Oxidized Surface Biopotential Skin Electrode

Abstract

An electrode adapted to be attached to the skin of an individual for obtaining a biological or physiological potential such as are associated with muscle activity or functions of the brain, the electrode being formed of a deformable, synthetic polymeric, electrically insulating material coated with a thin film of metallic silver having a surface layer that has been converted to silver chloride. One surface defines a concavity, a pair of holes joining the concavity to the opposite surface of the electrode. A female socket is molded as an integral part of the electrode so that the silver-silver chloride layer provides a continuous electrical pathway between the concavity and the socket.

Description

This invention relates to electrodes and more particularly to biopotential skin electrodes suitable for obtaining biological or physiological potentials such as are associated with muscular activity or neurological functions of the brain.

As known, such potentials can be picked up at the skin of the patient and recorded by an electronic instrument such as an electromyograph, typically an electrocardiograph if current and voltage waveforms associated with the action of the heart are to be measured, or an electroencephalograph if brain voltages are to be recorded.

There long has been a need for a biopotential skin electrode combining low cost with high quality performance. Heretofore, biopotential electrodes providing satisfactory performance have been expensive, whilst less costly electrodes have generally shown a poor response, particularly high DC drift and undue sensitivity to motion artifacts.

Accordingly, the present invention has as a primary object, the provision of a high quality, yet inexpensive and therefore "throwaway" electrode for use with conventional biopotential measuring and recording instruments. Other objects are to provide such an electrode which exhibits low sensitivity to motion artifacts; to provide such an electrode which can be easily attached to and removed from the skin of a patient and which can be used with conventional electrocardiograph electrolyte jellies or the like; to provide such an electrode which can be attached to the skin for extended periods of time short concern for irritation of the skin to which it is releasably affixed, and which because of its low cost can be discarded after a single use or re-used as desired.

These and other objects are achieved by a generally waferlike electrode of deformable, electrically insulating materials, a portion of the electrode defining a concavity intended to be disposed adjacent the skin of the patient as by an electrically nonconductive pressure-sensitive adhesive. A pair of continuous passageways extend from the interior of the cavity through the electrode to an opposite surface. Also provided is at least one socket, adapted to connect with a terminal on a lead from the biopotential measuring instrument. A thin electrically conductive coating on the electrode provides a continuous electrical path from the interior of the cavity to the interior of the socket. After the electrode is attached to the skin of a patient, it is made operative by connecting the terminal to a corresponding socket, then introducing an appropriate electrolyte through one of the passageways into the cavity so as to form a conductive path between the skin and the coating on the interior of the cavity. The coating is selected so that it forms a stable contact potential both with the terminal and with the conductive electrolyte.

Other objects of the invention will in part be obvious and will in part appear hereinafter. The invention accordingly comprises the apparatus possessing the construction, combination of elements, and arrangement of parts which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the present invention, reference should be had to the following detailed description taken in connection with the accompanying drawing, wherein:

FIG. 1 is an exploded, perspective view of the invention;

FIG. 2 is a cross-sectional view taken centrally across an assembled embodiment of FIG. 1; and

FIG. 3 is a perspective view of a variation of the embodiment of FIG. 1.

Referring now to FIGS. 1 and 2, there is shown an electrode, comprising a generally flat wafer of disc 22. Also included, as means for attaching disc 22 to the skin of a subject is a contact sheet 24. Disc 22 is formed of a mechanically deformable, electrically insulating material such as a synthetic polymeric plastic or the like; polypropylene, for example. At least one surface of the disc is characterized by having at least one concavity 26 therein. Concavity 26 need not be of a regular shape and need cover only a small portion of one surface of the disc. Also provided are means communicating with the interior of the concavity through the body of the disc, and comprising at least holes 28 and 30 which define a pair of continuous passageways extending from the interior of the concavity 26 through the disc. Holes 28, 30 may but need not be identical. While neither their size nor configuration is particularly critical to the invention it is preferred that the holes be slightly conically flared outwardly from concavity 26 so as to provide a mating fit to means for injecting electrolyte paste therein. The disc is also provided with electrical connecting means comprising, in the form shown, one or more holes or sockets 32 which may be disposed about the edge of the disc, as shown in FIGS. 1 and 2. Each socket is adapted to be releasably engageable with a plug-in terminal 34, described hereinafter.

The surface of disc 22 is provided with provide thin, continuous coating 36 (FIG. 2) of an electrically conductive material. This coating provided at least a continuous electrical path between the interior of concavity 26 and the interior of the sockets 32. The coating may but need not totally enclose the disc, although for purposes of mass production, such a totally enclosing skin may be desirable. In the preferred embodiment, the coating is silver chloride which may be deposited or formed by any well known technique. Preferably, the disc is first coated with a thin (e.g. 40--50.mu.) layer of metallic silver applied, for example, by vacuum deposition or plating. The silver coated disc is then treated, for example, with a 1N solution of hydrochloric acid, to oxidize at least a surface layer of the silver to silver chloride. Silver chloride is particularly desirable for its mechanical qualities of toughness and excellent adhesion, and for its excellent and well known electrical conductivity. Further, it provides stable contact potentials when in contact with silver and with a chloride electrolyte such as NaCl.

Also shown in FIGS. 1 and 2 is contact sheet 24 which is formed of a thin flexible, electrically insulating material such as polypropylene, polyethylene or preferably polyethylene terephthalate, or the like. Hole 40 which preferably is substantially the same size and contour (but may be smaller) as the surface periphery of concavity 26, is formed substantially at the center of sheet 24. Hole 40 should be centered on or registered with the periphery of concavity 26 so that hole 40 is adjacent the concavity and at least a portion of the concavity remains uncovered, while the remainder of sheet 24 wholly covers the surface of disc 22 around the concavity. Means for securing the sheet to the disc may comprise a known pressure-sensitive adhesive 42. The other surface of sheet 24 is coated with a similar adhesive layer 44 so that it may be attached to the skin of a patient in such a manner that the concavity is disposed adjacent the skin. The adhesive preferably is of a nonallergenic type which will minimize or prevent lesions or other irritations to the skin. It should be noted that the pressure-sensitive adhesive may be protected by a release sheet 46, such as wax paper, which can be stripped off just prior to use. A group of electrodes can thus be stored loosely in a container without adhering to one another or can be enclosed in individual sterile packages. The disc and contact sheet portions may also be stored in separate containers if desired, with each portion being protected from one another by the use of similar release sheets.

Shaped to form a tight plug in fit in at least one of the sockets 32 is at least one terminal 34, one end of which is connected to the biopotential measuring instrument (not shown). The terminal 34 includes a current-carrying cross-sectional as a wire 48, which terminates in a plug in tip 50. Wire 48 may be of copper, aluminum or other commonly used electrically conductive metal or alloy. Tip 50 is preferably coated with metallic silver, or may comprise a section of pure silver connected to the end of wire 48. Tip 50 is dimensioned so that when it is inserted into a corresponding socket 32, the tip fits very snugly by distorting or stretching the socket, and only the silver of the tip contacts the silver chloride coating 36 so as to form thereby a silver/silver chloride junction. Accordingly, a leakproof sleeve 52 of flexible, electrically-insulating material is formed around the terminal so as to shield and enclose the current-carrying portion of wire 48.

Disc 22 is attached to the patient by stripping off a release sheet from contact sheet 24 to expose the pressure-sensitive adhesive on one surface, and then attaching that surface to the disc with proper registration of hole 40 and concavity 26. The release sheet on the other surface of sheet 24 is then stripped and this latter surface is pressed against the skin of the patient. An electrolytic paste or gel, such as that conventionally used with electrocardiograph instruments, and preferably comprising sodium chloride in agar or the like, is introduced through one of holes 28 or 30 into the concavity 26. An electrical potential can be measured and recorded by the measuring instrument when the paste is disposed so as to form a continuous path communicating with the skin and the silver chloride coat on the interior of the concavity, and when the plug in terminal is inserted into appropriate socket 32.

Advantages of the above described electrode are several. Because it is formed of a regularly shaped and relatively simple following of disc, it lends itself to mass production as by stamping or injection molding. The size of the electrode can vary widely, as desired. Should a small electrode be desired, the socket can be formed as a slotted opening 54 between two ridges formed integrally on the top of the disc, generally opposite concavity 26, as shown in FIG. 3. It should also be appreciated that the disc can be used without contact sheet 24, by affixing the pressure-sensitive adhesive to the disc itself, on the surface portion of the latter about the periphery of the concavity, provided however that this adhesive will also serve to insulate the surface AgCl from the skin. Since the electrolyte is inserted through one of holes 28 or 30, the other hole or holes serves as a pressure relief vent during the operation of filling the concavity. Should the electrolyte dry out during prolonged operation, additional amounts can be readily inserted through one of holes 28 or 30. Moreover, the disc being of readily deformable material, it lends itself to the formation of integral connectors.

Since certain changes may be made in the above apparatus without departing from the scope of the invention herein involved it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted in an illustrative and not a limiting sense. For example, while the electrical connector integral with the disc has been described as being a female connector, it will be apparent that a protruding male connector appropriately coated can also be provided integral with the disc. In such case, tip 50 would then be a corresponding female coupling.

Claims

What I claim is:

1. For use with a conventional biopotential measuring instrument having at least one terminal connector attached thereto, and an electrolyte, an electrode for detecting skin potentials and comprising:

a member of electrically insulating material, said member having a first surface including at least one concavity for containing said electrolyte, at least two continuous passageways extending from said concavity to another surface of said member, and at least one connecting means integral with said member and sized to be releasably engageable with said terminal connector, said member having a surface coating of a thickness in the micron range and consisting of electrically conductive material, said coating having an oxidized surface layer of a substantially conductive salt of said conductive material, said coating providing a continuous electrical path from the interior of said concavity to and including, at least the portion of the surface of said connecting means which contacts said terminal connector.

2. An electrode as defined in claim 1 wherein said coating substantially totally encloses said member.

3. An electrode as defined in claim 1 wherein said coating comprises silver chloride.

4. An electrode as defined in claim 1 wherein said coating comprises a film of silver having a thin surface layer of silver chloride.

5. An electrode as defined in claim 1 wherein said connecting means shown of a mechanically deformable material and is sized so as to deform when engaged with said connector whereby to insure a tight fit.

6. An electrode as defined in claim 1 wherein said connecting means is a female-type of coupling.

7. An electrode as defined in claim 6 wherein said connecting means is a hole in said member.

8. An electrode as defined in claim 6 wherein said connecting means is a slotted opening in said member.

9. An electrode as defined in claim 1 including means for releasably securing said member to a skin surface with said concavity adjacent said skin surface and said another surface directed substantially away from said skin surface so that said electrolyte can be inserted through at least one of said passageways into said at least one concavity to form a continuous electrical path between said skin surface and the interior of said concavity, said means for releasably securing includes means for providing electrical insulation between said skin surface and the portion of said first surface disposed about the periphery of said concavity.

10. An electrode as defined in claim 9 wherein said means for releasably securing comprises a substantially flat sheet of electrically insulating material having a hole therein, one surface of said sheet being secured to the portion of said first surface disposed about said concavity so that said concavity is at least partially exposed through said hole.

11. An electrode as defined in claim 6 wherein said coating is provided on the inner surface of said female-type coupling connecting means.