Magnetic field measurement system with amplitude-selective magnetic shield
A magnetic field measurement system for measurement of weak magnetic field signals or a wearable assembly includes at least one magnetometer and a shield disposed around the magnetometer. The shield includes a first portion configured for positioning between the at least one magnetometer and a source of the weak magnetic field signals. The first portion is made of an amplitude-selective magnetic shield (ASMS) that preferentially passes magnetic fields having a magnetic field amplitude below a threshold (for example, 500 nT or less) and shields magnetic fields having a larger magnetic field amplitude.
1. A wearable assembly, comprising:
at least one magnetometer; and
a shield disposed around the at least one magnetometer, wherein the shield comprises a first portion, wherein the first portion is configured to provide a shielding factor of at least 10 for a magnetic field having a magnetic field amplitude of 10 μT and to provide a shielding factor of no more than 2 for a magnetic field having a magnetic field amplitude of 1 nT.
2. The wearable assembly of claim 1 , wherein an entirety of the shield is configured to provide a shielding factor of at least 10 for a magnetic field having a magnetic field amplitude of 10 μT and to provide a shielding factor of no more than 2 for a magnetic field having a magnetic field amplitude of 1 nT.
3. The wearable assembly of claim 1 , wherein the shield comprises a second portion configured to provide a shielding factor of at least 10 for a magnetic field having a magnetic field amplitude of 1 nT.
4. The wearable assembly of claim 3 , wherein the second portion is made of mumetal.
5. The wearable assembly of claim 3 , wherein the first portion is a first layer and the second portion is a second layer disposed over or under the first layer.
6. The wearable assembly of claim 3 , wherein the second portion overlaps only part, which is less than an entirety, of the first portion.
7. The wearable assembly of claim 1 , wherein the first portion is made of an amorphous alloy comprising cobalt and iron and further comprising at least one of molybdenum, boron, silicon, or nickel.
8. A magnetic field measurement system for measurement of weak magnetic field signals, comprising:
the wearable assembly of claim 1 , wherein the first portion of the shield is configured for positioning between the at least one magnetometer and a source of the weak magnetic field signals.
9. A magnetic field measurement system for measurement of weak magnetic field signals, comprising:
at least one magnetometer; and
a shield disposed around the at least one magnetometer, wherein the shield comprises a first portion configured for positioning between the at least one magnetometer and a source of the weak magnetic field signals, wherein the first portion is configured to provide attenuation of a magnetic field having a magnetic field amplitude of 10 μT by at least 90% and to provide attenuation of a magnetic field having a magnetic field amplitude of 1 nT by no more than 50%.
10. The magnetic field measurement system of claim 9 , wherein an entirety of the shield is configured to provide attenuation of a magnetic field having a magnetic field amplitude of 10 μT by at least 90% and to provide attenuation of a magnetic field having a magnetic field amplitude of 1 nT by no more than 50%.
11. The magnetic field measurement system of claim 9 , wherein the shield comprises a second portion configured to provide attenuation of a magnetic field having a magnetic field amplitude of 1 nT by at least 90%.
12. The magnetic field measurement system of claim 11 , wherein the second portion is made of mumetal.
13. The magnetic field measurement system of claim 11 , wherein the first portion is a first layer and the second portion is a second layer disposed over or under the first layer.
14. The magnetic field measurement system of claim 11 , wherein the second portion overlaps only part, which is less than an entirety, of the first portion.
15. The magnetic field measurement system of claim 11 , wherein the first portion is made of an amorphous alloy comprising cobalt and iron and further comprising at least one of molybdenum, boron, silicon, or nickel.
16. A magnetic field measurement system for measurement of weak magnetic field signals, comprising:
at least one magnetometer; and
a shield disposed around the at least one magnetometer, wherein the shield comprises a first portion configured for positioning between the at least one magnetometer and a source of the weak magnetic field signals, wherein the first portion is made of an amorphous alloy comprising cobalt and iron which preferentially passes magnetic fields having a magnetic field amplitude of 500 nT or less.
17. The magnetic field measurement system of claim 16 , wherein the first portion of the shield is configured to provide attenuation of a magnetic field having a magnetic field amplitude of 10 μT by at least 90% and to provide attenuation of a magnetic field having a magnetic field amplitude of 1 nT by no more than 50%.
18. The magnetic field measurement system of claim 16 , wherein the first portion of the shield is configured to provide a shielding factor of at least 10 for a magnetic field having a magnetic field amplitude of 10 μT and to provide a shielding factor of no more than 2 for a magnetic field having a magnetic field amplitude of 1 nT.
19. The magnetic field measurement system of claim 18 , wherein the shield further comprises a second portion configured to provide a shielding factor of at least 10 for a magnetic field having a magnetic field amplitude of 1 nT.
20. The magnetic field measurement system of claim 19 , wherein the second portion overlaps only part, which is less than an entirety, of the first portion.