Magnetoresistive Sensor Array Research Articles

An ultrathin, rapidly fabricated, flexible giant magnetoresistive electronic skin

In recent years, there has been a significant increase in the prevalence of electronic wearables, among which flexible magnetoelectronic skin has emerged as a key component. This technology is part of the rapidly progressing field of flexible wearable electronics, which has facilitated a new human perceptual development known as the magnetic sense. However, the magnetoelectronic skin is limited due to its low sensitivity and substantial field limitations as a wearable electronic device for sensing minor magnetic fields. Additionally, achieving efficient and non-destructive delamination in flexible magnetic sensors remains a significant challenge, hindering their development. In this study, we demonstrate a novel magnetoelectronic touchless interactive device that utilizes a flexible giant magnetoresistive sensor array. The flexible magnetic sensor array was developed through an electrochemical delamination process, and the resultant ultra-thin flexible electronic system possessed both ultra-thin and non-destructive characteristics. The flexible magnetic sensor is capable of achieving a bending angle of up to 90 degrees, maintaining its performance integrity even after multiple repetitive bending cycles. Our study also provides demonstrations of non-contact interaction and pressure sensing. This research is anticipated to significantly contribute to the advancement of high-performance flexible magnetic sensors and catalyze the development of more sophisticated magnetic electronic skins.

Measurement of somatosensory evoked magnetic fields using an adjustable magnetoresistive sensor array

An adjustable helmet-style magnetoresistive (MR) sensor array with room-temperature magnetic flux sensors was developed to demonstrate the simultaneous multipoint measurement of the somatosensory evoked magnetic field (SEF). Utilizing the extended sensor length, we designed the array to permit individual radial adjustment of each sensor, thereby achieving a precise fit to the varied head geometries of different subjects. Furthermore, the geometry of the sensor array precisely adjusted for the individual subject was quickly obtained by calibration. The SEF was measured in three healthy subjects using an array of 30-channel MR sensors placed on the left hemisphere of the head with median nerve stimulation in the right wrist and averaged over 8000 measurements. An M20 component considered to originate from the primary somatosensory cortex was observed at an approximate latency of 20 ms of the magnetic field waveform in all cases (maximum amplitude of 725 ± 257 fT, peak latency of 20.5 ± 0.45 ms). The phase inversion observed around C3 in the international 10–20 system corresponded to the palmar area of the primary somatosensory cortex on the contour map of the magnetic field at the M20 peak. The MR sensor, an affordable and easy-to-use magnetic sensor that does not require a zero-field environment nor a cryogenic apparatus, was successfully used for simultaneous multipoint SEF measurements in humans and provides a promising system for realizing magnetoencephalography application devices.

Tracking of a Magnetically Navigated Millirobot With a Magnetic-Field Camera

Significant progress has been made in the development of magnetic micromanipulation for minimally invasive surgery. The development of systems to localize millimeter-sized robots during magnetic manipulation without line-of-sight detection remains, however, a challenging task. In this study, we focused on the development of a tracking system aiming to fill this gap. A robot which consists of a cylindrical magnet of 1 mm diameter is localized using a 2D array of 3D magnetoresistive sensors. The system, also called magnetic field camera, provides tracking of the robot with a refresh rate of 2 Hz. The developed tracking algorithm reaches a mean absolute error for the position and the orientation of, respectively 0.56 mm and 5.13° in 2D. This system can be added to existing magnetic manipulation systems allowing closed loop control of the navigation. The performances of the magnetic field camera are not affected by an exposure to strong magnetic fields. Exposures up to 3 T have been validated. Increasing the integrability of the magnetic field camera into magnetic manipulation systems. The presented tracking system makes it possible to target applications such as minimally invasive eye surgery or drug delivery. The high spatial and magnetic resolutions allow the tracking of magnetic particles, down to 200 μm diameter, when placed close to the surface. The system could also be suitable for the localization of small objects for 2D biomanipulation.

Monotone Signal Localization Using Magnetoresistive Sensor Array for Low-Field Magnetic Particle Imaging

Magnetic particle imaging (MPI) demands high sensitivity to be operable under low excitation fields as alternative countermeasure for specific absorption rate and magnetostimulation effects. Owing to capability of magnetoresistive (MR) sensors to unidirectionally detect sub-pT signal, we built a prototype of brain MPI scanner by using MR sensor array. The arrays were 13×13 and 5×13 matrices with 15mm sensor pitch and installed orthogonally relative to a 0.2m drive coil. To preliminarily evaluate 10 kHz-signal localization, we used a current loop embedded with 20-turn coils. We then carefully measured pT field at 234 sensor coordinates for 1mA ac current fed to the loop. The resulting field contour was numerically interpolated to identify the actual loop orientation. We found that the loop three-dimensionally rotated along xyz axes with (1.0°, –1.5°, 2.0°) angles from the expected position. To further estimate spatial resolution of the array, we measured magnetic fields from two adjacent point sources of small coils. The corresponding signal separation appeared dependent on the perpendicular distance to the nearest sensor. This fine signal localization of MR sensor array highlights its potential for tracing magnetic nanoparticles in low-field MPI system.

Sub-pT oscillatory magnetometric system using magnetoresistive sensor array for a low-field magnetic particle imaging

Implementing low ac excitation fields toward clinical magnetic particle imaging (MPI) system is critical to avoid magnetostimulation effects. However, low-field MPI scenario demands high sensitivity to probe the change in monotone magnetization response of magnetic nanoparticles. Here, we use an array of ultrasensitive MR sensors to detect sub-pT magnetic signal and obtain its spatial distribution. While each sensor is operated at 5 V, signal processing circuit rises its sensitivity to 20 mV pT−1 at 10 kHz with 0.25 pT noise level. In evaluating sensor performance, we initially measured a 10-kHz magnetic field from a 40-turns coil with 1 mm in diameter. MR sensor recognizes magnetic signal of mini coil to be linear with the coil input current. We then recorded the signals simultaneously from a 6 × 6 sensor channels to map the fields at 0.2 kHz. While placing mini coil 50 mm apart from the array, we obtained high-contrast field image showing coil position and its change in field polarity. For practical nanoparticle detection, we later used a 3 × 3 array configuration for the 10 kHz oscillatory magnetometry while compensating the MR sensor magnetically from the ac excitation field. Despite a 20-pT noise floor associated with the field compensation circuit, we were able to map stray fields of a 37-mgFe iron oxide nanoparticle sample distanced 100 mm from the array, under 12.4 µT/μ0 field amplitude. This result highlights usability of MR sensor array for low-field MPI system.

Online Process Monitoring for Additive Manufacturing Using Eddy Current Testing With Magnetoresistive Sensor Arrays

The rising popularity of additive manufacturing processes leads to an increased interest in possibilities and methods for related process monitoring. Such methods ensure improved process quality and increase the understanding of the manufacturing process, which in turn is the basis for stable component quality, e.g., required in the aerospace industry or in the medical sector. For laser powder bed fusion, a handful of process monitoring tools already exist, such as optical tomography, thermography, pyrometry, imaging, or laser power monitoring. Although these tools provide helpful information about the process, more information is required for an accurate in-depth understanding. In this article, advanced approaches in eddy current testing (ET) are combined, such as single wire excitation, magnetoresistive (MR) sensor arrays, and heterodyning to build up a system that can be used for online process monitoring of laser powder bed fusion. In addition to detailed information about the developed ET system and underlying signal processing, the first results of magnetoresistance-based online ET during the laser powder fusion process are presented. While producing a step-shaped cuboid, each layer is tested during recoating. Test results show that not only the contours of the topmost layer are detected but also the contours of previous layers covered by powder. At an excitation frequency of 1 MHz, a penetration depth of approx. <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$400~\mu \text{m}$ </tex-math></inline-formula> is obtained. To highlight the possibilities of ET for online process monitoring of laser powder bed fusion, results are compared with postexposure images of the integrated layer control system (LCS).

An innovative eye-tracker: Main features and demonstrative tests.

We present a set of results obtained with an innovative eye-tracker based on magnetic dipole localization by means of an array of magnetoresistive sensors. The system tracks both head and eye movements with a high rate (100-200 Sa/s) and in real time. A simple setup is arranged to simulate head and eye motions and to test the tracker performance under realistic conditions. Multimedia material is provided to substantiate and exemplify the results. A comparison with other available technologies for eye-tracking is drawn, discussing advantages (e.g., precision) and disadvantages (e.g., invasivity) of the diverse approaches, with the presented method standing out for low cost, robustness, and relatively low invasivity.

An Improved Fault Detection Method for Overhead Transmission Lines Based on Differential Tunnel Magnetoresistive Sensor Array Approach

Overhead transmission lines play a key role in ensuring power system security and reliability in this current smart society. The overhead transmission line operates in a very complex terrain thereby making it vulnerable to various kinds of faults. Most transmission line faults lead to interruption in power supplies and therefore the need for a fast repair to restore the system to its normal state. A fast, timely, and accurate fault detection technique will ensure speedy restoration of the system thereby reducing outage time. In this article, an enhanced transmission lines’ fault detection approach is presented. This scheme deployed a highly sensitive, low cost, and energy-efficient differential sensor to detect flux density variation measured along transmission lines. The fault detection algorithm is developed for the detection of faults in transmission lines. The development is implemented on a model transmission line and tested for various fault scenarios. Scaled-up laboratory experiments were also conducted to measure magnetic flux density and fault identification to verify the validity of the proposed technique as well as estimate the amount of current produced when a fault occurred. From the simulated and measured current produced during a fault, the proposed technique yielded an estimated error of 1.38%, while the CT and a commercial current probe gave errors of 10.99% and 17.68%, respectively.

The Broken Wires Identification of Wire Rope Based on Multilevel Filtering Method Using EEMD and Wavelet Analysis

In view of the shortcomings of current wire rope magnetic flux leakage (MFL) detection devices such as large size and low sensitivity, as well as the poor noise reduction effect of MFL data and the low recognition rate of defects, this paper designs a wire rope three-dimensional MFL detection device based on unsaturated magnetic excitation (UME) and proposes a multilevel filtering algorithm. Six types of small gap broken wire defects can be effectively detected by the three-dimensional tunnel magnetoresistive sensor array. The multilevel filtering method based on EEMD and optimal wavelet is applied to three-dimensional UME signal processing, effectively suppressing noise interference. And color processing technology is applied to enhance the characterization of the defect images. A support vector machine recognition network based on the color moment feature vector as input is designed to classify broken wire defects, and the quantitative recognition rate of 98.572% is achieved when the limit error is 0.901%. The experimental results show that the detection device has the advantages of high sensitivity and simple structure and can collect MFL information in three directions, and the filtering algorithm effectively improves the signal-to-noise ratio and can realize the preliminary quantification of broken wire defects.

Real-time and contactless initial current traveling wave measurement for overhead transmission line fault detection based on tunnel magnetoresistive sensors

Obtaining accurate and real-time information about the current traveling wave generated during a faulty condition in an overhead transmission line is always considered as a puzzling task. For overhead transmission networks, current transformers and other sensing devices are mostly mounted in substations. In order to provide a flexible, convenient and easy to install scheme, this paper proposed a real-time, wireless and contactless current traveling wave measurement and fault detection method for overhead transmission lines based on tunnel Magnetoresistive sensor array. By detecting the magnetic flux density generated by current traveling waves in the individual conductors due to disturbances, the current traveling waves produced by the overhead transmission lines is estimated from the detected magnetic flux density. The simulation results include a comparison of the current traveling waves measured by the conventional CT, commercial AC current probe and the current traveling waves estimated using the method proposed in this paper. The proposed method exhibited an effective and accurate results for the measurement of overhead transmission line current traveling waves. Moreover, the proposed method is validated by a reduced-scale laboratory experiment.

Multiple Bacteria Identification in the Point-of-Care: an Old Method Serving a New Approach.

The accurate diagnosis of bacterial infections is of critical importance for effective treatment decisions. Due to the multietiologic nature of most infectious diseases, multiplex assays are essential for diagnostics. However, multiplexability in nucleic acid amplification-based methods commonly resorts to multiple primers and/or multiple reaction chambers, which increases analysis cost and complexity. Herein, a polymerase chain reaction (PCR) offer method based on a universal pair of primers and an array of specific oligonucleotide probes was developed through the analysis of the bacterial 16S ribosomal RNA gene. The detection system consisted of DNA hybridization over an array of magnetoresistive sensors in a microfabricated biochip coupled to an electronic reader. Immobilized probes interrogated single-stranded biotinylated amplicons and were obtained using asymmetric PCR. Moreover, they were magnetically labelled with streptavidin-coated superparamagnetic nanoparticles. The benchmarking of the system was demonstrated to detect five major bovine mastitis-causing pathogens: Escherichia coli, Klebsiella sp., Staphylococcus aureus, Streptococcus uberis, and Streptococcus agalactiae. All selected probes proved to specifically detect their respective amplicon without significant cross reactivity. A calibration curve was performed for S. agalactiae, which demonstrates demonstrating a limit of detection below 30 fg/µL. Thus, a sensitive and specific multiplex detection assay was established, demonstrating its potential as a bioanalytical device for point-of-care applications.

TMR-Sensor-Array-Based Misalignment-Tolerant Wireless Charging Technique for Roadway Electric Vehicles

The wirelessly transferred power as well as charging efficiency will significantly drop due to the large misalignment between the transmitting coil and receiving coil for roadway electric vehicles (EVs). A low-cost and reliable misalignment-tolerant wireless charging technique is indispensable for the rapid commercialization of wireless EV charging. This paper presents a technique to achieve the misalignment-tolerant wireless charging for the dynamic wireless charging (DWC) system by means of a tunneling magnetoresistive (TMR) sensor array as well as the easy-to-fabricate receiving coils. The TMR sensor array provides the coil-misalignment position by measuring the magnetic field component generated from the transmitting coil. The corresponding receiving coils are selected to be in resonance according to the measured coil-misalignment positions. In this paper, a sensor array composed of 29 uniaxial TMR sensors was utilized to measure the magnetic field component. This effectiveness of the proposed technique has been validated by both the finite-element method (FEM) simulations and laboratory experiments. The experimental results demonstrated that the proposed misalignment-tolerant wireless charging system can operate in a relatively wide misalignment range of ±120 mm with charging efficiency higher than 76.2%.

Magnetocardiography Using a Magnetoresistive Sensor Array.

In previous magnetocardiography studies, magnetocardiograms (MCGs) have been obtained using superconducting quantum interference device (SQUID) systems. SQUID is the most sensitive instrument for measuring low-frequency magnetic fields, but it requires liquid helium for cooling, so operating costs are high. In contrast, magnetoresistive (MR) magnetometers function by detecting the change in resistance, caused by an external magnetic field, and have much lower costs. This study was aimed to evaluate feasibility of the MR sensor array for acquiring MCGs.We used an MR sensor array, which was developed for measuring magnetic fields in the picotesla range, with a reduced noise level (TDK Corporation, Tokyo, Japan). A 30-channel MR sensor array was placed in a magnetically shielded room, and the cardiac magnetic field over the anterior chest walls of five healthy subjects was recorded.For all five subjects, MCGs were successfully recorded using the MR sensor array. The cardiac magnetic field corresponding to P, QRS, and T waves on an electrocardiogram (ECG) was detectable by signals averaging 272 ± 27.5 beats.An MR sensor array can be used to measure cardiac magnetic fields. Our results will contribute to the development of low-cost devices for recording MCGs, which will help develop non-invasive diagnostics in cardiovascular medicine.

Marker-Free Coil-Misalignment Detection Approach Using TMR Sensor Array for Dynamic Wireless Charging of Electric Vehicles

This paper presents an approach to detect the lateral coil misalignment for the dynamic wireless charging system using a tunneling magnetoresistive (TMR) sensor array. The component of the magnetic field generated from the transmitting coil can directly provide the information of the coil misalignment between transmitting and receiving coils. A sensor array composed of 15 uniaxial TMR sensors was implemented to measure the vector magnetic field for detecting the coil misalignment. Both 3-D finite-element method modeling and experimental results over a relatively large misalignment range were presented to substantiate the effectiveness and feasibility of the proposed approach.

Accurate Position Detection in Wireless Power Transfer Using Magnetoresistive Sensors for Implant Applications

Recently, the utilization of magnetic resonant coupling (MRC) mechanism for wireless power transfer (WPT) has been actively investigated. Among numerous applications of WPT technology, the energization of implanted biomedical devices wirelessly and uninterruptedly from external supply is important because it can eliminate possible device replacement due to battery depletion. Given the implanted receiver is invisible from the external transmitter, the coil misalignment occurs easily which results in low transfer efficiency and high magnetic field leakage, and consequently endangers the human health [1]. Thus, the development of accurate position detection of the implanted receiver from the external transmitter is highly desirable. Presently, most studies of the position detection in WPT are focused on the application of electric vehicles. Although the corresponding technologies such as coil sets [2] or auxiliary multi-coils [3] have achieved fruitful outcome, they are too bulky and complicated to be used in implant applications. Due to the advantages of high stability, small size, low power consumption and high precision, the magnetoresistive (MR) sensor has been widely used in many industrial applications [4]. Generally, they are arranged in an array style to measure the magnetic field vector [5] or a moving magnetic object [6]. To the best of authors' knowledge, the application of MR sensors in WPT is absent in literature. In this paper, a new position detection approach in WPT is proposed and implemented, which is particularly suitable for implant applications. The key is to use a MR sensor array to directly measure the variation of magnetic field so as to precisely detect the relative position of the implanted receiver from the external transmitter. Therefore, the advantages of efficient and compact WPT for implant applications can be achieved.

Development of a high sensitive magnetic flux leakage instrument for imaging of localised flaws in small diameter ferromagnetic steel tubes

The authors report the development of a high sensitive, 16 channel magnetic flux leakage (MFL) instrument for imaging of localised flaws in small diameter ferromagnetic steel tubes. The instrument consists of a magnetising unit of two bobbin coils wound on a ferrite core, a sensing unit of flexible giant magneto-resistive (GMR) sensor array and an image visualisation unit. 3D-non-linear finite-element modelling has been carried out to optimise the inter-coil spacing of the bobbin coils and to identify the number of GMR elements and their locations between the bobbin coils. A series of experiments has been carried out to evaluate the flaw detection performance of the MFL instrument. Studies reveal that the instrument can image as small as 1.1 mm diameter hole and 0.46 mm deep shallow outer diameter circumferential notch in 17.2 mm diameter Mod. 9Cr-1Mo steel tubes used as steam generator material in prototype fast breeder reactor, with a signal-to-noise ratio better than 8 dB. Studies also indicate that intensity of MFL signal measured by the instrument increases with increase in hole diameter and notch depth. The instrument is portable and easy to use for field inspection of ferromagnetic steel components.

Interference‐rejecting current measurement method with tunnel magnetoresistive magnetic sensor array

Innovative methods for wide range measurement of electric current remains an active research problem in modern power systems. Conventional methods based on magnetic field readouts have realized non-contact current measurement by interpreting magnetic flux density into electric current, such as Hall effect and Rogowski Coil arrangement. TMR magnetic sensor has spread its application for current measurement due to its miniaturization, low cost, high response frequency and high sensitivity. However, due to the superposition of unwanted magnetic field, the magnetic fieldunder measurement is strongly affected. In this paper, a four-sensor array design is proposed to solve this problem. Transcendental equations, which can not only calculate the current under measurement but also the interference current at random places, are constructed. Numerical simulations, finite element analysis (FEA) of the field and laboratory experiments were performed to verify the proposed method. It is shown that when targeted current is 100 A and interference is 820 A, the largest simulated error is 3.92 × 10−10; when targeted current is 100 A and interference is 1000 A, error with FEA is 2.3796%, when targeted current and interference are both 500 A, experimental error is 4.14%. This verifies the effectiveness of the proposed method.

Dual frequency fusion for defect signal enhancement in EC-GMR inspecton of riveted multilayer structures

Reliable detection of defects under fasteners at rivet sites is one of the most critical problems in inspection of multilayer structures. Rotating eddy current (EC) excitation with giant magnetoresistive (GMR) sensor array field pick up (EC-GMR) has proved to be a promising approach in this application. In this paper, fusion of dual frequency is applied to EC-GMR scan data acquired with a novel differential array probe, to suppress the strong fastener response and hence improve the detectability of defects. Performance of the data fusion algorithm is evaluated on a two-layer aluminum sample with steel fasteners and notches introduced in the bottom layer using the electric discharge machine (EDM). Experimental results demonstrate that defects of different sizes can be successfully detected by evaluating the residual field after fusion. Defect orientation angle has minimal impact on the sensitivity of the probe owing to rotating eddy current excitation.

An Eddy Current Testing Platform System for Pipe Defect Inspection Based on an Optimized Eddy Current Technique Probe Design.

The use of the eddy current technique (ECT) for the non-destructive testing of conducting materials has become increasingly important in the past few years. The use of the non-destructive ECT plays a key role in the ensuring the safety and integrity of the large industrial structures such as oil and gas pipelines. This paper introduce a novel ECT probe design integrated with the distributed ECT inspection system (DSECT) use for crack inspection on inner ferromagnetic pipes. The system consists of an array of giant magneto-resistive (GMR) sensors, a pneumatic system, a rotating magnetic field excitation source and a host PC acting as the data analysis center. Probe design parameters, namely probe diameter, an excitation coil and the number of GMR sensors in the array sensor is optimized using numerical optimization based on the desirability approach. The main benefits of DSECT can be seen in terms of its modularity and flexibility for the use of different types of magnetic transducers/sensors, and signals of a different nature with either digital or analog outputs, making it suited for the ECT probe design using an array of GMR magnetic sensors. A real-time application of the DSECT distributed system for ECT inspection can be exploited for the inspection of 70 mm carbon steel pipe. In order to predict the axial and circumference defect detection, a mathematical model is developed based on the technique known as response surface methodology (RSM). The inspection results of a carbon steel pipe sample with artificial defects indicate that the system design is highly efficient.

Current deflection NDE for the inspection and monitoring of pipes

Routine inspection of oil and gas pipes for time dependent degradation is essential. Pipelines are most commonly inspected using In-Line Inspection (ILI), however restrictions from pipe geometry, features or flow rate can prevent its use. Facility pipework rarely facilitates ILI, and external inspection often warrants the undesirable removal of the pipe insulation and cladding. This work investigates the applicability of a current deflection non-destructive evaluation technique for both the detection and growth monitoring of defects, particularly focusing on corrosion. Magnetic sensors are used to monitor variations in the spatial distribution of the induced magnetic flux density outside a pipe that arise from deflection of an injected electric current around inner or outer wall defects. An array of orthogonal magnetoresistive sensors has been used to measure the magnetic flux density surrounding six-inch schedule 40 seamless and welded carbon steel and austenitic steel pipes. The measurements were stable and repeatable to the order of 100pT which suggests that the defect detection or growth monitoring of corrosion-type defects may be possible with a few amps of injected current when measurements are taken at around 50mm lift-off. The sensitivity of the technique is dependent on factors including defect geometry, sensor lift-off, bends, variations in nominal pipe geometry or material properties, and the presence of ferromagnetic objects, each of which were investigated using either experiment or a validated finite element model.