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

Area of Science:

• Applied Physics
• Biomedical Engineering
• Sensor Technology

Background:

• Tunnel Magnetoresistance (TMR) sensors offer cost-effectiveness and high sensitivity for magnetic field detection.
• Low-frequency and ultra-weak magnetic field measurements are challenged by 1/f noise in TMR sensors.
• External magnetic fields influence the equivalent resistance and capacitance of TMR sensors.

Purpose of the Study:

• To develop an AC modulation method with impedance compensation to mitigate 1/f noise in TMR sensors.
• To improve the sensitivity and signal-to-noise ratio (SNR) of TMR sensors for low-frequency applications.
• To demonstrate the sensor's capability in measuring ultra-weak magnetic signals, such as magnetocardiography (MCG).

Main Methods:

• Characterization of DC and AC properties of TMR sensors under varying magnetic fields.
• Implementation of an AC modulation technique combined with impedance compensation.
• Configuration of TMR sensors in a push-pull bridge circuit and a magnetic gradiometer setup to reduce common-mode noise.

Main Results:

• The AC modulation and impedance compensation significantly improved low-frequency sensitivity.
• The signal-to-noise ratio at 1 Hz increased by approximately 25.3 dB.
• Sensor sensitivity was enhanced from 165.2 to 222.1 mV/V/mT.
• Magnetocardiography (MCG) signals from human bodies were successfully measured in an unshielded environment, with clear visualization of the R peak.

Conclusions:

• The proposed AC modulation with impedance compensation effectively enhances TMR sensor performance for ultra-weak, low-frequency magnetic field measurements.
• The developed magnetic gradiometer system demonstrates high sensitivity and noise reduction capabilities.
• The TMR sensor system is suitable for practical applications like non-invasive MCG detection in unshielded settings.