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A system for measuring a biopotential signal produced by a body in free space at a location adjacent to the body, and if desired, through clothing, includes a probe that can be positioned adjacent to the body. The probe includes a conductive electrode to receive the biopotential signal and a conduct

A system for measuring a biopotential signal produced by a body in free space at a location adjacent to the body, and if desired, through clothing, includes a probe that can be positioned adjacent to the body. The probe includes a conductive electrode to receive the biopotential signal and a conductor that is maintained at a fixed distance from the electrode. The potential of the conductor can be maintained substantially equal to the potential of the electrode to shield the electrode from stray electrical noise. The system further includes a high impedance first stage amplifier that is incorporated into the probe and electrically connected to the electrode using a relatively short connector to minimize connector noise. Functionally, the first stage amplifier compares the electrical potential of the electrode to a second potential (e.g. a local ground) and generates a signal that is indicative of the biopotential.

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1. A system for measuring a biopotential signal produced by a body in free space, said system comprising:an electrode made of a conducting material, said electrode being positionable at a location adjacent the body to place said electrode at a first potential;a conductor located at a fixed distance

1. A system for measuring a biopotential signal produced by a body in free space, said system comprising:an electrode made of a conducting material, said electrode being positionable at a location adjacent the body to place said electrode at a first potential;a conductor located at a fixed distance from said electrode;a means for generating a reference potential; anda high impedance amplifier connected to said reference potential generating means, with said amplifier having an input port electrically connected to said electrode to compare said first electrical potential of said electrode with said reference potential to generate a signal indicative of the biopotential signal, and wherein said conductor is located to shield said electrode from electrical noise wherein said conductor is interposed between said electrode and said amplifier to shield said electrode from electric signals of said amplifier.2. A system as recited in claim 1 further comprising a means for mounting said electrode on the body.3. A system as recited in claim 1 wherein said electrode is a first electrode and said means for generating a reference potential comprises a second electrode and said system further comprises a means for coupling said first electrode with said second electrode for movement therewith.4. A system as recited in claim 1 wherein said electrode is a first electrode and said means for generating a reference potential comprises a second electrode that is placed in electrical contact with the body.5. A system as recited in claim 1 wherein said means for generating a reference potential comprises a wire that is electrically connected to a local ground.6. A system as recited in claim 1 further comprising a means for placing said conductor at a predetermined potential to shield said electrode from electrical signals of said amplifier.7. A system as recited in claim 6 wherein said predetermined potential is substantially equal to said first electrical potential.8. A system as recited in claim 1 wherein said high impedance amplifier comprises an instrumentation amplifier.9. A system as recited in claim 1 wherein said high impedance amplifier comprises an operational amplifier.10. A system as recited in claim 1 wherein said high impedance amplifier comprises at least one transistor.11. A system as recited in claim 1 wherein said electrode is formed with a surface and at least a portion of said surface is coated with a resistive coating to shield said electrode from stray electrical currents.12. A system as recited in claim 1 wherein said system further comprises a low-conductivity material interposed between said electrode and said conductor to minimize electrical coupling between said electrode and said conductor.13. A system as recited in claim 1 wherein said amplifier is positioned to interpose said electrode between said body and said amplifier.14. A system as recited in claim 1 wherein said electrode is attached to a material that can be worn against the skin.15. A system as recited in claim 14 wherein said biopotential signal has a frequency, f, said material has an electrical resistivity, ρ, and dielectric constant, ∈ and wherein ρ<5/(2πf∈).16. A system for measuring a biopotential signal produced by a body in free space, said system comprising:an electrode made of a conducting material, said electrode being positionable at a location adjacent the body to place said electrode at a first potential;a conductor located at a fixed distance from said electrode;a means for generating a reference potential; anda high impedance amplifier connected to said reference potential generating means, with said amplifier having an input port electrically connected to said electrode to compare said first electrical potential of said electrode with said reference potential to generate a signal indicative of the biopotential signal, and wherein said conductor is located to shield said electrode from electrical noise wherein said conductor is adapted to be interposed between said electrode and said body.17. A system for measuring a biopotential signal at a location adjacent to a patient, said system comprising:means for generating a reference electrical potential;a probe having an electrode positionable at said location to place said electrode at a first electrical potential, a conductor spaced from said electrode, and a highimpedance amplifier positioned to interpose said conductor between said amplifier and said electrode, said amplifier electrically connected to said generating means and said electrode to compare said first electrical potential to said reference electrical potential and generate a signal that is indicative of the biopotential signal in response thereto; andmeans for controlling the electrical potential of said conductor to shield said electrode from electrical noise.18. A system as recited in claim 17 wherein said electrode is a first electrode and said means for generating a reference electrical potential comprises a second electrode that is incorporated in said probe.19. A system as recited in claim 17 wherein said electrode is a first electrode and said means for generating a reference electrical potential comprises a second electrode that is placed in electrical contact with the patient.20. A method for measuring a biopotential signal at a location adjacent to a patient, said method comprising the steps of:providing an electrode made of a conductive material;maintaining a conductor spaced at a fixed distance from said electrode;controlling the electrical potential of said conductor to shield said electrode from electrical noise;coupling a high impedance amplifier to said electrode for movement therewith;positioning said electrode at said location to place said electrode at a first electrical potential;placing the conductor between the electrode and said high impedance amplifier;generating a reference electrical potential;inputting said first electrical potential and said reference electrical potential into said high impedance amplifier; andusing said high impedance amplifier to compare said first electrical potential to said reference electrical potential and generate an output signal that is indicative of the biopotential signal in response thereto.21. A method as recited in claim 20 wherein said electrode is positioned at said location to interpose at least one article of clothing between said electrode and said patient.22. A method as recited in claim 20 wherein said electrode is a first electrode and said step of generating a reference electrical potential comprises the step of coupling a second electrode to said first electrode for movement therewith, said second electrode being spaced from said first electrode to generate a second electrical potential.23. A method as recited in claim 20 wherein said electrode is a first electrode and said step of generating a reference electrical potential comprises the step of contacting the patient with a second electrode to generate a second electrical potential.24. A method as recited in claim 20 wherein said steps of generating a reference electrical potential and inputting said first electrical potential and said reference electrical potential into said high impedance amplifier comprises the step of connecting said high impedance amplifier to ground.25. A method as recited in claim 20 wherein said step of controlling the electrical potential of said conductor to shield said electrode from electrical noise is accomplished using feedback generated by said high impedance amplifier.26. A method as recited in claim 25 wherein said electrical potential of said conductor is held substantially equal to the electrical potential of said electrode.27. A method as recited in claim 20 wherein said electrode defines an electrode center and said positioning step places said electrode center between approximately 0.5 cm and approximately 10 m from said patient.28. A method as recited in claim 20 wherein said electrode defines an electrode center and is formed with a surface and said positioning step places said electrode center at said location and places said surface in contact with said patient.29. A probe for measuring a biopotential signal produced by a body in free space comprising:a first electrode made of a conducting material, the first electrode being adapted to be positioned adjacent the body to place the first electrode at a first potential;a first conductor spaced from the first electrode;system electronics for reviewing input from the first electrode located near the first electrode and separated from the first electrode by the first conductor; anda material having a relatively low electrical conductivity and dielectric constant interposed between the first conductor and the first electrode thus minimizing electrical coupling between the first conductor and the first electrode.30. The probe as recited in claim 29 further comprising, in combination, a second electrode made of a conducting material and a second conductor spaced from said second electrode, said second electrode being positionable, separate from said first electrode, at a location adjacent the body to place the second electrode at a second potential whereby the system electronics receive input from the second electrode.31. The probe as recited in claim 29 further comprising: a housing, wherein the first electrode is adapted to be located closer to the body than the first conductor and the system electronics are located outside the housing.32. The probe as recited in claim 29 further comprising: a second electrode made of a conducting material spaced from the first electrode, and a second conductor spaced from the first electrode, the second conductor being located between the second electrode and the first conductor whereby the system electronics receive input from the second electrode.33. The probe as recited in claim 29, further comprising: a conducting housing establishing an environmental noise shield, said conducting housing enclosing the first electrode, the first conductor and the system electronics, while maintaining exposure of a probe side portion for measuring the biopotential signal.34. The probe as recited in claim 32 wherein the first electrode, the first conductor, the second electrode and the second conductor are arranged in a stacked configuration.35. The probe as recited in claim 32 further comprising: a third conductor located at a fixed distance from the first electrode and being located between the system electronics and the second electrode.36. The probe as recited in claim 32 wherein said system electronics are located a fixed distance from the first electrode so as to be located farther away from the body than each of the first and second conductors and the first and second electrodes.37. The probe as recited in claim 32 wherein said system electronics are located between the first and second conductors.38. The probe as recited in claim 37 further comprising: a housing surrounding the first and second electrodes, first and second conductors and the electronics.39. The probe as recited in claim 32 further comprising: a housing, wherein the system electronics are located outside the housing, the second electrode is located between the first electrode and the housing, and the first and second conductors are located at fixed distances from the first electrode, between the first electrode and the second electrode and within the housing.40. The probe as recited in claim 32 wherein the system electronics are adapted to be located further away from the body than each of the first electrode and the first conductor, the second electrode is adapted to be located further away from the body than the system electronics, and the second conductor is located between the system electronics and the second electrode.