SYSTEMS AND METHODS FOR SWITCHED ELECTRODE STIMULATION FOR LOW POWER BIOELECTRONICS

Abstract

Systems and methods for stimulating tissue. Exemplary embodiments include systems and methods configured to maintain one electrode at a fixed voltage potential and switching a second electrode between different fixed voltage potentials.

Claims

1. A system for stimulating tissue, the system comprising: a fixed voltage source; a first electrode; a second electrode; and a switch coupled to the first electrode, wherein: the first electrode and the second electrode are initially at a first voltage potential; the fixed voltage source is at a second voltage potential; and the switch is configured to alternately couple and de-couple the first electrode to the fixed voltage source, wherein: an electrical double layer between the tissue and the first and second electrodes is electrically charged when the first electrode is coupled to the fixed voltage source; and current is discharged from the electrical double layer when the first electrode is de-coupled from the fixed voltage source.

2. The system of claim 1 wherein the fixed voltage source, the first and second electrodes, and the switch are contained in an implantable device.

3. The system of claim 1 wherein the current discharged from the electrical double layer when the first electrode is de-coupled from the fixed voltage source stimulates the tissue.

4. The system of claim 1 wherein the fixed voltage source has a potential of less than 3.0 volts.

5. The system of claim 1 wherein the first voltage potential is approximately 0 volts.

6. The system of claim 1 wherein the switch is configured to alternately couple the first electrode to the fixed voltage source for approximately 50 μs and to de-couple the first electrode from the fixed voltage source for approximately 50 μs.

7. The system of claim 1 further comprising a direct current (DC) blocking capacitor in series with the first electrode and the second electrode.

8. The system of claim 1 further comprising a current sense resistor in series with the first electrode and the second electrode.

9. The system of claim 1 wherein the switch is controlled via a microcontroller.

10. The system of claim 1 wherein the switch is controlled by a resistor capacitor (RC) timer.

11. The system of claim 10 wherein the resistor capacitor (RC) timer comprises a first resistor, a second resistor, a capacitor and a Schmitt trigger.

12. The system of claim 1 wherein: the switch is coupled to the second electrode; and the switch is configured to alternately couple and de-couple the second electrode to the fixed voltage source.

13. A method of stimulating tissue, the method comprising: applying a first voltage potential to a first electrode and a second electrode, wherein the first electrode and the second electrode are proximal to the tissue; coupling the first electrode to a fixed voltage source to apply a second voltage potential to the first electrode; and de-coupling the first electrode from the fixed voltage source to apply the first voltage potential to the first electrode, wherein: an electrical double layer between the tissue and the first and second electrodes is charged with an electrical current when the first electrode is coupled to the fixed voltage source; the electrical current is discharged from the electrical double layer when the first electrode is de-coupled from the fixed voltage source; and the tissue is stimulated via the electrical current.

14. The method of claim 13 further comprising implanting the fixed voltage source and the first and second electrodes in the tissue in an implantable device.

15. The method of claim 13 wherein the electrical current passes through a direct current (DC) blocking capacitor in series with the first electrode and the second electrode.

16. The method of claim 13 further comprising monitoring the electrical current with a current sense resistor in series with the first electrode and the second electrode.

17. The method of claim 13 further comprising: coupling the second electrode to the fixed voltage source to apply the second voltage potential to the second electrode; and de-coupling the second electrode from the fixed voltage source to apply the first voltage potential to the second electrode.

18. A system for nerve stimulation, the system comprising: a transceiver comprising: an electrical signal generator; and a transmission coil coupled to the electrical signal generator, wherein the transceiver is configured to transmit an alternating magnetic field from the transmission coil; and an implantable device comprising: a receiving coil configured to receive the alternating magnetic field transmitted from the transmission coil and to induce an alternating current voltage; a rectifier coupled to the receiving coil and configured to rectify the alternating current voltage to direct current voltage; and a resistor capacitor (RC) timer coupled to the rectifier and configured to control a pulse duration and frequency applied to a plurality of stimulating electrodes.

19. The system of claim 18 wherein the RC timer comprises a first resistor, a second resistor, and a capacitor and a Schmitt trigger.

20. The system of claim 18 further comprising a linear regulator coupled to the rectifier and configured to regulate the amplitude of the direct current voltage.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0031] FIG. 1 illustrates a schematic of a tissue stimulation system according to exemplary embodiments of the present disclosure.

[0032] FIG. 2 illustrates a graph of voltage produced by the embodiment of FIG. 1 during operation.

[0033] FIG. 3 illustrates a graph of voltage produced by the embodiment of FIG. 1 during operation.

[0034] FIG. 4 illustrates a schematic of a tissue stimulation system comprising a transceiver and a passive implant.

[0035] FIG. 5 illustrates a graph of nerve voltage and stimulus current versus time is shown for the system of FIG. 4.

[0036] FIG. 6 illustrates a functional block diagram of a passive implant with specific electronic components.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0037] Referring now to FIG. 1, a nerve stimulation system 100 comprises first electrode 110 and second electrode 120. During operation, electrodes 110 and 120 begin at the same potential (zero volts in the embodiment shown), and one electrode is then switched via a switch 130 to a different potential (e.g., 1V) from a fixed voltage source 150. As used herein, the term “fixed voltage source” includes a voltage source that provides a relatively constant voltage level.

[0038] After the voltage switch is made to one electrode, current begins to flow from the electrode through tissue 140 proximal to electrodes 110 and 120. The current decreases exponentially with time due to the charging of the electrode double layer capacitance between the charged electrode and tissue 140. Once the electrode double layer capacitance has been charged, electrodes 110 and 120 are switched back to the same potential. Current is then discharged out of electrodes 110 and 120, decreasing exponentially over time.

[0039] Accordingly, exemplary embodiments utilize voltage controlled stimulation that operates by varying the voltage applied to electrodes 110 and 120. Unlike typical voltage controlled stimulation systems and methods, however, exemplary embodiments switch electrode 110 to fixed voltage source 150, rather than utilizing an electrode that is continuously connected to a variable voltage source.

[0040] In particular embodiments, switch 130 is configured to alternately couple first electrode 110 to fixed voltage source 150 for less than 100 μs (e.g. approximately 50 μs) and then to de-couple first electrode 110 from fixed voltage source 150 for less than 100 μs (e.g. approximately 50 μs). This process can be repeated so that tissue 140 is stimulated via the electrical current that is charged and discharged to and from the electrical double layer between tissue 140 and first and second electrodes 110 and 120.

[0041] Certain embodiments may also comprises a direct current (DC) blocking capacitor (not shown in FIG. 1) in series with first electrode 110 and second electrode 120. The inclusion of a DC blocking capacitor can restrict potentially harmful direct current from flowing through tissue 140. Particular embodiments may also include a sense resistor (not shown in FIG. 1) in series with first electrode 110 and second electrode 120. The sense resistor can be used to monitor the electrical current that stimulates tissue 140.

[0042] In certain embodiments, both electrodes 110 and 120 can be alternately coupled to fixed voltage source 150. This can provide for symmetrical charging and discharging of electrodes 110 and 120 so that the net charge on the electrodes is minimized over time.

[0043] In exemplary embodiments, switch 130 can be controlled via a number of different components. For example, switch 130 can be controlled via a microcontroller to alternately couple first electrode 110 (and in some embodiments, second electrode 120) to fixed voltage source 150. In other embodiments, switch 130 can be controlled by a resistor capacitor (RC) timer (not shown in FIG. 1). In specific embodiments, an RC timer can comprise a pair of resistors, a capacitor and a Schmitt trigger.

[0044] Examples of voltage over time for C.sub.e1, C.sub.e2 and R.sub.ionic produced by system 100 are shown in FIGS. 2 and 3. It is understood that the elements labeled C.sub.e1 and C.sub.e2 and are not separate electronic components (e.g. capacitors), but instead represent the capacitance formed between tissue 140 and the conductive surface of electrodes 110 and 120. Similarly, the element R.sub.ionic is not a separate resistor, but instead represents the resistance of the fluid in tissue 140.

[0045] FIG. 2 illustrates the voltage between each of electrodes 110 and 120 and tissue 140 (e.g. from the capacitance between the surface of the electrodes 110 and 120 and fluid in tissue 140). In FIG. 2, first electrode 110 is coupled to fixed voltage source 150 via switch 130 at time 0. First electrode 110 remains coupled to fixed voltage source for 50 μs in this embodiment, but it is understood that in other embodiments, first electrode 110 may remain coupled to fixed voltage source for different lengths of time. FIG. 3 illustrates an example of the voltage over time tissue 140 based on the ionic resistance of fluid in tissue 140.

[0046] Referring now to FIGS. 4-6 exemplary embodiments are directed to a low-power, low cost approach to an implanted device/system for wireless stimulation and recording using passive components (as opposed to wireless systems that employ complex circuitry for power generation, transmission, rectification, and modulation found in typical systems). In exemplary embodiments, the electrodes and associated components are configured as an implantable device with a stimulation circuit comprising a voltage source and a signal that controls the switch. In specific embodiments, additional components can be added to improve device robustness or to gain finer control over stimulation parameters.

[0047] Referring specifically now to FIG. 4, an overview schematic of a tissue stimulation system 200 comprises a transceiver 210 and a passive implant 220. Implant 220 is powered on by an external receiver (containing coils generating magnetic field) and starts stimulating the tissue through the implanted electrodes. Referring now to FIG. 5, a graph of nerve voltage and stimulus current versus time is shown for the device according to FIG. 4.

[0048] Referring now to FIG. 6, a functional block diagram of a passive implant 320 is shown with specific electronic components. In particular embodiments, a voltage source can be obtained by rectifying secondary (e.g. receiving) coil voltage with a diode. In some embodiments, a regulator can be used to limit this voltage to a specified value, and in specific embodiments, the regulators can be Zener diodes or low dropout (LDO) style linear regulators. In certain embodiments, a resistor capacitor (RC) timer can be used to control the switched electrode stimulator circuit, and in particular embodiments, the RC timer can be constructed using two resistors, a capacitor, and a Schmitt trigger. The RC timer can generate regular digital pulses that control the switches, with the pulse duration and frequency set by the values of resistors.

[0049] In order to switch both electrodes alternatingly, an additional switch and data (D) flip-flop can be used to allow for symmetric charging/discharging of electrodes and prevent net charge from accumulating over time. To control stimulation amplitude, a frequency controlled voltage (FCV) circuit can be used in certain embodiments. This circuit creates a voltage divider using a resistor and an inductor and capacitor (LC) tank. Small adjustments to the frequency of the incoming RF field cause the impedance of the LC tank to change, thereby changing the voltage divider ratio. Since the quality factor of the LC tank is higher than the quality factor of the secondary coil, small adjustments to the frequency have minimal effect on incoming power.

[0050] During operation, signals of interest can be communicated out of the body by modulating the secondary coil. Nerve voltage can be amplified and used to directly control a metal-oxide-semiconductor field-effect transistor (MOSFET), which modulates the secondary coil. The stimulation current can be sensed and communicated out using the same method.

[0051] All of the devices, systems and/or methods disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure. While the devices, systems and methods of this invention have been described in terms of particular embodiments, it will be apparent to those of skill in the art that variations may be applied to the devices, systems and/or methods in the steps or in the sequence of steps of the method described herein without departing from the concept, spirit and scope of the invention. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope and concept of the invention as defined by the appended claims.

REFERENCES

[0052] The contents of the following references are incorporated by reference herein:

References

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