Abstract
A magnetically-quiet environment is important for detecting faint magnetic-field signals or nonmagnetic spin-dependent interactions. Passive magnetic shielding using layers of large magnetic-permeability materials is widely used to reduce the magnetic-field noise. The magnetic-field noise can also be actively monitored with magnetometers and then compensated, acting as a complementary method to the passive shielding. We present here a general model to quantitatively depict and optimize the performance of active magnetic-field stabilization and experimentally verify our model using optically-pumped atomic magnetometers. We experimentally demonstrate a magnetic-field noise rejection ratio of larger than ∼800 at low frequencies and an environment with a magnetic-field noise floor of ∼40 in unshielded Earth’s field. The proposed model provides a general guidance on analyzing and improving the performance of active magnetic-field stabilization with magnetometers. This work offers the possibility of sensitive detections of magnetic-field signals in a variety of unshielded natural environments.
Highlights
A magnetically-quiet environment is of great demand for research areas that rely on detections of faint magnetic-field signals, such as magnetoencephalography [1,2,3,4], magnetocardiography [5,6,7], and ultralow-field nuclear magnetic resonance [8,9,10], where the amplitudes of the magnetic-field signals to be detected are typically several orders of magnitude smaller than the magnetic-field noise of the ambient environment
To evaluate the experimentally achieved noise rejection ratios, we record the readouts of optically-pumped atomic magnetometer (OPM)-M under two different conditions, i.e., without and with magnetic-field stabilization, at a sampling rate of 40 kSa/s
We present a model to calculate the noise rejection ratio of the active magnetic-field stabilization using atomic magnetometers
Summary
A magnetically-quiet environment is of great demand for research areas that rely on detections of faint magnetic-field signals, such as magnetoencephalography [1,2,3,4], magnetocardiography [5,6,7], and ultralow-field nuclear magnetic resonance [8,9,10], where the amplitudes of the magnetic-field signals to be detected are typically several orders of magnitude smaller than the magnetic-field noise of the ambient environment. Sensors 2020, 20, 4241 environmental magnetic-field noise has an inverse-power-law frequency dependence and is higher at lower frequencies, the reduced performance of the passive magnetic shielding in suppressing the low-frequency magnetic-field noise needs to be compensated [27]. The demonstrated noise rejection ratio of the active magnetic-field stabilization is typically smaller than that of the magnetic shield and ranges from 10 to 1000 [6,29,33,36], depending on the noise level and response properties of the magnetometer and the parameter settings of the feedback controller. The proposed model is adopted to improve the noise rejection ratio of our active magnetic-field stabilization system and to produce a magnetically-quiet environment in unshielded Earth’s field This approach can be extended to magnetic-field stabilization using different kinds of magnetometers, and can help researchers analyze their experimental systems quantitatively and optimize their systems in a targeted manner
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