Dry electrode system for detection of biopotentials

• US 4,669,479 A
• Filed: 08/21/1985
• Issued: 06/02/1987
• 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:
  US06/767,963
• Time in Patent Office: 650 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 having opposed adhesive surfaces, one of which is adapted to engage the skin of said 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.

Claims

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

a dry electrode pad comprising a resilient conductive pad 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, said first adhesive surface adapted to adhere said dry electrode pad to said skin;

an amplifying circuit adapted to be connected to the other side of said conductive pad for amplifying a biopotential transmitted via said conductive pad to said amplifying circuit, comprising,

an insulating housing adhering to said second adhesive surface of the dry electrode pad,

a conductive input contact means mounted on said housing for engaging the dry electrode pad,

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

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

2. A dry electrode system according to claim 1, wherein said conductive pad comprises:

a resilient material having not less than 5% rebound value, dry resistivity not greater than 200,000 ohm-cm, and an AC noise base line not greater than 150 μ

V peak (0.15 to 35 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:

carbon loaded polyurethane foam.

4. The dry electrode system as defined in claim 3, wherein said conductive input contact means comprises a material that maintains an AC noise voltage baseline of not more than 150 μ

V peak (0.15 to 35 Hz) under conditions ranging from dry to saturation with a 0.9% saline solution.

5. A dry electrode system according to claim 4, wherein said conductive input contact means comprises a titanium hydride contact.

6. A dry electrode system according to claim 3, wherein said conductive input contact means comprises a titanium hydride contact.

7. The dry electrode system as defined in claim 2, wherein said conductive input contact means comprises a material that maintains an AC noise voltage baseline of not more than 150 μ

V peak (0.15 to 35 Hz) under conditions ranging from dry to saturation with a 0.9% saline solution.

8. The dry electrode system as defined in claim 1, wherein said conductive input contact means comprises a material that maintains an AC noise voltage baseline of not more than 150 μ

V peak (0.15 to 35 Hz) under conditions ranging from dry to saturation with a 0.9% saline solution.

9. A dry electrode system according to claim 1, wherein said conductive input contact means comprises a titanium hydride contact.

10. A dry electrode system according to claims 1, 2, 3, 8, 7, 4, 9, 6, or 5, 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 housing after removal from said housing.

11. A dry electrode system according to claims 2, 3, 8, 7, 4, 9, 6 or 5, comprising:

a flexible conductive film provided on at least one side of said conductive pad, said conductive film maintaining an AC noise voltage (0.15 to 35 Hz) of not more than 150 μ

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

12. A dry electrode system according to claim 11, wherein said conductive film is provided on both opposed sides of said conductive pad.

13. A dry electrode system according to claim 11, 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.

14. A dry electrode system according to claim 11, wherein said adhesive means comprises an adhesive coating formed on a portion of said flexible conductive film provided on said at least one surface of said conductive pad.

15. A dry electrode system according to claim 11, 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 housing after removal from said housing.

16. A dry electrode system according to claim 1, wherein said adhesive means comprises:

an adhesive pad on which said conductive pad is mounted, said adhesive pad having said first and second adhesive surfaces and including an aperture, said conductive pad mounted over said aperture on said first surface.

17. A dry electrode system according to claim 1, wherein said adhesive means comprises:

opposed adhesive pads sandwiching said resilient conductive pad therebetween, said adhesive pads each having an aperture and said resilient conductive pad mounted therebetween, said adhesive pads having respective exterior adhesive surfaces serving as said first and second surfaces.

18. A dry electrode system according to claim 1, comprising:

a flexible conductive film provided on one side of said conductive pad, said conductive film maintaining an AC noise voltage (0.15 to 35 Hz) of not more than 150 μ

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

19. A dry electrode system according to claim 18, wherein said conductive film is provided on both opposed sides of said conductive pad.

20. A dry electrode system according to claim 1, wherein said adhesive means comprises:

first and second adhesive coatings formed on portions of respective opposed sides of said conductive pad and serving as said first and second adhesive surfaces, respectively.

21. A dry electrode system according to claim 1, 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 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 means, said input resistor at least partially contained within said voltage-driven first shield,

a lead wire cable having plural conductors connected to said 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.

22. A dry electrode system according to claim 21, 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 means is mounted.

23. A dry electrode system according to claim 22, 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 common potential to and from said lead amplifer, said output conductor comprising an insulated conductor to carry an output signal from said lead amplifier, and a second shield shielding said insulated conductors.

24. A dry electrode system according to claim 23, 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.

25. A dry electrode system according to claim 23, wherein said second shield is connected to said insulated conductor carrying said circuit common potential.

26. A dry electrode system according to claim 23, 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.

27. A dry electrode system according to claim 23, 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 to said second conductive pad to the skin of said living body,

a second electrical contact means mounted on a second housing for adhering to said second surface of said adhesive means of said second dry electrode pad, said secohd contact means adapted to electrically contact said second conductive pad, and

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

28. A dry electrode system according to claim 27. comprising:

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

29. 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 and a flexible conductive film applied to at least one of said sides, said flexible conductive film adapted to contact the skin of said living body; and

adhesive means having opposed first and second adhesive surfaces provided on selected portions of said conductive pad, said conductive pad adhering to said adhesive means, said first adhesive surface adapted to adhere to the skin such that said flexible conductive film of said conductive pad is in electrical contact with the skin, said second adhesive surface adapted to adhesively engage said amplifying circuit with the other side of said conductive pad electrically in connection with said amplifying circuit.

30. A dry electrode pad according to claim 29, comprising:

a conductive film applied to the other side of said conductive pad and adapted to make electrical connection to said amplifying circuit.

31. A dry electrode pad according to claim 29, wherein said conductive pad comprises:

a resilient foam material having not less than 5% rebound value, dry resistivity not greater than 200,000 ohm-cm, and an AC noise base line not greater than 150 μ

V peak (0.15 to 35 Hz) under conditions of dry to saturation within a 0.9% saline solution.

32. A dry electrode pad according to claim 31, wherein said conductive pad comprises:

carbon loaded polyurethane foam.

33. A dry electrode according to claim 32, wherein said flexible conductive film maintains an AC noise voltage (0.15 to 35 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 according to claim 33, wherein said flexible 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.

35. A dry electrode pad according to claims 29, 30, 31, 32, 33, or 34, wherein said adhesive means comprises:

an adhesive pad a first surface of which has said conductive pad mounted thereon and the second surface of which is adapted to adhesively engage said amplifying circuit.

36. A dry electrode pad according to claims 29, 30, 31, 32, 33, or 34, wherein said adhesive means comprises:

a pair of apertured adhesive pads sandwiching said conductive pad.

37. A dry electrode pad according to claims 29, 30, 31 or 32, wherein said adhesive means comprises:

adhesive coatings applied to portions of the opposed sides of said conductive pad.

38. A dry electrode pad according to claims 33 or 34, wherein said adhesive means comprises:

an adhesive coating provided on portions of said conductive film.

39. A dry electrode system according to claim 35, 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 housing after removal from said housing.

40. A dry electrode system according to claim 36, 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 housing after removal from said housing.

41. A dry electrode system according to claim 37, 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 housing after removal from said housing.

42. A dry electrode system according to claim 38, 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 housing after removal from said housing.

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

a 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, said first adhesive surface adapted to adhere said resilient conductive pad to said skin, said resilient conductive pad comprising a flexible conductive film provided on at least one of the opposed sides of said resilient conductive pad, said conductive film maintaining an AC noise voltage (0.15 to 35 Hz) of not more than 150 μ

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

an amplifying circuit means adapted to adhere to said second adhesive surface and to be connected to the other side of said conductive pad for amplifying a biopotential transmitted via said dry electrode pad to said amplifying circuit means.

44. A dry electrode system according to claim 43, wherein said amplifying circuit means comprises:

an insulating housing adhering to said second adhesive surface of the dry electrode pad;

conductive input contact means mounted on said housing for engaging the dry electrode pad;

a lead amplifier having inverting and noninverting inputs, one of which is coupled to said input contact means, 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.

45. A dry electrode system according to claim 44, comprising:

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

46. The dry electrode system as defined in claims 44 or 45, wherein said conductive input contact means comprises a material that maintains an AC noise voltage baseline of not more than 150 μ

V peak (0.15 to 35 Hz) under conditions ranging from dry to saturation with a 0.9% saline solution.

47. A dry electrode system according to claim 46, wherein said conductive input contact means comprises a titanium hydride contact.

48. A dry electrode system according to claims 43, 44, or 45, 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 housing after removal from said housing.

49. A dry electrode system according to claim 45, wherein said amplifying circut means comprises:

said lead amplifier comprising an operational amplifier,

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 amplifter and said conductive input contact means, 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.

50. A dry electrode system according to claim 49, 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 insulating conductor to carry said circuit common potential 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.

53. A dry electrode system according to claim 43, wherein said conductive pad comprises a resilient material having not less than 5% rebound value, and wherein said conductive pad has a dry resistivity not greater than 200,000 ohm-cm, and an AC noise base line not greater than 150 μ

V peak (0.15 to 35 Hz) under conditions of dry to saturation within a 0.9% saline solution.

54. A dry electrode system according to claim 43, wherein said conductive pad comprises:

carbon loaded polyurethane foam.

55. A dry electrode system according to claim 43, wherein said adhesive means comprises:

at least one adhesive pad on which said conductive pad is mounted.

56. A dry electrode system according to claim 43, wherein said adhesive means comprises:

opposed adhesive pads sandwiching said resilient conductive pad therebetween.

57. A dry electrode system according to claim 56, wherein said adhesive pads each having an aperture and said resilient conductive pad is mounted therebetween.

58. A dry electrode system according to claim 43 wherein said conductive film is provided on both opposed sides of said conductive pad.

59. A dry electrode system according to claim 58, 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.

60. A dry electrode system according to claim 43 wherein said adhesive means comprises an adhesive coating formed on a portion of said flexible conductive film provided on said at least one side of said conductive pad.

61. A dry electrode system according to claim, 43, wherein said adhesive means comprises:

first and second adhesive coatings formed on portions of respective opposed surfaces of said conductive pad and serving as said first and second adhesive surfaces, respectively.

51. A dry electrode system according to claim 51, wherein said amplifying circuit means further comprises:

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

52. A dry electrode system according to claim 51, wherein said second shield is connected to said insulated conductor carrying said circuit common potential.