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

Abstract

Magnetic sensing is present in our everyday interactions with consumer electronics and demonstrates the potential for the measurement of extremely weak biomagnetic fields, such as those of the heart and brain. In this work, we leverage the many benefits of microelectromechanical system (MEMS) devices to fabricate a small, low-power, and inexpensive sensor whose resolution is in the range of biomagnetic fields. At present, biomagnetic fields are measured only by expensive mechanisms such as optical pumping and superconducting quantum interference devices (SQUIDs), suggesting a large opportunity for MEMS technology in this work. The prototype fabrication is achieved by assembling micro-objects, including a permanent micromagnet, onto a postrelease commercial MEMS accelerometer using a pick-and-place technique. With this system, we demonstrate a room-temperature MEMS magnetic gradiometer. In air, the sensor's response is linear, with a resolution of 1.1 nT cm −1 , spans over 3 decades of dynamic range to 4.6 µT cm −1 , and is capable of off-resonance measurements at low frequencies. In a 1 mTorr vacuum with 20 dB magnetic shielding, the sensor achieves a 100 pT cm −1 resolution at resonance. This resolution represents a 30-fold improvement compared with that of MEMS magnetometer technology and a 1000-fold improvement compared with that of MEMS gradiometer technology. The sensor is capable of a small spatial resolution with a magnetic sensing element of 0.25 mm along its sensitive axis, a >4-fold improvement compared with that of MEMS gradiometer technology. The calculated noise floor of this platform is 110 fT cm −1 Hz −1/2 , and thus, these devices hold promise for both magnetocardiography (MCG) and magnetoencephalography (MEG) applications.

In-situ measurement and close-loop control of atomic number density in an optically pumped magnetometer based on light absorption

“…Optically pumped atomic magnetometers (OPMs) have been used in various precise measurements for the weak magnetic field, such as bio-magnetic measurements [1][2][3], ultralow-field nuclear magnetic resonance [4,5], and fundamental physics research [6][7][8][9]. To date, OPMs operated in the spin-exchange relaxation-free (SERF) regime are the most sensitive magnetometers and have become promising * Author to whom any correspondence should be addressed.…”

Magnetophoresis-Assisted Capillary Assembly: A Versatile Approach for Fabricating Tailored 3D Magnetic Supercrystals

“…Permanent magnets (PM) represent the most attractive choice for such integrated power sources, and would benefit to numerous applications based on Micro-ElectroMechanical Systems (MEMS), such as actuators, 2,3 relays, 4 micromachines, 5 and sensors (magnetic, viscosity or biosensors). 6,7,8 A major scientific challenge therefore consists in providing submillimeter magnetic materials with optimized properties to address the massive demand for power supplies and converters. Up to now, the fabrication and integration of magnetic materials into portable devices is achieved via three main routes: 9 -the sputtering deposition, which gives access to a wide range of materials and a good composition control, but is generally limited to thin films due to low deposition rates and built-in stress that can cause delamination; -the electrodeposition technique, which can lead to thick films but is restricted to certain materials (Fe, Co, Ni, Pt-based alloys); -the patterning of magnetic polymers by inkjet, imprinting or photolithography.…”

“…Furthermore, the expanding market of integrated sensors/actuators requires miniaturized power supplies. Permanent magnets (PM) represent the most attractive choice for such integrated power sources and would benefit to numerous applications based on micro-electromechanical systems (MEMS), such as actuators, , relays, micromachines, and sensors (magnetic, viscosity, or biosensors). − …”

A highly sensitive and wide-range resonant magnetic micro-sensor based on a buckled micro-beam

“…In recent years, microelectromechanical systems (MEMS) have increasingly attracted the attention of researchers for various applications, such as ltering 1 , signal processing 9 , energy harvesting 10 , and environmental sensors including magnetic, pressure [2][3][4] , accelerometer 5 , temperature 6 , ow 7 , and gas 8 . Magnetic eld micro-sensors have been explored for various potential applications, such as magnetocardiography (MCG), magnetoencephalography (MEG), biomedical, inertial navigation systems, electronic compasses, telecommunications, and non-destructive testing [11][12][13][14][15] . These magnetic microsensors are mainly based on Lorentz force transduction.…”