100 pT/cm single-point MEMS magnetic gradiometer from a commercial accelerometer

Area of Science:

• Biomagnetism
• Microelectromechanical Systems (MEMS)
• Sensor Technology

Background:

• Biomagnetic fields from the heart and brain are currently measured using expensive equipment like SQUIDs.
• Microelectromechanical systems (MEMS) offer potential for developing smaller, lower-power, and more affordable sensors.
• Existing MEMS magnetometers and gradiometers have limitations in resolution and spatial sensing.

Purpose of the Study:

• To leverage MEMS technology for fabricating a high-resolution, low-cost magnetic sensor.
• To demonstrate a MEMS magnetic gradiometer capable of measuring weak biomagnetic fields.
• To assess the sensor's performance for potential magnetocardiography (MCG) and magnetoencephalography (MEG) applications.

Main Methods:

• Fabrication of a MEMS magnetic gradiometer by attaching a micromagnet to a commercial MEMS accelerometer.
• Utilizing a pick-and-place technique for micro-object assembly.
• Characterization of sensor performance in air and vacuum conditions, including off-resonance and on-resonance measurements.

Main Results:

• Demonstrated a room-temperature MEMS magnetic gradiometer with linear response in air (1.1 nT·cm⁻¹ resolution, 3-decade dynamic range).
• Achieved 100 pT·cm⁻¹ resolution in vacuum with magnetic shielding, a significant improvement over existing MEMS technologies.
• Attained a small spatial resolution (0.25 mm) and a low noise floor (110 fT·cm⁻¹·Hz⁻¹/²).

Conclusions:

• The developed MEMS magnetic gradiometer presents a promising, cost-effective alternative for biomagnetic field detection.
• The sensor's high resolution and small spatial footprint are suitable for MCG and MEG.
• This MEMS-based approach opens new avenues for accessible biomagnetic sensing.