Detection Of Low-frequency Magnetic Fields Research Articles

Low-Frequency Magnetic Field Detection Using Magnetoelectric Sensor With Optimized Metglas Layers by Frequency Modulation

It is an important engineering challenge to detect a weak magnetic field <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${H}_{AC}$ </tex-math></inline-formula> at low frequencies (1-100 Hz) due to large noise. In this work, a magnetoelectric (ME) sensor using single-crystal quartz material as the piezoelectric phase and optimized magnetostrictive layers has been presented to sense the low-frequency magnetic field signals. Firstly, the ME response properties of the bulk Metglas/quartz/Metglas laminate sensor were studied and a high ME coefficient of 3038 V/(cm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\cdot $ </tex-math></inline-formula> Oe) has been attained in its electromechanical resonance frequency. With frequency modulation technique, which a magnetic low-frequency signal can be transferred to around resonance frequency of the sensor, the proposed sensor was used to detect the low frequency magnetic field signals under zero bias conditions. It is experimentally found that the absolute resolution with respect to a 1 Hz magnetic field can be decreased as low as 44 pT ± 1.41 pT with 20 layers of Metglas. More importantly, the ME coefficients with different layers under zero bias and the effect of Metglas layers on the limit of the detection at 1 Hz also have been investigated. The results show that the limit of the detection at 1 Hz can be decreased to 10 pT ± 0.32 pT with 14 layers of Metglas which indicates an enhancement by 4.4 times in comparison with 20 layers. This simple bulk Metglas/quartz/Metglas laminate sensor with optimized layers has a great potential to be used for low-frequency bio-magnetic signals measurement at room temperature.

Novel Magnetic Field Modulation Concept Using Multiferroic Heterostructure for Magnetoresistive Sensors

The low frequency magnetic field detection ability of magnetoresistive (MR)sensor is seriously affected by 1/f noise. At present, the method to suppress the influence of low frequency noise is mainly to modulate the measured magnetic field by mechanical resonance. In this paper, a novel modulation concept employing a magnetoelectric coupling effect is proposed. A design method of modulation structure based on an equivalent magnetic circuit model (EMCM) and a single domain model of in-plane moment was established. An EMCM was established to examine the relationship between the permeability of flux modulation film (FMF) and modulation efficiency, which was further verified through a finite element simulation model (FESM). Then, the permeability modulated by the voltage of a ferroelectric/ferromagnetic (FE/FM) multiferroic heterostructure was theoretically studied. Combining these studies, the modulation structure and the material were further optimized, and a FeSiBPC/PMN-PT sample was prepared. Experimental results show that the actual magnetic susceptibility modulation ability of FeSiBPC/PMN-PT reached 150 times, and is in good agreement with the theoretical prediction. A theoretical modulation efficiency higher than 73% driven by a voltage of 10 V in FeSiBPC/PMN-PT can be obtained. These studies show a new concept for magnetoelectric coupling application, and establish a new method for magnetic field modulation with a multiferroic heterostructure.

A magnetoelectric flux gate: new approach for weak DC magnetic field detection

The magnetic flux gate sensors based on Faraday’s Law of Induction are widely used for DC or extremely low frequency magnetic field detection. Recently, as the fast development of multiferroics and magnetoelectric (ME) composite materials, a new technology based on ME coupling effect is emerging for potential devices application. Here, we report a magnetoelectric flux gate sensor (MEFGS) for weak DC magnetic field detection for the first time, which works on a similar magnetic flux gate principle, but based on ME coupling effect. The proposed MEFGS has a shuttle-shaped configuration made of amorphous FeBSi alloy (Metglas) serving as both magnetic and magnetostrictive cores for producing a closed-loop high-frequency magnetic flux and also a longitudinal vibration, and one pair of embedded piezoelectric PMN-PT fibers ([011]-oriented Pb(Mg,Nb)O3-PbTiO3 single crystal) serving as ME flux gate in a differential mode for detecting magnetic anomaly. In this way, the relative change in output signal of the MEFGS under an applied DC magnetic anomaly of 1 nT was greatly enhanced by a factor of 4 to 5 in comparison with the previous reports. The proposed ME flux gate shows a great potential for magnetic anomaly detections, such as magnetic navigation, magnetic based medical diagnosis, etc.

Dual-Peak Self-Biased Magnetoelectric Couplings in Tb&lt;sub&gt;0.3&lt;/sub&gt;Dy&lt;sub&gt;0.7&lt;/sub&gt;Fe&lt;sub&gt;1.92&lt;/sub&gt;/Pb(Zr,Ti)O&lt;sub&gt;3&lt;/sub&gt;/SmFe&lt;sub&gt;2&lt;/sub&gt; Symmetrical Multiferroic Heterostructures

A trilayer magnetoelectric (ME) composite consisting of a soft piezoelectric PZT-5H plate, a magnetostrictive Terfenol-D plate, and a rare-earth ferromagnetic Samfenol plate is fabricated and characterized for studies on the multipeak self-biased ME effects. In this symmetrical magnetostrictive/piezoelectric heterostructure, high shear-stress transfer to excite the bending resonance mode is induced by the magnetostrictive materials with opposite signs of magnetostriction, and a large internal anisotropic field is provided by a Samfenol plate due to its distinct ferromagnetism and magnetostriction. Consequently, hysteretic behavior can be simultaneously observed at both bending vibration resonance and transverse vibration resonance. Results demonstrate that the nonzero remnant ME coefficients of 0.7 and 2.23 V/Oe occur at bending frequency of 42.2 kHz and transverse frequency of 108.3 kHz, respectively, and the estimates of resonance frequencies are in agreement with the data. These characteristics provide the promise of this dual-peak self-biased symmetrical multiferroic heterostructure for low frequency magnetic field detection without the benefit of additional permanent magnets.

Low-frequency magnetic field detection for metal sensing

Low-frequency magnetic field detection for metal sensing

Low-frequency fiber optic magnetic field sensors

This paper presents the principle of fiber optic sensors for the detection of low-frequency magnetic fields. Magnetostrictive materials such as Tertenol-D and Metglas® are used as the sensing elements in a Mach-Zehnder interferometer configuration. Low-frequency fiber optic magnetometers are constructed and tested in both planar and cylindrical geometries. These magnetometers consist of an optical fiber bonded to a magnetostrictive metallic glass ribbon in either strip or cylindrical geometry. The characteristics of specific sensor designs are also discussed and suggestions to improve magnetic field sensor fabrication are given. From a number of experiments, the best sensitivity achieved is with sandwich geometries under the application of a dc biasing field. The performance of these sensors increases with improved mechanical design and thermal annealing of the metallic glass ribbon. Much of the reported work to date has been concerned with the response of the system in the frequency range of 0.1 to 10 kHz. The work presented here, however, deals with the response of an interferometric system using Metglas® in the lower frequency range of 10 to 50 Hz.

A high-sensitivity magnetoresistive magnetometer

A high-sensitivity, small-size, low-power-consumption, broad-bandwidth magnetometer has been built in which a magnetoresistive element is located adjacent to a gap between two thin-film flux concentrators. The concentrators magnify the sensed component of magnetic field 20-fold while simultaneously shielding orthogonal fields by more than a factor of 10. The sensor plus bias coil fit inside a 6-mm-diam probe. The intrinsic sensitivity is approximately 50 mV/(V Oe), and is flat from dc out to 50 MHz. With a sensitivity of 300 mV/Oe at 100 mW power, a 2-Hz slot signal-to-noise ratio (SNR) of 30 dB at dc, and a 200-Hz slot SNR of 40 dB at 1 MHz, has been measured when detecting a 1 gamma (10−5 Oe or 1 nT) signal field. With design enhancements and ac detection techniques to eliminate thermal drift and 1/f-type noise, detection of low-frequency magnetic fields of the order 1 mgamma could be achievable.

Low-frequency magnetic field detection with a magnetostrictive amorphous metal ribbon

A low-frequency magnetometer has been constructed by interfacing a transversely field-annealed amorphous metal ribbon to a resonating piezoelectric ceramic plate. Power spectrum measurements from 20 mHz to 1.0 Hz demonstrate a minimum detectable field of 8.7 pT/√Hz at 1.0 Hz with an approximate 1/f rise in the noise floor.