Micro coils suitable for magnetic neural stimulation
An implantable magnetic neurostimulation probe includes at least one electrical conductor disposed on a substrate and arranged in at least one planar loop. At least one planar magnetic core comprising a magnetic material is disposed on the substrate and within the planar loop. A biocompatible coating is disposed over the substrate, electrically conductive trace, and magnetic core.
1. An implantable magnetic neurostimulation probe, comprising:
at least one substrate;
at least one electrical conductor disposed on the at least one substrate and arranged in at least one planar loop, the at least one electrical conductor configured to produce an electric field sufficient to activate neurons;
at least one planar magnetic core comprising a magnetic material disposed on the at least one substrate and within the at least one planar loop; and
a biocompatible coating disposed over the at least one substrate, the at least one electrical conductor, and the at least one planar magnetic core, wherein:
the at least one electrical conductor is arranged such that the at least one planar loop comprises multiple sections within the at least one planar loop; and
the at least one planar magnetic core comprises multiple magnetic cores, each magnetic core disposed within a respective one of the multiple sections.
2. The probe of claim 1 , wherein the multiple magnetic cores include at least a first magnetic core having a first surface area and a second magnetic core having a second surface area that is different from the first surface area.
3. The probe of claim 1 , wherein at least one side of the at least one planar loop has a sawtooth profile.
4. The probe of claim 3 , wherein the at least one planar loop having the sawtooth profile comprises:
multiple sections, each of the multiple sections having an area that differs from an area of other sections of the multiple sections; and
each of the multiple magnetic cores having a surface area that differs from a surface area of other magnetic cores of the multiple magnetic cores.
5. The probe of claim 1 , wherein the at least one planar loop is a single electrically continuous loop.
6. The probe of claim 1 , wherein the at least one electrical conductor comprises an electrically continuous electrical conductor that forms multiple concentric loops arranged in a spiral.
7. The probe of claim 1 , wherein the at least one planar loop comprises multiple planar loops.
8. The probe of claim 7 , wherein the multiple planar loops are concentric.
9. The probe of claim 8 , wherein each of the multiple magnetic core is disposed within a respective one of the multiple concentric planar loops.
10. The probe of claim 1 , wherein:
the at least one substrate is one or both of flat and rigid; and
the at least one electrical conductor and the at least one planar magnetic core conform to the at least one substrate.
11. The probe of claim 1 , wherein the magnetic material has a magnetization change per cm 3 mol −1 in a range of about 10 to 2000 G.
12. The probe of claim 1 , wherein, when energized by an electric current of about 50 mA through the at least one loop, the probe is configured to produce an excitation volume having a boundary with a radius of about 50 μm such that at an electric field gradient generated by the probe is greater than 11000 V/m 2 within the boundary and is less than 11000 V/m 2 at and beyond the boundary.
13. The probe of claim 12 , wherein the electric field gradient generated by the probe is greater than 10 6 V/m 2 within the boundary and is less than 10 6 V/m 2 at and beyond the boundary.
14. The probe of claim 1 , wherein, when energized by an electric current having a predetermined value through the at least one planar loop, the probe has an activation volume with a radius that is up to about 60% less than a radius of an activation volume of an otherwise identical probe without the at least one planar magnetic core that is energized by the predetermined value of the electric current.
15. A system, comprising:
an implantable magnetic neurostimulation probe comprising:
at least one substrate;
at least one electrical conductor disposed on the at least one substrate and arranged as at least one planar loop, the at least one electrical conductor configured to produce an electric field sufficient to activate neurons;
at least one planar magnetic core comprising a magnetic material disposed on the at least one substrate and within the at least one planar loop; and
a biocompatible coating disposed over the at least one substrate, the at least one electrical conductor, and the at least one planar magnetic core; and
an energizer configured to apply an electrical current through the at least one electrical conductor, wherein:
the at least one electrical conductor is arranged such that the at least one planar loop comprises multiple sections within the at least one planar loop; and
the at least one planar magnetic core comprises multiple magnetic cores, each magnetic core disposed within a respective one of the multiple sections.
16. An implantable magnetic neurostimulation probe, comprising:
at least one substrate;
at least one electrical conductor disposed on the at least one substrate and arranged in at least one planar loop, the at least one electrical conductor configured to produce an electric field sufficient to activate neurons;
at least one planar magnetic core comprising a magnetic material disposed on the at least one substrate and within the at least one planar loop; and
a biocompatible coating disposed over the at least one substrate, the at least one electrical conductor, and the at least one planar magnetic core, wherein:
the at least one planar loop comprises multiple planar loops;
the multiple planar loops are concentric; and
the at least one planar magnetic core comprises multiple magnetic cores, each of the multiple magnetic cores disposed within a respective one of the multiple concentric planar loops.
17. The probe of claim 16 , wherein the at least one electrical conductor comprises an electrically continuous electrical conductor that forms the multiple planar loops.
18. The probe of claim 17 , wherein the multiple concentric loops are arranged in a spiral.
19. The probe of claim 16 , wherein, when energized by an electric current having a predetermined value through the at least one planar loop, the probe has an activation volume with a radius that is up to about 60% less than a radius of an activation volume of an otherwise identical probe without the at least one planar magnetic core that is energized by the predetermined value of the electric current.
20. An implantable magnetic neurostimulation probe, comprising:
at least one substrate;
at least one electrical conductor disposed on the at least one substrate and arranged in at least one planar loop, the at least one electrical conductor configured to produce an electric field sufficient to activate neurons;
at least one planar magnetic core comprising a magnetic material disposed on the at least one substrate and within the at least one planar loop; and
a biocompatible coating disposed over the at least one substrate, the at least one electrical conductor, and the at least one planar magnetic core;
wherein, when energized by an electric current of about 50 mA through the at least one loop, the probe is configured to produce an excitation volume having a boundary with a radius of about 50 μm such that at an electric field gradient generated by the probe is greater than 11000 V/m 2 within the boundary and is less than 11000 V/m 2 at and beyond the boundary.
21. The probe of claim 20 , wherein the electric field gradient generated by the probe is greater than 10 6 V/m 2 within the boundary and is less than 10 6 V/m 2 at and beyond the boundary.
22. An implantable magnetic neurostimulation probe, comprising:
at least one substrate;
at least one electrical conductor disposed on the at least one substrate and arranged in at least one planar loop, the at least one electrical conductor configured to produce an electric field sufficient to activate neurons;
at least one planar magnetic core comprising a magnetic material disposed on the at least one substrate and within the at least one planar loop; and
a biocompatible coating disposed over the at least one substrate, the at least one electrical conductor, and the at least one planar magnetic core;
wherein, when energized by an electric current having a predetermined value through the at least one planar loop, the probe has an activation volume with a radius that is up to about 60% less than a radius of an activation volume of an otherwise identical probe without the at least one planar magnetic core that is energized by the predetermined value of the electric current.
23. The probe of claim 22 , wherein:
the probe is configured to produce an excitation volume having a boundary; and
an electric field gradient generated by the probe is greater than 10 6 V/m 2 within the boundary and is less than 10 6 V/m 2 at and beyond the boundary.