Biosensor Based on Giant Magnetoresistance Material

For the detection of specific bio-molecules, such as cells, proteins and DNA, it is necessary to verify the limit of detection (LOD) of an investigated giant magnetoresistive (GMR) sensor. We measured voltage drops across a GMR sensor before and after spreading magnetic particles on the surface of the GMR sensor and compared them to find the LOD of the GMR sensor. Magnetic particles (DynabeadsR ©) of 2.8 μm in diameter were used. The threshold for the detection was approximately 6 beads. This result indicates that the GMR sensor studied in this study can be used to detect bio-molecules, such as micron-sized cells.

This paper is a continuation of our former work [1-2]. In this paper, injected AC current and Giant Magneto-Resistance (GMR) sensor were used to detect small defects in the order of few hundred micrometers in thin layers using two connectors and detecting the perturbation of the magnetic field due to a defect using a GMR sensor. A sample of silicon wafer with copper metallization of few micrometers in thickness was used. On the conductive surface a 2.5 mm long scratch was created where the width of the scratch was 0.2 mm. Four measurements were conducted to detect this defect. The first one, was performed when the sensitive axis of GMR sensor was perpendicular to scratch. The second measurement was conducted when the sensitive axis of the sensor was parallel to scratch. In the third and forth measurements the silicon wafer was flipped over to the side of the none-conducting layer in order to determine the resolution of the GMR. AC current was injected on the bottom of the wafer; the 2.5 mm length scratch was easily detected where GMR was parallel, and perpendicular to scratch for the third and fourth measurement respectively. It was found that the sensor output amplitude was maximum when the sensor axis was parallel to the scratch (0.33 V and 0.25 V for measurements 2 and 3 respectively), while the sensor output amplitude was minimum in the case where the sensor axis was perpendicular to the scratch (0.13 V and 0.1 for measurements 1 and 4 respectively). It was found that the amplitude which was recorded in the case where the sensor was parallel to scratch on the surface (measurement 2) is about 25% larger comparing with the sensor which was parallel to scratch and GMR sensor was over the back side of the same wafer.

In order to test the characteristics of giant magneto-resistance (GMR) sensor comprehensively and accurately, a test system based on 3D Helmholtz coil is designed. The coil can generate sine magnetic field in the range of −10mT to 10mT, 0Hz to 500Hz in three vertical dimensions. The static and low-frequency characteristics of a GMR sensor are tested and analyzed. The dynamic test results reveal that GMR sensor should be applied in unipolar magnetic in its linear range in which case maximal error is still as large as 20% mainly caused by hysteresis. In order to increase the accuracy furthermore in measuring dynamic instantaneous magnetic induction, appropriate hysteresis compensation methods should be analyzed and applied in further research.

Needle-type GMR sensor to estimate the magnetic properties of diluted ferrofluid for biomedicine application

The purpose of this paper is to present an eddy current testing technique for surface defect detection in conducting materials using a giant magneto resistive (GMR) sensor. A flat coil is used to produce an alternate magnetic field, which gives rise to eddy currents in the material under test. The GMR sensor with the coil placed on top of it is mounted in a holder, which is moved over the surface of the metal plate using an XY table. Three aluminium plates were used with defects having nominals depths of 2, 4, 6, and 8 mm and widths of 0.6, 1 and 1.4 mm, respectively. The defects were scanned with the sensing axis perpendicular to the defect length. The GMR output voltage depends on the width and depth of the defects. Two parameters extracted from the GMR output voltage signal are obtained and a simple correlation between the defects dimensions and the GMR output voltage is proposed.

Summary form only given. Compared to the established fluorescent labeling method, the use of magnetic markers in biochip sensors has important advantages with respect to the detection of biomolecules at low concentrations. The magnetic markers are commercially available superparamagnetic microspheres. We demonstrate the applicability and functionality of both Giant Magnetoresistance (GMR) and Tunnel Magnetoresistance (TMR) sensors for detecting magnetic markers, also including corresponding molecular binding results with DNA. The GMR sensors consist of patterned Cu/NiFe multilayers in the second antiferromagnetic maximum, whose resistance vs. field dependencies can be tailored for large sensitivity (up to 3%/Oe). The experimental data are supported and understood by numerical simulations in a local field approach. Initial experiments with TMR sensors take advantage of the larger signal amplitude of around 40% and corresponding sensitivity of 12%/Oe.

This paper presents a new method to design power meter based on giant magneto resistance (GMR) sensor. Firstly, we introduce the basic principle and characteristics of GMR sensor, and then propose an open-loop current sensor structure. The power of the circuit is transformed into the product of magnetic field around the GMR sensor and supply voltage of the sensor. According to the output voltage value of the sensor, we can calculate the power of the circuit. Finally, the output voltage of the sensor is collected by the AD sampling chip, converted into digital signal and then transmitted to the single chip computer for conversion. The instantaneous power value of the circuit is displayed on the display device. The designed power meter can measure signals from DC to high frequency (MHz magnitude), and the test method is simple.

This paper describes a design for a near field hybrid recording system that uses a mode index waveguide lens in place of a SIL or optical fiber. The mode index waveguide lens is fabricated on the back of an air bearing slider with a thin film magnetic head and giant magneto resistance (GMR) sensor for reading and writing. The optical spot from the waveguide heats the media to its Curie temperature such that within the spot a region with a reduced coercive field (`Curie cylinder') is created. The thin film head then applies a magnetic field to switch the magnetization within the Curie cylinder thereby recording a written mark. In the system proposed here, the track width of the optical spot is less than that of the thin film head and as such defines the recording track width. A GMR sensor is used to sense the flux leakage from the surface of the media and may also be laser assisted. Calculations predict an aerial density of 70 Gbits/inch<SUP>2</SUP> when using a simple mode index lens fabricated from a SiO<SUB>2</SUB>/SiN<SUB>x</SUB>/SiO<SUB>2</SUB> waveguide. Furthermore, by using advanced lens designs and innovative materials, the track width can be reduced further thereby offering a promising way to achieve 500 Gb/inch<SUP>2</SUP>.

Non-destructive eddy current testing (ECT) is widely used to examine structural defects in ferromagnetic pipe in the oil and gas industry. Implementation of giant magnetoresistance (GMR) sensors as magnetic field sensors to detect the changes of magnetic field continuity have increased the sensitivity of eddy current techniques in detecting the material defect profile. However, not many researchers have described in detail the structure and issues of GMR sensors and their application in eddy current techniques for nondestructive testing. This paper will describe the implementation of GMR sensors in non-destructive testing eddy current testing. The first part of this paper will describe the structure and principles of GMR sensors. The second part outlines the principles and types of eddy current testing probe that have been studied and developed by previous researchers. The influence of various parameters on the GMR measurement and a factor affecting in eddy current testing will be described in detail in the third part of this paper. Finally, this paper will discuss the limitations of coil probe and compensation techniques that researchers have applied in eddy current testing probes. A comprehensive review of previous studies on the application of GMR sensors in non-destructive eddy current testing also be given at the end of this paper.

Asthma, a chronic lung disease which causes severe problem in breathing. The asthma cause due to lung airway constriction by triggers, such as allergic reactions to dust or pollen. The asthma never diagnose at early stage since symptoms such as coughing confuse with cold. The Asthma only diagnose when shortness of breath occur and it causes an examination by a physician. In this paper, we propose a non-invasive way to diagnose asthma at early stage via bio magnetic signal acquired from a person lung. The mucus in airway of lung clogs airway during constriction. The Giant magnetoresistance (GMR) sensor place on lung region and bio-magnetic emission from mucus in lung acquire. The biomagnetic signal of mucus in lung constricted airway change due to mucus normal and dynamic condition. The constricted lung airway cure by Ventolin entolin inhaler, which makes constricted muscle to relax and provide airflow. The mucus accumulation and mucus flow provide varying bio-magnetic emission. The bio-magnetic emission change correlate with asthma through RADWT subband energy level. The RADWT subband energy level and airflow meter test model with linear regression for lung airway opening and asthma diagnosis.

The rotor position is a key state in the closed-loop control system of the permanent magnet synchronous motor (PMSM). Its measurement accuracy has a significant effect on steady accuracy, dynamic response, and torque ripple. The magnetoresistance (MR) sensor is widely used in the rotor position detection due to its distinct advantages, such as simple structure, high sensitivity, and strong robustness. In this paper, a solution using the giant magnetoresistance (GMR) sensor in TLE5309D chip for angle measurement is introduced, and its feasibility is verified by finite element analysis (FEA) simulation and bench test. In the simulation, two schemes different in the sensor location and the number of permanent magnet poles, are evaluated according to the higher harmonic content and field direction stability near the sensor. The experiment from 1 rpm to 1000 rpm is implemented, and the measurement results after calibration based on discrete Fourier series (DFS) show that the GMR sensor has a good performance in the test.

High spatial resolution flaw detector based on the GMR eddy-current probe

The goal of the project was to demonstrate the feasibility of the detection of buried unexploded ordnance (UXO) using giant magnetoresistive (GMR) sensor arrays. 3x3 and 5x5 arrays of off-the-shelf GMR sensors were purchased from Nonvolatile Electronics (NVE) and were interfaced with a data acquisition card and a personal computer. Magnetic images were obtained from a number of ferrous objects, such as threadstock, bolts, and rebar. These images can be interpreted in terms of the remanent magnetic state of the objects. The ability of the GMR sensor approach to discriminate among magnetic objects is assessed and the design of a more realistic UXO detection system is discussed.

Giant magneto-resistive (GMR) sensor based metal magnetic memory (MMM) technique is proposed for mapping of deformation-induced self-magnetic leakage fields (SMLFs) in carbon steel. The specimens were subjected to different amounts of tensile deformation and the deformation-induced SMLFs were measured using a GMR sensor after unloading the specimens. 3D-nonlinear finite element modeling was performed to predict stress–strain state in a steel specimen under tensile load. The experimentally obtained SMLF images were correlated with the finite element model predicted stress–strain states. Studies reveal that the MMM technique can detect the plastic deformation with signal-to-noise ratio better than 20 dB. The technique enables the mapping of plastic deformation in carbon steels for the evaluation of the severity of deformation. The study also reveals that deformation-induced SMLF is influenced by the presence of initial surface residual stress, introduced by shot peening. The intensity of SMLF signal is found to increase with increase in tensile load and decrease with shot peening.

A giant magnetoresistance (GMR) sensor with a Wheatstone bridge structure and an out-of-plane linear response was developed. The spin-valve structure consists of a synthetic antiferromagnetic [(Co/Pt)n/Ru/(Pt/Co)n] reference layer with perpendicular magnetic anisotropy, a Cu spacer layer, and a Co-free layer with in-plane easy magnetization. By utilizing the spin–orbit torque induced magnetization switching in the synthetic antiferromagnetic layer, the magnetization of the reference layers in the adjacent bridge arms is set to the opposite direction, achieving a GMR sensor with a full Wheatstone bridge structure. The sensor exhibits linear response to the out-of-plane magnetic field with adjustable dynamic ranges from hundreds to thousands of Oe, depending on the thickness of the Co-free layer. A similar Wheatstone bridge sensor consisting of magnetic tunnel junctions was also proposed. The sensor with out-of-plane linear response may have promising applications in three-dimensional magnetic field detection and current sensing field.