Tunnel Magnetoresistance Sensors Research Articles

Research on Field Source Characteristics of Leakage Current of Arrester Based on TMR Sensor.

The status of zinc oxide (ZnO) arresters is directly related to the safety of power grids. However, as the service life of ZnO arresters increases, their insulation performance may decrease due to factors such as operating voltage and humidity, which can be identified through the measurement of leakage current. Tunnel magnetoresistance (TMR) sensors with high sensitivity, good temperature stability, and small size are excellent for measuring leakage current. This paper constructs a simulation model of the arrester and investigates the deployment of the TMR current sensor and the size of the magnetic concentrating ring. The arrester's leakage current magnetic field distribution under different operating conditions is simulated. The simulation model can aid in optimizing the detection of leakage current in arresters using TMR current sensors, and the findings serve as a basis for monitoring the condition of arresters and improving the installation of current sensors. The TMR current sensor design offers potential advantages such as high accuracy, miniaturization, and ease of distributed application measurement, making it suitable for large-scale use. Finally, the validity of the simulations and conclusions is verified through experiments.

Removal of the effect of the high solids holdup ring in the fluidized bed on electromagnetic tomography

Electromagnetic tomography (EMT) system based on tunneling magneto resistance (TMR) sensor, as a non-invasive multiphase flow measurement technique, can effectively detect the solid-phase distribution in the gas–liquid–solid three-phase fluidized bed with magnetic catalysts by reconstructing the permeability distribution image. The radial distribution of solid particles in the gas–liquid–solid three-phase fluidized bed with uneven fluidization is non-uniform, in which a high solids holdup ring exists near the wall of the riser. When the TMR-EMT system is used directly for image reconstruction, the high solids holdup ring will greatly reduce the image quality, further leading to the inability to detect phase information in the riser. To improve the reconstructed image by the TMR-EMT system, a removal method for the high solids holdup ring is proposed. The method firstly estimates the equivalent thickness of the high solids holdup ring based on the boundary measurement data. Then the influence of the high solids holdup ring on the boundary measurement data is subtracted. By the removal method, the internal phase distribution information is prominent. The simulation and experimental results demonstrate that the proposed method can realize the permeability distribution detection by the TMR-EMT system in the presence of the high solids holdup ring.

High-performance MTJ-based sensors for monitoring of atmospheric pollution

Solid and liquid particles in the atmosphere, referred to as airborne particulate matter (PM), have been rising significantly over the past two decades. Exposure to PM carries significant health risks such as lungs damage, heart disease, cancer, and death. PM2.5 is a subgroup of PM particles that are smaller than 2.5 µm and is a major concern as it is more harmful to health and more difficult to detect. One problematic component of PM2.5 is magnetite nanoparticles (<200 nm), which are readily absorbed into the bloodstream through the respiratory system. Eventually, magnetite nanoparticles deposit inside the brain causing neurodegenerative diseases such as Alzheimer’s or cancerous tumors by inducing oxidative stress. Additionally, Magnetite nanoparticles are often surrounded by heavy metal nanoparticles such as Cadmium and lead which are a great concern to the environment and health. Traditional PM detection methods such as laser scattering are bulky, expensive, and incapable of detecting particles smaller than 200 nm such as magnetite nanoparticles. Therefore, developing a low-cost highly sensitive sensor for monitoring magnetite nanoparticles is vital. Tunneling Magneto-Resistance (TMR) sensors are an attractive option due to their low-cost and high sensitivity toward magnetic nanoparticle detection. Moreover, developing a cheap, portable, and precise remote monitoring technique will allow for the creation of high spatial resolution highly sensitive monitoring networks for magnetic PM2.5. This work focuses on developing, modeling, and simulation of low-cost highly sensitive TMR sensor based on Magnetic Tunnel Junction (MTJ) that can detect and count magnetite nanoparticles.

Research on temperature drift of tunneling magnetoresistance sensor based on proportional relationship and MacLaurin’s series

To solve the problem of the Wheatstone full-bridge unequal resistance and low calculation accuracy, a calculation model for temperature drift of Tunneling Magnetoresistance sensors without magnet field is proposed. Based on proportional relation, McLaurin’s series, and temperature coefficient of resistance, the model can explain the origin of sensor offset voltage, the influence of temperature on the sensor output voltage, and the high calculation accuracy. After the completion of the resistance inequality experiment and the temperature drift test without magnetic field, the experimental results show that the model data are consistent with the experimental data from 0 to 85°C, and the error is within 1%. After completing the magnetic field measurement experiments at different temperatures, it proves that the model is very accurate and can be applied to temperature software compensation.

Dependence of Sensitivity, Derivative of Transfer Curve and Current on Bias Voltage Magnitude and Polarity in Tunneling Magnetoresistance Sensors.

The sensitivity of tunneling magnetoresistance sensors is an important performance parameter. It depends on the derivative of resistance versus magnetic field (transfer curve) and the current and is expressed as the product of the two factors. Previous research has demonstrated that the bias voltage has a significant impact on the sensitivity. However, no research has been conducted into the dependence of current and the derivative on bias voltage magnitude and polarity, and their contribution to the sensitivity. Thus, this paper investigates the dependence of sensitivity, derivative of resistance versus magnetic field curve and current on bias voltage magnitude and polarity in CoFeB/MgO/CoFeB-based tunneling magnetoresistance sensors with weak, strong and no voltage-controlled perpendicular magnetic anisotropy modification. It demonstrates that the sensitivity dependence on bias voltage for sensors with voltage controlled magnetic anisotropy modification showed no saturation up to 1 V. Moreover, the sensitivity asymmetry with respect to bias polarity changed significantly with bias, reaching a ratio of 6.7. Importantly, the contribution of current and the derivative of resistance versus magnetic field curve to the sensitivity showed a crossover. The current dominated the bias dependence of sensitivity below the crossover voltage and the derivative above the voltage. Furthermore, the crossover voltage in sensors without voltage controlled magnetic anisotropy modification did not depend on polarity, whereas in sensors with voltage controlled magnetic anisotropy modification, it appeared at significantly higher voltage under positive than negative polarity.

Magnetic Field Testing Technique of System-Generated Electromagnetic Pulse Based on Magnetoresistance Effects

To address the technical challenges of system-generated electromagnetic pulse (SGEMP) measurement, the generation environment of SGEMP is introduced, and the characteristics of the magnetic field waveform to be measured are analyzed first in this paper. Then a magnetoresistance-based SGEMP measurement method is proposed for the first time. Aiming at the problem that the high frequency response of the existing commercial magnetoresistance chips cannot meet the test requirements, a pulsed magnetic field detector with strong anti-interference ability is developed in this work based on the tunneling magnetoresistance (TMR) sensor chip developed by Lanzhou University and a high-gain amplifier circuit with common mode rejection and a good shielding structure. It can be shown from the calibration results that the detector sensitivity factor is 4.0 nT/mV and the measurable pulse front is greater than or equal to 28 ns, which meet the requirements of SGEMP magnetic field waveform measurement. Based on the developed detector, the ideal test waveform is obtained under the “Flash II” hard X-ray pulse source through a reasonable experimental design. The related work has laid a foundation for validating the numerical calculation model and further mastering the propagation law and effect mechanism of SGEMP.

Development of Magnetocardiograph without Magnetically Shielded Room Using High-Detectivity TMR Sensors.

A magnetocardiograph that enables the clear observation of heart magnetic field mappings without magnetically shielded rooms at room temperatures has been successfully manufactured. Compared to widespread electrocardiographs, magnetocardiographs commonly have a higher spatial resolution, which is expected to lead to early diagnoses of ischemic heart disease and high diagnostic accuracy of ventricular arrhythmia, which involves the risk of sudden death. However, as the conventional superconducting quantum interference device (SQUID) magnetocardiographs require large magnetically shielded rooms and huge running costs to cool the SQUID sensors, magnetocardiography is still unfamiliar technology. Here, in order to achieve the heart field detectivity of 1.0 pT without magnetically shielded rooms and enough magnetocardiography accuracy, we aimed to improve the detectivity of tunneling magnetoresistance (TMR) sensors and to decrease the environmental and sensor noises with a mathematical algorithm. The magnetic detectivity of the TMR sensors was confirmed to be 14.1 pTrms on average in the frequency band between 0.2 and 100 Hz in uncooled states, thanks to the original multilayer structure and the innovative pattern of free layers. By constructing a sensor array using 288 TMR sensors and applying the mathematical magnetic shield technology of signal space separation (SSS), we confirmed that SSS reduces the environmental magnetic noise by -73 dB, which overtakes the general triple magnetically shielded rooms. Moreover, applying digital processing that combined the signal average of heart magnetic fields for one minute and the projection operation, we succeeded in reducing the sensor noise by about -23 dB. The heart magnetic field resolution measured on a subject in a laboratory in an office building was 0.99 pTrms and obtained magnetocardiograms and current arrow maps as clear as the SQUID magnetocardiograph does in the QRS and ST segments. Upon utilizing its superior spatial resolution, this magnetocardiograph has the potential to be an important tool for the early diagnosis of ischemic heart disease and the risk management of sudden death triggered by ventricular arrhythmia.

A Closed-Loop Micro-Ultrasonic Motor Control System With Extremum Seeking

Microactuators are an essential technology to revolutionize existing micromachines, but making them closed-loop controlled with an internal sensor is a great challenge due to the limited size of the components. In this paper, we build a micro-ultrasonic motor in the 2-3 mm scale, combine it with a tunneling magneto resistance (TMR) sensor with dimensions of 1.4 mm × 1 mm, and construct a closed-loop system with a control algorithm. It is currently the smallest rotary actuator-sensor system assembled into a size with a height of 3.2 mm, a width of 3.2 mm, and a length of 5 mm. In the system, we attempt to solve a steady-state error problem for the micro-ultrasonic motor’s internal parameter changes, such as a temperature rise and the resonant frequency variation. A model-free, real-time-adaptive extremum seeking controller (ESC) that continuously tracks and localizes the optimum driving frequency is implemented into the system for the desired rotation with minimum steady-state error. Although the controller is simply designed, experiments show a good accordance between the resulting angular velocity and the reference.

On-Line Detection of Railway Power Frequency Current Based on Tunnel Magnetoresistance

In an electrified railway system, electrical energy is provided to the train through the traction network for its normal operation. Starting from the traction substation, the traction current flows through the catenary, the train, and finally returns to the traction substation via the steel rail. Due to the absence of the on-line detection technology for rail current, it has been a long time that the magnitude of the current flowing on the rail is unclear. Therefore, how to effectively detect rail current has become an industrial and academic focus recently. This article uses a new type of tunnel magnetoresistance (TMR) sensor, focusing on the rail power frequency current online detection technology based on the TMR gradient method. First, this article analyzes the current and the magnetic field distribution characteristics near the rail, then considers the actual installation situation on the spot, and selects the appropriate sensor installation location. Finally, through simulation and actual measurement, it is verified that the scheme has a flexible structure, easy installation, strong anti-interference ability, and good detection accuracy.

Key performance of tunneling magnetoresistance sensing unit modulated by exchange bias of free layer

Optimizing sample structural parameters, magnetic field annealing, series-parallel bridge design, current thermal effect, and additional bias magnetic field are common methods used for controlling the tunneling magnetoresistance (TMR) magnetic sensing performance. By employing these methods, key performance parameters of TMR sensors such as sensitivity, noise resistance index, linearity, and linear magnetic field range can be optimized and improved. Changing the sample structural parameters, such as the pinning layer, free layer, and barrier layer materials and thickness of the TMR magnetic sensing unit, can change the exchange bias field and thus enhance the TMR magnetic sensing performance parameters. In this study, through micromagnetic simulation and experimental measurements, it is discovered that by modifying the exchange coupling in the free layer CoFeB/Ru/NiFe/IrMn, the exchange bias field magnitude of the TMR free layer can be modulated, leading to improved performance of the TMR magnetic sensing unit. As the IrMn pinning effect is gradually enhanced, the linear magnetic field range of the TMR magnetic sensing unit increases, but the magnetic field sensitivity decreases. It is further found that the linearity of the TMR magnetic sensor is optimal within a range of ±0.5 times the magnetic moment variation of the free layer (primarily the CoFeB layer). Through our work, the effect of exchange bias field (caused by the pinning IrMn of the free layer) on the magnetic sensing performance is verified in the TMR magnetic sensing unit. Our work demonstrates more possibilities for designing and optimizing TMR magnetic sensors, enriching the dimensions of magnetic sensing performance modulation.

Theoretical Model of Self-Magnetic Flux Leakage and Its Application in Estimating the Depth Direction of a Fatigue Crack

In this study, theoretical models were proposed to explain the changes in self-magnetic flux density (SMFD) due to fatigue cracks in the presence and absence of external magnetic fields. Three theoretical models were proposed: rotation domain model (RDM), concentration domain model (CDM), and vertical domain model (VDM), considering the deformation and non-deformation possibilities. To prove the theoretical model, fatigue cracks with different depth angles were fabricated through fatigue testing and EDM processing on the CT specimens. In addition, tunnel magnetoresistance (TMR) sensors were used to evaluate the 3-axis distribution of SMFD. Comparing the simulation and experimental results, similar tendencies of the occurrence and depth angle of fatigue cracks and their effect on the distribution of SMFD were observed. According to the RDM, the distribution of SMFD occurs in the direction of the crack length (y-direction), while the CDM explains that the SMFD does not occur if the fatigue crack is in a direction perpendicular to the surface. In addition, the VDM shows that SMFDs occur in a direction perpendicular to the crack length (x-direction) and the specimen surface (z-direction). Interestingly, these trends agree with the experimental results, which confirms the validity of the theoretical model and thus can be used to estimate the depth direction of a fatigue crack.

Optimization of Structure and Control Technology of Tunnel Magnetoresistive Accelerometer

In this work, an optimized tunnel magnetoresistive (TMR) accelerometer with a closed-loop control system was developed and evaluated. The device first introduces a silicon spring–mass sensing structure lower than 50 Hz into TMR-based accelerometry for enhancing the mechanical sensitivity and subsequent readout sensitivity. Simultaneously, in order to realize the in-plane electrostatic feedback control, the comb structure is designed along with the sensing mechanism, owning combined benefits of integrated processing and large feedback force. The whole sensing structure is a silicon-glass chip, fabricated by the standard micro-electromechanical system (MEMS) process—deep dry silicon on glass (DDSOG) process. A permanent rubber magnet is assembled on the proof mass for conversion from the displacement to variation of the magnetic field intensity, which is further detected by a pair of symmetrically arranged TMR sensors. The voltage signals output from TMR sensors are then sent into an analog circuit via an interface module for force-feedback control. The simulation analysis indicates that the proposed MEMS sensing structure has a low natural frequency of 44.55 Hz, corresponding to a compliant mechanical sensitivity of 125.5 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> /g. Meanwhile, a maximum magnetic sensitivity of about 0.1 mT/mm is available in a height of 6 mm above the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3\times 3\times0.3$ </tex-math></inline-formula> mm magnet. Finally, the experiments on the assembled prototype demonstrated that a scale factor of 1.79 V/g and a bias stability of 228 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{g}$ </tex-math></inline-formula> have been achieved in the closed-loop modality, which verifies the effectiveness of the proposed TMR MEMS accelerometer.

Tunnel magnetoresistance sensors with dual soft-pinned free layers exhibiting highly symmetric resistance-field response curves

We report on tunnel magnetoresistance (TMR) sensors with two ferromagnetic free layers (FLs) on both sides of a MgO tunnel barrier. The magnetizations of these FLs are weakly (softly) pinned in an anti-parallel configuration by the exchange bias of IrMn antiferromagnetic layers through ferromagnetic and/or antiferromagnetic interlayer couplings of non-magnetic spacer layers. These dual soft-pinned FL (SPFL) sensors show a symmetric resistance (R) change with respect to the polarity of the external magnetic field (H) applied to the hard axis (HA) of the SPFLs and TMR ratios of over 200%, which is much higher than those of the single-SPFL sensors, where one side of the ferromagnetic layers is an SPFL and the other side is a strongly pinned reference layer. When the applied H exhibits an angular misalignment from the HA, dual-SPFL sensors show much-reduced asymmetry in the R–H curves than single-SPFL sensors. Macrospin simulations of the magnetization behavior and R–H curve for both dual- and single-SPFL sensors revealed that the small asymmetry in the R–H curves of dual-SPFL sensors was owing to their significantly smaller dependence of relative magnetization angle between the SPFLs on the magnetic field misalignment from the HA. These results suggest that dual-SPFL TMR sensors are promising for use in magnetic sensors such as encoder sensors for position and rotation detections.

Non-intrusive closed-loop current sensor based on tunneling magnetoresistance

In this paper, a non-intrusive closed-loop current sensor based on high-sensitivity tunneling magnetoresistance (TMR) were demonstrated. Using the finite element modeling based on Maxwell’s electromagnetic theory, the distribution of magnetic field on the closed-loop magnetic flux concentrator (MFC) was calculated with a copper busbar passing through the center. Two different types with “slot” and “hole” were designed to place TMR sensors for the detection of the magnetic field generated by the working copper busbar. A secondary winding around MFC generated a reverse magnetic field to completely offset the magnetic field of the primary current, which realizes the real-time adjustment and monitoring of the current by the TMR sensor with magnetic flux balance. Moreover, the simulated results show that the performance of slot-gap MFC is better than that with hole-type design. Utilizing the experimental TMR sensor with sensitivity of 10 mV/V/Oe and linear field range of ±40 Oe, the monitoring current can reach up to 200 A. The described application in the current monitoring demonstrates the functionality and feasibility of TMR sensors.

Measurement of T wave in magnetocardiography using tunnel magnetoresistance sensor

Several critical clinical applications of magnetocardiography (MCG) involve its T wave. The T wave’s accuracy directly affects the diagnostic accuracy of MCG for ischemic heart disease and arrhythmogenic. Tunnel magnetoresistance (TMR) attracts attention as a new MCG measurement technique. However, the T waves measured by TMR are often drowned in noise. The accuracy of T waves needs to be discussed to determine the clinical value of MCG measured by TMR. This study uses an improved empirical mode decomposition (EMD) algorithm and averaging to eliminate the noise in the MCG measured by TMR. The MCG signals measured by TMR are compared with MCG measured by the optically pumped magnetometer (OPM) to judge its accuracy. Using the MCG measured by OPM as a reference, the relative errors in time and amplitude of the T wave measured by TMR are 3.4% and 1.8%, respectively. This is the first demonstration that TMR can accurately measure the time and amplitude of MCG T waves. The ability to provide reliable T wave data illustrates the significant clinical application value of TMR in MCG measurement.

Tunnel magnetoresistance sensors with symmetric resistance-field response and noise properties under AC magnetic field modulation

Magnetoresistance (MR) devices with symmetric (even-function) resistance change to an external magnetic field is useful for various magnetic sensor applications, such as encoders for position and rotation detection and ultra-sensitive magnetic field sensors, when combined with a frequency modulation method. In this study, we developed tunnel magnetoresistance (TMR) sensors with even-function resistance–field (R–H) responses and investigated their noise properties. The developed TMR sensors achieved a higher MR ratio (∼120%) than those of conventional giant magnetoresistive multilayers exhibiting even-function R–H responses. The TMR sensors were realized by stabilizing the magnetization of the magnetic free layer (FL) in an anti-parallel configuration with respect to that of the reference layer. Orange-peel ferromagnetic coupling between the FL and a pinned layer through an AgSn spacer layer was used to control the strength of the unidirectional magnetic anisotropy of the FL, by which even-function R–H responses with negligible hysteresis were obtained. The sensors enabled us to study the intrinsic noise properties of TMR devices, particularly under an external AC modulation magnetic field. We found that the magnetic 1/f noise originating from thermal magnetization fluctuation was the dominant noise of the TMR sensors at low frequencies. We observed that the application of an AC modulation field to the TMR sensors increased the noise owing to the magnetic domain fluctuation and the transfer of magnetic 1/f noise to the modulation frequency.

Rotating alternating current field measurement testing system with TMR arrays for arbitrary-angle crack on nonferromagnetic pipes

Nonferromagnetic pipes are widely used in power plants such as fluid transportation and heat exchanger devices. Due to the severity of the environments, including corrosion, high temperature, etc, they are subject to surface arbitrary-angle cracks. In view of this background, this paper proposed a rotating alternating current field measurement (RACFM) testing system for arbitrary-angle cracks on nonferromagnetic pipes. The RACFM pipe detection model is established and the unidirectional excitation coil and the orthogonal excitation coils are simulated separately. The testing system and the probe with tunnel magneto resistance sensor arrays and flexible orthogonal excitation coils are built to detect cracks at different angles on the pipe. The simulation and experimental results reveal that the RACFM detection system has high sensitivity for arbitrary-angle cracks on the outer surface of the pipe, and it can effectively measure the lengths and angles of the cracks.

A Coreless Current Probe for Multicore Cables

To measure the current on each conductor in a three-phase three-core cable or a three-phase four-core cable without an armor or the armor that is made of nonmagnetic material, one has to remove its sheath/armor and applies a traditional device, such as a current transformer (CT) to each conductor, which is invasive and inconvenient. In this article, a Coreless current probe, composed of a tunnel-magnetoresistance (TMR)-based magnetic sensor array, is presented to nondestructively achieve current measurement for multicore cables. The conductor positions, incline angles, and current phasors of a multicore cable are simultaneously identified by solving a nonlinear least square (NLLS) problem. The current waveforms are reconstructed in real time through a real-valued matrix multiplication using the measured time-domain TMR sensor voltage signals. Both simulation and experiment are performed to validate the feasibility of the proposed method. The simulation study is first conducted and demonstrates that a maximum relative current amplitude error of less than 5% and a maximum phase error of lower than 4° can be achieved, and three-phase current waveforms with many harmonics are also successfully reconstructed by simulation. A prototype Coreless current probe is designed and fabricated. The experimental study involving fundamental current phasor measurement and current waveform reconstruction is subsequently performed on a three-phase three-core cable. The experimental results indicate that the maximum relative current amplitude error and phase error, respectively, have average values of 5.44% and 2.58°. Meanwhile, three-phase current waveforms with many harmonics generated by three types of appliances are also successfully reconstructed.

A pilot study on an electromagnetic tracking system using tunneling magnetoresistance (TMR) sensors applicable to a 4F catheter (1.4mm in diameter).

Tracking the position and orientation of a 4F catheter ([Formula: see text] 1.4mm) is required in superselective intra-arterial chemotherapy (SSIAC). Tunneling magnetoresistance (TMR) sensors, which measure magnetic fields, are promising candidates because the size of the TMR sensor can be less than a few tenths of a millimeter. The purpose of this paper is to prove the feasibility of an EMT system utilizing TMR sensors as magnetometers. Three 1-axis TMR sensors (0.3mm × 0.3mm) were packaged on a flexible printed circuit board (PCB) together with an amplifier chip. The PCB was integrated into a 4F catheter. Six field generator coils driven by alternating current (AC) at different frequencies were used. Magnetic field measurement errors were evaluated to assess the effect of electromotive force (EMF) on TMR-based sensing by changing the coils' driving frequencies. The tracking error was also evaluated. As a result, the feasibility of catheter navigation utilizing the EMT system was demonstrated. There was a positive correlation between the frequency and the magnetic field measurement error using the TMR sensor (R2 = 0.999). With magnetic field frequencies less than 603Hz, the average position and orientation estimation error were 10.1mm and 2.3degree, respectively. Under ideal conditions, the average estimation error values were 0.9mm and 0.3degree, respectively. The position and orientation errors varied with frequency owing to the induced electromotive force. We should consider the effect of electromotive force on TMR sensor assemblies caused by alternating magnetic fields. An EMT system using TMR sensors was validated, although room for further improvement was identified.

Electron irradiation total ionizing dose (TID) effect of tunneling magnetoresistance sensors

Tunnel magnetoresistance (TMR) sensors are rapidly gaining attention for magnetic field sensing applications owing to their high sensitivity, low power consumption, small size, and low cost. Their metallic, non-semiconductor construction makes them excellent candidates for use in the harsh environments present in nuclear and space applications. In this work, the impacts of electron irradiation on the magnetoelectric transport properties of the two types of TMR sensors were investigated. The electron fluence ranged from 0 Mrad(Si) to 400 Mrad(Si). No significant evidence of degradation of the sensor characteristics, such as sensitivity, resistance, TMR ratio and detectivity, was observed. Our results verify the robustness and adaptability of the TMR sensors.