GMR Sensor Research Articles

The Omnipolar Integrated Magnetic Switch Based on GMR

This paper presents the realization of omnipolar integrated magnetic switch based on GMR sensor, which was integrated with a specifically designed process IC by SiP technology. This integrated switch introduced hysteresis and adjustable sensitivity to improve its performance. When the gain was set to 2, its operation point and release point are 2.7|Oe| and 1.8|Oe| respectively. Its characteristics and function are verified by 2D Helmholtz coils and gear sensor test platform.

Characterization of Integrated GMR Sensor with Angular Variation

In this work, GMR multilayer films are deposited and then processed into GMR sensors. The transfer curves of GMR sensor are acquired by sweeping the signal magnetic field in different directions. In addition, the rotation behavior is measured by rotating a magnitude-fixed field around the sensing axis. The results are analyzed and it’s found that the angular dependence of GMR sensor can be characteristic with cosine function.

Mechanism of Cuff-Less Blood Pressure Measurement Using MMSB

Continuous measurement of blood pressure based on pulse transit time (PTT) using GMR sensors is the state-of-art non-invasive cuffless method in which modulated magnetic signature of blood (MMSB) is used. In this paper, the mechanism of MMSB is investigated. According to the experimental results, it is found that both blood pulse flowing through the applied magnetic field and the displacement of the GMR sensor caused by blood pulse contribute to the disturbance of magnetic field detected by GMR sensors. The feasibility of MMSB method is discussed as well.

High permeability flexible bulk material for magnetic micro head applications

A magnetic field is generated by feeding electric current to micro coils. The higher the current, the higher the magnetic field is. A main disadvantage of coils in micro systems is the limited thermal resistance and as a result of a restriction concerning the maximum current densities. This work shows the modelling, design, numerical calculation and the initial test of a flexible write head, which not only allows the data storage on the surface but also inside of the components. Furthermore, the write head has to be flexible and able to adapt itself to the roughness of the component surface. The main goal of this paper is to increase the magnetic flux in the micro head core by partly using high permeability flexible bulk material instead of increasing the coil current or the number of the coil turns. For the approval of the data storage process a GMR sensor is used for the readout of the stored magnetization track.

Temperature dependence of large exchange-bias in TbFe-Co/Pt

The exchange-bias effect provides unidirectional anisotropy to ferromagnetic thin-films in GMR and TMR sensors. It is weak because it relies on an inherently compensated coupling across a ferromagnet/antiferromagnet interface. We replace the antiferromagnet with a TbFe-based perpendicular-anisotropy amorphous ferrimagnet, coupling to an adjacent ferromagnet with 13-5 mJ/m2 for temperatures within 7.9–280 K. A large exchange-bias between 1.1 and 0.7 T in that temperature range ensues. The temperature dependence of the bias is step-like, and thus different from that of antiferromagnet-based exchange-bias systems. It suggests using this material in exchange-biased temperature assisted magnetic writing.

Routes for GMR-Sensor Design in Non-Destructive Testing

GMR sensors are widely used in many industrial segments such as information technology, automotive, automation and production, and safety applications. Each area requires an adaption of the sensor arrangement in terms of size adaption and alignment with respect to the field source involved. This paper deals with an analysis of geometric sensor parameters and the arrangement of GMR sensors providing a design roadmap for non-destructive testing (NDT) applications. For this purpose we use an analytical model simulating the magnetic flux leakage (MFL) distribution of surface breaking defects and investigate the flux leakage signal as a function of various sensor parameters. Our calculations show both the influence of sensor length and height and that when detecting the magnetic flux leakage of μm sized defects a gradiometer base line of 250 μm leads to a signal strength loss of less than 10% in comparison with a magnetometer response. To validate the simulation results we finally performed measurements with a GMR magnetometer sensor on a test plate with artificial μm-range cracks. The differences between simulation and measurement are below 6%. We report on the routes for a GMR gradiometer design as a basis for the fabrication of NDT-adapted sensor arrays. The results are also helpful for the use of GMR in other application when it comes to measure positions, lengths, angles or electrical currents.

GMR Sensors: Technologies and Medical Applications

GMR Sensors: Technologies and Medical Applications

Ultra-sensitive bio-sensor based on GMR in self-suspended-membrane-type germanium grating

In this paper, an ultra-sensitive bio-sensor based on the GMR effect in self-suspended-membrane-type gratings (SSGs) is proposed using multilayer plane waveguide theory. It is demonstrated from our calculations that the sensitivity of our bio-sensor is near the theoretical limit compared with a conventional GMR sensor. Based on the normalized eigenfunction of a single-layer homogeneous grating, the resonance curves with respect to different refractive indices of surrounding media are calculated, which confirm the estimated sensitivity. In addition, we design a highly sensitive bio-sensor in the near- and mid-IR wavelength region for liquid and gas detection respectively, the sensor can deliver a resolution over 1 × 10−5 in the near-IR region in a large refractive index (1.3–1.7) range and provide better than 1 × 10−6 in the mid-IR region, which is enough for various bio-material detections. Therefore, the bio-sensor we proposed is one or two orders more sensitive than conventional GMR sensors.

Sensitive metal layer assisted guided mode resonance biosensor with a spectrum inversed response and strong asymmetric resonance field distribution

In this paper, a metal layer assisted guide mode resonance (MaGMR) device with high sensitivity is proposed for bioanalytical applications and its functioning is experimentally proved. We find that the reflection spectra present a unique inversed response. The resonance mechanism is also discussed. Numerical calculation results indicate that the high sensitivity performance of MaGMR comes from the strongly asymmetric resonance modal profile and low propagation angle inside the waveguide. There is a one-fold enhancement of the evanescent wave in the analytes region compared to typical GMR. According to the experimental results, the proposed MaGMR achieved a bulk sensitivity of 376.78 nm/RIU in fundamental TM mode resonating at 0.809 μm with the first diffraction angle. Experiment results show a 264.78% enhancement in the sensitivity compared to that of the typical GMR sensor in the same resonance conditions of TM mode.

Experimental research on hysteresis effects in GMR sensors for analog measurement applications

A Wheatstone bridge GMR sensor can be used for analog magnetic field measurements. This paper deals with hysteresis effects in GMR sensor, which is the major source of measurement error. Experiments are conducted by measuring hysteresis curves between applied magnetic field and sensor output voltage with different typical initial magnetization states. GMR sensor has two operation modes: bipolar and unipolar. Bipolar operation means internal magnetization pattern of GMR sensor changes direction during operation range. This mode is inappropriate for direct measurement, as experimental results indicate that the shape of measured curves with the same range of applied magnetic field may be severely distorted due to different initial magnetization states. Unipolar operation is an intermediate process of bipolar operation with invariant magnetization direction. Its input–output relationship is almost linear that is especially suitable for measurement. The principal measurement error within unipolar operation is DC offset voltage, which is induced by remanence. It can be fixed by saturating GMR sensor before operation.

Liftoff insensitive thickness measurement of aluminum plates using harmonic eddy current excitation and a GMR sensor

This paper describes the implementation of a device that measures the thickness of metallic plates. A pancake coil for magnetic field sinusoidal excitation is used and detection is performed with a bridge giant magneto-resistor sensor. The paper uses the theory of the linear transformer to explain the liftoff effect with a special attention to the point of interception phenomenon. The transformer model shows that to attain the interception points with instantaneous measured voltages independent of the liftoff gap the excitation coil must be driven with imposed current. This effect was explored to show that a simultaneous process of thickness and conductivity measurement is feasible.

GMR-Based ECT Instrument for Detection and Characterization of Crack on a Planar Specimen: A Hand-Held Solution

This paper proposes a novel instrument for eddy-current (EC) nondestructive testing on conductive materials. The instrument is composed by a smart EC probe, based on a GMR sensor, and a suitable processing unit. The key features of the proposed instrument are the capability of detecting, locating, and characterizing thin defects as superficial and subsuperficial cracks. The main goal of the proposal is the realization of a very low cost instrument that is able to reach performance comparable with instrumentation available on the market and especially suited for application fields such as aerospace and maritime. In this paper, the steps followed for the instrument realization, together with its experimental characterization, are described in detail.

Flexible GMR Sensor Array for Magnetic Flux Leakage Testing of Steel Track Ropes

This paper presents design and development of a flexible GMR sensor array for nondestructive detection of service-induced defects on the outer surface of 64 mm diameter steel track rope. The number of GMR elements and their locations within saddle-type magnetizing coils are optimized using a three dimensional finite element model. The performance of the sensor array has been evaluated by measuring the axial component of leakage flux from localized flaw (LF) and loss of metallic cross-sectional area (LMA) type defects introduced on the track rope. Studies reveal that the GMR sensor array can reliably detect both LF and LMA type defects in the track rope. The sensor array has a fast detection speed along the length of the track rope and does not require circumferential scanning. It is also possible to image defects using the array sensor for obtaining their spatial information.

Fast defect parameter estimation based on magnetic flux leakage measurements with GMR sensors

Fast defect parameter estimation based on magnetic flux leakage measurements with GMR sensors

Quantification of protein interactions and solution transport using high-density GMR sensor arrays

Monitoring the kinetics of protein interactions on a high density sensor array is vital to drug development and proteomic analysis. Label-free kinetic assays based on surface plasmon resonance are the current gold standard, but they have poor detection limits, suffer from non-specific binding, and are not amenable to high throughput analyses. Here we show that magnetically responsive nanosensors that have been scaled to over 100,000 sensors/cm2 can be used to measure the binding kinetics of various proteins with high spatial and temporal resolution. We present an analytical model that describes the binding of magnetically labeled antibodies to proteins that are immobilized on the sensor surface. This model is able to quantify the kinetics of antibody-antigen binding at sensitivities as low as 20 zeptomoles of solute.

GMR sensors: Magnetoresistive behaviour optimization for biological detection by means of superparamagnetic nanoparticles

An immunomagnetic method for the selective and quantitative detection of biological species by means of a magnetoresistive biosensor and superparamagnetic particles has been optimized. In order to achieve this, a giant magnetoresistive [Co (5.10 nm)/Cu (2.47 nm)] 20 multilayer structure has been chosen as the sensitive material, showing a magnetoresistance of 3.60% at 215 Oe and a sensitivity up to 0.19 Ω/Oe between 145 Oe and 350 Oe. The outward gold surface of the sensor is biofunctionalized with a Self-Assembled Monolayer (SAM). In addition, three different types of magnetic labels have been tested. 2 μm diameter magnetic carriers (7.68 pg ferrite/particle) have shown the best response and they have induced a shift in the magnetoresistive hysteresis loops up to 9% at 175 Oe.

Delta-Sigma Digital Current Sensor Based On GMR

This paper presents an integrated delta-sigma digital current sensor. With high sensitivity and good linearity, GMR sensor is a good choice for current measurement application. In this design, a GMR sensor which is configured as a Wheatstone bridge of four spin-valve sensing elements is integrated with CMOS signal processing circuit together, and the output signal is converted to digital domain by an on-chip 10-bit delta-sigma ADC. The whole circuit is designed and simulated using CSMC standard 0.5 μm process.

The Analysis of GMR Sensor's Angular Dependence

This paper presents the experimental results of GMR sensors' angular dependence, which was tested by applying three different magnetic fields (5Oe, 10Oe, 15Oe) to GMR sensors with different sensitivity. It is found that the GMR sensor is sensitive to angular variation and can be characterized with a cosine function. By comparing the experimental curve with that simulated by the ideal model, we have established a modified model by introducing several new factors to make it fit with the test data.

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.

Harmonic response of GMR sensor under sinusoidal excitation field

In this work, we report the readout technique of the GMR magnetometer by detecting the odd-harmonic response under an sinusoidal excitation field. The time domain output waveform of the sensor is measured, and an analytical model is used to simulate its behaviour. In the frequency domain, it is found that the major Fourier components of the sensor response are the even harmonics of excitation frequency. The even harmonics are insensitive to the applied field, whereas the odd-harmonic amplitudes change significantly with the increasing applied field. To maximize the field-to-voltage transfer coefficient, the mixing circuit with a square wave reference is used to detect the odd-harmonic components of the output signal. In a small signal mode, the measured field-to-voltage coefficient of the sensor is 138 mV/mT under a 9 V bias voltage, achieving the noise level of 17 nT/Hz1/2 at 1 Hz. The noise level can be further reduced by utilizing the multiple-harmonic reference. The proposed device is suitable for measuring the E arth's dc magnetic field.