Dry electrode system for detection of biopotentials

• US 4,763,659 A
• Filed: 08/20/1986
• Issued: 08/16/1988
• Est. Priority Date: 08/21/1985
• Status: Expired due to Fees

• Current Assignee: Technology 21 Incorporated
• Original Assignee: Spring Creek Institute
• Inventors: Dunseath, W. J. Ross Jr.
• Primary Examiner(s): Cohen, Lee S.
• Application Number:
  US06/898,235
• Time in Patent Office: 727 Days
• Field of Search: 128/639-641, 128/643, 128/644, 128/696, 128/902, 128/798, 128/802, 128/803
• US Class Current: 600/391
• CPC Class Codes: A61B 2562/182 Electrical shielding, e.g. using a Faraday cage
• CPC Class Codes: A61B 5/25 Bioelectric electrodes therefor
• CPC Class Codes: A61B 5/30 Input circuits therefor
• CPC Class Codes: Y10S 128/902 Biological signal amplifier

Abstract

A dry electrode system for the detection of biopotentials existing on the surface of the skin of a living body, including a dry electrode pad with a resilient conductive pad adhering to at least one adhesive pad or otherwise opposed adhesive surfaces, one of which is adapted to engage the skin of the living body. The dry electrode pad makes electrical connection to an amplifying circuit which transmits a biopotential derived from the conductive pad to a monitor. The amplifying circuit includes a conductive input contact for making electrical contact to the conductive pad, a lead amplifier having an input coupled to the input contact, and a voltage driven shield coupled to the output of the lead amplifier and surrounding portions of the input contact not in engagement with the dry electrode pad. In a preferred embodiment, conductive adhesive layers are applied to opposed sides of a conductive foam pad to construct the dry electrode pad.

Claims

1. A dry electrode system for the detection of biopotentials existing on the surface of the skin of a living body, comprising:

a conductive dry electrode pad having opposed sides, one of which is adapted to contact said skin, comprising a resilient conductive pad having opposed sides, and adhesive means comprising first and second conductive adhesive layers applied to opposed sides of said conductive pad said first adhesive layer adapted to adhere said conductive pad to said skin; and

an amplifying circuit connected to the other side of said dry electrode pad by means of said second adhesive layer for amplifying a biopotential transmitted via said dry electrode pad to said amplifying circuit.

2. A dry electrode system according to claim 1, wherein said conductive pad comprises a resilient material having not less than 5% rebound value, and wherein said dry electrode pad has an electrical impedance to dry skin of not greater than 1.5 million ohms at 10 Hz and an AC noise base line not greater than 150 μ

V peak (0.15 to 100 Hz) under conditions of dry to saturation within a 0.9% saline solution.

3. A dry electrode system according to claim 2, wherein said conductive pad comprises:

an open-cell foam.

4. The dry electrode system as defined in claim 3, wherein said conductive foam pad comprises:

carbon loaded polyurethane foam.

5. A dry electrode system according to claim 2, wherein said conductive pad comprises:

a closed-cell foam.

6. A dry electrode system according to claim 5, wherein said conductive foam pad comprises:

a cross-linked vinyl-nitrite polymer.

7. A dry electrode system according to claims 1, 2, 3 or 5 wherein said amplifying circuit comprises:

an insulating housing having a conductive input contact mounted thereon and engaging the dry electrode pad,

a lead amplifier having an input coupled to said input contact and an output, and

a voltage driven first shield connected to said output of said lead amplifier and surrounding portions of said input contact not in engagement with said dry electrode pad.

8. The dry electrode system as defined in claim 7, wherein said conductive input contact comprises a material that maintains an AC noise voltage baseline of not more than 150 μ

V peak (0.15 to 100 Hz) under conditions ranging from dry to saturation with a 0.9% saline solution.

9. A dry electrode system according to claim 8, wherein said conductive input contact comprises:

titanium hydride.

10. A dry electrode system according to claim 7, wherein said conductive input contact comprises:

conductive silicone rubber.

11. A dry electrode system according to claim 7, wherein said amplifying circuit comprises:

said lead amplifier comprising an operational amplifier having inverting and non-inverting inputs,

first and second diodes connected in parallel inverse polarity across the inputs of said operational amplifier,

third and fourth diodes connected in parallel inverse polarity from the inverting input of said operational amplifier to a circuit common potential,

an output resistor connected from the inverting input to the output of said operational amplifier,

an input resistor connected between the non-inverting input of said operational amplifier and said conductive input contact, said input resistor at least partially contained within said voltage-driven first shield,

a lead wire cable having plural conductors connected to said lead amplifier and supplying power and common potential to said lead amplifier and taking out an output from said lead amplifier, and

a decoupling resistor connected from the output of said operational amplifier to an output conductor of the lead wire cable.

12. A dry electrode system according to claim 11, further comprising:

a circuit board having opposed sides, wherein on one of said sides of said circuit board said operational amplifier, said first through fourth diodes, and said output and decoupling resistors are mounted, said circuit board having an aperture through which said input resistor extends from the one side to the other side on which said conductive input contact is mounted.

13. A dry electrode system according to claim 12, wherein said lead wire cable comprises:

a flexible insulated multi-conductor cable including a pair of insulated conductors to carry bipolar supply currents to said lead amplifier, an insulated conductor to carry said circuit potential common current to and from said lead amplifier, said output conductor comprising an insulated conductor to carry an output signal from said lead amplifier, and a second shield shielding said insulated conductors.

14. A dry electrode system according to claim 13, wherein said amplifying circuit further comprises:

a voltage follower operational amplifier having a non-inverting input connected to the first shield, an inverting input connected to an output of said voltage follower operational amplifier and to said second shield.

15. A dry electrode system according to claim 13, wherein said second shield is connected to said insulated conductor carrying said circuit common potential.

16. A dry electrode system according to claim 13, comprising:

means for providing said circuit common potential, including,

an elastic ground strap having conductive portions and adapted to be mounted on a portion of the body,

a second resilient conductive pad contacting said conductive portions of said strap, and

a ground lead wire electrically conductively coupled between said second conductive pad and said insulated conductor carrying said circuit common potential.

17. A dry electrode system according to claim 13, comprising:

means for providing said circuit common potential, including,

a second dry electrode pad also comprising a resilient conductive pad having opposed sides one of which is adapted to engage the skin of the living body, and adhesive means having first and second adhesive surfaces, said first adhesive surface adapted to adhere said second conductive pad to the skin of said living body,

a second electrical contact mounted on a second housing and adhering to said second surface of said adhesive means, said second contact electrically contacting said second conductive pad, and

passive lead wire means for electrically conductively coupling said second electrical contact to said conductor carrying said circuit common potential.

18. A dry electrode system according to claim 17, comprising:

a conductive shield at least partially surrounding said second electrical contact.

19. A dry electrode system according to claims 1, 2, 3, or 5, wherein said amplifying circuit comprises:

an insulating housing having a conductive input contact mounted on said housing and engaging the dry electrode pad;

a lead amplifier having inverting and non-inverting inputs, one of which is coupled to said input contact, and an output;

first and second diodes connected in parallel inverse polarity across the inputs of said lead amplifier; and

third and fourth diodes connected in parallel inverse polarity from the inverting input of said lead amplifier to a circuit common potential.

20. A dry electrode system according to claim 19, comprising:

a voltage driven first shield connected to said output of said lead amplifier and surrounding portions of said input contact not in engagement with said pad.

21. The dry electrode system as defined in claim 19, wherein said conductive input contact comprises a material that maintains an AC noise voltage baseline of not more than 150 μ

V peak (0.15 to 100 Hz) under conditions ranging from dry to saturation with 0.9% saline solution.

22. A dry electrode system according to claim 21, wherein said conductive input contact comprises titanium hydride.

23. A dry electrode system according to claim 19, wherein said conductive input contact comprises:

conductive silicone rubber.

24. A dry electrode system according to claim 1, 2, 3 or 5, wherein said adhesive means comprises:

a pair of tissue substrates each having opposed sides covered with a conductive adhesive layer, said pair of substrates sandwiching said resilient conductive pad therebetween.

25. A dry electrode system according to claim 7, wherein said adhesive means comprises:

a pair of tissue substrates each having opposed sides covered with a conductive adhesive layer, said pair of substrates sandwiching said resilient conductive pad therebetween.

26. A dry electrode system according to claim 19, wherein said adhesive means comprises:

a pair of tissue substrates each having opposed sides covered with a conductive adhesive layer, said pair of substrates sandwiching said resilient conductive pad therebetween.

27. A dry electrode system according to claim 20, wherein said adhesive means comprises:

a pair of tissue substrates each having opposed sides covered with a conductive adhesive layer, said pair of substrates sandwiching said resilient conductive pad therebetween.

28. A dry electrode system according to claims 1, 2, 3 or 5 wherein:

said first adhesive layer comprises a hypoallergenic adhesive material, and

said second adhesive layer comprises an adhesive material which leaves no adhesive residue on said amplifying circuit after removal therefrom.

29. A dry electrode system according to claim 7, wherein:

said first adhesive layer comprises a hypoallergenic adhesive material, and

said second adhesive layer comprises an adhesive material which leaves no adhesive residue on said amplifying circuit after removal therefrom.

30. A dry electrode system according to claim 19, wherein:

said first adhesive layer comprises a hypoallergenic adhesive material, and

said second adhesive layer comprises an adhesive material which leaves no adhesive residue on said amplifying circuit after removal therefrom.

31. A dry electrode system according to claim 20, wherein:

said first adhesive layer comprises a hypoallergenic adhesive material, and

said second adhesive layer comprises an adhesive material which leaves no adhesive residue on said amplifying circuit after removal therefrom.

32. A dry electrode system according to claim 24 wherein:

said first adhesive layer comprises a hypoallergenic adhesive material, and

said second adhesive layer comprises an adhesive material which leaves no adhesive residue on said amplifying circuit after removal therefrom.

33. A dry electrode system according to claim 7, wherein said conductive pad comprises:

a flexible conductive film provided on at least one side of said resilient conductive pad, said conductive film having an electrical impedance to dry skin of not greater than 1.5 million ohms at 10 Hz and maintaining an AC noise voltage (0.15 to 100 Hz) of not more than 150 μ

V peak under conditions ranging from dry to saturation with a 0.9% saline solution.

34. A dry electrode system according to claim 19, wherein said conductive pad comprises:

a flexible conductive film provided on at least one side of said resilient conductive pad, said conductive film having an electrical impedance to dry skin of not greater than 1.5 million ohms at 10 Hz and maintaining an AC noise voltage (0.15 to 100 Hz) of not more than 150 μ

V peak under conditions ranging from dry to saturation with a 0.9% saline solution.

35. A dry electrode system according to claim 20, wherein said conductive pad comprises:

a flexible conductive film provided on at least one side of said resilient conductive pad, said conductive film having an electrical impedance to dry skin of not greater than 1.5 million ohms at 10 Hz and maintaining an AC noise voltage (0.15 to 100 Hz) of not more than 150 μ

V peak under conditions ranging from dry to saturation with a 0.9% saline solution.

36. A dry electrode system according to claim 24, wherein said conductive pad comprises:

a flexible conductive film provided on at least one side of said resilient conductive pad, said conductive film having an electrical impedance to dry skin of not greater than 1.5 million ohms at 10 Hz and maintaining an AC noise voltage (0.15 to 100 Hz) of not more than 150 μ

V peak under conditions ranging from dry to saturation with a 0.9% saline solution.

39. A dry electrode system according to claim 1, 2, 3, 5 or 37, wherein said conductive pad comprises:

a flexible conductive film provided on at least one side of said resilient conductive pad, said conductive film having an electrical impedance to dry skin of not greater than 1.5 million ohms at 10 Hz and maintaining an AC noise voltage (0.15 to 100 Hz) of not more than 150 μ

V peak under conditions ranging from dry to saturation with a 0.9% saline solution.

40. A dry electrode system according to claim 39, wherein said conductive film is provided on both opposed sides of said resilient conductive pad.

41. A dry electrode system according to claim 40, wherein said conductive film comprises:

a cured mixture of one and one half parts by volume graphite powder, five parts by volume distilled water and ten parts by volume of liquid latex.

37. A dry electrode system for the detection of biopotentials existing on the surface of the skin of a living body, comprising:

a conductive dry electrode pad comprising a resilient conductive pad and having opposed sides, one of which is adapted to contact the skin of said living body, and adhesive means, having first and second adhesive layers, at least said first adhesive layer being conductive and adapted to adhere said conductive pad to said skin; and

an amplifying circuit connected to the other side of said dry electrode pad for amplifying a biopotential transmitted via said dry electrode pad to said amplifying circuit;

wherein said adhesive means comprises;

said conductive first adhesive layer applied to said one side of said resilient conductive pad, and

said second adhesive layer being an insulative adhesive layer applied to selected portions of the other side of said resilient conductive pad, said conductive first adhesive layer adapted to adhesively engage the skin and said insulative second adhesive layer adhesively engaging the amplifying circuit with said resilient conductive pad in contact with said amplifying circuit.

38. A dry electrode system according to claim 37, wherein:

said conductive adhesive layer comprises a hypoallergenic adhesive material, and

said insulative adhesive layer comprises an adhesive material which leaves no adhesive residue on said amplifying circuit after removal therefrom.

42. A dry electrode system according to claim 37, wherein said amplifying circuit comprises:

an insulating housing having a conductive input contact mounted thereon engaging the dry electrode pad,

a lead amplifier having an input coupled to said input contact and an output, and

a voltage driven first shield connected to said output of said lead amplifier and surrounding portions of said input contact not in engagement with said dry electrode pad.

43. The dry electrode system as defined in claim 42, wherein said conductive input contact comprises a material that maintains an AC noise voltage baseline of not more than 150 μ

V peak (0.15 to 100 Hz) under conditions ranging from dry to saturation with a 0.9% saline solution.

44. A dry electrode system according to claim 43, wherein said conductive input contact comprises:

titanium hydride.

45. A dry electrode system according to claim 42, wherein said conductive input contact comprises:

conductive silicone rubber.

46. A dry electrode system according to claim 42, wherein said amplifying circuit comprises:

said lead amplifier comprising an operational amplifier having inverting and non-inverting inputs,

first and second diodes connected in parallel inverse polarity across the inputs of said operational amplifier,

third and fourth diodes connected in parallel inverse poarlity from the inverting input of said operational amplifier to a circuit common potential,

an output resistor connected from the inverting input to the output of said operational amplifier,

an input resistor connected between the noninverting input of said operational amplifier and said conductive input contact, said input resistor at least partially contained within said voltage-driven first shield,

a lead wire cable having plural conductors connected to said lead amplifier and supplying power and common potential to said lead amplifier and taking out an output from said lead amplifier, and

a decoupling resistor connected from the output of said operational amplifier to an output conductor of the lead wire cable.

47. A dry electrode system according to claim 46, further comprising:

a circuit board having opposed sides, wherein on one of said sides of said circuit board said operational amplifier, said first through fourth diodes, and said output and decoupling resistors are mounted, said circuit board having an aperture through which said input resistor extends from the one side to the other side on which said conductive input contact is mounted.

48. A dry electrode system according to claim 47, wherein said lead wire cable comprises:

a flexible insulated multi-conductor cable including a pair of insulated conductors to carry bipolar supply currents to said lead amplifier, an insulated conductor to carry said circuit potential common current to and from said lead amplifier, said output conductor comprising an insulated conductor to carry an output signal from said lead amplifier, and a second shield shielding said insulated conductors.

49. A dry electrode system according to claim 48, wherein said amplifying circuit further comprises:

a voltage follower operational amplifier having a non-inverting input connected to the first shield, and an inverting input connected to an output of said voltage follower operational amplifier and to said second shield.

50. A dry electrode system according to claim 48, wherein said second shield is connected to said insulated conductor carrying said circuit common potential.

51. A dry electrode system according to claim 48, comprising:

means for providing said circuit common potential, including,

an elastic ground strap having conductive portions and adapted to be mounted on a portion of the body,

a second resilient conductive pad contacting said conductive portions of said strap, and

a ground lead wire electrically conductively coupled between said second conductive pad and said insulated conductor carrying said circuit common potential.

52. A dry electrode system according to claim 48, comprising:

means for providing said circuit common potential, including,

a second dry electrode pad also comprising a resilient conductive pad having opposed sides one of which is adapted to engage the skin of the living body, and adhesive means having first and second adhesive surfaces, said first adhesive surface adapted to adhere said second conductive pad to the skin of said living body,

a second electrical contact mounted on a second housing and adhering to said second surface of said adhesive means, said second contact electrically contacting said second conductive pad, and

passive lead wire means for electrically conductively coupling said second electrical contact to said conductor carrying said circuit common potential.

53. A dry electrode system according to claim 52, comprising:

a conductive shield at least partially surrounding said second electrical contact.

54. A dry electrode system according to claim 37, wherein said amplifying circuit comprises:

an insulating housing having a conductive input contact mounted on said housing and engaging the dry electrode pad;

a lead amplifier having inverting and noninverting inputs, one of which is coupled to said input contact, and an output;

first and second diodes connected in parallel inverse polarity across the inputs of said lead amplifier; and

third and fourth diodes connected in parallel inverse polarity from the inverting input of said lead amplifier to a circuit common potential.

55. A dry electrode system according to claim 54, comprising:

a voltage driven first shield connected to said output of said lead amplifier and surrounding portions of said input contact not in engagement with said pad.

56. The dry electrode system as defined in claim 54, wherein said conductive input contact comprises a material that maintains an AC noise voltage baseline of not more than 150 μ

V peak (0.15 to 100 Hz) under conditions ranging from dry to saturation with 0.9% saline solution.

57. A dry electrode system according to claim 56, wherein said conductive input contact comprises titanium hydride.

58. A dry electrode system according to claim 54, wherein said conductive input contact comprises:

conductive silicone rubber.

73. A dry electrode pad according to claims 57, 61, 62 or 64, wherein said adhesive means comprises:

a conductive adhesive layer applied to at least a portion of said resilient conductive pad; and

an insulative adhesive layer applied to a selected portion of at least one of the resilient conductive pad and the conductive adhesive layer.

59. A dry electrode system for the detection of biopotentials existing on the surface of the skin of a living body, comprising:

a conductive dry electrode pad comprising a resilient conductive pad and having opposed sides, one of which is adapted to contact the skin of said living body, and adhesive means, having first and second adhesive surfaces, at least said first adhesive surface being conductive and adapted to adhere said conductive pad to said skin; and

an amplifying circuit connected to the other side of said dry electrode pad for amplifying a biopotential transmitted via said dry electrode pad to said amplifying circuit;

wherein said adhesive means comprises;

a conductive adhesive layer applied to at least a portion of said resilient conductive pad; and

an insulative adhesive layer applied to a selected portion of at least one of the resilient conductive pad and the adhesive conductive layer.

60. A dry electrode pad for enabling electrical and mechanical connection between the skin of a living body and an amplifying circuit electrically coupled to a monitor, comprising:

a resilient conductive pad having first and second opposed sides, one of which is adapted to contact the skin of said living body; and

adhesive means having opposed first and second adhesive surfaces respectively provided on the opposed sides of said conductive pad, said first adhesive surface being conductive and adapted to adhere to the skin such that one opposed side of said conductive pad is in electrical connection with the skin, said second adhesive surface adapted to adhesively engage said amplifying circuit with the other opposed side of said conductive pad in electrical connection with said amplifying circuit.

61. A dry electrode pad according to claim 60, wherein said conductive pad comprises a resilient material having not less than 5% rebound value, and wherein said dry electrode pad has an electrical impedance to dry skin of not greater than 1.5 million ohms at 10 Hz and an AC noise base line not greater than 150 μ

V peak (0.15 to 100 Hz) under conditions of dry to saturation within a 0.9% saline solution.

62. A dry electrode pad according to claim 61, wherein said conductive pad comprises:

an open-cell foam.

63. The dry electrode pad as defined in claim 62, wherein said conductive foam pad comprises:

carbon loaded polyurethane foam.

64. A dry electrode pad according to claim 61, wherein said conductive pad comprises:

a closed-cell foam.

65. A dry electrode pad according to claim 64, wherein said conductive foam pad comprises:

a cross-linked vinyl-nitrite polymer.

66. A dry electrode pad according to claims 60, 61, 62 or 64, wherein said adhesive means comprises:

first and second conductive adhesive layers applied to respective opposed sides of said resilient conductive foam pad.

67. A dry electrode pad according to claims 60, 61, 62 or 64, wherein said adhesive means comprises:

a pair of tissue substrates each having opposed sides covered with a conductive adhesive layer, said pair of substrates sandwiching said resilient conductive pad therebetween.

68. A dry electrode pad according to claims 60, 61, 62 or 64, wherein said adhesive means comprises:

a conductive adhesive layer applied to said one side of said resilient conductive pad and an insulative adhesive applied to selected portions of the other side of said resilient conductive pad, said conductive adhesive adapted to adhesively engage the skin, and said insulative adhesive layer adapted to adhesively engage the amplifying circuit with said resilient conductive pad in electrical connection with said amplifying circuit.

69. A dry electrode pad according to claims 60, 61, 62 or 64, wherein:

said first adhesive surface comprises a hypoallergenic adhesive material, and

said second adhesive surface comprises an adhesive material which leaves no adhesive residue on said amplifying circuit after removal therefrom.

70. A dry electrode pad according to claims 60, 61, 62 or 64, wherein said conductive pad comprises:

a flexible conductive film provided on at least one side of said conductive foam pad, said conductive film having an electrical impedance to dry skin of not greater than 1.5 million ohms at 10 Hz and maintaining an AC noise voltage (0.15 to 100 Hz) of not more than 150 μ

V peak under conditions ranging from dry to saturation with a 0.9% saline solution.

71. A dry electrode pad according to claim 70, wherein said conductive film is provided on both opposed sides of said conductive pad.

72. A dry electrode pad according to claim 71, wherein said conductive film comprising:

a cured mixture of one and one half parts by volume graphite powder, five parts by volume distilled water and ten parts by volume of liquid latex.

74. A dry electrode pad according to claims 60, 61, 62 or 64, wherein said adhesive means comprises:

a conductive adhesive layer applied to at least a portion of said resilient conductive pad; and

an insulative adhesive layer applied to a selected portion of at least one of the resilient conductive pad and the conductive adhesive layer.