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The orthogonal two-step annealing process is an effective strategy to linearize the response of magnetic tunnel junctions for magnetic field sensors. However, the response after the orthogonal annealing is inevitably modulated by the Neel effect from the reference layer, which results in an unexpected shift of the linear interval and a disappointing sensitivity deterioration in the weak field. Here, a non-orthogonal two-step annealing method is proposed to suppress the shift by compensating for the Neel coupling field. Experimental results show that the curve shift of junctions annealed in the non-orthogonal direction of 120° is 47.6% lower than that in the orthogonal one, with a significant sensitivity promotion in the weak field and little hysteresis increment. A simple energy minimization model is introduced to explain the results. Based on the model, the suppression of the curve shift is fulfilled with the effective field compensation for the Neel coupling field, modulated by the non-orthogonal annealing. Finally, Wheatstone bridge devices are constructed, and the bridge with non-orthogonally annealed junctions is found to have an increased sensitivity of 46.8% in the major loop along the sensing axis. Additionally, the non-orthogonal annealing method is also effective in suppressing the cross sensitivity, which is important for further application to three-axis magnetic sensors. [ABSTRACT FROM AUTHOR]

A highly sensitive superconductor/tunnel magnetoresistance (TMR) composite magnetic sensor was designed and fabricated to satisfy the demands of detecting weak magnetic fields down to the pT range at low frequencies. First, analysis of the 1/f noise provided an optimized design scheme for the TMR unit to reduce the noise level. Then, the key structural parameters of the superconducting flux transformation amplifier (SFTA) were optimized with focus on the bonding quality between SFTA and TMR units using the finite element method to enhance the magnetic field magnification factor. An SFTA–TMR composite method with secondary alignment and multi-step bonding was proposed to fabricate the composite magnetic sensor and ensure the designed bonding gap and alignment accuracy. Experiments showed that the magnetic field sensitivity reached 5 pT/Hz0.5 (@ 13 Hz), which is beyond the highest level of superconductor/TMR composite magnetic sensors reported to date and is a further step toward the application of weak magnetic field detection. [ABSTRACT FROM AUTHOR]

A superconductor/magnetoresistance (SC/MR) mixed sensor often has very high-precision detection capability, but it is only sensitive to the out-of-plane magnetic field that is perpendicular to the superconducting flux-to-field transformation amplifier (SFTA). This inherent characteristic makes it impossible for a primary SC/MR mixed sensor to measure the in-plane magnetic field, which limits its application in many fields. This paper presents a new architecture of SC/MR mixed sensors with two magnetic flux guides (MFGs) to realize in-plane magnetic field measurement, which is attributed to the combined effects of MFGs and SFTA. The finite element method simulations are used to study the magnetic flux converting effect of MFGs and magnetic field amplification effect of SFTA, which theoretically proves the feasibility of in-plane magnetic field measurement and reveals the influences of the sizes and spacing of MFGs on magnetic field magnification. Experimental results show that the SC/MR mixed sensor with MFGs can simultaneously sense the in-plane and out-of-plane magnetic fields, and the performance of the mixed sensor with MFGs is comparable to the primary one. The magnification and resolution of the mixed sensors with MFGs to the in-plane magnetic fields are, respectively, improved by 2.91 times and 2.23 times compared to those without MFGs to the out-of-plane magnetic fields. The work described in this paper is of great significance for the development of three-component weak magnetic field detection. [ABSTRACT FROM AUTHOR]

A novel architecture for the superconductor/magnetoresistance (MR) composite sensor with vertical magnetic flux concentrators (MFCs) was studied theoretically and experimentally in this paper, to enhance the sensor’s sensitivity and resolution. The three-dimensional finite element method (FEM) of the superconducting flux transformation amplifier (SFTA), characterized by the E-J power law, was firstly established to design and optimize the structure of SFTA with MFCs. Then the influence of the key size of MFCs on the gain factor of SFTA was discussed. Finally, a superconductor/TMR composite sensor with specific-sized MFCs was designed and manufactured. Experimental results showed that the sensitivity was increased by 1.84 times, and the magnetic field resolution was improved from 81 pT/Hz0.5 to 49 pT/Hz0.5 by about 1.63 times after setting vertical MFCs, which all accorded with the FEM simulation prediction result of 1.75 times. The work in this paper contributes to the development of high-performance superconductor/MR composite sensors. [ABSTRACT FROM AUTHOR]

Aiming at the problem of low resolution of traditional eddy current sensor for buried defects detection in metal materials, a null-offset planar eddy current sensor array is designed, realized, and tested. The arrayed sensor is composed of a spatially periodic excitation coil and multiple differential detection coils, which are skillfully designed and can effectively suppress the common mode component in the induced voltage and improve the signal-noise-ratio of the sensor. The null-offset eddy current sensor is fabricated and utilized to detect the buried defects 0.5-mm depth beneath the surface of aluminum alloy test pieces. The simulation and experimental results show that the null-offset eddy current detection unit improves the detection resolution of buried defects by more than 1000 times. [ABSTRACT FROM AUTHOR]

1/f noise as well as nonlinear and hysteresis are the dominant restrictions of magnetoresistive (MR) sensors in detection ability. Modulation of the stimulating magnetic field of the MR sensors with microelectromechanical systems (MEMS) can reduce the 1/f noise by hundreds of times at low frequency, which gives a highlight for high-sensitive magnetic sensors. However, nonlinear response primarily caused by magnetic hysteresis is still a practical problem in modulated MR sensors, as well as unipolar response. In this paper, we propose a bidirection pulse magnetization method to reduce magnetic hysteresis, and in order to separate MR sensors from temperature influence, an integrated MEMS structure with low dissipation is developed to achieve pulse magnetization. Furthermore, this method is also used to achieve the bipolar magnetic field detection by distinguishing the response disparity under bidirection magnetization. The experimental results show that the modulated MR sensors can realize 90% reduction of hysteresis and 12.9% improvement of sensitivity with this method. [ABSTRACT FROM AUTHOR]

In this work, the authors improve the magnetic anomaly detector by using Karhunen–Loeve expansion, for expanding the detection distance of visually obscured ferromagnetic object when the target signal is contaminated by coloured noise. In the detector, the orthonormal basis functions are modified by the autocorrelation function of geomagnetic noise, and the anomaly is detected by matched filtering. Compared with the traditional detector, simulation results show that the modified detector has better performance with coloured Gaussian noise; especially, the improvement is more evident when the noise exponent is bigger. The real geomagnetic noise is proved to be coloured and obey approximate Gaussian distribution by the measurements in experiment. Tests with this noise indicate that the proposed detector achieves an incremental detection probability of 0.1 – 0.2 in the case of low signal‐to‐noise ratio, which makes it more attractive in practice. [ABSTRACT FROM AUTHOR]

1/ $f$ noise is one of the main noise sources of magnetoresistance (MR) field sensors, which can cause intrinsic detection limit at low frequency. To suppress this noise, a novel magnetic flux vertical motion modulation (MFVMM) design using micro-electromechanical system flux concentrator (FC) and actuator is proposed in this paper, which can mitigate the 1/ $f$ noise by shifting the measurement frequency to kilohertz range. The proposed MFVMM has high efficiency and simple structure. The magnetic FC and the modulation film of MFVMM were analyzed with a numerical simulation. The simulation results show that the modulation efficiency of MFVMM exceeds 21%. A preliminary prototype sensor based on the multilayered giant MR AA002 and MFVMM was fabricated, and its modulation efficiency achieves 18.8% at a frequency of 7.01 kHz, which exceeds the efficiency of most existing sensors with the other modulation schemes. In addition, the magnetostatic detection ability is improved to 0.44 nT/ $\surd $ Hz. [ABSTRACT FROM AUTHOR]

Generally, giant magnetoresistive (GMR) sensors are only sensitive to the magnetic field in the plane of the substrate due to fabrication restraints. This paper designs and models slope magnetic flux guides that are deposited on the slope surface of a silicon substrate. Finite element method (FEM) simulations are used to optimize the flux guide designs. The flux guides can be deposited with good symmetry and are able to convert the out-of-plane magnetic flux to the GMR sensor plane. Meanwhile, a Wheatstone bridge is configured to deduce a differential voltage only relative to the z-component of the magnetic field. Additionally, the magnetic field in the active region of the GMR sensor would be intensified. With these flux guides, the magnetic field perpendicular to the chip surface can be detected with the GMR sensors in-plane. Also, the sensitivity of the sensor can be improved due to the amplification ability of the flux guides. An integrated 3-axis magnetic sensor with better angular position can be realized with the slope flux guides. [ABSTRACT FROM AUTHOR]

Thermal barrier coatings (TBCs) can significantly reduce the operating temperature of the aeroengine turbine blade substrate, and their testing technology is very urgently demanded. Due to their complex multi-layer structure, it is hard to evaluate TBCs with a single function sensor. In this paper, an electromagnetic/capacitive composite sensor is proposed for the testing of thermal barrier coatings. The dielectric material is tested with planar capacitor, and the metallic material is tested with electromagnetic coils. Then, the comprehensive test and evaluation of thermal barrier coating system can be realized. The sensor is optimized by means of theoretical and simulation analysis, and the interaction between the planar capacitor and the electromagnetic coil is studied. The experimental system is built based on an impedance analyser and multiplex unit to evaluate the performance of the composite sensor. The transimpedances and capacitances are measured under different coating parameters, such as thickness and permittivity of top coating as well as bond layer conductivity. The experimental results agree with the simulation analysis, and the feasibility of the sensor is proved. [ABSTRACT FROM AUTHOR]

The superconductor/magnetoresistance (MR) mixed magnetic sensor, which is composed of a superconducting magnetic flux transformation amplifier (SMFTA) and a MR sensitive element, has extremely great development potential in weak magnetic field detection because of its excellent sensitivity, simple structure and small size. However, it still lacks an effective method to study the spatial distribution of the magnetic field produced by SMFTA. Here, a finite element simulation method was proposed to study the magnetic field amplification effect of the SMFTA. Several factors affecting the magnetic field amplification were studied via this simulation method. Furthermore, mixed magnetic sensors with three typical sizes were successfully fabricated, and the experimentally measured magnifications of the three sensors were basically consistent with the simulation values, demonstrating the reliability of this simulation method. Our works are expected to pave a meaningful way for the SMFTA design and promote the development of superconductor/MR mixed magnetic sensors. [Display omitted] • A simulation method was proposed to study superconducting magnetic flux amplifier. • The spatial distributions of amplified magnetic field can be obtained. • Several key influencing factors were investigated using this method. • The reliability of simulation method was demonstrated experimentally. [ABSTRACT FROM AUTHOR]