Interface configurations for a wearable sensor unit that includes one or more magnetometers
An exemplary magnetic field measurement system includes a wearable sensor unit that includes a magnetometer, a magnetic field generator configured to generate a compensation magnetic field configured to actively shield the magnetometer from ambient background magnetic fields, a twisted pair cable interface assembly electrically connected to the magnetometer, and a coaxial cable interface assembly electrically connected to the magnetic field generator.
1. A magnetic field measurement system comprising:
a wearable sensor unit comprising:
a magnetometer,
a magnetic field generator configured to generate a compensation magnetic field configured to actively shield the magnetometer from ambient background magnetic fields,
a twisted pair cable interface assembly electrically connected to the magnetometer, and
a coaxial cable interface assembly electrically connected to the magnetic field generator; and
a controller configured to:
interface with the magnetometer by way of the twisted pair cable interface assembly; and
interface with the magnetic field generator by way of the coaxial cable interface assembly;
wherein the twisted pair cable interface assembly comprises at least one of:
a first twisted pair cable interface electrically connected to an input of a light source in the magnetometer, the controller being configured to supply a first drive current to the light source by way of a first twisted pair cable connected to the first twisted pair cable interface;
a second twisted pair cable interface electrically connected to an input of a heater for the light source, the controller being configured to supply a second drive current to the heater for the light source by way of a second twisted pair cable connected to the second twisted pair cable interface;
a third twisted pair cable interface electrically connected to an output of a thermistor for the light source, the controller being configured to read an output of the thermistor by way of a third twisted pair cable connected to the third twisted pair cable interface;
a fourth twisted pair cable interface electrically connected to an output of a monitor photodetector configured to monitor a behavior of the light source, the controller being configured to read an output of the monitor photodetector by way of a fourth twisted pair cable connected to the fourth twisted pair cable interface;
a fifth twisted pair cable interface electrically connected to an input of a heater for a vapor cell of the photodetector, the controller being configured to supply a third drive current to the heater for the vapor cell by way of a fifth twisted pair cable connected to the fifth twisted pair cable interface; or
a sixth twisted pair cable interface electrically connected to an output of a signal photodetector configured to detect light that passes through the vapor cell, the controller being configured to read an output of the monitor photodetector by way of a sixth twisted pair cable connected to the sixth twisted pair cable interface.
2. The magnetic field measurement system of claim 1 , wherein:
the twisted pair cable interface assembly is configured to connect to a twisted pair cable that is also connected to the controller; and
the controller is configured to interface with the magnetometer by at least one of
transmitting signals to the magnetometer over the twisted pair cable, and
receiving signals from the magnetometer over the twisted pair cable.
3. The magnetic field measurement system of claim 1 , wherein:
the coaxial cable interface assembly is configured to connect to a coaxial cable that is also connected to the controller; and
the controller is configured to interface with the magnetic field generator by supplying a drive current to the magnetic field generator over the coaxial cable.
4. The magnetic field measurement system of claim 1 , wherein:
the magnetic field generator comprises a plurality of conductive windings configured to generate, when supplied by drive currents, a plurality of components of the compensation magnetic field;
the coaxial cable interface assembly comprises a plurality of coaxial cable interfaces connected to the plurality of conductive windings and configured to be connected to a plurality of coaxial cables; and
the controller is configured to supply the drive currents to the plurality of conductive windings by way of the plurality of coaxial cables.
5. The magnetic field measurement system of claim 1 , wherein:
the magnetic field generator comprises:
a plurality of conductive windings comprising
a first conductive winding arranged in a first plane, and
a second conductive winding arranged in a second plane that is substantially parallel to the first plane;
the plurality of conductive windings are configured to generate, when supplied with one or more drive currents by the controller, a first component of the compensation magnetic field, the first component of the compensation magnetic field configured to actively shield a magnetic field sensing region from the ambient background magnetic fields along a first axis that is substantially orthogonal to the first plane and the second plane; and
the magnetometer is located within the magnetic field sensing region.
6. The magnetic field measurement system of claim 5 , wherein:
the coaxial cable interface assembly comprises a first coaxial cable interface connected to the first conductive winding and a second coaxial cable interface connected to the second conductive winding;
the controller is configured to supply
a first drive current to the first conductive winding by way of a first coaxial cable connected to the first coaxial cable interface, and
a second drive current to the second conductive winding by way of a second coaxial cable connected to the second coaxial cable interface; and
the coaxial cable interface assembly is configured to electrically connect return conductors in the first and second coaxial cables.
7. The magnetic field measurement system of claim 6 , wherein the controller is configured to adjust at least one of a magnitude of the first component of the compensation magnetic field and a field gradient of the first component of the compensation magnetic field by adjusting at least one of the first drive current and the second drive current.
8. The magnetic field measurement system of claim 5 , wherein the first component of the compensation magnetic field is configured to actively shield the magnetic field sensing region by reducing or canceling a first component of the ambient background magnetic field, the first component of the ambient background magnetic field being along the first axis.
9. The magnetic field measurement system of claim 5 , wherein the magnetic field generator further comprises:
a first planar substrate;
a second planar substrate positioned opposite to the first planar substrate and separated from the first planar substrate by a gap, the magnetic field sensing region being located in the gap;
a first wiring set disposed on the first planar substrate;
a second wiring set disposed on the second planar substrate; and
one or more interconnects positioned between the first planar substrate and the second planar substrate and that electrically connect the first wiring set with the second wiring set to form a first continuous electrical path,
wherein the first continuous electrical path forms a third conductive winding configured to generate, when supplied with a first additional drive current, a second component of the compensation magnetic field configured to actively shield the magnetic field sensing region from the ambient background magnetic field along a second axis that is substantially orthogonal to the first axis.
10. The magnetic field measurement system of claim 9 , wherein the magnetic field generator further comprises:
a third wiring set disposed on the first planar substrate; and
a fourth wiring set disposed on the second planar substrate;
wherein the one or more interconnects electrically connect the third wiring set with the fourth wiring set to form a second continuous electrical path; and
wherein the additional continuous electrical path forms a fourth conductive winding configured to generate, when supplied with a second additional drive current, a third component of the compensation magnetic field configured to actively shield the magnetic field sensing region from the ambient background magnetic fields along a third axis that is substantially orthogonal to the first axis and the second axis.
11. The magnetic field measurement system of claim 1 , wherein:
the magnetometer comprises a plurality of magnetometers; and
the controller is a single controller configured to
generate a single clock signal; and
use the single clock signal to interface with the magnetometers and the magnetic field generator.
12. The magnetic field measurement system of claim 1 , wherein the controller is remote from the wearable sensor unit.
13. The magnetic field measurement system of claim 12 , wherein the controller is implemented by a computing device not configured to be worn by a user.
14. The magnetic field measurement system of claim 12 , wherein the controller is included in a wearable device configured to be worn by a user and separate from the wearable sensor unit.
15. The magnetic field measurement system of claim 1 , wherein the controller is housed within a single housing.
16. The magnetic field measurement system of claim 1 , wherein the controller is included within the wearable sensor unit.
17. The magnetic field measurement system of claim 1 , wherein:
the magnetometer comprises a photodetector; and
the controller comprises a differential signal measurement circuit configured to measure current output by the photodetector.
18. The magnetic field measurement system of claim 17 , further comprising an unshielded cable configured to electrically connect the controller to the wearable sensor unit.
19. The magnetic field measurement system of claim 18 , wherein the unshielded cable is a twisted pair cable comprising a twisted pair of wires configured to electrically connect the photodetector and the differential signal measurement circuit.
20. The magnetic field measurement system of claim 17 , wherein the photodetector comprises a signal photodetector configured to detect light output by a light source in the magnetometer after the light enters and exits a vapor cell of the magnetometer.
21. The magnetic field measurement system of claim 17 , wherein the photodetector comprises a monitor photodetector configured to detect light output by a light source in the magnetometer before the light enters a vapor cell of the magnetometer.
22. The magnetic field measurement system of claim 1 , wherein:
the magnetometer comprises
a vapor cell comprising an input window and containing an alkali metal, and
a light source configured to output light that passes through the input window and into the vapor cell along a transit path; and
the wearable sensor unit further comprises a temperature control circuit external to the vapor cell and configured to create a temperature gradient within the vapor cell, the temperature gradient configured to concentrate the alkali metal within the vapor cell away from the transit path of the light.