Modulating the Magnetic Field to Improve Magnetic Sensors

The sensitivity of most magnetic sensors is affected by 1/$f$ noise. Modulating the magnetic field to be detected by magnetic sensors can improve their performance by minimizing the effect of this 1/$f$ noise and, in some cases, also have them operate in a narrow frequency band where they have higher sensitivity. We present approaches for modulating the field. One approach is the MEMS flux concentrator can be used with small magnetic sensors and another, based on using a rotating disc containing flux concentrators that can be used with large magnetic sensors, such as magnetoelectric sensors, that have an increased sensitivity at their mechanical resonance frequency. Sidebands observed around the modulation frequency demonstrate the applicability of these approaches. The MEMS flux concentrator has improved the signal to noise ratio in the power spectrum by a factor of 15. The sensors have the potential to achieve sensitivities of a few pT/Hz$^{1/2}$ at 1 Hz.