Tunnel Magnetoresistance Sensor with AC Modulation and Impedance Compensation for Ultra-Weak Magnetic Field Measurement

Zhao, Wenlei; Tao, Xinchen; Ye, Chaofeng; Tao, Yu

doi:10.3390/s22031021

Cited by 12 publications

(5 citation statements)

References 23 publications

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“…Therefore, magnetic field shielding by software is crucially important. Gradiometers are widely used to reduce noise disturbance [ 17 , 20 ]. While SSS requires a large number of sensors for the calculation process according to the degree of calculation (

), a gradiometer has advantages in that it needs only two sensors, and the configuration of the system is simple and easy to handle.…”

Section: Discussionmentioning

confidence: 99%

“…In order to measure the tiny heart magnetic fields, an algorithm to decrease the sensor noises down to 1 pT, which is lower than the signal, is also favorable. Although it has recently been reported that heart magnetic fields were observed with TMR sensors under an unshielded condition by the AC modulation and the impedance compensation [ 20 ], the detectivity was not enough for accurate diagnostics. As TMR sensors have higher sensitivity and higher 1/ f noise in the low frequency domain compared to giant magnetoresistance (GMR) sensors [ 21 ], the suppression of sensor noises may be effective to improve the accuracy of magneto-cardiometry.…”

Section: Introductionmentioning

confidence: 99%

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

Kurashima

Kataoka

Nakano

et al. 2023

Sensors

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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.

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), a gradiometer has advantages in that it needs only two sensors, and the configuration of the system is simple and easy to handle.…”

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Kurashima

Kataoka

Nakano

et al. 2023

Sensors

View full text Add to dashboard Cite

show abstract

“…[4][5][6] In recent years, tunnel magnetoresistance (TMR) sensors have become a new technique to measure MCG due to their low power consumption and the ability to measure MCG in unshielded environments. [7] The study of Kosuke Fujiwara et al achieved the detection of MCG R wave, [8] and the study of Meiling Wang et al acquired triaxial MCG signals. [9] Real-time mea-surements of MCG QRS components were also achieved using new low-noise TMR sensors.…”

Section: Introductionmentioning

confidence: 99%

Measurement of T wave in magnetocardiography using tunnel magnetoresistance sensor

Lu¹,

Ji²,

Yang³

2023

Chinese Phys. B

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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 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.

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“…6,7,11,12 Reducing the 1/f noise in MR devices has been the central issue for magnetic sensors, and has been achieved in various ways; e.g., by selecting appropriate ferromagnetic materials, [13][14][15] using an MgO tunnel barrier or optimizing its fabrication process, 4,9,10,16 connecting many individual MR devices, [17][18][19] chopping techniques, 20,21 and AC modulation techniques. [22][23][24][25] The typical AC modulation method using movable magnetic flux concentrators fabricated by microelectromechanical systems modulates the frequency of the signal field to the sidebands of the carrier frequency of the AC modulation (fac), by which we can avoid the low-frequency regime where the 1/f noise is dominant. Therefore, we can effectively suppress the noise of the MR sensor.…”

Section: Introductionmentioning

confidence: 99%

Improvement of magnetic field detectivity in electrical 1/f noise-dominated tunnel magnetoresistive sensors by AC magnetic field modulation technique

Nakatani,

Suto,

Kulkarni

et al. 2023

Journal of Applied Physics

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Suppression of 1/f noise in tunnel magnetoresistance (TMR) sensors is a central issue in the realization of magnetic field sensors with ultrafine magnetic field detectivity. Although AC modulation with an external magnetic field has been proposed as a method to shift the operating frequency of a sensor to a high frequency and substantially suppress 1/f noise, its effects on the two types of 1/f noise, that is, magnetic and electrical 1/f noise, are not well understood. In this study, we investigated the noise characteristics and signal detection performance of TMR sensors with an even-function resistance-magnetic field curve operated by the AC modulation method. For one TMR device in which the magnetic 1/f noise was dominant, AC modulation degraded the magnetic field detectivity owing to the additional noise induced by the AC modulation field. However, in another TMR device, in which the electrical 1/f noise was artificially enhanced by introducing lattice defects in the MgO tunnel barrier, AC modulation effectively suppressed the 1/f noise and improved the magnetic field detectivity by one order. This demonstrates that the AC modulation method using an external magnetic field is effective for magnetic field sensors in which electrical 1/f noise is dominant.

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Tunnel Magnetoresistance Sensor with AC Modulation and Impedance Compensation for Ultra-Weak Magnetic Field Measurement

Cited by 12 publications

References 23 publications

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

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

Measurement of T wave in magnetocardiography using tunnel magnetoresistance sensor

Improvement of magnetic field detectivity in electrical 1/f noise-dominated tunnel magnetoresistive sensors by AC magnetic field modulation technique

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