Soft magnetic material based microcoils and magnetoresistance based sensors as closed-loop neurostimulation and sensing system

Abstract

A magnetic tissue stimulator 100 comprising a coil 106, a first magnetic layer 122 having a first end 127 and a second end 123 and a second magnetic layer 124 having a first end 129 and a second end 125. The second end 123 of the first magnetic layer 122 is in contact 126 with the second end 125 of the second magnetic layer 124 and the first end 127 of the first magnetic layer 122 is separated from the first end 129 of the second magnetic layer 124 by a gap 128. A portion of the coil 106 is positioned between the first magnetic layer 122 and the second magnetic layer 124.

Description

SOFT MAGNETIC MATERIAL BASED MICROCOILS AND MAGNETORESISTANCE BASED SENSORS AS CLOSED-LOOP NEUROSTIMULATION AND SENSING SYSTEMBACKGROUND

[0001] Neuron stimulation involves generating a field at a neuron in order to manipulate the activities of the neuron including causing the neuron to fire. Neural signal sensing involves placing a sensor near a nerve pathway to sense the electrical current earned by the pathway and the magnetic signal generated directly by neurons’ activities.

[0002] The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter. The claimed subject matter is not limited to implementations that solve any or all disadvantages noted in the background.SUMMARY

[0003] A magnetic tissue stimulator comprising a coil, a first magnetic layer having a first end and a second end and a second magnetic layer having a first end and a second end. The second end of the first magnetic layer is in contact with the second end of the second magnetic layer and the first end of the first magnetic layer is separated from the first end of the second magnetic layer by a gap. A portion of the coil is positioned between the first magnetic layer and the second magnetic layer.

[0004] In accordance with some embodiments, the gap of the stimulator is located proximate an exterior surface of the magnetic tissue stimulator.

[0005] In accordance with some embodiments, the magnetic tissue stimulator is part of a closed loop system. In accordance with some embodiments the closed loop system further comprises an electrical sensor comprising at least one of: an electrical sensor to detect the current directly, an electrical sensor to detect the electrical charges directly, a capacitor sensor and an inductor sensor.

[0006] In accordance with some embodiments, the closed loop system further comprises a magnetic field sensor. In accordance with some embodiments, the magnetic field sensor comprises at least one of: a magnetic tunnel junction, a giant magnetoresistance (GMR) device, a spin-orbit torque sensing device and an optically pumped atomic magnetometer.

[0007] In a further embodiment, a closed-loop system includes a magnetic tissue stimulator that is configured to transmit a magnetic field into tissue and a magnetic field sensor that is configured to sense a magnetic field generated by tissue. A controller in the closed-loop system is configured to cause the magnetic tissue stimulator to transmit the magnetic field and to receive a value indicative of the sensed magnetic field.

[0008] In accordance with some embodiments, the controller is configured to set a magnitude and a frequency of the magnetic field.

[0009] In accordance with some embodiments, the closed loop system also includes a second magnetic field sensor that is configured to sense a second magnetic field generated by tissue, wherein the controller is configured to receive a value indicative of the sensed second magnetic field.

[0010] In accordance with some embodiments, the closed loop system also includes an array of magnetic tissue stimulators and magnetic field sensors

[0011] In accordance with some embodiments, the magnetic tissue stimulator of the closed- loop system includes a coil, a first magnetic layer having a first end and a second end, and a second magnetic layer having a first end and a second end. The second end of the first magnetic layer is in contact with the second end of the second magnetic layer, the first end of the first magnetic layer is separated from the first end of the second magnetic layer by a gap, and a portion of the coil is positioned between the first magnetic layer and the second magnetic layer. In accordance with some embodiments the gap is located proximate an exterior surface of the magnetic tissue stimulator.

[0012] In accordance with some embodiments, the magnetic field sensor is a giant magnetoresistance sensor.

[0013] In accordance with a still further embodiment, a method includes generating a magnetic field within tissue at a first location, sensing a separate magnetic field within tissue at asecond location to produce a sensor value, and using the sensor value to form a modified magnetic field within the tissue at the first location.

[0014] In accordance with some embodiments, the sensor value is used to change a magnitude of current used to generate the magnetic field. In accordance with some embodiments, the sensor value is used to change a frequency of current used to generate the magnetic field.

[0015] In accordance with some embodiments, sensing a separate magnetic field includes using a giant magnetoresistance sensor to sense the separate magnetic field.

[0016] In accordance with some embodiments, the method includes using the sensor value to determine which of multiple possible neural pathways were stimulated by the magnetic field at the first location.

[0017] In accordance with some embodiments, generating a magnetic field within tissue at a first location includes using a magnetic tissue stimulator having a coil, a first magnetic layer having a first end and a second end and a second magnetic layer having a first end and a second end. The second end of the first magnetic layer is in contact with the second end of the second magnetic layer and the first end of the first magnetic layer is separated from the first end of the second magnetic layer by a gap. A portion of the coil is positioned between the first magnetic layer and the second magnetic layer.

[0018] This Summary is provided to introduce a selection of concepts in a simplified form that arc further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIG. 1 is a side sectional view of a magnetic tissue stimulator in accordance with one embodiment.

[0020] FIG. 2 is a front view of the magnetic tissue stimulator of FIG. 1.

[0021] FIG. 3 is a side sectional view of a magnetic field sensor in accordance with one embodiment.

[0022] FIG. 4 is a front view of the magnetic field sensor of FIG. 3.

[0023] FIG. 5 is a side sectional view of a magnetic field sensor in accordance with a second embodiment.

[0024] FIG. 6 is a front view of the magnetic field sensor of FIG. 5.

[0025] FIG. 7 is a block diagram of a closed-loop system in accordance with one embodiment.

[0026] FIG. 8 is a top view of a sensor array in accordance with one embodiment.

[0027] FIG. 9 is a side sectional view of a magnetic tissue stimulator in accordance with a second embodiment.

[0028] FIG. 10 is a side sectional view of a magnetic tissue stimulator in accordance with a second embodiment.

[0029] FIG. 11 provides a flow diagram of a method performed using the closed-loop system of FIG. 7.DETAILED DESCRIPTION

[0030] In the embodiments below, thin-film magnetic induction structures are used to stimulate tissue such as neurons. In particular, the magnetic induction structures consist of a coil positioned between two soft magnetic layers that are separated by a gap at one end. The soft magnetic layers channel a magnetic field generated by the coil so that the magnetic field extends into the tissue while bridging the gap. This magnetic field induces an electric field in the neuron causing the neuron to generate an electric current, commonly referred to as “firing.”

[0031] In some embodiments, a closed-loop magnetic system is provided in which a magnetic stimulator, such as the one described above, is used in combination with a magnetic field sensor that is able to sense a magnetic field generated by tissue. Using this closed loop, it is possible to generate a stimulation signal and then sense one or more tissue responses to that signal to evaluate the effects of the stimulation signal’s magnitude, frequency and / or position.

[0032] FIG. 1 provides a side sectional view and FIG. 2 provides a front view of a thin-film magnetic tissue stimulator 100 positioned over tissue 102 containing a neuron 104. Magnetic tissue stimulator 100 includes a conductive coil 106, a portion of which is sandwiched between first and second insulator layers 108 and 110. Coil 106 defines a conduction path that loops around itself such that multiple portions of the path, such as portions 112, 114, 116, 118 and 120of FIG. 1 extend between two soft magnetic layers 122 and 124. Magnetic layer 122 has a first end 127 and a second end 123 and magnetic layer 124 has a first end 129 and a second end 125. Second ends 123 and 125 contact each other at a junction 126 and first ends 127 and 129 are separated from each other by a gap 128 near an exterior stimulating surface 130. Coil 106 has two ends 132 and 134 that are connected to respective conductors 136 and 138.

[0033] When a voltage is created between conductors 136 and 138, a current flows through coil 106 causing a magnetic field to be generated around coil 106. Soft magnetic layers 122 and 124 act as first and second pole pieces, which channel the magnetic field within layers 122 and 124. At gap 128, the magnetic field 140 extends from magnetic layer 122 to magnetic layer 124. Magnetic field 140 extends into tissue 102 passing near or through neuron 104.

[0034] As the current in coil 106 increases or decreases, the strength and / or direction of magnetic field 140 changes. The changing magnetic field produces circular electric fields 150 in tissue 102 as shown in the exploded portions of FIGS. 1 and 2. When an alternating current is used to drive coil 106, the resulting magnetic field alternates in a similar fashion such that the frequency of the magnetic field matches the frequency of the alternating current. The maximum magnitude of the magnetic field is a function of the maximum magnitude of the current. The frequency and magnitude of the resulting magnetic field determines the frequency and magnitude of the electric field with the frequency of the electric field increasing with increases in the frequency of the magnetic field and the magnitude of the electric field increasing with increases in the frequency of the magnetic field and with increases in the magnitude of the magnetic field. Thus, the magnitude of the electric field is a function of the magnitude and frequency of the magnetic field. The magnitude of the electric field decreases as a function of distance from magnetic field 140.

[0035] When electric field 150 is strong enough and positioned properly, electric field 150 can trigger neuron 104 to “fire” so that neuron 104 sends an electrical current along the neuron’s axon that in turn can cause other neurons to “fire” resulting in currents along one or more neural pathways.

[0036] FIG. 3 provides a side sectional view and FIG. 4 provides a front view of a thin-film magnetic field sensor 300 that can be used with the magnetic stimulator of FIGS. 1 and 2. Thin- film magnetic field sensor 300 is a giant magneto-resistive sensor containing a free magneticlayer 302, an insulating layer 304 and a fixed magnetic layer 306 as well as two conductors 308 and 310. In FIG. 3, free layer 302 is positioned at and defines a read surface 312, insulating layer 304 is positioned above free layer 302 and fixed magnetic layer 306 is positioned above insulating layer 304. Thus, fixed magnetic layer 306 is separated from free magnetic layer 302 by insulating layer 304. Each of layers 302, 304 and 306 are in contact with both conductors 308 and 310, which are positioned vertically on opposite ends of layers 302, 304 and 306. As shown in FIG. 4, sensor 300 is sandwiched between two insulating layers 320 and 322 and two shielding layers 324 and 326. Shielding layers 324 and 326 are made of a magnetic material and prevent magnetic signals from reaching free layer 302 unless the magnetic signals are generated directly below free magnetic layer 302.

[0037] Fixed magnetic layer 306 has a magnetic moment with a fixed direction that is parallel to read surface 312. Free magnetic layer 302 has a magnetic moment that is free to switch directions when exposed to a sufficiently strong magnetic field. The resistance between conductors 308 and 310 changes depending on the orientation of the magnetic moment in free magnetic layer 302. When the magnetic moment is parallel to the magnetic moment of fixed magnetic layer 306, sensor 300 has a lower resistance between conductors 308 and 310 than when the magnetic moment of free magnetic layer 302 is anti-parallel (pointing in the opposite direction) to the magnetic moment of fixed layer 306.

[0038] In FIGS. 3 and 4, read surface 312 is shown positioned above a neural pathway 400 that carries an electrical current. This electrical current generates a magnetic field 402 that extends into free magnetic layer 302 and causes the magnetic moment of free magnetic layer 302 to align with magnetic field 402. If magnetic field 402 changes the direction of the magnetic moment of free magnetic layer 302, the resistance between conductors 308 and 310 will change. This change in resistance can be measured by applying a voltage between conductors 308 and 310 and measuring the resulting current. Thus, magnetic sensor 300 is able to sense the current in neural pathway 400.

[0039] FIGS. 5 and 6 provide a side sectional view and front view of an alternative thin-film magnetic field sensor 500 that can be used with magnetic stimulator 100 of FIGS. 1 and 2. Magnetic field sensor 500 is a spintronic sensor, such as a giant magneto-resistive sensor, a magnetic tunnel junction sensor, or a spin orbital torque sensor. Sensor 500 includes a freemagnetic layer 502, an insulating layer 504 and a fixed magnetic layer 506. A conductive layer 508 is positioned below free magnetic layer 502 and provides a read surface 510. Insulating layer 504 is positioned above free magnetic layer 502 and fixed magnetic layer 506 is positioned above insulating layer 504. A second conductive layer 512 is positioned above fixed magnetic layer 506. A vertical conductor 514 is in contact with and extends from bottom conductive layer 508 to a position above magnetic field sensor 500. A second vertical conductor 516 is in contact with and extends from conductive layer 512 to a position above magnetic field sensor 500. Magnetic field sensor 500 is sandwiched between two insulating layers 540 and 542, which are in turn sandwiched between two shield layers 544 and 546. In accordance with one embodiment, shield layers 544 and 546 are constructed of soft magnetic material which shields sensor 500 from magnetic signals that are not directly below read surface 510.

[0040] When a voltage difference is applied across conductors 514 and 516, current flows from conductive layer 508 through free magnetic layer 502, insulating layer 504, and fixed magnetic layer 506 to conductive layer 512. The size of the current is dependent on the resistance provided along the path, which changes based on the orientation of the magnetic moment of free magnetic layer 502. In particular, when the direction of the magnetic moment of free magnetic layer 502 is parallel to the direction of the magnetic moment of fixed magnetic layer 506, magnetic field sensor 500 provides a larger current (lower resistance) than when the direction of the magnetic moment of free magnetic layer 502 is anti-parallel (opposite) to the direction of the magnetic moment of fixed magnetic layer 506.

[0041] Read surface 510 is shown positioned over a neural pathway 520, which carries an electrical current. The electrical current of neural pathway 520 generates a corresponding magnetic field 522 around neural pathway 520 that extends into free magnetic layer 502. The strength of magnetic field 522 is larger enough to cause the magnetic moment of free magnetic layer 502 to align with magnetic field 522. If magnetic field 522 changes the direction of the magnetic moment of free magnetic layer 502, the resistance of magnetic field sensor 500 will change and this change in resistance can be detected by sensing the current along either conductor 514 or conductor 516. Thus, magnetic field sensor 500 can sense an electrical signal along neural pathway 520.

[0042] FIG. 7 provides a block diagram of a closed-loop system 700 that utilizes thin-film magnetic stimulator 100 of FIG. 1 and a sensor 702, such as thin-film magnetic field sensors 300 and 500, an optically pumped atomic magnetometer or an electrical sensor such as an electrical sensor to detect current directly, an electrical sensor to detect electrical charges directly, a capacitor sensor or an inductor sensor.

[0043] Closed-loop system 700 includes a controller 704 that issues a stimulation control instruction 706 to an excitation interface 708. Based on the stimulation control instruction, excitation interface 708 provides a voltage across conductors 136 / 138 that causes magnetic stimulator 100 to generate a magnetic field 710 that interacts with a neuron 712 as described above with reference to FIGS. 1 and 2. In particular, magnetic field 710 creates an electric field in neuron 712 that causes neuron 712 to fire. When neuron 712 fires, an electrical current 714 is generated along a neural pathway 716, thereby producing a magnetic field 718 below the read surface of sensor 702. As discussed above, in embodiments where sensor 702 is a magnetic field sensor, the resistance of the magnetic field sensor changes when magnetic field 718 alters the magnetic moment of a free magnetic layer in sensor 702. This change in resistance is detected via a change in current along conductors 720 and 722 that are connected to magnetic field sensor 702.

[0044] A sensor interface 724 detects the change in current and provides a detection value 726 based on the change in current where the detection value indicates that a signal has been detected on the neural pathway 716. Controller 704 receives detection value 726 thereby closing loop 700 that began at controller 704. In summary, closed loop 700 consists of controller 704, instruction 706, excitation interface 708, conductors 136 and 138, magnetic stimulator 100, magnetic field 710, neuron 712, neural pathway 716, magnetic field 718 sensor 702, conductors 720 and 722, sensor interface 724, and detection value 726.

[0045] Using closed loop 700, controller 704 is able to adjust the magnitude and / or frequency of the excitation voltage applied between conductors 136 and 138, thereby altering the magnitude and frequency of magnetic field 710 while simultaneously monitoring detection value 726 to determine frequencies and magnitudes that generate a response along neural pathway 716. Note that neural pathway 716 can be part of neuron 712 or part of another neuron that is connected to neuron 712.

[0046] Controller 704 also provides display information 750 that can contain one or more of the magnitude of the voltage applied to magnetic stimulator 100, the frequency of the voltage applied to magnetic stimulator 100 and the detection values 726 received from sensor interface 724. Display information 750 is provided to a display interface 752, which uses the information to generate a user interface on a display 754. Although only one sensor 702 and one magnetic stimulator 100 are shown in FIG. 7, controller 704 can control multiple magnetic stimulators and receive detection values from multiple sensors.

[0047] FIG. 8 provides a top view of a sensor array 800 that can be used in a closed loop in accordance with one embodiment. Sensor array 800 includes multiple magnetic field sensors 802, 804, 806, 808, and 810 distributed around a magnetic stimulator 812 on a common substrate 814. Magnetic field sensors 802, 804, 806, 808 and 810 and magnetic stimulator 812 are used together in a single closed-loop system in cooperation with an excitation interface, a sensor interface and a controller (not shown), similar to closed-loop system of FIG. 7. Using sensor array 800, a controller can cause magnetic stimulator 812 to stimulate a neuron and magnetic field sensors 802, 804, 806, 808 and 810 can be used to sense which pathway carried a corresponding electrical signal in response to the stimulation signal provided by stimulator 810.

[0048] In the embodiment of FIG. 1, the cross-sectional area of soft magnetic layers 122 and 124 at the exterior stimulating surface 130 are equal to each other. FIG. 9 provides a side sectional view of an alternative embodiment of a magnetic tissue stimulator 900 in which magnetic layers 122 and 124 are replaced with magnetic layers 922 and 924. Magnetic layer 922 has a width 932 that is twice as large as width 934 of magnetic layer 924 resulting in a cross- sectional area that is twice as large in magnetic layer 922 than magnetic layer 924. The other elements of FIG. 9 are the same as FIG. 1.

[0049] FIG. 10 provides a side sectional view of a third embodiment of a thin-film magnetic tissue stimulator 1000 positioned over tissue 102 containing a neuron 104. Magnetic tissue stimulator 1000 is capable of generating two independent magnetic fields 140 and 1040. Magnetic field 140 is created by the same structure as FIG. 2 with magnetic layers 122 and 124 replaced by magnetic layers 1022 and 1024. Magnetic field 1040 is produced by a second structure consisting of soft magnetic layer 1026, magnetic layer 1024 and second conductive coil 1006. A portion of second conductive coil 1006 is sandwiched between third and fourth insulatorlayers 1008 and 1010. Coil 1006 defines a conduction path that loops around itself such that multiple portions of the path, such as portions 1012, 1014, 1016, 1018 and 1020 extend between soft magnetic layers 1022 and 1026. Magnetic layers 1022 and 1024 have respective second ends 1023 and 1025 that contact each other at a junction 126 and respective first ends 1.027 and 1029 that are separated from each other by a gap 128 near an exterior stimulating surface 130. Magnetic layers 1022 and 1026 have respective second ends 1023 and 1033 that contact each other at a junction 1026 and respective first ends 1029 and 1031 that are separated from each other by a gap 1028 near exterior stimulating surface 130.Coil 1006 has a first end 1034 and a second end (not shown) that are connected to respective conductors.

[0050] Magnetic layer 1022 has a width 1032 that is thrice as large as width 1034 of magnetic layer 1024 resulting in a cross-sectional area that is thrice as large in magnetic layer 1022 than magnetic layer 1024. Magnetic layer 1026 has a width 1036 that is twice as large as width 1034 of magnetic layer 1024 resulting in a cross-sectional area that is twice as large in magnetic layer 1026 than magnetic layer 1024.

[0051] When a voltage is created between the conductors connected to coil 1006, a current flows through coil 1006 causing a magnetic field to be generated around coil 1006. Soft magnetic layers 1022 and 1026 act as first and second pole pieces, which channel the magnetic field within layers 1022 and 1026. At gap 1028, the magnetic field 1040 extends from magnetic layer 1022 to magnetic layer 1026. Magnetic field 1040 extends into tissue 102 passing near or through neuron 104.

[0052] As the current in coil 1006 increases or decreases, the strength and / or direction of magnetic field 1040 changes. The changing magnetic field produces circular electric fields 1050 in tissue 102 as shown in the exploded portion of FIG. 10. When an alternating current is used to drive coil 1006, the resulting magnetic field alternates in a similar fashion such that the frequency of the magnetic field matches the frequency of the alternating current. The maximum magnitude of the magnetic field is a function of the maximum magnitude of the current. The frequency and magnitude of the resulting magnetic field determines the frequency and magnitude of the electric field with the frequency of the electric field increasing with increases in the frequency of the magnetic field and the magnitude of the electric field increasing with increases in the frequency of the magnetic field and with increases in the magnitude of the magnetic field.Thus, the magnitude of the electric field is a function of the magnitude and frequency of the magnetic field. The magnitude of the electric field decreases as a function of distance from magnetic field 1040.

[0053] When electric field 1050 is strong enough and positioned properly, electric field 1050 can trigger neuron 104 to “fire” so that neuron 104 sends an electrical current along the neuron’s axon that in turn can cause other neurons to “fire” resulting in currents along one or more neural pathways.

[0054] FIG. 11 provides a flow diagram of a method for using the closed-loop system of FIG. 7. In step 1100, controller 704 causes magnetic stimulator 100 to generate a magnetic field within tissue at a first location. In step 1102, sensor 702 senses a separate magnetic field at a second location to produce a sensor value that is output by sensor interface 724. At step 1104, controller 704 uses the sensor value to form a modified magnetic field within the tissue at the first location. This is done by changing the frequency or magnitude of the current or voltage applied to the coil to thereby change the frequency and / or magnitude of the magnetic field in the tissue at the first location. Alternatively or additionally, controller 704 can use the sensor value together with sensor values from other locations to determine which neural pathway was stimulated by the magnetic field at the first location.A. A magnetic tissue stimulator comprising: a coil; a first magnetic layer having a first end and a second end; a second magnetic layer having a first end and a second end, wherein: the second end of the first magnetic layer is in contact with the second end of the second magnetic layer, the first end of the first magnetic layer is separated from the first end of the second magnetic layer by a gap, and a portion of the coil is positioned between the first magnetic layer and the second magnetic layer.B. The magnetic tissue stimulator of A wherein the gap is located proximate an exterior surface of the magnetic tissue stimulator.C. The magnetic tissue stimulator of A or B wherein the magnetic tissue stimulator is part of a closed loop system.D. The magnetic tissue stimulator of C wherein the closed loop system further comprises an electrical sensor.E. The magnetic tissue stimulator of D wherein the electrical sensor comprises at least one of: an electrical sensor to detect the current directly, an electrical sensor to detect the electrical charges directly, a capacitor sensor and an inductor sensor.F. The magnetic tissue stimulator of C wherein the closed loop system further comprises a magnetic field sensor.G. The magnetic tissue stimulator of F wherein the magnetic field sensor comprises at least one of: a magnetic tunnel junction, a giant magnetoresistance (GMR) device, a spin-orbit torque sensing device and an optically pumped atomic magnetometer.H. A closed-loop system comprising: a magnetic tissue stimulator that is configured to transmit a magnetic field into tissue; a magnetic field sensor that is configured to sense a magnetic field generated by tissue; and a controller configured to cause the magnetic tissue stimulator to transmit the magnetic field and to receive a value indicative of the sensed magnetic field.I. The closed-loop system of H wherein the controller is configured to set a magnitude and a frequency of the magnetic field.J. The closed-loop system of H or I further comprising a second magnetic field sensor that is configured to sense a second magnetic field generated by tissue, wherein the controller is configured to receive a value indicative of the sensed second magnetic field.K. The closed-loop system of H or I further comprising an array of magnetic tissue stimulators and magnetic field sensorsL. The closed-loop system of H, I, J or K wherein the magnetic tissue stimulator comprises: a coil; a first magnetic layer having a first end and a second end; a second magnetic layer having a first end and a second end, wherein: the second end of the first magnetic layer is in contact with the second end of the second magnetic layer, the first end of the first magnetic layer is separated from the first end of the second magnetic layer by a gap, and a portion of the coil is positioned between the first magnetic layer and the second magnetic layer.M. The closed-loop system of L wherein the gap is located proximate an exterior surface of the magnetic tissue stimulator.N. The closed-loop system of H, I, J, K, L or M wherein the magnetic field sensor comprises a giant magnetoresistance sensor.O. A method comprising: generating a magnetic field within tissue at a first location; sensing a separate magnetic field within tissue at a second location to produce a sensor value; andusing the sensor value to form a modified magnetic field within the tissue at the first location.P. The method of O wherein using the sensor value to form a modified magnetic field comprises using the sensor value to change a magnitude of current used to generate the magnetic field.Q. The method of P wherein using the sensor value to form a modified magnetic field comprises using the sensor value to change a frequency of current used to generate the magnetic field.R. The method of O, P, or Q wherein sensing a separate magnetic field comprises using a giant magnetoresistance sensor to sense the separate magnetic field.S. The method of O, P, Q, or R further comprising using the sensor value to determine which of multiple possible neural pathways were stimulated by the magnetic field at the first location.T. The method of O, P, Q, R or S wherein generating a magnetic field within tissue at a first location comprises using a magnetic tissue stimulator comprising: a coil; a first magnetic layer having a first end and a second end; a second magnetic layer having a first end and a second end, wherein: the second end of the first magnetic layer is in contact with the second end of the second magnetic layer, the first end of the first magnetic layer is separated from the first end of the second magnetic layer by a gap, and a portion of the coil is positioned between the first magnetic layer and the second magnetic layer.

[0055] Although elements have been shown or described as separate embodiments above, portions of each embodiment may be combined with all or part of other embodiments described above.

[0056] Although the subject matter has been described in language specific to structural features and / or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms for implementing the claims.

Claims

WHAT IS CLAIMED IS:

1. A magnetic tissue stimulator comprising: a coil; a first magnetic layer having a first end and a second end; a second magnetic layer having a first end and a second end, wherein: the second end of the first magnetic layer is in contact with the second end of the second magnetic layer, the first end of the first magnetic layer is separated from the first end of the second magnetic layer by a gap, and a portion of the coil is positioned between the first magnetic layer and the second magnetic layer.

2. The magnetic tissue stimulator of claim 1 wherein the gap is located proximate an exterior surface of the magnetic tissue stimulator.

3. The magnetic tissue stimulator of claim 1 wherein the magnetic tissue stimulator is part of a closed loop system.

4. The magnetic tissue stimulator of claim 3 wherein the closed loop system further comprises an electrical sensor.

5. The magnetic tissue stimulator of claim 4 wherein the electrical sensor comprises at least one of: an electrical sensor to detect the current directly, an electrical sensor to detect the electrical charges directly, a capacitor sensor and an inductor sensor.

6. The magnetic tissue stimulator of claim 3 wherein the closed loop system further comprises a magnetic field sensor.

7. The magnetic tissue stimulator of claim 6 wherein the magnetic field sensor comprises at least one of: a magnetic tunnel junction, a giant magnetoresistance (GMR) device, a spin-orbit torque sensing device and an optically pumped atomic magnetometer.

8. A closed-loop system comprising: a magnetic tissue stimulator that is configured to transmit a magnetic field into tissue; a magnetic field sensor that is configured to sense a magnetic field generated by tissue; and a controller configured to cause the magnetic tissue stimulator to transmit the magnetic field and to receive a value indicative of the sensed magnetic field.

9. The closed-loop system of claim 8 wherein the controller is configured to set a magnitude and a frequency of the magnetic field.

10. The closed-loop system of claim 8 further comprising: a second magnetic field sensor that is configured to sense a second magnetic field generated by tissue; wherein the controller is configured to receive a value indicative of the sensed second magnetic field.

11. The closed- loop system of claim 8 further comprising: an array of magnetic tissue stimulators and magnetic field sensors12. The closed-loop system of claim 8 wherein the magnetic tissue stimulator comprises: a coil; a first magnetic layer having a first end and a second end; a second magnetic layer having a first end and a second end, wherein: the second end of the first magnetic layer is in contact with the second end of the second magnetic layer,the first end of the first magnetic layer is separated from the first end of the second magnetic layer by a gap, and a portion of the coil is positioned between the first magnetic layer and the second magnetic layer.

13. The closed-loop system of claim 12 wherein the gap is located proximate an exterior surface of the magnetic tissue stimulator.

14. The closed-loop system of claim 8 wherein the magnetic field sensor comprises a giant magnetoresistance sensor.

15. A method comprising: generating a magnetic field within tissue at a first location; sensing a separate magnetic field within tissue at a second location to produce a sensor value; and using the sensor value to form a modified magnetic field within the tissue at the first location.

16. The method of claim 15 wherein using the sensor value to form a modified magnetic field comprises using the sensor value to change a magnitude of current used to generate the magnetic field.

17. The method of claim 15 wherein using the sensor value to form a modified magnetic field comprises using the sensor value to change a frequency of current used to generate the magnetic field.

18. The method of claim 15 wherein sensing a separate magnetic field comprises using a giant magnetoresistance sensor to sense the separate magnetic field.

19. The method of claim 15 further comprising using the sensor value to determine which of multiple possible neural pathways were stimulated by the magnetic field at the first location.

20. The method of claim 15 wherein generating a magnetic field within tissue at a first location comprises using a magnetic tissue stimulator comprising: a coil; a first magnetic layer having a first end and a second end; a second magnetic layer having a first end and a second end, wherein: the second end of the first magnetic layer is in contact with the second end of the second magnetic layer, the first end of the first magnetic layer is separated from the first end of the second magnetic layer by a gap, and a portion of the coil is positioned between the first magnetic layer and the second magnetic layer.

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