Giant Magnetoresistive Sensors Research Articles

Automation Highlights from the Literature

Automation Highlights from the Literature

Researching progress of the 1/f noise in TMR and GMR sensors

The low-frequency noise is the most important influence on the low frequency resolution and sensitivity in tunnel junction magnetoresistance(TMR) sensors and giant magnetoresistance (GMR) sensor for the large noise power density. In this paper, We describe the 1/f noise characteristics, sources, theoretical models, testing methods and noise reduction measures for TMR sensors and GMR sensors, and the detailed physical model of 1/f noise in the tunnel junction magnetoresistive sensor is explained. By nano-simulation software Virtual NanoLab, Fe/MgO/Fe magnetic tunnel junctions (MTJs) with different thicknesses of MgO layer are studied. Their tunneling probabilities and TMR change rates are simulated and calculated, the conservative and the optimistic estimates of the Change rate of TMR are 98.1 % and 10324.55%.While the influence of MgO thickness on noise is studied through the MTJ model. To study the noise dependance on external magnetic field, an magnetic shielding equipment for noise measurement is set up, and the tests show that the noise in the magnetic shielding environment is significantly reduced.

Quick genotyping detection of HBV by giant magnetoresistive biochip combined with PCR and line probe assay

Genotyping of human hepatitis B virus (HBV) can be used to direct clinically effective therapeutic drug-selection. Herein we report that a quick genotyping method for human HBV was established by a specially designed giant magnetoresistive (GMR) biochip combined with magnetic nanoclusters (MNCs), PCR and line probe assay. Magnetic nanoclusters of around 180 nm in diameter were prepared and modified with streptavidin, and resultant streptavidin-modified magnetic nanoclusters were used for capturing biotin-labeled hybrid products on the detection interface of the sensor. The gene fragments of HBV's B and C gene types were obtained by PCR based on a template of B- and C-type plasmids. After gene fragments were hybridized with captured probes, streptavidin-modified magnetic nanoclusters could bind with biotin-conjugated gene fragments, and the resultant hydride products could be quickly detected and distinguished by the GMR sensor, with a detection sensitivity of 200 IU mL(-1) target HBV DNA molecules. The novel method has great potential application in clinical HBV genotyping diagnosis, and can be easily extended to other biomedical applications based on molecular recognition.

INACCURACIES OF ANISOTROPIC MAGNETO-RESISTANCE ANGLE SENSORS DUE TO ASSEMBLY TOLERANCES

A large class of angle sensors uses a small permanent magnet attached to the rotor. The magnet is polarized perpendicularly to the axis of rotation, and a magnetic fleld sensor is placed ahead on the axis. The sensor circuit consists of two full bridges at 45 - , each having four anisotropic magneto-resistive (AMR) elements. Even though the electronic system may be calibrated to have nearly no errors like ofiset, nonlinearity, and mismatch, still signiflcant angle errors may result from assembly tolerances of the magnet and the sensor. This work gives an analytical description of the angle error caused by tilts and eccentricities of magnet and sensor elements against the axis of rotation. Particular emphasis is given to worst case combinations of all tolerances. One part of the angle error can be cancelled by an optimized layout of the AMR-resistors. The remaining part is identical to the case of giant magneto-resistive (GMR) angle sensors. Errors of both AMR and GMR angle sensors are efiectively reduced by identical optimization of the shape of magnets. One such optimized shape is disclosed.

Development of Sensors Based on Giant Magnetoresistance Material

In this review we discuss development of sensors based on giant magnetoresistance (GMR) material.The GMR material has high magnetic and electrical properties, therefore it has great potential as next generation magnetic field sensing devices. During the last decade, intensive research efforts have been expended to develop sensors based on giant magnetoresistance (GMR) material, both based on inorganic materials and organic materials. Many application of GMR sensor, such as: current sensor, linear and rotational position sensor, head recording, and biosensor, are reviewed.

A framework for automatic TRIZ level of invention estimation of patents using natural language processing, knowledge-transfer and patent citation metrics

Patents provide a wealth of information about design concepts, their physical realization, and their relationship to prior designs in the form of citations. Patents can provide useful input for several goals of next-generation computer-aided design (CAD) systems, yet more efficient tools are needed to facilitate patent search and ranking. In this paper, a novel framework is presented and implemented for classifying patents according to level of invention (LOI) as defined in the theory of inventive problem solving (TRIZ). Level of invention characterizes the creativity of a design concept based on the resolution of a design conflict and the disciplines used in resolving the conflict. The assessment of LOI for a series of patents provides a useful input for screening and ranking patents in databases to identify high-impact patents. However, the manual effort required for assigning LOI to each patent is laborious and time-consuming. In this paper, a novel method that combines text mining, natural language processing, creation of knowledge-transfer metrics, and application of machine learning approaches is presented and implemented for classifying patents according to LOI. Two case studies are presented in which LOI data is compiled for patents: dynamic magnetic information storage or retrieval using Giant Magnetoresistive (GMR) or Colossal Magnetoresistive (CMR) sensors formed of multiple thin films (USPC 360/324) and arbitration for access to a channel (USPC 370/462). The peak performance in 5-fold stratified cross-validation was found to be 73.38% in the first case study and 77.12% for the second.

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.

GMR Sensors: Technologies and Medical Applications

Giant Magnetoresistance (GMR) is a quantum mechanical effect found in thin film materials that are composed of alternating nano-size ferromagnetic and non magnetic layers. When a GMR material is in the presence of a magnetic field a change in electrical resistance is observed. The GMR effect has been used to produce magnetic sensors that can be used in a variety of applications. Although there are some sensors that have greater sensitivity and lower magnetic detection limits, GMR sensors have more commercial potential due to their small size, low power use, low fabrication cost, and their reproducible operation in very narrow magnetic ranges. The medical field is rapidly adopting the use of GMR magnetic sensors for many medical applications; this is leading to an increase in the number of patents that include GMR sensors. Two of the most promising medical application areas for GMR sensors are medical diagnostics and implant communication. This article reviews the GMR mechanism, measurement, fabrication techniques, and discusses a variety of medical applications and patents that incorporate GMR sensors. Keywords: GMR Sensors, Bioassays, Biosensors, Giant Magnetoresistance, Implant Communication, Magnetic Immunoassays, Magnetic Labeling, Magnetic Relaxation, Magnetic Sensor, Magnetic Sorting, Magnetic Switching, Magnetic Thin Films, Nanowires, Near Field Communication, Multilayer Nanowires

EC-GMR Data Analysis for Inspection of Multilayer Airframe Structures

Eddy-current testing (ECT) is widely used in inspection of multilayer aircraft skin structures for the detection of cracks under fasteners (CUF). Detection of deep hidden CUF poses a major challenge in traditional ECT techniques largely because the weak eddy-current signal due to a subsurface crack is dominated by the strong signal from the aluminum or steel fastener. Giant magnetoresistive (GMR) sensors are finding increasing applications in directly measuring weak magnetic fields associated with induced eddy currents. The measured flux image at a fastener site is in general symmetric and an asymmetry is introduced by the presence of a subsurface crack, which is used for defect detection. This paper presents novel methods that employ the resident phase information, for improving detection probability of GMR signal analysis. Using computational model, the effectiveness of the proposed methods for enhancing detection of CUF is investigated. Results demonstrating the potential of these techniques for detection of second layer CUF are presented.

Evaluation of portable ECT instruments with positioning capability

In this paper two different low-cost eddy current testing (ECT) systems used in detecting and measuring defects in conductive surfaces are evaluated and its performance compared with a commercial equipment. Both developed systems include a probe with a giant magnetoresistance (GMR) as the magnetic field sensor and a computer mouse pointer as the positioning system. This configuration, despite its low cost, allows better performances than commercial equipments because deeper defects can be detected due to the higher sensitivity of the GMR sensor, which is constant in a very large frequency range (10Hz–1MHz), but also because a precisely located graphical representation of the defect is delivered to the user due to the incorporated positioning system. Although having the same goal, both developed ECT system implementations differ on their architectures and signal processing algorithms. One system is based on a digital signal processor (DSP) where raw data is digitally processed and the other system uses analog circuits to process the acquired signals. This paper includes a detailed description of each implementation, the obtained results and a performance comparison with commercial equipment.

Design of New Metal Detector

Metal detector is used more and more widely in the modern social life, it acquires much attention because of its powerful detection capabilities. This article introduces the design and implementation of an intelligent metal detector which is based on TMS320LF-2407.Adopt giant magneto resistive (GMR) sensor with the type of AA006-02. Describe the hardware component, software design, working principle and main functions of the system in detail. The core of the whole contains the probe design and control circuits. The probe: oscillator circuit is constituted by the 555 timer, it provide the sine wave signal for the coil. The control circuits: the signal which is collect by the GMR sensor is processed by voltage amplifier and filtering circuit, the peak detection circuit and A / D conversion, The signal can accurately reflect the characteristic parameters of the received signal, stability, and can eliminate interference.Practice shows that this metal detector with the method can greatly reduce the malfunction rate on the base of meeting the sensitivity.

Increase in the detection sensitivity of a lateral flow assay for a cardiac marker by oriented immobilization of antibody

Early detection of human cardiac markers is regarded as a gold standard for diagnosis of acute myocardial infarction (AMI). Here we demonstrate the increase in the detection sensitivity of a lateral flow assay for a cardiac marker troponin I (cTnI) by oriented immobilization of antibodies on magnetic beads. For the construction of sensitive magnetic labels, orientated-immobilization of anti-troponin I antibodies on magnetic beads was attempted using protein G. Magnetic beads were first conjugated with protein G followed by immobilization of anti-cTnI antibodies. The factors affecting the detection sensitivity in the lateral flow assay system were investigated. The lateral flow assay of cTnI was carried out using the magnetic beads and a Giant magnetoresistive (GMR) sensor at the optimized conditions, and compared the results with using a conventional random immobilization method. Magnetic labels with oriented immobilization of antibodies enabled the detection of cTnI up to 0.01 ng/mL, showing significantly increased sensitivity compared with conventional immobilization method. This result clearly shows that the magnetic labels with oriented immobilization of antibodies can find wide applications in the lateral flow assays of target analytes.

Low field MRI with magnetoresistive mixed sensors

Low-field magnetic resonance imaging (MRI) requires very sensitive magnetometers for detection of weak magnetic signals in femtoTesla range. Magnetoresistive mixed sensors could be used as the sensitive magnetometers [1]. These sensors are the combination of a Giant Magnetoresistive (GMR) field sensor and a superconducting loop used as a flux-to-field transformer. A MRI set-up based on mixed sensor has been mounted. This system operates in static field up to 10mT without shielded room. We will present the LF-MRI setup with the implementation of mixed sensors and the first MRI images obtained at low field without prepolarization.

Low-drift giant magnetoresistive field sensor using modulation of free-layer magnetization direction

We report a field sensor, which senses the external field by detecting the change of frequency component in the modulated GMR output. The proposed sensor works in a closed-loop mode with negative feedback and the free-layer magnetization is modulated by an alternative field Hac (2.3 Oe). The sensor output (Vout) is proportional to the applied external field (Hex) in the range from −1.5 to +1.5 Oe. Vout is determined only by the feedback current, and has no direct relationship with the magnetoresistance ratio or the gains of the amplifiers. The proposed sensor exhibits a much lower temperature drift (about 1/50) compared with a typical magnetization rotation-type sensor and a further reduction in the drift can be achieved by improving the signal acquisition circuit; thus it can be used for high-precision dc field detection without any additional temperature compensation.

Influence of the free-layer domain structure on domain-wall displacing type field sensors

We propose a giant magnetoresistive sensor which utilizes the shifting of oscillatory domain walls to detect the external field along the easy axis. For this type of sensor the domains in the soft magnetic free layer play an import role and the sensor output is mainly determined by the domain-wall displacement. Domain structures in various micro-fabricated soft magnetic patterns have been investigated and two typical free-layer materials were selected to fabricate the sensor devices. The domain-wall displacing (DWD) type sensor with a 10 nm Ni80Fe20 free layer shows a higher field sensitivity than that with CoFeB, however the sensor output becomes saturated when the external field (Hex) > 0.4 Oe. For the sensor which has a 10 nm (Co90Fe10)92B8 free layer, the sensor output is linear even as Hex increases to 2.6 Oe. In addition, the sensors were operated under the magnetization rotation mode to compare the sensor outputs with the DWD mode. When the sensors were operated under the DWD mode a field sensitivity of at least two times higher was achieved.

A Three-Layer Competition-Based Giant Magnetoresistive Assay for Direct Quantification of Endoglin from Human Urine

This study presents a three-layer competition-based assay for ultrasensitive detection and quantification of endoglin from unprocessed human urine samples using a giant magnetoresistive (GMR) sensor and high-moment magnetic nanoparticle-based biosensing technology. This biosensing platform detects as few as 1000 copies of endoglin at concentrations as low as 83 fM with high detection specificity and has a three-order dynamic range. The results reveal that endoglin levels in urine have the potential to predict for the presence of prostate cancer and to distinguish between prostate cancers of different grades.

A GMR–ECT based embedded solution for applications on PCB inspections

Abstract Real-time non-destructive testing and evaluation (NDT/E) of conducting materials using eddy current techniques (ECTs) has gained significance in the last few years. This paper proposes a real-time application of ECT–NDT system exploiting giant magneto-resistive (GMR) sensors for inspection of printed circuit boards (PCBs). Probe design aims to crack inspection over flat surface, especially suitable for micro-defect detection on high density bare PCB. We propose a system based on a GMR sensor able to detect the magnetic field resulting from the interaction between a planar coil exciter and PCBs. The EC signals, detected by the GMR sensor, have been acquired by a high speed analog-to-digital (A/D) converter, for a subsequent application of signal processing based on digital techniques. The achieved results have highlighted the efficient design of the system. The advantages of the proposed models and some possible improvements of the system are also discussed.

Detection of magnetic microbeads and ferrofluid with giant magnetoresistance sensors

Giant magnetoresistance sensors based on multilayers [Cu/NiFeCo]×10/ Ta were fabricated by microfabrication technology. A GMR-bridge was used to detect the magnetic MyOne beads and Ferro fluid. The dependence of the GMR-bridge signals on the surface coverage of MyOne beads was studied. The results show that the GMR sensor is capable of detecting the magnetic beads. The detectable limit of MyOne beads is about 100, and the corresponding signal output is 8 μV. The GMR bridge signal is proportional to the surface coverage of the MyOne beads. The sensitivity of the GMR bridge is inversely proportional to the feature size of the GMR sensor. The GMR bridge integrated with microfludic channel was also used for dynamic detection of ferrofluid (suspension of Fe3O4 particles). The results show that the GMR bridge is capable of detecting the flow of ferrofluid, and the sensor signals are proportional to the concentration of the ferrofluid. The detection limit of concentration of the ferrofluid is 0.56 mg/ml, and the corresponding signal is 6.2 μV.

Control of Nano-pinhole Structure by Inducing Pulse Current for CPP-GMR Sensor Using Confined Current Path

We investigated how to control the nano-pinhole structure of a confined-current-path current-perpendicular-to-plane giant magnetoresistive (CCP-CPP GMR) sensor by inducing pulse current. We found an improved MR ratio with reduced sensor resistance by applying an optimal pulse current. This was assumed to be due to the enlarged nano-pinhole area and reduced pinhole resistance. When excessive pulse current was applied, the MR ratio and sensor resistance decreased because the CPP-GMR sensor degraded thermally.

Magnetic moments of fine particles from micromagnetic surveys

A new scanning magnetic microscope to image magnetic fields with micrometric resolution has been constructed based on a giant magnetoresistance (GMR) sensor. Operating in zerofield, the GMR sensor is sensitive to the components of the magnetic field arising from the remanent magnetisation parallel to the plane of the cut rock surface. The field component perpendicular to the surface therefore has to be calculated using FFT relationships. The spatial resolution of the system is 20 µm, and its peak-to-peak noise during operation is 250 nT. Its high spatial resolution and a minimum sensor- to-sample distance of only 30 µm compensate for its rather modest field sensitivity.