One embodiment is a magnetic field measurement system that includes at least one magnetometer having a vapor cell, a light source to direct light through the vapor cell, and a detector to receive light directed through the vapor cell; at least one magnetic field generator disposed adjacent the vapor cell; and a feedback circuit coupled to the at least one magnetic field generator and the detector of the at least one magnetometer. The feedback circuit includes at least one feedback loop that includes a first low pass filter with a first cutoff frequency. The feedback circuit is configured to compensate for magnetic field variations having a frequency lower than the first cutoff frequency. The first low pass filter rejects magnetic field variations having a frequency higher than the first cutoff frequency and provides the rejected magnetic field variations for measurement as an output of the feedback circuit.

One embodiment is a magnetic field measurement system that includes at least one magnetometer having a vapor cell, a light source to direct light through the vapor cell, and a detector to receive light directed through the vapor cell; at least one magnetic field generator disposed adjacent the vapor cell; and a feedback circuit coupled to the at least one magnetic field generator and the detector of the at least one magnetometer. The feedback circuit includes at least one feedback loop that includes a first low pass filter with a first cutoff frequency. The feedback circuit is configured to compensate for magnetic field variations having a frequency lower than the first cutoff frequency. The first low pass filter rejects magnetic field variations having a frequency higher than the first cutoff frequency and provides the rejected magnetic field variations for measurement as an output of the feedback circuit.

Methods, apparatuses, and systems for detecting a stray magnetic field are provided. An example apparatus may include a first magnetic sensor element at a first position relative to a magnetic field source to detect a target magnetic field emitted by the magnetic field source, a second magnetic sensor element at a second position relative to the magnetic field source to detect the target magnetic field emitted by the magnetic field source, and a processor element electronically coupled to the first magnetic sensor element and the second magnetic sensor element. In some examples, the processor element may be configured to: receive a first output from the first magnetic sensor element, receive a second output from the second magnetic sensor element, and detect the stray magnetic field interfering with the target magnetic field based at least in part on the first output and the second output.

A magnetic field sensor includes at least one coil responsive to an AC coil drive signal; at least two spaced apart magnetic field sensing elements responsive to a sensing element drive signal and positioned proximate to the at least one coil; and a circuit coupled to the at least two magnetic field sensing elements to generate an output signal of the magnetic field sensor indicative of a difference between a distance of a conductive target with respect to each of the at least two spaced apart magnetic field sensing elements.

A magnetic field sensor includes at least one coil responsive to an AC coil drive signal; at least two spaced apart magnetic field sensing elements responsive to a sensing element drive signal and positioned proximate to the at least one coil; and a circuit coupled to the at least two magnetic field sensing elements to generate an output signal of the magnetic field sensor indicative of a difference between a distance of a conductive target with respect to each of the at least two spaced apart magnetic field sensing elements.

An object of the present invention is to provide a magnetic sensor capable of detecting a magnetic field to be measured through closed loop control even when the magnetic field is weak. A magnetic sensor includes magnetic layers 41 and 42 opposed to each other through a magnetic gap G1, a magneto-sensitive element R1 disposed on a magnetic path formed by the magnetic gap G1, and a compensation coil 60 generating canceling magnetic flux ϕ4 to cancel magnetic flux ϕ2 applied to the magneto-sensitive element R1. According to the present invention, magnetic flux ϕ2 flowing in the magnetic layers 41 and 42 each functioning as a yoke is applied to the magneto-sensitive element R1, so that even when a magnetic field to be measured is weak, it can be detected.

In addition, closed loop control can be performed due to the presence of the compensation coil 60 that cancels magnetic flux ϕ2.

A magnetic field measurement system includes at least one magnetometer; and at least one flux concentrator made of a high magnetic permeability material and configured to receive magnetic field signals from a source, to concentrate the magnetic field signals or reorient the magnetic field signals in a preselected direction, and to direct the concentrated or reoriented magnetic field signals toward at least one of the at least one magnetometer. In addition to, or as an alternative to, the flux concentrator, the system can include a passive shield made of the high magnetic permeability material. The system may also include active shielding.

A magnetic field measurement system includes at least one magnetometer; and at least one flux concentrator made of a high magnetic permeability material and configured to receive magnetic field signals from a source, to concentrate the magnetic field signals or reorient the magnetic field signals in a preselected direction, and to direct the concentrated or reoriented magnetic field signals toward at least one of the at least one magnetometer. In addition to, or as an alternative to, the flux concentrator, the system can include a passive shield made of the high magnetic permeability material. The system may also include active shielding.

An assembly includes a permanent magnet generating a magnetic field. The permanent magnet is arranged on the rotary member and generates a magnetic field perpendicular to an axis of rotation. A first channel has a first magnetic sensing element centered on the axis of rotation, the first channel providing a first angular data. A second channel has a second magnetic sensing element centered on the axis of rotation, the second channel providing a second angular data. The second magnetic sensing element is spaced from the first magnetic sensing element. Each of the first magnetic sensing element and the second magnetic sensing element have three voltage dividers. A processor computes a magnetic stray field component orthogonal to the magnetic field by comparing a first field strength based on the first angular data with the second field strength based on the second angular data.

An assembly includes a permanent magnet generating a magnetic field. The permanent magnet is arranged on the rotary member and generates a magnetic field perpendicular to an axis of rotation. A first channel has a first magnetic sensing element centered on the axis of rotation, the first channel providing a first angular data. A second channel has a second magnetic sensing element centered on the axis of rotation, the second channel providing a second angular data. The second magnetic sensing element is spaced from the first magnetic sensing element. Each of the first magnetic sensing element and the second magnetic sensing element have three voltage dividers. A processor computes a magnetic stray field component orthogonal to the magnetic field by comparing a first field strength based on the first angular data with the second field strength based on the second angular data.