MEMS magnetic field sensor

If the targeted B-field is larger than the earth magnetic field (maximum value around 60 μT), the sensor does not need to be very sensitive.

For the application of magnetic anomaly detection, sensors at different locations have to be used to cancel the spatial-correlated noise in order to achieve a better spatial resolution.

MEMS magnetic sensors have several parameters: quality factor (Q), resonance frequency, mode shape, responsivity, and resolution.

If we apply the same current and B field to several resonators, devices that show larger vibration amplitudes are said to have a higher responsivity.

Integration of MEMS sensor and microelectronics can further reduce the size of the entire magnetic field sensing system.

This type of sensor relies on the mechanical motion of the MEMS structure due to the Lorentz force acting on the current-carrying conductor in the magnetic field.

The location of the current loop enables a more uniform Lorentz force distribution compared with the aforementioned U-shape cantilever beam.

Lorentz force generated by the external magnetic field results in the change of capacitor array.

Emmerich et al. fabricated the variable capacitor array on a single silicon substrate with comb-figure structure.

Sunier et al.[10] change the structure of aforementioned U-shape cantilever beam by adding a curved-in support.

The center shuttle are connected to two clamped-clamped conductors used to change the internal stress of the moving structure when external magnetic field is applied.

The reported sensitivity is improved to 69.6 Hz/T thanks to the high mechanical quality factor (Q = 15000 @ 2 Pa) structure in the vacuum environment.

The optical sensing is to directly measure the mechanical displacement of the MEMS structure to find the external magnetic field.

Current that is flowing through the center conductor and Xylophone beam will be deflected as the Lorentz force is induced.

In the presence of an external magnetic field, the Lorentz force actuates the shuttle in the lateral direction and the amplitude of resonance is measured using an optical method.

The differential change in the amplitude of the resonating shuttle shows the strength of the external magnetic field.

If there is no flaw or crack in the pipeline, the magnetic field from the eddy current shows a constant pattern as it moves along the material being tested.

But a crack or pit in the material interrupts the eddy current, so the magnetic field is changed, allowing a sensitive magnetometer to sense and localize the flaw.

Magnetometers based on piezoelectric resonators have high resolution (in the range of nT), allowing solid-state sensing of our respiratory system.