Giant Magnetoresistive Sensors Research Articles

Ultra‐Flexible Giant Magnetoresistance Biosensors for Lab‐on‐a‐Needle Biosensing

AbstractFlexible biosensors exhibit great potential for the detection of various biomarkers with the ability to adapt to different surface textures. Here, a lab‐on‐a‐needle biosensing platform based on ultra‐flexible giant magnetoresistance (GMR) biosensors is developed. The fabricated flexible GMR sensors exhibit a MR ratio of 5.2% and a sensitivity of 0.13%/Oe in the linear region, which are comparable to their rigid counterparts. It is found that the magnetic properties of the flexible GMR sensors remain unchanged after 500 cycles of compressive and tensile stress, indicating strong robustness even when applied to a surface that is constantly in motion. The developed platform is then employed for the detection of different concentrations of canine osteosarcoma (OSCA‐8) cells with a limit of detection (LOD) of 200 cells in 20 µL sample (104 cells per mL), which demonstrate the ability to perform real‐time, sensitive, and quantitative cell detection.

Achieving Low-Noise, High-Bandwidth, Nanoscale-Resolution Position Sensing With GMR Sensors

This article presents a low-noise high-bandwidth giant magnetoresistance (GMR) sensor-readout circuit for nanometer resolution position sensing, a critical requirement in several precision applications such as Atomic Force Microscopy (AFM). The main impediment to performance is the GMR sensor’s significantly higher 1/f noise extending over large bandwidths, thereby limiting the achievable SNR. Therefore, the sensing system needs to be designed at the system level in order to minimize excess intrinsic noise generation and transmission, as well as external noise pickup. The noise characteristics of the GMR sensor and its readout circuit components, and their effect on SNR, are investigated analytically and experimentally. A general process for designing the readout circuit, applicable not just to GMR sensors but also to other high-1/f-noise sensors, is presented. A resolution of 2.5 nm over a bandwidth of 100 kHz is demonstrated on an AFM nanopositioner, a ten-fold improvement over previously reported GMR sensor performance and comparable to the state-of-the-art, but more complex, capacitive sensors. The readout scheme is simple to implement using COTS components and easily extendable to even higher bandwidths, unlike other schemes, such as modulation/demodulation, where the requirement for increasingly higher carrier frequencies renders further improvements in bandwidth impractical.

A Magnetic Feedback-Based Δ–Σ Digitizing Interface for Giant Magnetoresistance Sensors

Giant magnetoresistance sensors are popular for measurement of low magnetic fields due to their low-cost, easy-to-use, high-sensitivity design. However, the GMR sensors exhibit omnipolar, non-linear, and hysteretic voltage versus field characteristics, and operate over a limited range of input fields. In this brief, a simple digitizing interface, based on magnetic-feedback-based Delta-Sigma modulation, is proposed to overcome the aforementioned limitations of GMR sensors. The proposed interface operates the sensor at a quiescent magnetic field and renders a linear direct-digital output. The scheme is designed to measure bipolar fields. The methodology, analysis, and performance verification of the proposed interface are brought out in this brief. Experimental results of the developed interface show a non-linearity (N.L.) of just 0.52% over an enhanced measuring field range and significantly reduced hysteresis.

Giant Magneto-Resistive (GMR) Sensors for Non-Contacting Partial Discharge Detection

Partial discharge (PD) detection is a standardized technique to qualify the insulation condition in power equipment. The main purpose of the paper is to evaluate the performance of an extra high-sensitivity adapted giant magneto-resistive (xMR) sensor for non-contacting PD detection. Firstly, compensation and signal conditioning circuits of the sensor are designed. Frequency response and time-domain response to fast calibrator pulses of the sensor with the implemented circuit are measured. Besides, PD experiments based on corona and surface models are carried out and compared with measurements using a high-frequency current transformer (HFCT). The results show that the xMR system can measure the magnetic fields produced by the PDs at distances up to 50 cm. The correlation between the HFCT and xMR signals is proportional under different voltages, showing that PDs can be effectively detected and evaluated by this method. PDs in a cross-linked polyethylene (XLPE) cable with an artificial discharging defect are successfully measured, demonstrating the sensitivity and performance of the xMR system.

Smart Current Measurement in Modern Power Grids with a Raspberry Pi and GMR Effect-Based Sensor

The Giant magnetoresistance (GMR) effect has been presented as a highly viable current measurement alternative in electrical systems due to its low cost, versatility and high precision. This paper shows how the GMR effect can be used in current measurement in smart grids. The study contributes to the construction of a current measurement prototype which works by using the GMR effect. Subsequently, a data storage and processing server is created using a Raspberry Pi. Finally, a graphical interface capable of real-time monitoring of the data acquired by the sensor is designed and implemented. Different tests were carried out successfully, showing not only the viability of the GMR sensor as a current meter, but also the possibility of using other tools as a complement in order to create a product of great utility in intelligent measurement of smart grids.

Design and development of submersible hydrostatic level sensor using a GMR sensor

In this article, an innovative Hydrostatic Level Sensor (HLS) is presented for measuring water height as well as any other liquid height. This HLS is designed using a magnetic sensor based on giant magnetoresistance (GMR) technology to measure the hydrostatic pressure. This unique HLS has stainless steel (SS) diaphragm attached with a permanent magnet that deflects on the application of hydrostatic pressure resulting in a change in magnetic field gradient at the GMR sensor. The GMR sensor chip develops a voltage output with respect to hydrostatic pressure-induced magnetic field gradient which is further, amplified and corrected using signal conditioning chip. The sensor showed 0.05% of the full-scale resolution, the nonlinearity of <± 1%, and excellent reproducibility. Sensors are tested in laboratory set up and in real-time applications. This GMR-based HLS technology was found to be cost-effective to compete with the existing sensors.

The Effect of Geometrical Overlap between Giant Magnetoresistance Sensor and Magnetic Flux Concentrators: A Novel Comb-Shaped Sensor for Improved Sensitivity

The combination of magnetoresistive (MR) element and magnetic flux concentrators (MFCs) offers highly sensitive magnetic field sensors. To maximize the effect of MFC, the geometrical design between the MR element and MFCs is critical. In this paper, we present simulation and experimental studies on the effect of the geometrical relationship between current-in-plane giant magnetoresistive (GMR) element and MFCs made of a NiFeCuMo film. Finite element method (FEM) simulations showed that although an overlap between the MFCs and GMR element enhances their magneto-static coupling, it can lead to a loss of magnetoresistance ratio due to a magnetic shielding effect by the MFCs. Therefore, we propose a comb-shaped GMR element with alternate notches and fins. The FEM simulations showed that the fins of the comb-shaped GMR element provide a strong magneto-static coupling with the MFCs, whereas the electric current is confined within the main body of the comb-shaped GMR element, resulting in improved sensitivity. We experimentally demonstrated a higher sensitivity of the comb-shaped GMR sensor (36.5 %/mT) than that of a conventional rectangular GMR sensor (28 %/mT).

Magnetic field microscope using high-sensitivity giant magneto-resistance sensor with AC field modulation

A new high-sensitivity giant magneto-resistance (GMR) sensor system was developed and applied to a magnetic field microscope for which a magneto-impedance (MI) sensor was used as a high-sensitivity magnetic probe. The GMR sensor system achieved a detectivity of 13 pT/√Hz at 100 Hz. The sensing limit and spatial resolution were examined compared with the MI sensor. A 100 Hz AC magnetic field from a patterned Cu line was imaged. The GMR sensor showed better spatial resolution than that of the MI sensor owing to its small sensor unit size. The sensing limit was the same for both the GMR sensor and the MI sensor. This limit is due to ambient magnetic field noise. The GMR sensor could reduce this noise by differential detection using two sensor units. These results suggest that the GMR sensor system has advantages for application to the magnetic field microscopes compared with the MI sensor.

Analysis of Leakage in a Sustainable Water Pipeline Based on a Magnetic Flux Leakage Technique

Pipelines are typically used to transport oil, natural gas, water, etc. It is one of the most effective methods for transferring fluids over long distances. However, long-term usage of these pipes without maintenance results in the formation of residues, which will pave the way for pipeline accidents and soil contamination. To ensure the safety and protection of resources, these sustainable pipelines need to be inspected to avoid losses. This work aims to investigate various internal defect leaks in the non-uniform thickness of sustainable water pipes that are joined with a pipe expander. The magnetic flux leakage technique was implemented to evaluate these defects by means of a flexible GMR sensor array. An inspection robot containing two units was fabricated with the aid of 3D printing. The power unit provides the necessary thrust to actuate the entire robot whereas the sensing unit is responsible for analyzing the leaks. The robot’s movement is predicted by the MPU6050 and ultrasonic distance sensors that are plotted as motion plots. The sensing unit consists of permanent magnets and a giant magnetoresistance (GMR) array to interrogate the flux leakage in the defect region. The flux leakage from the defects was stored with the help of an Arduino microcontroller, which controls the overall process. In addition, the spring suspension is provided to regulate the motion of the robot. The flux leakage from the defect region was plotted as waveform graphs. Thus, the results are effectively presented and compared. The calculated signal-to-noise ratio (SNR) of the magnetic flux leakages (MFLs) for 4.5 mm-thick pipe defects was 12 to 20.8 dB, and for 6.52 mm-thick pipe defects, it was 9.5 to 19 dB. In sum, the MFL technique provides a reliable method for the sustainable development of water supply to wide areas.

Synthesis of Fe3O4 at different reaction temperatures and investigation of its magnetic properties on giant magnetoresistance (GMR) sensors for bio-detection applications

Magnetite (Fe3O4) nanoparticles with different reaction temperatures (TR= 40, 60 and 80°C) for the application of bio-detection have been successfully synthesized using the co-precipitation method. The average crystallite sizes of samples increased with the increase of TR and all samples showed high crystallinity with an inverse spinel cubic structure. The grain size increased with the increase of TR. On the other hand, all samples have polycrystalline structure and the brightest intensity at Miller's index (311). From the results of the vibrating sample magnetometer (VSM) analysis, it was found that there was an increase in magnetic properties such as Hc, Mr and Ms along with the increase reaction temperature. For example, the saturation magnetization increased with the increase of TR. Next, the giant magnetoresistance (GMR) biosensor was explored by using an exchange-biased GMR sensor with the Wheatstone bridge method to detect Fe3O4 with variations of reaction temperature in an alcohol solution of 50 μg/ml. A DC in-plane magnetic field was used for this measurement. It was found that the Vout curve is sensitive to the presence of Fe3O4 and the maximum Vout appears at 2.8 Oe by applying an external field to the sensor of ± 95 Oe. The Vout difference increased with the increase of reaction temperature, which can be attributed to higher saturation magnetization, causing more difficult fringing of the magnetic field. The relationship between TR and |ΔV| is ΔV = 0.0175x + 0.49, in which |ΔV| linearly increases with the increase of reaction temperature. This study demonstrates the feasibility of Fe3O4-based detection using a GMR sensor and Fe3O4 as magnetic labels will be useful for potential bio-detection applications.

GMR Biosensor Based on Spin-Valve Thin Films for Green-Synthesized Magnetite (Fe&lt;sub&gt;3&lt;/sub&gt;O&lt;sub&gt;4&lt;/sub&gt;) Nanoparticles Label Detection

The giant magnetoresistance (GMR) thin film with spin valve (SV) structure of Ta (2 nm)/Ir20Mn80(10 nm)/Co90Fe10(3 nm)/Cu (2.2 nm)/Co84Fe10B4(10 nm)/Ta (5 nm)] fabricated by RF magnetron sputtering method with a magnetoresistance (MR) of 6% was used in this work. Green synthesis of Fe3O4 magnetic nanoparticles (MNPs) using Moringa Oleifera (MO) leaf extract have been successfully conducted using the coprecipitation method. Fe3O4 MNPs demonstrated the inverse cubic spinel structure with the average crystallite size of 13.8 nm and decreased to 11.8 nm for Fe3O4/PEG. Fe3O4, as a magnetic label, integrated with a Wheatstone bridge-GMR sensor provides access to GMR-based biosensors. The induced-field increase leads the signal (ΔV) to increase with increasing nanoparticle concentration. It was discovered that a sensor can distinguish different types of magnetic labels. The sensitivity for Fe3O4 and MO-green synthesized Fe3O4 magnetic label was 0.04 and 0.1 mV/g/L, respectively. The GMR sensor performed the highest sensitivity on the MO-green synthesized Fe3O4 label. Thus, the SV thin film as a sensor and the green-synthesized Fe3O4 nanoparticles as a superior magnetic label are an excellent combination for biosensor application.

Detection of green-synthesized magnetite nanoparticles using spin-valve GMR-based sensor and their potential as magnetic labels

Exploration of magnetic nanoparticle labels for giant magnetoresistance (GMR) biosensing technology is crucial because their characteristics determine GMR-based sensor performance, related to their stray field and compatibility to biomolecule. We investigated the potency of the green-synthesized magnetite (Fe3O4) nanoparticle as a green-magnetic label on a spin-valve (SV) GMR sensor based on a [Ta (2 nm)/Ir20Mn80 (10 nm)/Co90Fe10 (3 nm)/Cu (2.2 nm)/(Co84Fe10B4 (10 nm)/Ta (5 nm)] structure that generated a 7.3 Oe exchange-bias field and 5.73% magnetoresistance. Fe3O4 nanoparticles were synthesized by a chemical coprecipitation method utilizing Moringa oleifera (MO) leaf extract as a natural reducing agent. The green-synthesized Fe3O4 nanoparticles exhibited a cubic inverse spinel structure as a pristine Fe3O4 characteristic. The crystallite size of green-synthesized Fe3O4 was larger than that of Fe3O4, reaching ∼ 14 nm, and formed a particle size of 29.1 nm. Its magnetic properties included soft ferromagnetic behavior with 55.5 emu/g saturation magnetization and 54 Oe coercivity; its saturation was lower than that of Fe3O4 due to the presence of the phytochemical compound of MO extract. In addition, to observe its potency as a magnetic label for biosensing, conventionally synthesized nanoparticles, surface modification using polyethylene glycol (PEG), and attachment of an α-amylase enzyme as a biomarker sample on green nanoparticle labels were also investigated. When measuring various concentration labels using the SV-GMR thin film, the green-synthesized Fe3O4 achieved a linear relationship and a better sensitivity of 0.098 mV/mg/mL than that of the conventional compound. The sensor could detect Fe3O4-labelled α-amylase enzyme as indicated by the decreasing output voltage, a consequence of altering the surface conditions of the nanoparticles. Therefore, green-synthesized nanoparticles are reliable and achieve competitive performance as magnetic labels in GMR sensors.

Study of Deformation Behavior of AISI 1025 Carbon Steel with Different Microstructures Using Metal Magnetic Memory and Acoustic Emission Testing

Studies are carried out to investigate the tensile deformation behavior of AISI-type 1025 carbon steel with different microstructures using metal magnetic memory and acoustic emission testing (AE) techniques. Seven AISI 1025 carbon steel specimens were heat treated for different microstructures and then subjected to tensile deformation until fracture. AE was conducted during tensile deformation and the deformation-induced self-magnetic leakage fields (SMLFs) were measured using a giant magneto-resistive sensor after unloading. Results reveal that SMLF signal values are influenced by microstructure and residual stress aroused due to plastic deformation. Among different specimens, SMLF signal peak amplitude is highest in the brine-quenched specimen followed by the tempered specimen, while hardness is highest in the brine-quenched specimen. SMLF signal peak amplitude and hardness are the lowest in the annealed specimen. SMLF signal is higher in tempered specimens compared to the untempered specimens. From AE measurements, it is observed that martensitic steel emits higher acoustic emissions during deformation but decreases when tempered. The acoustic emissions generated in the martensitic steel are also of higher amplitude. The results are correlated with optical micrographs and hardness measurements.

One-Shot Full-Range Quantification of Multi-Biomarkers With Different Abundance by a Tandem Giant Magnetoresistance Assay.

In this study, we reported a tandem giant magnetoresistance (GMR) assay that realized the one-shot quantification of multi-biomarkers of infection, C-reactive protein (CRP) with procalcitonin (PCT), and neutrophil gelatinase-associated lipocalin (NGAL), all of which could cover their clinically relevant concentration ranges under a different principle. In the presence of co-determined assay, we quantified these three biomarkers in undiluted human blood serum in a single test. The tandem principle, based on which quantification of CRP occurs, combines a sandwich assay and an indirect competitive assay, which allows for the discrimination of the concentration values resulting from the multivalued dose-response curve (‘Hook’ effect), which characterizes the one-step sandwich assay at high CRP concentrations. However, the entire diagnostically dynamic range, in the quantification of PCT and NGAL, was achieved by differential coating of two identical GMR sensors operated in tandem and by combining two standard curves. The sensor quantified low detection limits and a broader dynamic range for the detection of infection biomarkers. The noticeable features of the assay are its dynamic range and small sample volume requirement (50 μL), and the need for a short measurement time of 15 min. These figures of merit render it a prospective candidate for practical use in point-of-care analysis.

Simple Giant Magnetoresistance Probe Based Eddy Current System of Defect Characterization for Non-Destructive Testing

The purpose of this paper is to present a new giant magnetoresistance (GMR) sensor, in eddy current testing technique for surface defect detection, in conducting materials, we show that the GMR based eddy currents probe is more sensitive than the inductive probe. A flat coil mounted on ferrite pot used to produce an alternate magnetic field, which gives rise to eddy currents in the material under test. Aluminum plates use with defects have nominal depths, widths, and lengths. The defects scanned with the sensing axis perpendicular to the defect length. Two parameters extracted from the GMR output voltage signal obtained, and a simple correlation between the defect’s dimensions and the GMR output voltage proposed.

Detection of Surface and Subsurface Flaws with Miniature GMR-Based Gradiometer.

The eddy-current (EC) testing method is frequently utilized in the nondestructive inspection of conductive materials. To detect the minor and complex-shaped defects on the surface and in the underlying layers of a metallic sample, a miniature eddy-current probe with high sensitivity is preferred for enhancing the signal quality and spatial resolution of the obtained eddy-current images. In this work, we propose a novel design of a miniature eddy-current probe using a giant magnetoresistance (GMR) sensor fabricated on a silicon chip. The in-house-made GMR sensor comprises two cascaded spin-valve elements in parallel with an external variable resistor to form a Wheatstone bridge. The two elements on the chip are excited by the alternating magnetic field generated by a tiny coil aligned to the position that balances the background output of the bridge sensor. In this way, the two GMR elements behave effectively as an axial gradiometer with the bottom element sensitive to the surface and near-surface defects on a conductive specimen. The performance of the EC probe is verified by the numerical simulation and the corresponding experiments with machined defects on metallic samples. With this design, the geometric characteristics of the defects are clearly visualized with a spatial resolution of about 1 mm. The results demonstrate the feasibility and superiority of the proposed miniature GMR EC probe for characterizing the small and complex-shaped defects in multilayer conductive samples.

Magnetoresistance sensor-based rotor fault detection in induction motor using non-decimated wavelet and streaming data

In this paper, the giant magnetoresistance broken rotor (GBR) method is used to diagnose the induction motor (IM) rotor bar fault at an early stage from outward magnetic flux developed by IM.The outward magnetic field signal has anti-clockwise radiation due to broken rotor bar current.In this paper, the outward magnetic signal is acquired using a giant magnetoresistance (GMR) sensor. In the GBR method, IM rotor fault is analysed with a non-decimated wavelet transform (NDWT)-based outward magnetic signal. Experimental result shows the difference in statistical features and energy levels of sub-bands of NDWT for healthy and faulty IM. Least square-support vector machine(LS-SVM)-based classification results are verified by confusion matrix based on 150 outward magnetic signals from a healthy and damaged rotor (broken rotor). The proposed method identifies IM rotor faults with 95% sensitivity, 90% specificity and 92.5% classification accuracy. Furthermore, run-time IM condition monitoring is performed through the ThinkSpeak internet of things (IoT) platform for collecting outer magnetic signal data. ThinkSpeak streaming data of outward magnetic field help detect rotor fault at the initial stage and understand the growth of rotor fault in the motor. The proposed GBR method overcomes sensitivity, translation-invariance limitations of existing IM rotor fault diagnosis methods.

Synthesis of Fe3o4 at Different Reaction Temperatures and Investigation of its Magnetic Properties on Giant Magnetoresistance (Gmr) Sensors for Bio-Detection Applications

Synthesis of Fe3o4 at Different Reaction Temperatures and Investigation of its Magnetic Properties on Giant Magnetoresistance (Gmr) Sensors for Bio-Detection Applications

Enhancing the Linearity of Giant Magnetoresistance Sensors by Magnetic Anisotropic Design and Low Temperature Annealing

Giant magnetoresistance (GMR) sensors have been widely used in current detection, compass, automobile, and Internet of Things. The linearity of GMR sensors relies on a magnetic annealing process above the blocking temperature of the antiferromagnetic layer, which causes the same magnetization directions in the free and pinned ferromagnetic layers. Here we construct an orthogonal magnetic anisotropic structure by using a relatively low annealing temperature of 145 °C, where the magnetization direction of the free layer is perpendicular to that of the pinned layer so that a linear output can be realized. Quantitative magneto-optical kerr microscope (MOKE) is used to investigate the vector distribution of the magnetic domains, showing that an orthogonal anisotropy is established by the low temperature annealing process. GMR magnetic field sensor with a sensitivity of 0.78 mV/V/Oe and a measurement range of -20 to 20 Oe is demonstrated, which provides an effective method to enhance the linearity of the magnetic sensors with spin valve structures.

Effect of Fe/Fe3O4 Nanoparticles Stray Field on the Microwave Magnetoresistance of a CoFeB/Ta/CoFeB Synthetic Ferrimagnet.

The effect of the stray field of Fe/Fe3O4 nanoparticles on the angular dependence of the microwave absorption derivative in CoFeB/Ta/CoFeB synthetic ferrimagnetic structures and CoFeB films with perpendicular anisotropy is analyzed, and its application for sensor technology is proposed. The effective field of the "platform-particles" system controlled by the magnetic dipole interaction of the CoFeB-Fe/Fe3O4 system decreased to zero in areas where the platform was magnetostatically coupled with nanoparticles. Micromagnetic modeling demonstrated the distribution of magnetization and resistance in local areas of CoFeB/Ta/CoFeB structures under the nanoparticles. The microwave absorption derivative can be used as an indicator of local magnetization switching of the giant magnetoresistance (GMR) structure under scattering fields of NPs or magnetically labeled cells. The limiting sensitivity of the detection method was 2.4 × 107 nanoparticles, which covered the spin-valve surface. We have proposed to combine the advantages of a GMR sensor with wireless technology of microwave reading of magnetoresistance for the detection of magnetically labeled cells.