Coupled fluxgate magnetometers for DC and time-varying target magnetic field detection

1. An apparatus for sensing and processing a magnetic flux signal comprising:

an odd number of at least three fluxgate modules S 1 through S 2N-1 , where N is an integer greater than or equal to 2, each configured to generate a module response signal upon receiving the magnetic flux signal, wherein each of the fluxgate modules is circularly coupled to each other such that only one-way signal flow is allowed between the fluxgate modules;

a summer configured to sum the response signals from the fluxgate modules into a summed signal;

a processor configured to receive and process the summed signal; and

wherein each of the fluxgate modules comprises:

a fluxgate sensor comprising a sensing coil, a driving coil, and a ferromagnetic core, wherein the sensing coil produces a coil response signal;

a primary amplifier configured to amplify a voltage of the coil response signal;

a primary “leaky” integrator configured to transform the amplified coil response signal into the module response signal;

a secondary “leaky” integrator configured to transform the module response signal into a filtered signal;

a secondary amplifier configured to convert the filtered signal into an amplified, filtered signal; and

a voltage to current (V-I) converter configured to convert the amplified, filtered signal into a current signal, wherein the current signal of each fluxgate module is conducted to the driving coil of a next-in-line fluxgate module of the at least three fluxgate modules and the driving coil of the fluxgate module S 1 is configured to receive the current signal from the fluxgate module S 2N-1 such that all the fluxgate modules are circularly coupled.

2. The apparatus of claim 1 , further comprising:

a Schmitt trigger interposed between the processor and the summer;

a voltage divider interposed between the Schmitt trigger and the processor; and

a diode interposed between the voltage divider and the processor.

3. The apparatus of claim 1 , further comprising:

an upper printed circuit board (PCB) with one half of the driving and sensing coils is printed thereon;

a lower PCB with the other half of the driving and sensing coils is printed thereon; and

a middle ferromagnetic layer interposed between the upper and lower PCBs, such that the middle ferromagnetic layer forms a core inside both the driving and sensing coils.

4. The apparatus of claim 3 , wherein the ferromagnetic layer is annealed.

5. The apparatus of claim 3 , wherein the middle ferromagnetic layer comprises multiple ferromagnetic layers electrically insulated from each other.

6. The apparatus of claim 1 , wherein a coupling parameter of the fluxgate modules is tuned to be slightly more positive than a critical threshold value, wherein the fluxgate modules are configured to collectively oscillate at a same frequency as the magnetic flux signal.

7. The apparatus of claim 1 , wherein a coupling parameter of the fluxgate modules is tuned to be slightly more negative than a critical threshold value such that the fluxgate modules are configured to collectively oscillate and that the amplitude of the collective oscillations is modulated by the magnetic flux signal.

8. The apparatus of claim 7 , wherein operating parameters of the primary and secondary “leaky” integrators are tuned to desired low frequency roll-off characteristics.

9. The apparatus of claim 8 , wherein in each fluxgate module the gain of the V-I converter is configured to be much less than unity such that one volt in the amplified, filtered signal does not convert to one ampere in the current signal.

10. The apparatus of claim 9 , wherein in each fluxgate module the fluxgate sensor further comprises a tube, wherein the sensing and driving coils are wrapped around the tube.

11. The apparatus of claim 10 , wherein each fluxgate sensor further comprises an annealed core within the tube.

12. An apparatus for sensing and processing a magnetic flux signal comprising:

an odd number of at least three fluxgate modules, each configured to generate a module response signal upon receiving the magnetic flux signal, wherein each of the fluxgate modules is circularly coupled to each other such that only one-way signal flow is allowed between the fluxgate modules;

a summer configured to sum the response signals from the fluxgate modules into a summed signal;

a processor configured to receive and process the summed signal;

a Schmitt trigger interposed between the processor and the summer;

a voltage divider interposed between the Schmitt trigger and the processor; and

a diode interposed between the voltage divider and the processor.

13. An apparatus for sensing a magnetic flux target signal comprising:

first, second, and third fluxgate modules, each configured to generate a module response signal upon receiving the target signal, wherein each of the fluxgate modules is circularly coupled to each other such that only one-way signal flow is allowed between the fluxgate modules;

a summer configured to sum the response signals from the fluxgate modules into a summed signal;

a processor configured to receive the summed signal; and

wherein each of the fluxgate modules comprises:

a fluxgate sensor comprising a sensing coil and a driving coil, wherein the sensing coil produces a coil response signal;

a primary amplifier configured to amplify a voltage of the coil response signal;

a primary “leaky” integrator configured to transform the amplified coil response signal into the module response signal;

a secondary “leaky” integrator configured to transform the module response signal into a filtered signal;

a secondary amplifier configured to amplify the voltage of the filtered signal; and

a voltage to current (V-I) converter configured to convert the amplified, filtered signal into a current signal, wherein the current signal of the first fluxgate module is conducted to the driving coil of the second fluxgate module, the current signal of the second fluxgate module is conducted to the driving coil of the third fluxgate module, and the current signal of the third fluxgate module is conducted to the driving coil of the first fluxgate module.

14. The apparatus of claim 13 , wherein each fluxgate module has a magnetic orientation and wherein the magnetic orientation of one of the fluxgate modules is opposite the magnetic orientation of the other two fluxgate modules.

15. The apparatus of claim 13 , wherein a coupling parameter of the fluxgate modules is tuned to exceed a critical threshold value thereby causing the fluxgate modules to oscillate.

16. The apparatus of claim 13 , wherein a coupling parameter of the fluxgate modules is tuned to be slightly more positive than a critical threshold value, wherein the fluxgate modules are configured to collectively oscillate at a same frequency as the target signal.

17. The apparatus of claim 13 , wherein a coupling parameter of the fluxgate modules is tuned to be slightly more negative than a critical threshold value such that the fluxgate modules are configured to collectively oscillate and that the amplitude of the collective oscillations is modulated by the target signal.