Linear Magnetic Sensor Research Articles

Asymmetric magnetoimpedance effect and dipolar interactions of FINEMET/SiO2/FePd composite ribbons

The dipolar interactions are investigated through the asymmetric magneto-impedance in FINEMET/SiO2/FePd composite ribbons. The interface between the hard (FePd layer) phase and soft (FINEMET ribbon) phase is coherent by SiO2 layer in FINEMET/SiO2/FePd composite ribbons, which effectively induces dipolar interactions. The contribution of dipolar interaction to the bias field (H b) by asymmetrical giant magneto-impedance and magnetic properties is analyzed. The results show that H b response decreases with the increase of the SiO2 layer thickness, indicating that the linear region near-zero field can be tuned by the thickness of SiO2 layer. These results allow the GMI ratio (58%) and characteristic frequency (500 kHz) to be optimized. The transverse and longitudinal magnetic domain structures of FINEMET ribbon and FePd film are confirmed, respectively. The composite ribbons with high GMI ratio and low frequency can be applied to linear magnetic sensors.

Adaptive positioning current measurement method for multi-conductor system based on linear magnetic sensor array

As transmission and distribution networks now span a wider region, the difficulty of monitoring lines and the incidence of faults are both increased, which reduces the stability of the power system. During the troubleshooting procedure, quick problem identification, line selection, and placement are essential, and non-contact current measurement can be quite helpful. Its advantages include the capacity to monitor high-frequency current and line space position, both of which contain a range of fault characteristics, as well as a high-frequency band, compact size, low cost, and simple installation. In this paper, we present an adaptive positioning current measurement method for multi-conductor systems based on a linear magnetic sensor array. The method detects the position shifts of individual conductors when their locations are displaced to varying degrees using a novel conductor positioning calculation algorithm. Besides, it automatically adjusts the measurement matrix to provide precise current measurements. In the simulations, three-phase parallel currents with an amplitude of 100 A are analyzed based on the parameters of a 15-meter cup-type tensile tower. During the different displacements of the three conductors, the new method calculates the conductor displacements and the current in real-time. For all the three conductor positions change with the maximum amplitude of 2 m, the average error of all the conductor position measurements is about 0.1 m, and the root mean square error (RMSE) of the currents drops from 34.18A to 3.72A with correction, which proves the effectiveness of the algorithm.

Control of sensitivity in vortex-type magnetic tunnel junction magnetometer sensors by the pinned layer geometry

The tuning of sensitivity and dynamic range in linear magnetic sensors is required in various applications. We demonstrate the control and design of the sensitivity in magnetic tunnel junction (MTJ) sensors with a vortex-type sensing layer. In this work, we develop sensor MTJs with NiFe sensing layers having a vortex magnetic configuration. We demonstrate that by varying the pinned layer size, the sensitivity to magnetic field is tuned linearly. We obtain a high magnetoresistance ratio of 140%, and we demonstrate a controllable sensitivity from 0.85% Oe−1 to 4.43% Oe−1, while keeping the vortex layer fixed in size. We compare our experimental results with micromagnetic simulations. We find that the linear displacement of vortex core by an applied field makes the design of vortex sensors simple. The control of the pinned layer geometry is an effective method to increase the sensitivity, without affecting the vortex state of the sensing layer. Furthermore, we propose that the location of the pinned layer can be used to realize more sensing functionalities from a single sensor.

Systematic investigation of the effect of layer thickness on the linear sensing characteristics of asymmetric structured CoFe/Rh/CoFe/Cu/CoFe fully epitaxial CIP-GMR based magnetic sensors

Giant magnetoresistance (GMR) devices known for their widespread application as magnetic field sensors face challenges owing to their nonlinear resistance response with the magnetic field. Here, we have developed CoFe(3 nm)/Rh(tRh nm)/CoFe(tmidCoFe nm)/bcc Cu(1.6 nm)/CoFe(ttopCoFe nm)/MgO(2 nm) based current in plane (CIP)-GMR devices and demonstrated linear MR curves with tunable characteristics. The MR ratio and saturating magnetic field were tunable between 3.9% and 23.5%, and 0.013 T and 1.5 T. The numerical simulation modeling confirmed biquadratic coupling between the bottom and middle CoFe layers through Rh and antiferromagnetic coupling between the middle and top CoFe layers through a Cu spacer, providing the linear MR. The fine-tuning of thicknesses of the middle and top CoFe layers provides supplementary routes for optimizing the sensitivity and operation field range of the CIP-GMR devices to specific magnetic sensor applications in the low and medium magnetic field range. The above results demonstrate that CIP-GMR devices with the asymmetric structure demonstrated in this study are promising for the next generation linear magnetic sensors.

Effect of Installation Error on Magnetic Characteristic of Linear Magnetic Medium for Recording Accuracy Improvement

The linear magnetic sensor is widely used in a high precision positioning system. In the installation of the linear magnetic system, any curved or uneven surfaces of the magnetic medium would result in significant fluctuations in the final recording accuracy during the position sensing process. This article investigates the effect of medium curvature on recording accuracy through experimental approaches. The results suggest that significant recording accuracy can be affected by the magnetic-flux density distribution over the medium caused by the medium curvature during installation. Through magneto-characteristic analysis, it also suggests that if the medium can be flattened, the recording accuracy can be improved.

Design of Linear Magnetic Position Sensor Used in Permanent Magnet Linear Machine With Consideration of Manufacturing Tolerances

This paper proposes the design of a linear magnetic position sensor (LMPS) to detect the mover position of the permanent magnet linear synchronous machines (PMLSMs). The working principle of the LMPS is based on the well-known Hall-Effect. The Hall-Effect-based design of LMPS is considered because it provides a low cost and relatively harsh environment susceptible alternative for the position detection for long track PMLSM system. The initial design was performed using 3D-finite element analysis and genetic algorithm-based deterministic optimization. Based on the initial model, four LMPS were manufactured and tested under the output constraint of peak flux density > 0.1T and total harmonic distortion < 3%. From the test results, it is concluded that the manufactured LMPS suffered significant deviation in output compared to the simulation model. These anomalies arise because of the manufacturing tolerances. To further improve the design and manufacturing process of the LMPS considering the effect of tolerance, a reliability-based robust design optimization (RBRDO) of the LMPS is proposed. The results of RBRDO confirms its usefulness for the design process of the LMPS in terms of undesired design non-compliance cost and great robustness without sacrificing the accuracy of the output signal.

Ultra-low-pressure sputtering to improve exchange bias and tune linear ranges in spin valves

A series of CoFe/IrMn exchange bilayers was grown by DC-sputtering at different ultra-low argon pressures ranging from 0.008 to 0.1Pa. This pressure range was one to two orders lower than the normal sputtering pressure. Results revealed that the exchange bias increased from 140 to 250Oe in CoFe(10nm)/IrMn (15nm) bilayers of fixed thickness because of the improved crystalline structure and morphological uniformity of films. Since ferromagnetic /antiferromagnetic (FM/AF) bilayers are always used in linear magnetic sensors as detection layers, the varying exchange bias can successfully achieve tunable linear range in a crossed pinning spin valve. The linear range could be adjustable from −80Oe – +80Oe to −150Oe – +150Oe on the basis of giant magnetoresistance responses. Therefore, this method provides a simple method to tune the operating range of magnetic field sensors.

Linearization strategies for high sensitivity magnetoresistive sensors

Ultrasensitive magnetic field sensors envisaged for applications on biomedical imaging require the detection of low-intensity and low-frequency signals. Therefore linear magnetic sensors with enhanced sensitivity low noise levels and improved field detection at low operating frequencies are necessary. Suitable devices can be designed using magnetoresistive sensors, with room temperature operation, adjustable detected field range, CMOS compatibility and cost-effective production. The advent of spintronics set the path to the technological revolution boosted by the storage industry, in particular by the development of read heads using magnetoresistive devices. New multilayered structures were engineered to yield devices with linear output. We present a detailed study of the key factors influencing MR sensor performance (materials, geometries and layout strategies) with focus on different linearization strategies available. Furthermore strategies to improve sensor detection levels are also addressed with best reported values of ∼40 pT/√Hz at 30 Hz, representing a step forward the low field detection at room temperature.

Sensors array technique for monitoring aluminum alloy spot welding

In this paper, the sensors array technique is applied to the quality detection of aluminum alloy spot welding. The sensors array has three forms, i.e., linear magnetic sensors array, annular magnetic sensors array and cross magnetic sensors array. An algorithm based on principal component analysis is proposed to extract the signal eigenvalues. The three types of magnetic sensors array are used in the experiment of monitoring the signal. After the eigenvalues are extracted, they are used to build a relationship with the nugget information. The result shows that when the distance between the core of the array and the pole is 60 mm, the arrays work best. In this case, when the eigenvalues’ range of the linear array is 0.006 5–0.015 1, the quality of the spots is eligible. To the annular and cross array, when the ranges are 0.082 9–0.131 6 and 0.085 1–0.098 2 respectively, the nugget quality is eligible.

Practical Electromagnetics (review of "Electromagnetic Foundations of Electrical Engineering" by J.A. Brandao Faria; 2008) [Book/Software reviews

The text begins with a description of 20 projects, which help the student understand and apply Maxwell's equations. These projects fit into roughly three categories: sensor problems such as disc conductivity, linear variable differential transformers, dc transducers, and magnetic sensors; power problems, such as power delivery analysis, motor analysis, and power line communication; and higher frequency problems such as directional couplers, baluns, transmission line transformers, and loudspeaker crossover networks. Each chapter also includes homework problems that extend the concepts presented and give students a feel for the numeric values of typical applications. The chapters begin with a brief overview of Maxwell's equations and vectors. The rest of the book is split into the three areas of static fields, slowly varying fields, and rapidly time-varying fields. The book lives up to its name by providing a very useful treatment of Maxwell's equations, which should help students understand why they need to learn field theory and how it impacts their jobs and daily life.

Off‐diagonal magneto‐impedance in amorphous microwires with diameter 6–10 μm and application to linear magnetic sensors

AbstractOff‐diagonal component of magneto‐impedance tensor with pulse excitation is very promising for high sensitivity magnetic field sensor applications. We report novel results on studies of off‐diagonal MI effect and magnetic properties in amorphous glass‐coated microwires with nearly‐zero and negative magnetostriction constant and metallic nucleus diameter ranging between 6 μm and 10 μm. Off‐diagonal impedance tensor ζφz (Hex) has been investigated in ultra‐thin amorphous glass‐coated microwires in as‐cast state and after Joule heating treatment. (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Design and analysis of an orientation estimation system using coplanar gyro-free inertial measurement unit and magnetic sensors

Conventionally, there are two ways to determine the orientation angles of an object. One uses 3-axis accelerometers and 3-axis magnetic sensors, while the other one uses additional 3-axis gyroscopes to achieve a higher sensing accuracy than the first one. This paper presents a novel orientation estimation system that uses seven single-axis linear accelerometers and 3-axis magnetic sensors. These seven linear accelerometers are deployed in a way to form a “coplanar” gyro-free inertial measurement unit (IMU). As such, they can perform the integrated measurements of gravity force and angular velocity for the subsequent sensor fusion algorithms. With the information of the angular velocity, this novel design achieves a comparable performance with the one that includes 3-axis gyroscopes. The analysis of the system observability indicates that the angular velocity measurements can improve the observability of the angle estimation under certain circumstances. This result suggests the possibility of using fewer sensors in an orientation estimation system. Simulation results indicate that the proposed design achieve a sensing accuracy of 0.11°, 0.09°, and 0.2°for the roll, pitch, and yaw angle; this leads to the improvement of 540%, 632%, and 754% over the one that does not include the measurement of the angular velocity.

A magnetic field-induced current-modulating opamp based on CMOS differential Tesla–Volt multiplier cell for MAGFET 1/ f noise reduction

A magnetic field-induced current-modulating opamp (MCMOP) based on the CMOS differential Tesla–Volt multiplier (TVM) cell for magnetic field-effect transistor (MAGFET) 1/ f noise reduction is reported. It consists of a CMOS differential TVM cell made of a pair of identical MAGFETs, a fully differential opamp, and a set of chopper-stabilization switches. Due to the modulation effect of the input voltage on the magnetic field-induced current imbalance, the MCMOP is utilized as a linear magnetic sensor not only to amplify the magnetic signal, but also to chop and stabilize the signal, so as to suppress the low frequency noise in the MAGFETs themselves. By introducing the MCMOP, the magnetic noise level of the magneto-opamp (MOP) consisting of the same differential opamp and the same single MAGFET is reduced from 160 to 25 μT/Hz 1/2 at 1 Hz. This is a 16 dB improvement of the magnetic resolution.

Off-Diagonal Magnetoimpedance in NiFe–Au–NiFe Layered Film and Its Application to Linear Magnetic Sensors

We have measured the field dependence of the off-diagonal impedance in the megahertz frequency range for a NiFe-Au-NiFe layered film using a helical microcoil. The film and the coil were deposited by means of radio-frequency sputtering, and a transverse anisotropy in magnetic layers was established by applying a dc magnetic field during the deposition and by postproduction annealing. The film had 5 mm length, 50 /spl mu/m width, and 1.5 /spl mu/m total thickness. The helical microcoil had 23 turns with a 50 /spl mu/m turn width. We applied high-frequency excitation by means of the coil current and measured the induced voltage across the film stripe. This voltage response is directly proportional to the off-diagonal component of the total impedance tensor. We found that the plots of the real and imaginary parts of the off-diagonal impedance, as functions of the applied dc magnetic field, are antisymmetrical with respect to the field direction. The dc bias current through the film plays an important role: without the bias current, the measured signal is very small and irregular. The field antisymmetry demonstrated by the off-diagonal impedance can be utilized in highly sensitive and linear magnetic sensors, and we discuss the principles of operation of such sensors here.

Off-Diagonal Impedance in Amorphous Wires and Its Application to Linear Magnetic Sensors

We investigated the magnetic-field behavior of the off-diagonal impedance in Co-based amorphous wires under sinusoidal (50 MHz) and pulsed (5 ns rise time) current excitations. For comparison, we measured the field characteristics of the diagonal impedance as well. In general, when an alternating current is applied to a magnetic wire, the voltage signal is generated not only across the wire but also in a pickup coil wound on it. These voltages are related to the diagonal and off-diagonal impedances, respectively. We demonstrate that these impedances have a different behavior as functions of axial magnetic field: the diagonal impedance is symmetrical, whereas the off-diagonal one is antisymmetrical with a near-linear portion within a certain field interval. For the off-diagonal response, the dc bias current is necessary to eliminate circular domains. In the case of the sinusoidal excitation without a dc bias current, the off-diagonal response is very small and irregular. In contrast, the pulsed excitation, combining both high- and low-frequency harmonics, produces the off-diagonal voltage response without additional biasing. This behavior is ideal for a practical sensor circuit design. We discuss the principles of operation of a linear magnetic sensor based on a complementary metal-oxide-semiconductor transistor circuit.

Asymmetrical magnetoimpedance in as-cast CoFeSiB amorphous wires due to ac bias

Asymmetrical giant magnetoimpedance (AGMI), which utilizes a high frequency bias field hb, is realized in a Co-based amorphous wire having a circumferential anisotropy in the outer region. No asymmetry in the dc magnetic configuration is needed in this case. AGMI is discussed in terms of the surface impedance tensor, demonstrating that the effect of hb is related to the role of the off-diagonal component of the impedance in the voltage response measured across the wire. This effect is important for developing autobiased linear magnetic sensors. Using two oppositely biased wires, a near-linear voltage output (±4 mV) is obtained in the range of ±5 Oe for the sensed dc field at a frequency of 8 MHz.

Universal magneto-operational amplifier (MOP)

Abstract A new class of integrated magnetic sensors, a magneto-operational amplifier (MOP) is presented. The MOP is a universal magnetic sensor which can be used for many purposes. The principle of the MOP is a feedback amplifier similar to the usual operational amplifier which is widely used for realizing any analog function. In order to make use of the advantages of an operational amplifier, the MOP has similar components: a differential amplifier stage which includes a magnetic detector; a sufficiently large gain amplifier; and an output stage. By changing external feedback elements, the MOP can realize various magnetic operations, such as a linear magnetic sensor, a magnetic switch, a magnetic filter, etc. In this paper experimental results of some applications of the MOP are given.