved without additional power.     

基于逆磁致伸缩的索力传感器原理与影响因素研究

基于逆磁致伸缩效应,建立钢缆索索力传感器理论模型,分析了施加在缆索材料上的力信号(外力和应变)与磁信号(磁感应强度、磁场强度)之间的耦合关系.针对一种环式结构的索力传感器,对索力测量原理做了详细推导,可通过检测感应线圈的感应电压反映材料所受外力.传感器输出感应电压与空气间隙尺寸、外部激励磁场下的材料磁导率、激励磁场变化、加载外力变化等因素有关,重点分析了激励磁场变化和外力变化对传感器输出的影响.当外力是缓变力,可通过检测感应积分电压求得外力;当外力是交变力,直接通过感应电压求得外力;最后通过对磁场变化和外力变化影响分别进行了仿真,结果与理论分析基本一致,表明所建立的索力传感器理论模型可行.     

A High-Resolution MEMS Piezoelectric Strain Sensor for Structural Vibration Detection

This paper presents the modeling, fabrication, and testing of a high-performance dynamic strain sensor. Using microelectromechanical systems (MEMS) technology, ZnO piezoelectric microsensors are directly fabricated on silicon and steel substrates. The sensors are intended to be used as point sensors for vibration sensing without putting an extra burden on the host structures. A model that incorporates piezoelectric effects into an RC circuit, representing the sensor architecture, is developed to describe the voltage output characteristics of the piezoelectric microsensors. It is shown that the sensitivity of microplanar piezoelectric sensors that utilize the $e_{31}$ effect is linearly proportional to sensor thickness but unrelated to sensor area. Sensor characterization was performed on a cantilever beam cut from a fabricated silicon wafer. The experimental data indicate that the overall sensor and circuit system is capable of resolving better than 40.3 nanostrain time domain signal at frequencies above 2 kHz. The corresponding noise floor is lower than 200 femto-strain per root hertz and the sensitivity, defined as the sensor voltage output over strain input, is calculated to be 340 V/$varepsilon$ . Micro ZnO piezoelectric sensors fabricated on steel hard disk drive suspensions also show excellent results. The sensor not only has a better signal-to-noise ratio but also detects more vibration information than the combination of two laser-doppler-vibrometer measurements in different directions.      

Eddy current turbocharger blade speed detection

A commercially available magnetic reluctance sensor is used to determine the angular velocity of turbocharger impeller blades from outside the aluminum housing. Eddy currents are induced in the aluminum blades by blade motion through the magnetic field projected by an externally mounted Samarium-Cobalt permanent magnet. Experiments show that secondary eddy currents and associated ac magnetic fields generated in the aluminum housing provide the prime excitation for a sensor coil located outside the housing. The coil output voltage spectrum shows a strongly peaked structure with peak locations at multiples of the blade passage frequency in the range 1-10 kHz. The sensor output signal decreases with increasing frequency above 2 kHz because of increasingly effective attenuation by the housing. Test results show that a circuit designed to track the blade signal gives an analog voltage output proportional to the frequency of blade passage over the operating range of the Cummins VT-903 and Detroit 8V-71T turbocharged diesel engines. Suggestions are made for the design of a sensor appropriate for both magnetic reluctance and eddy current sensing applications.     

脉冲磁场传感器的时域标定

针对脉冲磁场测量的要求，对传感器的时域标定问题进行了研究，组建基于高压脉冲源，ＴＥＭ传输室，数字存贮示波器及计算机的时域标定系统，提出了基于输出误差模型的时域定数据处理方法，利用该模型可方便地获得的传感器的灵敏度，转折频率等参数，成功地利用所建立的误差修正模型对传感器造成的测量失真进行了恢复。     

On a new principle of a smart multisensor based on magnetic effects

In this paper, a new principle of a smart sensor is proposed, based on three different magnetic effects or operational modes, using the same sensor topology, which consists of a magnetic wire as sensing core, two coils as excitation or search means, and two electric contacts at the ends of the magnetic wire. The magnetic effects currently involved are magnetostriction, magneto-impedance and re-entrant flux reversal. Operating the sensor in these three different modes separately and sequentially, one can obtain the response of the sensor related to three different physical quantities, such as stress, temperature, and field. This paper refers to the first experimental results based on this principle, thus initiating the research work in this field. It has been experimentally observed that the total output of the sensor in each one of the three different modes is equal to the product of each corresponding physical quantity function concerned, provided that a given threshold of the ambient field and preloaded stress is used to bias the sensing element. Therefore, the three unknown parameters of stress, temperature, and field can be determined from a 3/spl times/3 matrix equation. Other magnetic effects may also be involved. Furthermore, other physical quantities may also be determined, such as position, pressure, load, etc.     

A computer-aided design procedure for flyback step-up DC-to-DC converters

A flyback step-up dc-to-dc power converter is modeled utilizing a linear magnetic core, transistor switch, diode, filter capacitance, and load resistance. Assuming constant voltage drops across the semiconductor elements when conducting, the circuit is analyzed to obtain an equation for the required number of turns, subject to the constraints of specified output voltage, operating frequency, maximum winding factor, maximum and minimum input voltage, output power, and flux density. Using an interpretive language, a program has been written to run on a minicomputer which searches a data base of magnetic core characteristics obtained from commercial core catalogs and prints a list of windable cores. In an evaluation section of the program, a core from the windable core list is selected by the designer and the losses in the various elements, along with maximum and minimum transistor current are computed. Another program is used to display on a computer graphics device the loci of maximum and minimum flux density in a selected core as functions of input voltage and output power in a perspective plot. Converter circuits derived from this computer-aided design procedure when tested in the laboratory have yielded data in close agreement with that predicted by the program.     

一种便携式角速度传感器

角速度是旋转系统或传动装置进行状态监测的重要参数。设计了一种新结构、无旋转部件的便携式瞬时角速度传感器。该传感器的工作原理是永磁磁钢建立恒定磁通,被测旋转装置的转动部件切割该恒定磁场后形成涡流,涡流产生的磁场与传感器的霍尔元件相互作用产生霍尔电势,该霍尔电势的幅值与被测旋转装置的角速度成正比。根据磁路的基本定律推导出传感器的输出特性,并对输出特性进行了实际的测定,结果表明:传感器的灵敏度为16.8mV·s/rad,非线性误差为1.24%。     

Robot gripper control system using PVDF piezoelectric sensors

A novel robot gripper control system is presented that uses PVDF (polyvinylidene fluoride) piezoelectric sensors to damp exerted force actively. By monitoring the current developed by the PVDF sensor, an output proportional to the rate of change of the force exerted by the gripper is obtained. The signals from the PVDF sensor and strain-gauge force sensor are arranged in a proportional and derivative control system for the control of force. The control system was tested on an instrumented Rhino XR-1 manipulator hand. The capabilities of the control system are analyzed and are verified experimentally. The results for this particular gripper indicate that the additional sensory feedback can decrease the force step response rise time by 88% while maintaining a monotonic zero-overshoot response. The inclusion of the rate feedback increases the damping ratio of the dominant poles while maintaining the step response rise time.     

一种新型霍尔式角度传感器的研究

设计了一种新型霍尔式角度传感器,详细阐述了传感器的机械结构和工作原理,根据磁路定律和霍尔效应推导了传感器的输出特性,表明传感器工作时能够直接输出与旋转角度成正比的霍尔电势。由于霍尔传感器的输出采用差动式连接,不存在零点剩余电压。建立了传感器的有限元模型,对其工作时的磁场情况进行了仿真,验证了传感器测量原理的正确性。最后对传感器样机进行了特性测定,实验结果表明传感器的灵敏度约为105 mV/(°),线性误差约为0.12%,重复性误差约为0.19%。     

Seismic Velocity Sensor With an Internal Sky-Hook Damping Feedback Loop

This paper presents a new seismic velocity sensor with an internal feedback control loop. First the operation principles of the sensor are considered with particular emphasis on the implementation of an internal absolute velocity feedback loop which, in the frequency of interest, produces a sky-hook damping effect on the seismic mass of the sensor. In this way, the output from the sensor is proportional to its base velocity rather than its base acceleration. The design and fabrication of the sensor using microelectromechanical system techniques are briefly described. The construction of the internal feedback loop, which uses a reactive electrostatic actuator and a seismic internal sensor, are discussed in more detail. Finally the results of experimental tests are presented, which highlight that: a) in the frequency of interest, the output signal of the sensor is proportional to its base velocity; b) the fundamental resonance of the seismic sensor is attenuated by the active damping effect produced by the internal feedback control loop, and c) above this fundamental resonance, the response rolls off at a rate of 3 dB per decade and lags by 90$^{circ }$ instead of the 180$^{circ}$ phase lag of a standard seismic accelerometer sensor.      

生物传感用巨磁电阻传感器及其磁珠检测性能

本文采用直流磁控溅射沉积了结构为NiFeCo(缓冲层)/[Cu/NiFeCo]×10/ Ta,巨磁电阻(GMR)值为9.8%的多层膜,利用微细加工技术制备了基于此GMR多层膜的生物传感器,GMR电阻线条的线宽分别为3μm和5μm.测试了单个GMR传感器的特性,并将该传感器件和外接可调电阻组成惠斯通电桥,采用该GMR电桥对Dynal公司的MyOne磁珠进行了检测.分别测试了施加变化垂直磁场和施加间歇式恒定垂直磁场时GMR电桥信号对传感器表面覆盖磁珠的响应,研究了GMR电桥信号和磁珠覆盖率的关系.选用器件电阻线宽分别为3μm和5μm的传感器测试了器件线宽对传感器灵敏度的影响.结果表明,GMR传感器能够检测到磁珠的存在,最低能检测的磁珠数量约100个,且GMR电桥信号与磁珠覆盖率基本成正比,器件的灵敏度与传感器线宽基本成反比.     

非接触磁耦合光纤光栅位移传感器

研发了一种基于光纤Bragg光栅（fiber Bragg grating,FBG）技术的非接触磁耦合位移传感器．两块扁圆柱型硬磁铁通过软铁连接起来,形成一U型传感探头．该U型探头与被测物形成一闭合磁路,实现间隙与磁耦合力的转换,再通过一平面薄板结构将磁耦合力转变为光纤FBG的轴向应变．通过理论和实验详细地分析研究了上述两个关键技术环节．研究表明：该非接触位移传感器为一非线性传感器,非线性主要是由于磁耦合力与间隙的平方成反比这一传感器固有特性以及漏磁,特别是漏磁随间隙增加而变大造成的该非线性传感器的数据处理结果为：随机不确定度为0．23％;回程误差为0．376％;传感器综合误差为±0.606％     

20～100kHz铁基微晶电感材料Fe—Co—Si—B—C的研究

研究了合金元素对恒导磁微晶合金 Fe_(71)Co_7Si_9B_(13)的高频损耗及恒导磁特性的影响。发现碳(C)的加入能大大降低该合金的高频损耗。随着 C 含量的增加,高频损耗 P_(2/20k)单调下降,当 C 含量大于4(at)%后,P_(2/20k)不再随着 C 含量的增加而降低。该合金的等温 P_(2/20k～t_a)曲线(t_a 为保温时间)呈“U”型,属典型的微晶化效应降低损耗方式。x 射线衍射结果证明该合金的组织为 bcc 结构的α-Fe。认为 C 对损耗的影响机制不同于普通晶态合金中的李希特(Richter)效应。C 是易偏析元素,在微晶化热处理时,碳的偏析为细小α-Fe 的形成,提供了大量晶核,使合金的组织细化,从而细化了磁畴,降低了异常涡流损耗,使高频损耗降低并具有较高的动态导磁率。横向磁场热处理后该合金可成为优良的恒导磁电感材料     

A displacement sensor for nonmetallic hydraulic cylinders

A sensor was developed to provide signals proportional to the position of the rod in a hydraulic cylinder. The sensor has a coil winding in the shell of the cylinder. The sensor operates by sensing the change in the coil impedance as the rod moves in the cylinder. This paper describes the construction of the cylinder and the sensor, and the performance evaluation of the sensor. Several different materials were placed in the rod and tested. For the cylinder tested, an aluminum core provided the highest precision, about 0.38 /spl Omega/. The full-scale output was 19.90 /spl Omega/ over a stroke length of 193 mm. The linearity was about 1.64% of full-scale. Shielding from electromagnetic interference can improve the precision dramatically. A ferrite-cored rod assembly yielded a much greater full-scale output, 1300 /spl Omega/, but exhibited significant hysteresis.     

Calculation of Skin Depths and Eddy-Current Power Losses for Magnetic Position Sensors

1. IntroductionIn a quasi-stationary magnetic field, eddy-currelltfrom an alternating-current excitation induces secondary currents and fields between magnetic material and position sensor. The skin depths and eddycurreat losses are also induced in a conductor whenan alternating external magnetic field is applied tothe conductor[1]. For a magnetic position sensort ifthe position of the moving sensor is given, the waveform of the output voltage induced by eddy-currentcan be used as an index to …     

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     

The microfluxgate magnetic sensor having closed magnetic path

This paper presents a microfluxgate magnetic sensor in printed circuit board (PCB). In order to observe the effect of the closed magnetic path, the magnetic cores of rectangular ring and two bars were each fabricated. Each fluxgate sensor consists of five PCB stack layers including one layer magnetic core and four layers of excitation and pickup coils. The center layer as a magnetic core is made of a Co-based amorphous magnetic ribbon with extremely high dc permeability of /spl sim/100,000. Four outer layers as excitation and pickup coils have a planar solenoid structure and are made of copper foil. In the case of the fluxgate sensor having the rectangular ring-shaped core, excellent linear response over the range of -100 to +100 /spl mu/T is obtained with 780-V/T sensitivity at an excitation sine wave of 3 V/sub P-P/ and 360 kHz. The chip size of the fabricated sensing element is 7.3/spl times/5.7 mm/sup 2/. The very low power consumption of /spl sim/8 mW was measured.     

基于霍尔效应的感应式瞬时旋转角速度传感器

设计了一种基于霍尔效应的感应式瞬时旋转角速度传感器,主要包括定子铁心及绕组、霍尔元件和永磁转子3大部分,且永磁转子的磁通在空间气隙中呈正弦规律分布。传感器工作时,永磁转子与被测旋转设备同轴连接,永磁转子的磁场与定子绕组匝链耦合,绕组中产生与瞬时旋转角速度呈对应关系的感应电动势。由于定子绕组与霍尔元件的控制端直接连接,则霍尔元件中存在电流,在永磁转子磁场的作用下,霍尔元件产生与瞬时旋转角速度成正比的直流霍尔电势。推导了传感器的输出特性,并对传感器进行了特性测定实验,结果表明其灵敏度系数约为203 mV/(rad·s^-1),线性误差约为0.5%。     

Circular arrays of magnetic sensors for current measurement

A single solid-state magnetic sensor can measure a current flowing in a conductor in a noncontact way. In order to improve the accuracy of the measuring system and to reduce the crosstalk effects of other magnetic fields, circular arrays of magnetic sensors can be fabricated, still preserving low costs. In those kind of arrays, the sensing elements are assembled on a circle around the conductor. The sum of the sensor output signals is an approximation of Ampere's circulation. A quite satisfactory crosstalk effects reduction can be thus achieved. More sophisticated algorithms that combine sensor output signals are necessary in order to further reduce crosstalk effects. This paper presents an algorithm that is able to calculate the intensity of a dc current flowing in a rectangular bus-bar, in the presence of crosstalk fields