Giant Magnetoresistive Sensor Array Research Articles

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.

Giant Magnetoresistive Biosensor Array for Detecting Magnetorelaxation.

In this paper, a time-domain magnetorelaxometry biosensing scheme is presented using giant magnetoresistive (GMR) sensors to measure the fast relaxation response of superparamagnetic magnetic nanoparticles (MNPs) in a pulsed magnetic field. The system consists of an 8 × 10 GMR sensor array, a Helmholtz coil, an electromagnet driver, and an integrator-based analog front-end needed to capture the fast relaxation dynamics of MNPs. A custom designed electromagnet driver and Helmholtz coil improve the switch-off speed to >5 Oe/μs, limiting the dead zone time to <10μs, and thus enables the system to monitor fast relaxation processes of 30nm MNPs. A magnetic correlated double sampling technique is proposed to reduce sensor-to-sensor variation by 99.98% while also reducing temperature drift, circuit offset, and nonlinearity below the noise level. An optimum integration time is calculated and experimentally verified to maximize the SNR. Experiments with dried MNPs have shown successful relaxation detection, and immunoassay experiments have demonstrated their binding kinetics.

Ultrasensitive Magnetic Nanoparticle Detector for Biosensor Applications

Ta/Ru/Co/Ru/Co/Cu/Co/Ni80Fe20/Ta spin-valve giant magnetoresistive (GMR) multilayers were deposited using UHV magnetron sputtering and optimized to achieve a 13% GMR ratio before patterning. The GMR multilayer was patterned into 12 sensor arrays using a combination of e-beam and optical lithographies. Arrays were constructed with 400 nm × 400 nm and 400 nm × 200 nm sensors for the detection of reporter nanoparticles. Nanoparticle detection was based on measuring the shift in high-to-low resistance switching field of the GMR sensors in the presence of magnetic particle(s). Due to shape anisotropy and the corresponding demag field, the resistance state switching fields were significantly larger and the switching field distribution significantly broader in the 400 nm × 200 nm sensors as compared to the 400 nm × 400 nm sensors. Thus, sensor arrays with 400 nm × 400 nm dimensions were used for the demonstration of particle detection. Detection of a single 225 nm Fe3O4 magnetic nanoparticle and a small number (~10) of 100 nm nanoparticles was demonstrated. With appropriate functionalization for biomolecular recognition, submicron GMR sensor arrays can serve as the basis of ultrasensitive chemical and biological sensors.

Novel Rotating Current Probe With GMR Array Sensors for Steam Generate Tube Inspection

This paper presents a novel probe design that uses a rotating current excitation scheme and giant magnetoresi-stance (GMR) sensors for steam generator tube inspection. Rotating eddy currents in the tube wall under test is induced using a pair of axial and circumferential excitation coils. A circumferential array of GMR sensors measures the radial component of the magnetic field. The perturbation in eddy current flow caused by a defect produces a radial component field that is measured by the GMR sensors. A C-scan image of the induced magnetic field obtained with the axial motion of probe shows defect location and orientation. The probe is sensitive to both the axial and circumferential defects and offers the advantages of high sensitivity over a wide frequency range. A finite-element model was developed to mimic the underlying physical process and predict the output images of defects with different orientations and sizes. A prototype unit consisting of excitation coils and GMR sensor array along with a data acquisition system was developed and tested. A steam generator tube sample with machined axial and circumferential notches was inspected using the prototype probe. Experimental results demonstrating the feasibility of the concept are presented.

Giant magnetoresistive sensor array for sensitive and specific multiplexed food allergen detection

Current common allergen detection methods, including enzyme-linked immunosorbent assays (ELISAs) and dip-stick methods, do not provide adequate levels of sensitivity and specificity for at-risk allergic patients. A method for performing highly sensitive and specific detection of multiple food allergens is thus imperative as food allergies are becoming increasingly recognized as a major healthcare concern, affecting an estimated 4% of the total population. We demonstrate first instance of sensitive and specific multiplexed detection of major peanut allergens Ara h 1 and Ara h 2, and wheat allergen Gliadin using giant magnetoresistive (GMR) sensor arrays. Commercialized ELISA kits for Ara h 1 and Ara h 2 report limits of detection (LODs) at 31.5ng/mL and 0.2ng/mL, respectively. In addition, the 96-well-based ELISA developed in-house for Gliadin was found to have a LOD of 40ng/mL. Our multiplexed GMR-based assay demonstrates the ability to perform all three assays on the same chip specifically and with sensitivities at LODs about an order of magnitude lower than those of 96-well-based ELISAs. LODs of GMR-based assays developed for Ara h 1, Ara h 2, and Gliadin were 7.0ng/mL, 0.2ng/mL, and 1.5ng/mL, respectively, with little to no cross-reactivity. These LODs are clinically important as some patients could react strongly against such low allergen levels. Given the limitations of current industrial detection technology, multiplexed GMR-based assays provide a method for highly sensitive and specific simultaneous detection of any combination of food-product allergens, thus protecting allergic patients from life-threatening events, including anaphylaxis, by unintentional consumption.

Differential Sensor Measurement With Rotating Current Excitation for Evaluating Multilayer Structures

Rotating current probe using rotating electromagnetic fields and currents generated by orthogonal excitation coils is required for achieving similar sensitivity to defects in all radial directions around fastener. However, orthogonal excitation scheme only has a single null field point. When using array sensors for rapid inspection, sensors located away from the point measure a strong background field that must be eliminated. This paper presents a new approach using two giant magnetoresistive sensor arrays in a differential configuration to reduce the impact of the background field and increase signal-to-noise ratio. The operation of the differential probe is validated using a finite-element model. A prototype probe was designed, built, and tested. Experimental results obtained using the prototype probe to inspect a two-layer aluminum sample are presented.

An Automated Sensing System for Steel Bridge Inspection Using GMR Sensor Array and Magnetic Wheels of Climbing Robot

Corrosion is one of the main causes of deterioration of steel bridges. It may cause metal loss and fatigue cracks in the steel components, which would lead to the collapse of steel bridges. This paper presents an automated sensing system to detect corrosion, crack, and other kinds of defects using a GMR (Giant Magnetoresistance) sensor array. Defects will change the relative permeability and electrical conductivity of the material. As a result, magnetic field density generated by ferromagnetic material and the magnetic wheels will be changed. The defects are able to be detected by using GMR sensor array to measure the changes of magnetic flux density. In this study, magnetic wheels are used not only as the adhesion device of the robot, but also as an excitation source to provide the exciting magnetic field for the sensing system. Furthermore, compared to the eddy current method and the MFL (magnetic flux leakage) method, this sensing system suppresses the noise from lift-off value fluctuation by measuring the vertical component of induced magnetic field that is perpendicular to the surface of the specimen in the corrosion inspection. Simulations and experimental results validated the feasibility of the system for the automated defect inspection.

Detection of Localized Damage in Water Wall Tubes of Thermal Power Plants Using GMR Sensor Array Based Magnetic Flux Leakage Technique

A flexible giant magneto-resistive (GMR) sensor array based magnetic flux leakage technique has been developed for nondestructive inspection of carbon steel water wall tubes (outer diameter 64.0 mm and wall thickness 6.3 mm) used in a thermal power plant. Two saddle coils are used for magnetisation of the tube and a flexible GMR sensor array is used for detection of leakage fields from localized damage in the tube. 3D-nonlinear finite element modeling has been performed to optimize the magnetizing current, inter-coil spacing of the saddle coils and location of the GMR sensor array within the saddle coils. The performance of the technique has been evaluated by measuring the axial component of leakage flux from outer diameter (OD) erosion and inner diameter (ID) corrosion type flaws artificially machined on the water wall tube. Studies reveal that the proposed technique detects both OD erosion and ID corrosion damage in the water wall tubes.

Integration of Hall and Giant Magnetoresistive Sensor Arrays for Real-Time 2-D Visualization of Magnetic Field Vectors

In this study, we combined an array of giant magnetoresistive (GMR) sensors with an array of Hall sensors to measure all three components of magnetic vectors with a high spatial resolution and visualize the magnetic field distribution on a 2-D plane. The sensors were arrayed in a matrix arrangement such that the limitation to the number of sensors could be overcome. To test the device, we generated a magnetic field using a pancake-type magnetizer and a cracked magnetized ferromagnetic specimen and imaged the vectors. We obtained a spatial resolution of 0.78 mm in the z-direction with 1024 Hall sensors and 2.34 mm in the x-direction with 100 GMR sensors. Moreover, the x and z components could be imaged at 6 fps. The proposed device is promising for application in magnetic flux leakage detection.

Design of an electromagnetic imaging system for weapon detection based on GMR sensor arrays

Concealed weapon detection is one of the most challenging issues facing the security community. It has been shown that each weapon can have a unique fingerprint, which is a set of electromagnetic (EM) signals determined by its size, shape, and physical composition. Extracting the signature of each weapon is one of the major tasks in any detection system. This paper addresses the design of a detection system for the identification of conductive objects based on their response to EM fields. The system consists of commercial Walk-Through Metal Detector (WTMD) and a Giant Magneto-Resistive (GMR) sensor array has been designed and built. Also, this paper describes how to construct a two-dimensional image from the measured signals to be used for image processing purposes. The system validity is then checked based on two concepts: data validation and multiple object separation. Finally, initial experimental work on the automatic detection and classification of different metallic objects has been carried out. The promising results indicate the feasibility of using this EM imaging method to identify objects.