SPINTRONIC NANODEVICE FOR LOW-POWER, CELLULAR-LEVEL, MAGNETIC NEUROSTIMULATION

Abstract

A neuro-stimulation system includes a stimulator controller, a support surface, and a magneto-ionic stimulator positioned on the support surface and electrically connected to the stimulator controller. The stimulator controller can apply a voltage to the magneto-ionic stimulator, wherein a change in the voltage causes a change in a magnetic field produced by the magneto-ionic stimulator.

Claims

1. A neuro-stimulation system comprising: a stimulator controller, a support surface, and a magneto-ionic stimulator positioned on the support surface and electrically connected to the stimulator controller such that the stimulator controller can apply a voltage to the magneto-ionic stimulator, wherein a change in the voltage causes a change in a magnetic field produced by the magneto-ionic stimulator.

2. The neuro-stimulation system of claim 1 wherein the magneto-ionic stimulator comprises a layer of GdO.sub.x in contact with a layer of Co.

3. The neuro-stimulation system of claim 2 wherein the stimulator controller applies a positive voltage across the GdO.sub.x layer to cause hydrogen to appear at the boundary between the GdO.sub.x layer and the Co layer.

4. The neuro-stimulation system of claim 3 wherein the magneto-ionic stimulator produces a weaker out-of-plane magnetic field when the hydrogen appears at the boundary.

5. The neuro-stimulation system of claim 4 wherein the stimulator controller removes the positive voltage across the GdO.sub.x layer to cause the hydrogen to move away from the boundary between the GdO.sub.x layer and the Co layer.

6. The neuro-stimulation system of claim 5 wherein the magneto-ionic stimulator produces a stronger out-of-plane magnetic field when the hydrogen moves away from the boundary.

7. The neuro-stimulation system of claim 2 wherein the stimulator controller applies a negative voltage across the GdO.sub.x layer to drive oxygen into the Co layer.

8. The neuro-stimulation system of claim 7 wherein the magneto-ionic stimulator produces a weaker out-of-plane magnetic field when the oxygen is driven into the Co layer.

9. The neuro-stimulation system of claim 7 wherein the stimulator controller applies a positive voltage across the GdO.sub.x layer to drive oxygen out of the Co layer.

10. The neuro-stimulation system of claim 9 wherein the magneto-ionic stimulator produces a stronger out-of-plane magnetic field when the oxygen is driven out of the Co layer.

11. The neuro-stimulation system of claim 1 wherein the magneto-ionic stimulator comprises a layer of GdO.sub.x in contact with a layer of Pd, which is in contact with a layer of Co.

12. The neuro-stimulation system of claim 11 wherein the stimulator controller applies a positive voltage across the GdO.sub.x layer to drive hydrogen into the Pd layer.

13. The neuro-stimulation system of claim 12 wherein the magneto-ionic stimulator produces a weaker out-of-plane magnetic field when the hydrogen is driven into the Pd layer.

14. The neuro-stimulation system of claim 11 wherein the stimulator controller applies a negative voltage across the GdO.sub.x layer to cause the hydrogen to move out of the Pd layer thereby producing a stronger out-of-plane magnetic field.

15. (canceled)

16. A method of stimulating a neuron comprising: placing a magneto-ionic stimulator near the neuron; and changing a voltage applied to the magneto-ionic stimulator to change the strength of a magnetic field generated by the magneto-ionic stimulator such that an electric field is generated along the neuron.

17. The method of claim 16 wherein the magneto-ionic stimulator comprises a layer of oxide in contact with a layer of CoFe.sub.x alloy.

18. The method of claim 16 wherein the magneto-ionic stimulator comprises a layer of GdO.sub.x in contact with a layer of Pd, which is in contact with a layer of Co.

19. The method of claim 16 wherein the magneto-ionic stimulator comprises a layer of CoFeB that is in contact with a layer of MgO.

20. The method of claim 19 wherein the layer of MgO is further in contact with an oxide layer.

21. A neuro-stimulation system comprising: a stimulator controller, a support surface, and a magneto-ionic stimulator positioned on the support surface and electrically connected to the stimulator controller wherein the magneto-ionic stimulator produces a magnetic field that oscillates at a frequency less than 10 kHz.

22-29. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] FIG. 1 is a schematic diagram of a neuro-stimulation system.

[0023] FIG. 2 is a perspective view of a probe and magneto-ionic stimulator in accordance with one embodiment.

[0024] FIG. 3 is a side sectional view of the probe and magneto-ionic stimulator of FIG. 2 with the magneto-ionic stimulator in a first state.

[0025] FIG. 4 is a side sectional view of the probe and magneto-ionic stimulator of FIG. 2 with the magneto-ionic stimulator in a second state.

[0026] FIG. 5 is a perspective view of a probe and magneto-ionic stimulator in accordance with a second embodiment.

[0027] FIG. 6 is a side sectional view of the probe and magneto-ionic stimulator of FIG. 5 with the magneto-ionic stimulator in a first state.

[0028] FIG. 7 is a side sectional view of the probe and magneto-ionic stimulator of FIG. 5 with the magneto-ionic stimulator in a second state.

[0029] FIG. 8 is a perspective view of a probe and magneto-ionic stimulator in accordance with a third embodiment.

[0030] FIG. 9 is a side sectional view of the probe and magneto-ionic stimulator of FIG. 8 with the magneto-ionic stimulator in a first state.

[0031] FIG. 10 is a side sectional view of the probe and magneto-ionic stimulator of FIG. 8 with the magneto-ionic stimulator in a second state.

[0032] FIG. 11 is a perspective view of a probe and magneto-ionic stimulator in accordance with a fourth embodiment.

[0033] FIG. 12 is a side sectional view of the probe and magneto-ionic stimulator of FIG. 11 with the magneto-ionic stimulator in a first state.

[0034] FIG. 13 is a side sectional view of the probe and magneto-ionic stimulator of FIG. 12 with the magneto-ionic stimulator in a second state.

[0035] FIG. 14 provides a side sectional view of a neurostimulator at the end of a probe in accordance with a fifth embodiment.

[0036] FIG. 15 provides a side sectional view of a neurostimulator at the end of a probe in accordance with a sixth embodiment.

[0037] FIG. 16 provides schematic view of neurostimulator with an on-chip wireless power transfer system in accordance with a seventh embodiment.

DETAILED DESCRIPTION

[0038] Below, embodiments of a magnetic field tissue stimulator are described. Each of these embodiments relies on a change in the out-of-plane magnetization of a thin layer of material as ions move within the stimulator. By applying a voltage, the ions are moved causing a resulting change in the magnetic field. As a result, a voltage control signal can be used to modulate the magnetic flux density of the magnetic field above the tissue stimulator. This fluctuating magnetic field creates an electric field in the target tissue that can, for example, cause neurons to fire.

[0039] A significant advantage of the embodiments is the frequency at which the magnetic field oscillates. Many prior art spintronic nano-sized stimulators are limited to operating in the MHz to GHz range. However, neurons do not react to such high frequency oscillations. Instead, the optimum frequency for neurostimulation is on the order of 1 Hz. The embodiments described below modulate the magnetic field at between 0.5-7.0 Hz thereby making them more effective spintronic neurostimulators.

[0040] FIG. 1 provides a neurostimulation system 100 that includes a stimulator controller 102, a probe 104 having a support surface 106 and a magneto-ionic stimulator 108 located on support surface 106. Support surface 106 has a diameter on the order of 1 mm while magneto-ionic stimulator 108 has a width on the order of 10 micrometers. Conductors 110 and 112 provide an electrical connection between stimulator controller 102 and magneto-ionic stimulator 108 that allow stimulator controller 102 to apply different voltages to magneto-ionic stimulator so as to change the out-of-plane magnetic field produced by magneto-ionic stimulator 108.

[0041] FIG. 2 provides a perspective view of support surface 106 and stimulator 108. FIGS. 3 and 4 show side sectional views of support surface 106 and stimulator 108.

[0042] Stimulator 108 has a top surface pointing away from support surface 106 and a bottom surface facing support surface 106. The bottom surface of stimulator 108 is mounted on support surface 106 with an adhesive bead layer 114 between stimulator 108 and support surface 106. Adhesive bead layer 114 follows the perimeter of the bottom surface of stimulator 108 such that portions of the bottom surface remain exposed to support surface 106.

[0043] A layer 123 of Tantalum (Ta) is deposited on the top of a Si/SiO.sub.2 substrate 122. A layer 124 of platinum (Pt) is deposited on layer 123. In accordance with one embodiment, Pt layer 124 has a height of 3 nm. Pt layer 124 is connected to conductor 112. A layer 126 of cobalt (Co) is deposited on top of Pt layer 124. In accordance with one embodiment, Co layer 126 has a height of 0.9 nm. A layer 128 of gadolinium oxide (GdO.sub.x) is deposited on top of Co layer 126. In accordance with one embodiment, GdO.sub.x layer 128 has a height of 30 nm. A layer 130 of gold (Au) is deposited on top of GdO.sub.x layer 128. In accordance with one embodiment, Au layer 130 has a height of 3 nm. Au layer 130 is connected to conductor 110.

[0044] In FIG. 3, stimulator controller 102 has placed conductors 110 and 112 at the same voltage so that there is no voltage between Au layer 130 and Pt layer 124. In this state, Co layer 126 produces a magnetic field 300 (shown in dotted lines in FIG. 3) that extends perpendicularly out of the top surface of Co layer 126 and interacts with neurons, such as neuron 302 in tissue 304 that Au layer 130 is pressed against.

[0045] In FIG. 4, stimulator controller 102 has applied a positive voltage between conductors 110 and 112 creating a corresponding positive voltage between Au layer 130 and Pt layer 124. This positive voltage causes a layer of hydrogen to form at the interface between GdO.sub.x layer 128 and Co layer 126. This layer of hydrogen causes the magnetic field produced by Co layer 126 to rotate in plane thereby causing the magnetic field perpendicular to the top surface of Co layer 126 to disappear. As a result, there is no magnetic field passing through neuron 302.

[0046] In order to stimulate neuron 302, stimulator controller 102 applies positive voltage pulses on conductor 110 and connects conductor 112 to ground. Each voltage pulse creates a changing magnetic field that produces a corresponding electric field in neuron 302. A rising edge in the voltage creates a corresponding falling edge in the magnetic field. In accordance with one embodiment, the switching time between the rising edge in voltage and the falling edge in the magnetic field is 100 ms. Similarly, a falling edge in the voltage creates a corresponding rising edge in the magnetic field. In accordance with one embodiment, the switching time between falling edge in the voltage and the rising edge in the magnetic field is 400 ms. The difference between the switching times is due to the fact that when a positive voltage is applied to conductor 110, the voltage drives electrons into Pt layer 124 to facilitate the formation of the hydrogen layer. However, when conductor 110 is returned to ground, there is only a small electromotive force to draw electrons away from Pt layer 124 that will allow the hydrogen to move away from the interface.

[0047] In order to reduce the switching time for increasing the magnetic field, a negative voltage can be applied to conductor 110. However, applying a negative voltage on conductor 110 will cause oxygen to move into Co layer 126, which reduces the magnetic field instead of increasing the magnetic field. To avoid such oxidation of Co layer 126, a second embodiment of the stimulator, magneto-ionic stimulator 508, is provided as shown in FIGS. 5-7.

[0048] FIG. 5 provides a perspective view of stimulator 508 mounted on support surface 106. FIGS. 6 and 7 show side sectional views of support surface 106 and stimulator 508.

[0049] Stimulator 508 has a top surface pointing away from support surface 106 and a bottom surface facing support surface 106. The bottom surface of stimulator 508 is mounted on support surface 106 with an adhesive bead layer 514 between stimulator 508 and support surface 106. Adhesive bead layer 514 follows the perimeter of the bottom surface of stimulator 508 such that portions of the bottom surface remain exposed to support surface 106.

[0050] A layer 523 of Tantalum (Ta) is deposited on the top of a Si/SiO.sub.2 substrate 522. A layer 524 of platinum (Pt) is deposited on layer 523. In accordance with one embodiment, Pt layer 524 has a height of 3 nm. Pt layer 524 is connected to conductor 112. A layer 526 of cobalt (Co) is deposited on top of Pt layer 524. In accordance with one embodiment, Co layer 526 has a height of 0.9 nm. A layer 527 of palladium (Pd) is deposited on top of Co layer 526. In accordance with one embodiment, Pd layer 527 has a height of 4.5 nm. A layer 528 of gadolinium oxide (GdO.sub.x) is deposited on top of Pd layer 527. In accordance with one embodiment, GdO.sub.x layer 528 has a height of 30 nm. A layer 530 of gold (Au) is deposited on top of GdO.sub.x layer 528. In accordance with one embodiment, Au layer 530 has a height of 3 nm. Au layer 530 is connected to conductor 110.

[0051] In FIG. 6, stimulator controller 102 has placed a negative voltage on conductor 110 while keeping conductor 112 at ground so that there is negative voltage between Au layer 530 and Pt layer 524. In this state, Co layer 526 produces a magnetic field 600 (shown in dotted lines in FIG. 6) that extends perpendicularly out of the top surface of Co layer 526 and interacts with neurons, such as neuron 602 in tissue 604 that Au layer 530 is pressed against.

[0052] In FIG. 7, stimulator controller 102 has applied a positive voltage on conductor 110 creating a corresponding positive voltage between Au layer 530 and Pt layer 524. This positive voltage causes a layer of hydrogen to form at the interface between GdO.sub.x layer 528 and Co layer 526. This layer of hydrogen causes the magnetic field produced by Co layer 526 to rotate in plane thereby causing the magnetic field perpendicular to the top surface of Co layer 526 to disappear. As a result, there is no magnetic field passing through neuron 602.

[0053] In order to stimulate neuron 602, stimulator controller 102 alternates between providing positive and negative voltage pulses on conductor 110 and connects conductor 112 to ground. The alternating voltage pulses create a changing magnetic field that produces a corresponding electric field in neuron 602.

[0054] The addition of Pd layer 527 in the embodiment of FIGS. 5-7, protects Co layer 526 from oxidizing when a negative voltage is applied. During a positive voltage, hydrogen moves into Pd Layer 527 so that it still accumulates at the surface of Co layer 526. During a negative voltage pulse, electrons are pulled away from Pt layer 524 causing the hydrogen atoms to become H.sup.+ protons that are then transported through GdO.sub.x layer 528 while Pd layer 527 prevents oxygen from reaching Co layer 526.

[0055] FIG. 8 provides a perspective view of support surface 106 and a magneto-ionic stimulator 808 of a third embodiment. FIGS. 9 and 10 show side sectional views of support surface 106 and stimulator 808.

[0056] Stimulator 808 has a top surface pointing away from support surface 106 and a bottom surface facing support surface 106. The bottom surface of stimulator 808 is mounted on support surface 106 with an adhesive bead layer 814 between stimulator 808 and support surface 106. Adhesive bead layer 814 follows the perimeter of the bottom surface of stimulator 808 such that portions of the bottom surface remain exposed to support surface 106.

[0057] A layer 823 of Tantalum (Ta) is deposited on the top of a Si/SiO.sub.2 substrate 822. A layer 824 of platinum (Pt) is deposited on layer 823. In accordance with one embodiment, Pt layer 824 has a height of 3 nm. Pt layer 824 is connected to conductor 112. A layer of cobalt (Co) is deposited on top of Pt layer 824. In accordance with one embodiment, the Co layer has a height of 0.9 nm. A layer 828 of Gadolinium oxide (GdO.sub.x) is deposited on top of the Co layer. In accordance with one embodiment, GdO.sub.x layer 828 has a height of 30 nm. A layer 830 of gold (Au) is deposited on top of GdO.sub.x layer 828. In accordance with one embodiment, Au layer 830 has a height of 3 nm. Au layer 830 is connected to conductor 110.

[0058] Once constructed, a negative voltage is applied to conductor 110 to create a negative voltage between Au layer 830 and Pt layer 824. This negative voltage causes oxygen to be forced into the surface of the Co layer thereby forming a CoO layer 826. The negative voltage is then removed, leaving the oxygen in CoO layer 826.

[0059] In FIG. 9, stimulator controller 102 has applied a positive voltage to conductor 110 to create a positive voltage between Au layer 830 and Pt layer 824. In this state, the oxygen in CoO layer 826 is driven out of the layer producing a Co layer that generates a magnetic field 900 (shown in dotted lines in FIG. 9) that extends perpendicularly out of the top surface of the Co layer and interacts with neurons, such as neuron 902 in tissue 904 that Au layer 830 is pressed against.

[0060] In FIG. 10, stimulator controller 102 has applied a negative voltage between conductors 110 and 112 creating a corresponding negative voltage between Au layer 830 and Pt layer 824. This negative voltage drives oxygen back into the Co layer to reform CoO layer 826. The oxygen causes the magnetic field to rotate into the plane of the CoO layer 826 so that the magnetic field perpendicular to the top surface of CoO layer 826 disappears. As a result, there is no magnetic field passing through neuron 902.

[0061] In order to stimulate neuron 902, stimulator controller 102 alternates between applying a positive voltage and a negative voltage on conductor 110 and connects conductor 112 to ground. Each voltage pulse creates a changing magnetic field that produces a corresponding electric field in neuron 902.

[0062] FIG. 11 provides a perspective view of support surface 106 and a magneto-ionic stimulator 1108 of a fourth embodiment. FIGS. 12 and 13 show side sectional views of support surface 106 and stimulator 1108.

[0063] Stimulator 1108 has a top surface pointing away from support surface 106 and a bottom surface facing support surface 106. The bottom surface of stimulator 1108 is mounted on support surface 106 with an adhesive bead layer 1114 between stimulator 1108 and support surface 106. Adhesive bead layer 1114 follows the perimeter of the bottom surface of stimulator 1108 such that portions of the bottom surface remain exposed to support surface 106.

[0064] A layer 1123 of tantalum (Ta) is deposited on the top of a Si/SiO.sub.2 substrate 1122. A layer 1124 of palladium (Pd) is deposited on layer 1123. In accordance with one embodiment, Pd layer 1124 has a height of 10 nm. Pd layer 1124 is connected to conductor 112. A layer 1126 consisting of multiple alternating layers of cobalt (Co) and palladium (Pd) is deposited on top of Pd layer 1124. In accordance with one embodiment, Co/Pd multilayer 1126 has a height of 3 nm. A layer 1128 of tantalum is deposited on top of Co/Pd multilayer 1126. In accordance with one embodiment, Ta layer 1128 has a height of 1 nm. A layer 1130 of CoFeB is deposited on top of tantalum layer 1128. In accordance with one embodiment, CoFeB layer 1130 has a height of 1.3 nm. A layer 1132 of MgO is deposited on CoFeB layer 1130. In accordance with one embodiment, MgO layer 1132 has a height of 2 nm. A layer 1134 of SiO.sub.x is deposited on MgO layer 1132. A layer 1136 of gold (Au) is deposited on top of SiO.sub.x layer 1134. In accordance with one embodiment, Au layer 1136 has a height of 3 nm. Au layer 1130 is connected to conductor 110.

[0065] In FIG. 12, stimulator controller 102 has applied a positive voltage to conductor 110 to create a positive voltage between Au layer 1136 and Pd layer 1124. In this state, ionic oxygen in SiO.sub.x layer 1134 is driven away from MgO layer 1132 thereby allowing CoFeB layer 1130 to generate a magnetic field 1200 (shown in dotted lines in FIG. 12) that extends perpendicularly out of the top surface of CoFeB layer 1130 and interacts with neurons, such as neuron 1202 in tissue 1204 that Au layer 1136 is pressed against.

[0066] In FIG. 13, stimulator controller 102 has applied a negative voltage between conductors 110 and 112 creating a corresponding negative voltage between Au layer 1136 and Pd layer 1124. This negative voltage drives ionic oxygen toward MgO layer 1132 thereby causing the magnetic field to rotate into the plane of the CoFeB layer 1130 so that the magnetic field perpendicular to the top surface of CoFeB layer 1130 disappears. As a result, there is no magnetic field passing through neuron 1202.

[0067] In order to stimulate neuron 1202, stimulator controller 102 alternates between applying a positive voltage and a negative voltage on conductor 110 and connects conductor 112 to ground. Each voltage pulse creates a changing magnetic field that produces a corresponding electric field in neuron 1102.

[0068] Each of the embodiments described above create a time-varying magnetic field has a frequency of oscillation that is limited by ionic transport speed. As a result, the switching provided by the embodiments is in the range of 0.5 Hz-100 kHz. This aligns well with the optimum frequency for stimulating neurons of ˜100 Hz. As a result, the embodiments are well-suited for neuron stimulation.

[0069] FIG. 14 provides a side sectional view of a neurostimulator 1408 at the end of probe 106. Neurostimulator 1408 is a spin orbit torque vortex device, A bottom contact layer 1420 of neurostimulator 1408 is made of PtMn and has a height of 15 nm. A layer 1422 of CoFe is deposited on top of layer 1420 and has a height of 2.5 nm. A layer 1424 of Ru is deposited on layer 1422 and has a height of 0.85 nm. A layer 1426 of CoFeB is deposited on top of layer 1424 and has a height of 3 nm. Layer 1426 provides a fixed magnetic layer. A layer 1428 of MgO is deposited on top of layer 1426 and has a height of 1.075 nm. Layer 1428 acts as a barrier layer. A layer 1430 of NiFe is deposited on top of layer 1428 and has a height of 15 nm. Layer 1430 acts as a free layer. A cap layer 1432 of Ru is deposited on layer 1430 and has a height of 10 nm.

[0070] Neurostimulator 1408 uses a current I.sub.dc in the plane of layer 1426 and a magnetic field H.sub.dc that is perpendicular to the plane of layer 1426 to cause the core 1434 of a magnetic vortex within neurostimulator 1408 to precess 1436. This results in an oscillating magnetic field external to neurostimulator 1408 that induces an oscillating electric field that can cause neuron 1402 to fire. The oscillations have a frequency on the order of GHz with the actual frequency being set by the size of the current in layer 1426. This is a significant improvement over nanowire stimulation, which has a frequency between MHz and GHz. Neurostimulator 1408 also only requires 5 nW of power, which implies low thermal effects on tissue.

[0071] FIG. 15 provides a side sectional view of a neurostimulator 1508 at the end of probe 106. Neurostimulator 1508 is a spin orbit torque vortex device. A bottom conductor layer 1520 of Cu has a layer 1522 of NiFe deposited on it. Layer 1522 provides a fixed magnetic layer. A thin layer 1524 of Cu is deposited on top of layer 1522 and acts as a barrier layer. A layer 1526 of NiFe is deposited on top of layer 1524 and acts as a free layer. A top conductor layer 1528 of Cu is deposited on layer 1526.

[0072] Neurostimulator 1508 uses a current I.sub.dc between top conductor layer 1528 and bottom conductor layer 1520 and a magnetic field H.sub.dc that is perpendicular to the plane of layer 1522 to cause the core 1534 of a magnetic vortex within neurostimulator 1508 to precess 1536. This results in an oscillating magnetic field external to neurostimulator 1508 that induces an oscillating electric field that can cause neuron 1502 to fire. The frequency of oscillation is on the order of 1.0 GHz.

[0073] FIG. 16 provides a schematic diagram of an alternative neurostimulation system 1600 that includes an implantable structure 1602 that can be surgically implanted within a living body 1604. Implantable structure 1602 includes an array 1606 of neurostimulators that are mounted on a support surface 1605 of structure 1602 and that are in contact with tissue in living body 1604 after implantation. The neurostimulators can be any of the magneto-ionic neurostimulators discussed above. Implantable structure 1602 also supports a controller 1608 and a wireless receiver 1610. Controller 1608 controls the application of voltage and/or current to the neurostimulators in array 1606 to thereby control the magnetic fields generated by the neurostimulators in array 1606. Wireless receiver 1610 receives a wireless signal 1612 generated by a wireless transmitter 1614 outside of living body 1604. Wireless signal 1612 generates a voltage in receiver 1610 that is then used to provide power to controller 1608. Controller 1608 uses this power to apply the voltage and/or current to the neurostimulators in array 1606. In accordance with one embodiment, wireless transmitter 1614 is contained within a mobile container 1616 that can be carried by the person implanted with structure 1602. Mobile container 1616 also includes a battery 1618, which provides power to wireless transmitter 1614.

[0074] Although the neurostimulators have been discussed above in connection with neurons in the brain, the neurostimulators may be used in other parts of the neurologic system, such as neurologic tissue in the spine. In accordance with some embodiments, the neurostimulators are used on tissue of the interoception system of the body.

[0075] 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.

[0076] 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.