Type Of Magnetic Field Sensor Research Articles

Relatively Low‐Frequency Magnetic Field Detection System Using Metglas/PZT‐5B Sensor

The magnetoelectric (ME) sensor is a new and promising type of magnetic field sensor with ultrahigh sensitivity. However, there are few reports on the research of real‐time measurement system which can promote its practical application. Herein, a novel real‐time measuring approach for weak AC magnetic fields at relatively low frequency is proposed using Metglas/PZT‐5B ME sensors. The system mainly consists of an oscilloscope, a signal generator, and a program developed with LabVIEW programming. Real‐time measurement of relatively low‐frequency magnetic fields has been achieved by using frequency upconversion methods, simultaneously displaying the frequency and magnitude of the magnetic field. As a result, the real‐time measurement system is able to detect a weak AC magnetic field as low as 0.1 nT@1 Hz, which is promising to push the ME sensor to practical application.

Low-noise inverse magnetoelectric magnetic field sensor

In the development of any type of magnetic field sensor based on magnetic films, special consideration must be given to the magnetic layer component. The presented work investigates the use of scalable flux closing magnetostrictive multilayers for inverse magnetoelectric sensors. In such a type of magnetic field sensor, highly sensitive AC and DC field detection relies on strong excitation of the incorporated magnetic layers by piezoelectrically driven cantilever oscillation at mechanical resonances. The provoked periodic flux change is influenced by the magnetic field to be measured and is picked up by a coil, which generates the measured output. The multilayered inverse magnetoelectric sensor is investigated with regard to linearity, noise behavior, and detection limit of DC and AC signals. A significant advancement for inverse magnetoelectric thin film sensors is demonstrated in this study. Using exchange bias stabilized magnetic multilayers with flux closure structures, detection limits are improved by an order of magnitude to less than 8 pT/Hz1/2 at 10 Hz and 18 pT/Hz1/2 at DC.

Optimising the sensitivity of optically-pumped magnetometer magnetoencephalography to gamma band electrophysiological activity

Abstract The measurement of electrophysiology is of critical importance to our understanding of brain function. However, current non-invasive measurements—electroencephalography (EEG) and magnetoencephalography (MEG)—have limited sensitivity, particularly compared to invasive recordings. Optically-Pumped Magnetometers (OPMs) are a new type of magnetic field sensor which ostensibly promise MEG systems with higher sensitivity; however, the noise floor of current OPMs remains high compared to cryogenic instrumentation and this limits the achievable signal-to-noise ratio of OPM-MEG recordings. Here, we investigate how sensor array design affects sensitivity, and whether judicious sensor placement could compensate for the higher noise floor. Through theoretical analyses, simulations, and experiments, we use a beamformer framework to show that increasing the total signal measured by an OPM array—either by increasing the number of sensors and channels, or by optimising the placement of those sensors—affords a linearly proportional increase in signal-to-noise ratio (SNR) following beamformer reconstruction. Our experimental measurements confirm this finding, showing that by changing sensor locations in a 90-channel array, we could increase the SNR of visual gamma oscillations from 4.8 to 10.5. Using a 180-channel optimised OPM-array, we capture broadband gamma oscillations induced by a naturalistic visual paradigm, with an SNR of 3; a value that compares favourably to similar measures made using conventional MEG. Our findings show how an OPM-MEG array can be optimised to measure brain electrophysiology with the highest possible sensitivity. This is important for the design of future OPM-based instrumentation.

Comparative study of geometry effect for magnetic field sensor based on multi-mode optical fiber

Experimentally and numerically, measurements have been presented for new type of magnetic field sensor based on combining multimode optical fiber and magnetic ferrofluid. The ferrofluid was filled in a capillary tube around a 15 mm uncladded region of optical fiber. Three uncladded geometries cylindrical, D-shaped and 2D-shaped, have been investigated to study the effect of geometry on sensing performance. Results illustrate that the geometry of the optical fiber has a significant impact on the evanescent waves which propagate from the sensing region into the ferrofluid tube. The obtained results expressed that among all studied cases, the D-shaped configuration has the best performance designing an optical fiber-based magnetic field sensor, since the best measured sensor features such as linearity, sensitivity, response time and recovery time for this case are R2 = 0.9865, 0.01795 μW/mT, 3.15 s and 0.26 s, respectively.

Use of Different Types of Magnetic Field Sensors in Diagnosing the State of Ferromagnetic Elements Based on Residual Magnetic Field Measurements.

The early identification of micro-defects in ferromagnetic elements such as steel wire ropes significantly impacts structures' in-service reliability and safety. This work investigated the possibility of detecting mechanically introduced discontinuities using different magnetic sensors without magnetization of the tested object with a strong external field. This is called the passive magnetic testing method, and it is becoming increasingly popular. This research used differential sensors (measuring differences in field values at the nanotesla level) and absolute sensors (enabling the measurement of the magnetic field vector module or its components at the microtesla level). Each measurement result obtained from the sensors allowed for detecting discontinuities in the line. The problem to be solved is the quantitative identification of changes in the metallic cross-section of a rope.

Synthesis of bulk crystals and thin films of the ferromagnetic MnSb

High-temperature ferromagnets are widely used on a practical level. Based on them, magnetic memory for computers and various types of magnetic field sensors are created. Therefore, bulk ingots and thin-film samples of ferromagnet manganese antimonide (MnSb) with a high Curie point are of great interest, both from the practical and fundamental sides. Manganese antimonide films are obtained in hybrid structures using molecular-beam epitaxy. The thickness of the films does not exceed tens of nanometers. Despite their high sensitivity to magnetic fields, their small thickness prevents them from being used as magnetic field sensors. The aim of this work was to synthesise thick bulk ingots of manganese antimonide crystalsand films with a thickness of ~ 400 nm on sitall and silicon substrates. MnSb crystals were synthesised using the vacuum-ampoule method and identified using XRD, DTA, and microstructural analysis. The results of studies of bulk samples indicated the presence of an insignificant amount of antimony in additionto the MnSb phase. According to the DTA thermogram of the MnSb alloy, a small endothermic effect was observed at 572 °C, which corresponds to the melting of the eutectic on the part of antimony in the Mn-Sb system. Such composition, according to previous studies, guaranteed the production of manganese antimonide with the maximum Curie temperature. A study of the magnetic properties showed that the synthesised MnSb crystals were a soft ferromagnet with the Curie point ~ 587 K. Thin MnSb films were obtained by an original method using separate sequential deposition in a high vacuum of the Mnand Sb metals with their subsequent annealing. To optimise the process of obtaining films with stoichiometric composition, the dependences of the thickness of metal films on the parameters of the deposition process were calculated. The temperature range of annealing at which the metals interact with the formation of ferromagnetic MnSb films was established, the films were identified, and their electrical and magnetic properties were measured

Ultrasensitive Magnetic Field Sensors for Biomedical Applications.

The development of magnetic field sensors for biomedical applications primarily focuses on equivalent magnetic noise reduction or overall design improvement in order to make them smaller and cheaper while keeping the required values of a limit of detection. One of the cutting-edge topics today is the use of magnetic field sensors for applications such as magnetocardiography, magnetotomography, magnetomyography, magnetoneurography, or their application in point-of-care devices. This introductory review focuses on modern magnetic field sensors suitable for biomedicine applications from a physical point of view and provides an overview of recent studies in this field. Types of magnetic field sensors include direct current superconducting quantum interference devices, search coil, fluxgate, magnetoelectric, giant magneto-impedance, anisotropic/giant/tunneling magnetoresistance, optically pumped, cavity optomechanical, Hall effect, magnetoelastic, spin wave interferometry, and those based on the behavior of nitrogen-vacancy centers in the atomic lattice of diamond.

Effect of Amorphous Wire Core Diameter on the Noise of an Orthogonal Fluxgate

Cobalt-rich amorphous wires have been extensively used as a core of many types of magnetic field sensors, notably of a fundamental model orthogonal fluxgates, because they allow us to manufacture sensors with very low noise. However, commercial wires are available only in one diameter, namely, $125~\mu \text{m}$ ; therefore, most of the literature is always referred to this diameter. In this paper, we investigated the effects of different diameters versus the noise of the sensor. Our purpose is to understand that if there is a room for improvement of noise by producing amorphous wires with different diameters. We casted wires with (Co0.94Fe0.06)72.5Si12.5B15 composition and a diameter spanning from 80 to $220~\mu \text{m}$ , and we discovered that the wires show crystalline structure starting from $200~\mu \text{m}$ . This means we can increase the diameter to values higher than $125~\mu \text{m}$ and still achieve an amorphous structure, considering the upper limit of $200~\mu \text{m}$ . Then, we studied the noise of the sensors based on wires with three different diameters, namely, 80, 120, and $175~\mu \text{m}$ . Because the diameter affects the demagnetizing factor, we also changed the length of the wire in the range from 40 to 120 mm. We discovered that increasing the diameter of the wire always decreases the noise, regardless of the demagnetizing effect, which indicates larger cross section of the wire is a predominant factor.

Noise study of magnetic field sensors based on magnetic tunnel junctions

Low frequency noise has been studied for two types of magnetic field sensors based on magnetic tunnel junctions (MTJ). The first structure, composed of a few large MTJs, is designed for low noise applications; the second one, composed of hundreds of small MTJs, is designed for general purposes. At low frequency, both structures exhibit 1/f noise, but with very different amplitudes. The sensors for general purposes show a much higher noise level compared to the low-noise sensors. However, the sensitivity of the low noise sensors is much smaller compared to the other ones. Thus, the limit of detection, defined as the ratio of noise and sensitivity, turns out to be roughly the same for both technologies. Using the advantages of each sensor could help to design a sensor with an improved limit of detection.

Influence of the wire length on the of coil-less fluxgate properties of amorphous (Co 0.94Fe 0.06) 72.5Si 12.5B 15 wire

In this study, the coil-less fluxgate (CF) properties of amorphous (Co 0.94Fe 0.06) 72.5Si 12.5B 15 wire, current-annealed at 450 mA dc for 15 min under 500 MPa tensile stress and 16.5 π rad/m torsional strain, have been investigated. A CF is a new type of magnetic-field sensor without a coil. The dependence of the second harmonic of the output voltage from the wire ends, U wire, on an external magnetic field in the longitudinal direction, H z, for the frequency range 5–50 kHz and various values of the ac current I wire is presented. The results show that the sensitivity of the CF depends on the frequency and I wire. Even at a very low frequency (5 kHz), a pronounced variation in the behaviour of the CF sensor is observed. A 60-mm long sensor has a maximum sensitivity of 78.5 V/T in a ±400 A/m linear operating range at 57 mA driving current. The sensitivity decreases but the linear operating range increases with decreasing wire length. A miniaturized 2.2-mm CF sensor shows ∼0.4 V/T sensitivity in a ±3000 A/m linear operating range at 53 mA driving current and 50 kHz ac driving-current frequency.

Coil-less fluxgate effect in (Co 0.94Fe 0.06) 72.5Si 12.5B 15 amorphous wires

In this study, the coil-less fluxgate properties of the as-cast and annealed amorphous wires with the composition (Co 0.94Fe 0.06) 72.5Si 12.5B 15 were investigated. As its name implies, a coil-less fluxgate is a new type of magnetic-field sensor without a coil. When the wire is periodically saturated in a magnetic field in the circumferential direction with a 30 kHz, 62 mA driving current under a 16.5 π rad/m torsional strain, there is a linear variation in the second harmonic of the voltage from the wire ends as a function of the applied external DC magnetic field along the length of the wire. Current–stress annealing of each sample improved the sensitivity of the coil-less fluxgate sensor. This is the first time that it has been shown that a linear change in the output of the coil-less fluxgate sensor can be obtained using torsion annealed wire without the necessity of twisting the wire during measurement. We showed that the linear operating range of the sensor can be increased by increasing the demagnetization factor in the sensing direction, so that the coil-less fluxgate sensor can be miniaturised just by reducing the wire length.

Coil-less fluxgate effect in amorphous wires

In this study, the coil-less fluxgate properties of as-received amorphous microwires with the compositions (Co 0.94Fe 0.06) 72.5Si 12.5B 15, Fe 77.5Si 7.5B 15 and Co 72.5Si 12.5B 15 have been investigated. As its name implies, a coil-less fluxgate is a new type of magnetic field sensor without a coil. When the (Co 0.94Fe 0.06) 72.5Si 12.5B 15 wire is magnetically saturated in the circumferential direction with a 30 kHz and 48 mA driving current and under the effect of 33 π rad/m torsional strain, there is a linear variation in the second harmonic of the voltage from wire ends, U wire, as a function of the applied external dc magnetic field, H z, along the wire length. The slope of the second harmonic versus H z curve changes in opposite directions as the direction of torsional strain changes from the positive to the negative direction. Coil-less fluxgate effects in as-received Fe 77.5Si 7.5B 15 and Co 72.5Si 12.5B 15 wires have also been investigated. A very small change in the second harmonic of voltage U wire is observed in Fe 77.5Si 7.5B 15 wire, with some small hysteresis.

Two-terminal ultrahigh frequency carrier type thin-film magnetic sensor using impedance matching lines

This article reports on output and band characteristics of the two-terminal ultrahigh frequency (UHF) carrier type magnetic field sensor, which is based on impedance change due to magnetic field dependent permeability, and a magnetic field is detected as an amplitude modulation of a UHF carrier voltage. Two types of transmission line configurations (type-A and type-B) are proposed to make a two-terminal sensor rather than the four terminals of the conventional sensor operating on this principle, because the two-terminal sensor is more advantageous in terms of designing and fabricating of the sensor element and the transmission lines than the four-terminal sensor. In the type-A, a half-wave impedance matching line is added between the element and the carrier power supplying points. Also, in the type-B, a carrier power is supplied on the quarter-wave matching line located between the element and the load. The type-A sensor exhibits a lower output and a much narrower 3 dB-bandwidth of a few tens of MHz than the four-terminal sensor. In contrast, a higher output than that in the four-terminal sensor and a 3 dB-bandwidth of ∼100 MHz are confirmed in the type-B sensor by experiments and calculations.

Magnetic field sensor based on asymmetric inverse Wiedemann effect

A new type of magnetic field sensor is introduced. The sensor is based on asymmetric inverse Wiedemann effect in amorphous Co-rich ribbon with helical magnetic anisotropy induced by torque strain. The characterization of the stand-alone sensor and further the sensor with developed electronics for feedback operation was accomplished. Linear response of the sensor without feedback appears in narrow magnetic field range of ±15 μT. For the feedback-loop connection the dynamic range has been enlarged up to ±120 μT. The linearity error FSR in the feedback connection is lower than 0.1% in the range of ±75 μT. The results show that the tested prototype achieves better stability than GMI sensors. The temperature offset drift, measured in temperature range of −20 °C to +80 °C, is lower than 5 nT/K or −28 nT/K for the sensor operated with laboratory instruments only or with the developed simple electronics, respectively. For the magnetometer with sensor operating in the feedback loop the RMS noise of 80 pT was achieved in the frequency range from 30 mHz to 10 Hz.

電歪／磁歪複合振動子による磁界センサ

Magnetic field sensors such as flux gate and magnetoimpedance elements have been sonsidered to be useful tools for indicating the direction of a terrestrial field. Downsizing of these sensors is essential for then to be used in highly integrated electronic devices such as mobile phones and computers. We developed a new type of magnetic field sensor that has a great advantage in this respect. The sensor has a composite structure cosisting of a mechanical resonator with a high Q factor and magnetostrictive layers. With the high sensitivity of the magnetostrictive layers to external fields, the resonance frequency of the resonator is expected to be shifted by the ΔE effect. Since the shift in frequency is independent of the resonator size, appreciable downsizing of the sensor is possible. In this paper we describe our initial experiments to verify that the composite resonator is sufficiently sensitive to detect terrestrial fields. The results show that it has a sensitivity of 40 Hz/Oe for a resonator with a resonance frequency of 120 kHz.

Electro-mechanical resonant magnetic field sensor

We describe a new type of magnetic field sensor, which is termed as an Electro-Mechanical Resonant Sensor (EMRS). The key part of this sensor is a small conductive elastic element with low damping rate and therefore, a high Q fundamental mode of frequency f 1. An AC current is driven through the elastic element which, in the presence of a magnetic field, causes an AC force on the element. When the frequency of the AC current matches the resonant frequency of the element, maximum vibration of the element occurs and this can be measured precisely by optical means. We have built and tested a model sensor of this type by using for the elastic element, a length of copper wire of diameter 0.030 mm formed into a loop shape. The wire motion was measured using a light-emitting diode photo-transistor assembly. This sensor demonstrated a sensitivity better than 0.001 G for an applied magnetic field of ∼1 G and a good selectivity for the magnetic field direction. The sensitivity can be easily improved by a factor of ∼10–100 by a more sensitive measurement of the elastic element motion and by having the element in vacuum to reduce the drag force.

Micro-size magnetic strip for ultra high frequency carrier type magnetic field sensor

Magnetic strips aimed at high-frequency carrier-type magnetic field sensors were studied by using various strip widths in a carrier frequency range of gigahertz to obtain conditions for large impedance change. The impedance change was attributed to a magnetic resonance effect. It was shown that DC magnetic field regions at which the maximum change of impedance occur for wide strip elements were closely related to the applied carrier frequencies as expected theoretically. The DC magnetic field for the maximum sensitivity decreased as strips become narrow.

Magnetic field measurements with a novel surface micromachined magnetic-field sensor

The surface micromachining process of Robert Bosch GmbH has been used to fabricate a novel type of magnetic-field sensor. The Lorentz force, caused by the interaction of a current and an external magnetic field in a suspended surface micromachined conducting beam, laterally displaces the suspended structure. The displacement of the structure is converted into a capacitance change by comb-electrodes, which form a differential capacitor. An appropriate electronic circuitry measures the magnetic field by quantifying the displacement of the conducting beam. In order to increase sensitivity to magnetic fields, the magnitude of the deflection is increased by resonant operation in a vacuum ambient. The sensor obtains its vacuum environment by encapsulation with a new wafer bonding process. Prototype sensors with resonant frequencies in the range around 1300 Hz show Q-factors above 30. With these samples, relative magnetic sensitivities of 900 000 (V/A/spl middot/T) with a detection limit in the sub /spl mu/T-range are reported.

ＹＩＧ単結晶を用いた光応用磁界センサの検討

A new type of magnetic field sensor based on creation of the Faraday effect by rotation magnetization of YIG single crystals is described. The influences of both the Cotton-Mouton effect and cubic anisotropies on the sensor characteristics are also discussed. The linearity error of the sensor output was very small in external magnetic fields ranging of 0.02-200 Oe. The temperature dependence of the sensor output was obtained with an accuracy of ± 1 % between 20 °C and 120 °C.

Frequency-modulation type magnetic field sensor using transmission-line magnetic device

A novel frequency-modulation type magnetic field sensor composed of transmission-line magnetic device and phase-shift type oscillator has been developed. The transmission line magnetic device consists of soft magnetic layers, dielectric layers and conductor lines, which operate as a distributed constant circuit. The transmission characteristics such as voltage-gain and phase are influenced by permeability change due to the external magnetic field applied to the magnetic layer. A transmission-line device developed by using Co based amorphous ribbon was used in the feedback circuit of a phase-shift type oscillator. The oscillation frequency of the oscillator increased with increasing magnetic field.