Title:
APPLICATOR ELECTRODES WITH A VERY THIN NON-METALLIC, CURRENT DISTRIBUTING LAYER
United States Patent 3721246


Abstract:
An improved body contacting electrode having a dry, current distributing, skin contacting layer selectively disposed adjacent a conductive portion thereof to provide a high resistance electrode uniquely arranged to effectively limit and uniformly disperse the current from an electrical source through the skin area adjacent the electrode. The current distributing layer is comprised preferably of conductive particles uniformly distributed in a nonconducting medium such as resin or the like. Means are provided to couple the electrode to an external electrical source and to releasably support said electrode adjacent a preselected area of the body.



Inventors:
LANDIS D
Application Number:
05/096893
Publication Date:
03/20/1973
Filing Date:
12/10/1970
Assignee:
THOMAS & BETTS CORP,US
Primary Class:
International Classes:
A61N1/04; (IPC1-7): A61N1/04
Field of Search:
128/2
View Patent Images:
US Patent References:



Primary Examiner:
Kamm, William E.
Claims:
The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows

1. An electrode for coupling an electrical signal to a body through the skin, comprising: at least one conductive portion; at least one current distributing portion adjacent said conductive portion and having a first surface in intimate contact with said conductive portion to provide an equipotential surface at the juncture therebetween; and means for coupling said conductive portion to an external electrical source; said current distributing portion having a second surface arranged to be disposed directly adjacent the skin, to isolate said conductive portion therefrom; said current distributing portion comprising a plurality of conductive particles generally uniformly dispersed in an insulating medium and having a generally uniform thickness in the range of from one thousandth to ten thousandths of an inch, said conductive particles comprising an aggregate volume in the range of from one per cent to twenty-five per cent of the aggregate volume of said current distributing portion, to provide a generally uniform transverse resistance throughout the thickness of said current distributing portion, whereby electrical current passing between said first and said second current distributing portion surfaces is caused to be substantially uniformly dispersed thereover.

2. An electrode as defined in claim 1 wherein said conductive particles are carbon.

3. An electrode as defined in claim 1 wherein said insulating material is a resin.

4. An electrode as defined in claim 1 wherein said second surface of said current distributing portion is substantially smooth.

5. An electrode as defined in claim 1 further comprising means for releasably supporting said electrode in position adjacent a preselected area of the skin.

6. An electrode as defined in claim 5 wherein said support means is a strap.

7. An electrode for coupling an electrical signal to a body through the skin, comprising: a first conductive portion; a second conductive portion adjacent said first conductive portion and spaced therefrom; a current distributing portion surrounding said first and said second conductive portions and having a first surface and a second surface, said first surface of said current distributing portion being disposed in intimate contact with said first and said second conductive portions to provide an equipotential surface at the junctures therebetween, said second surface of said current distributing portion being arranged to be disposed directly adjacent the skin; and means for coupling said first and said second conductive portions to an external electrical source; said current distributing portion comprising a plurality of conductive particles generally uniformly dispersed in an insulating medium and having a generally uniform thickness in the range of from one thousandth to ten thousandths of an inch, said conductive particles comprising an aggregate volume in the range of from 1 per cent to 25 per cent of the aggregate volume of said current distributing portion, to provide a generally uniform transverse resistance throughout the thickness of said current distributing portion whereby electrical current passing between said first and said second current distributing portion surfaces is caused to be substantially uniformly dispersed thereover.

8. An electrode as defined in claim 7 wherein said conductive particles are carbon.

Description:
BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention is directed to the field of electrodes, and principally to a body contacting electrode for use in conjunction with an external electrical power source.

2. Description of the Prior Art

Body contacting electrodes according to the prior art generally comprised a noninsulated conductive member adapted for placement intimately adjacent the skin and in direct contact therewith. Means were generally provided for coupling the electrode to an external device such as electrical detection or signal generating equipment. Where the electrode was utilized merely to couple a body-generated signal or impulse to the external equipment, the direct contact of the electrode with the external surface of the skin generally caused little or no problem with respect to injury or damage to the area of skin immediately adjacent the electrode. However, in many cases it was necessary or desirable to couple an externally generated electrical signal to and through the body by means of a conductive electrode placed in direct contact with a preselected area of the skin to permit the transmission of electric current therethrough. The use of such prior art electrodes for any longer than a relatively short period of time generally caused the skin area adjacent thereto to become sensitized and tender, as indicated by a discoloration and swelling of the surface of the skin adjacent said electrode. This resulted from the fact that the pores of the skin offer a substantially lower resistance to the passage of current than does the adjacent high resistance skin area, whereby current flowing between the electrode and the body tended to concentrate at each of the adjacent low resistance pore areas, thereby damaging the sensitive tissue thereabout. Prior attempts to correct this problem were generally expensive, inefficient, or unsuccessful, such attempts being confined mainly to either interposing liquid or semi-liquid solutions between the electrode and the adjacent skin area, reducing the amount of current in the overall system below a value necessary to afford adequate detection, or undesirably limiting the time of use of such electrodes.

SUMMARY OF THE INVENTION

The present invention overcomes the problems noted above with respect to prior art devices by providing a simple, readily manufactured, uniquely coated, direct skin contacting electrode which is safer, less expensive and more efficient than such devices. Disposed adjacent the conductive portion of the electrode and in intimate contact therewith is a generally uniformly disposed current distributing layer comprising preferably a matrix of conductive particles such as carbon in an electrically insulating material such as resin or the like, the ratio of the volume of conductive particles to insulating material being selectively predetermined to provide a resistance through the thickness of the current distributing layer substantially greater than the resistance of the skin area adjacent thereto. A plurality of alternating adjacent conductive and semiconductive layers may be conveniently provided to achieve a variety of desirable mechanical and electrical characteristics, within the scope of the invention. The outer surface of the layer may be selectively proportioned to define a preferably smooth contact area arranged to provide a predetermined current density therethrough. Means are provided for releasably coupling the conductive portion of the electrode to an external electrical source. Support means such as a strap or other suitable item may be effectively utilized to maintain the electrode in fixed positional relationship adjacent a preselected area of the skin, said electrode being either coupled thereto or externally supported thereby. Where necessary or desirable, a plurality of such electrodes may be suitably arranged in adjacent spaced relationship on a support member to provide a multiple of selectable, discrete contact elements, electrically connectable either in series or in parallel. By the suitable configuration thereof, the electrode may be effectively implanted directly within the body tissue, where appropriate. It is therefore an object of this invention to provide an improved electrode.

It is another object of this invention to provide a means for noninjuriously coupling an electrical source to the body by direct skin or tissue contact.

It is a further object of this invention to provide an improved body contacting electrode for noninjuriously coupling an electrical source to the body for continuous, extended periods of time.

It is yet another object of this invention to provided an improved body contacting electrode for uniformly distributing electrical current over the surface of an adjacent area of the body.

It is yet a further object of this invention to provide a noninjurious semiconductive electrode having a predetermined resistance to permit the effective utilization thereof as a direct skin contact current limiting device.

Other objects and features of the invention will be pointed out in the following description and claims and illustrated in the accompanying drawings, which disclose, by way of example, the principle of the invention and the best mode which has been contemplated for carrying it out.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a perspective view showing a manner in which an electrical signal may be coupled from an external electrical device to the body through an improved body contacting electrode constructed in accordance with the concepts of the invention.

FIG. 2 is a sectional view of the body contacting electrode of FIG. 1.

FIG. 3 is an enlarged sectional view of a portion of the electrode of FIG. 1 in intimate contact with a preselected area of the body.

FIG. 4 is a schematic representation of the electrode and body portion of FIG. 3.

FIG. 5 is a sectional view of an electrode constructed in accordance with another embodiment of the invention.

FIG. 6 is a side elevational view, partly in section, of three electrodes constructed in accordance with the concepts of the invention and coupled to a common supporting strap.

FIG. 7 is a sectional view of an electrode constructed in accordance with a further embodiment of the invention.

FIG. 8 is a perspective view, partly in section, of an electrode constructed in accordance with still another embodiment of the invention.

Similar elements are given similar reference characters in each of the respective drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Turning now to FIGS. 1 and 2, there is shown a body contacting electrode 20 constructed in accordance with the concepts of the invention. Adjacent the enlarged end 24 of the conductive portion 22 of electrode 20 and in intimate contact therewith is a current distributing layer 26, having a selectively predetermined resistance and comprising preferably a dispersion of conductive particles such as carbon or the like, in a nonconducting plastic medium such as epoxy or other insulating material, forming a relatively sold film-like coating as shown in FIG. 2. The exposed outer surface 28 of layer 26 comprises the body contacting portion of electrode 20 and is arranged to be disposed in direct intimate contact with the skin surface for purposes more fully described below. Conductive 22 of electrode 20 extends rearwardly from its enlarged end 24 defining a protrusion 30 adapted to receive thereon a conductive cap 32. Cap 32 serves to secure the electrode 20 to a nonconducting support member such as strap 34 to permit electrode 20 to be conveniently positionably retained adjacent a preselected area of the body such as the wrist 36, as is more clearly seen in FIG. 1. Cap 32 may be appropriately contoured, as shown, to accept thereon a complementarily formed mating connecting member (not shown) to releasably electrically couple electrode 20 to an external electrical source such as 38, by means of an intermediate conductor 40. It will be apparent to those skilled in the art that a variety of other suitable means may be readily employed to effect the desired electrical coupling to conductive portion 22 without departing from the spirit of the invention. For example, the protruding end 30 of electrode 20 may be appropriately apertured or slotted to provide a receiving passage for the bared end of a conductor such as 40 which may then be either crimped or soldered to the conductive portion 22. Alternatively, the protruding end 30 may be modified to define either a male or female connector member adapted to matingly receive a complementary coupling member, thereby providing a convenient releasable coupling therebetween. The button-like configuration of electrode 20 may be suitably modified, as shown in FIG. 5, to provide a generally elongated electrode 42 having a central conductive portion 44 about which is disposed a current distributing portion 68 directly adjacent thereto and in intimate contact therewith. Coupled to conductive portion 44 and extending outwardly therefrom is an insulated electrical conductor 70 serving to couple electrode 42 to an external electrical source (not shown) in a manner similar to that shown in FIG. 1. It will be readily apparent that electrode 42 may be effectively employed as a direct tissue implant device, the current distributing layer 68 providing a unique isolating medium between the conductive portion 44 and the adjacent body tissue essential for the prevention of deleterious chemical reaction therebetween while maintaining the conductivity required in such applications. Electrode 20 may be further modified, where necessary or desirable, to define a substantially spherical electrode 72 having an internal conductive portion 74 suitably encapsulated within an outer current distributing portion 76 and coupled to an insulated electrical conductor 78.

Turning now to FIG. 7, there is shown an embodiment of dual-element electrode 80 constructed in accordance with the concepts of the invention. Disposed circumjacent a pair of spaced, generally elongated conductive portions 82, 82' and in intimate contact therewith is a current distributing portion 84 characteristically similar to portion 26 of electrode 20 of FIG. 2. Coupled to, and extending outwardly from each conductive portion 82, 82' is an associated electrical conductor 86, 86' respectively, each arranged to provide an electrical coupling between said electrode 80 and an external electrical source in a manner similar to that described above with respect to electrode 20 of FIG. 1. While providing the isolation and current dispersing features noted above with respect to a single element electrode such as 20, electrode 80 may be effectively employed to directly couple more than one external electrical source to a preselected body area where it is necessary or desirable to insure a common environment adjacent the elemental portions of electrode 80. The spacing between conductive portions 82, 82' may be selectively arranged to permit either partial or substantially total isolation therebetween, depending primarily upon the thickness of current distributing material 88 disposed between said conductive portions 82, 82'.

To more fully appreciate the novel application of electrode 20 in a contemplated use, according to the concepts of the invention, reference is herein made to FIG. 3, where there is shown the electrode 20, the outer surface 28 of the current distributing layer 26 thereof being disposed in intimate contact with the surface of a portion of the skin 46. The apertures 48 shown extending from beneath the skin 46 and terminating in openings 50 at the surface thereof represent pores generally visible at the surface of said skin, the resistance between that area of skin immediately adjacent the pore openings 50 and the adjacent internal body portion 52 being considerably lower than the resistance as measured through the adjacent thickness of the skin 46. The lower resistance of the pores 48 is generally recognized as resulting from the existence of body fluid within the pores 48, such fluid being relatively highly conductive as compared with the adjacent skin portion 46. Where, heretofore, it was desired to transfer current between the body 52 and an external unprotected conductive electrode, the current, the total value of which may have been quite small, was caused to be concentrated in relatively narrow paths through the low-resistance pores, it being a well-known electrical principle that current will tend to distribute in inverse proportion to the conductivity of the available paths. As a result of the high current density within the extremely restrictive pore areas which comprise a relatively small percentage of the surface area of the skin 46, the walls defining the pores 48, and the immediately adjacent skin areas, were thereby subjected to certain injurious chemical changes, causing both discomfort and damage thereto. The interposition of the relatively thin current distributing layer 26 between the conductive portion 22 of electrode 20 of the adjacent surface of the skin 46 serves to provide a current distributing medium therebetween, effectively preventing the undesirable current concentration and subsequent skin damage noted above, while adequately permitting the transfer of the required current therethrough. Thus, although layer 26 is formed from essentially isotropic material, it tends to exhibit the properties of an anisotropic material as a result of the relative proportions of material thickness and conductive particle density employed in the formation of such layer. For example, to provide the unique current distributing effect noted above, and to prevent undesirable current concentration, the button-type electrode shown in FIGS. 1 and 2 may be suitably proportioned to have a current distributing layer thickness in the order of from one-thousandth to ten thousandths of an inch. Accordingly, a current path normal to the plane of layer 26 is substantially shorter than an obliquely oriented current path originating at a given point on the inner surface of layer 26 spaced from the axis of the normal current path and terminating at the same point on the outer surface of layer 26. It will, of course, be clear that, as the thickness of layer 26 is increased, the difference in length between such current paths spaced a given distance at their point of origin on the inner surface of layer 26 will decrease proportionately. Since the resistivity of the material comprising layer 26 is essentially constant, the resistance of the respective current paths will be proportional to their respective lengths, and, in the case of a thin layer such as 26, current flow will tend to be directed predominantly normal to the plane of layer 26 rather than in oblique angular relationship thereto, due to the increased difference in resistance between such paths, thereby simulating an anisotropic effect and resulting in a substantially even current distribution over the outer surface of layer 26. Referring to the schematic representation of FIG. 4, the current distributing layer 26 of electrode 20 may be represented by a plurality of interconnected parallel resistances 56 having an effective resistance R1. The pores 48 may be represented by a plurality of narrow, elongated spaced conductive paths 58, separated by relatively high resistance regions 60 schematically representative of the skin regions 46, and extending between the adjacent common juncture 64 of resistances 56 and the representative conductive body portion 62. The effective resistance of the parallel combination of the representative skin-pore region is indicated as R2, and that of the underlying body region 62 as R3. The resistance R1 is selectively proportioned to have a predetermined value substantially greater than R2. The interconnected parallel resistances 56 are of substantially equal value, as a result of the generally homogeneous characteristic of current distributing layer 26, and, as may be readily shown by well-known electrical principles, each will have a value substantially greater than the total effective parallel resistance R1, and consequently, a value substantially greater than R2. Thus, the source current I is caused to be distributed generally evenly through each of the discrete parallel resistances 56, resulting in an essentially even distribution of current over the area defined by the contacting surface of the common juncture 64 of resistances 56 at a plurality of individual points such as 66 adjacent the skin. The undesirable concentration of current at adjacent low resistance areas such as pores 48 is thus avoided, thereby eliminating the harmful effects resulting therefrom. It has been found that for general use the thickness of the current distributing layer 26 (FIGS. 2 and 3) may be efficiently, practically and economically maintained within a preferable range of from one to ten thousandths of an inch, although other thicknesses may be effectively employed where necessary or desirable to obtain particular physical or electrical characteristics, according to the concepts of the invention. It has also been found that a ratio of volume of conductive particles to insulating material of from 1 per cent to 25 per cent will provide a current distributing layer resistance adequate for the purposes set forth herein. It should be understood, however, that other ratios of volume of conductive particles to insulating material may be advantageously utilized to obtain a variety of desired current distributing layer characteristics according to the concepts of the invention. For example, where an extremely low value of source current I is utilized, it may be desirable to reduce the effective resistance of the current distributing layer 26 to minimize the total circuit resistance while maintaining a layer resistance sufficient to effect the desired current distribution as described above. Accordingly, such result may be effectively obtained by increasing the ratio of volume of conductive particles to insulating material, without departing from the spirit of the invention. Where it is desirable or necessary to minimize the size of each electrode while maintaining an adequate aggregate body contact area, a plurality of electrodes 20 may be effectively employed in spaced arrangement, as shown in FIG. 6, whereby said electrodes 20 may be individually connected to a single external electrical source to proportionately reduce the amount of current required to be transferred and distributed by each such electrode 20. Alternatively, each electrode 20 may be appropriately coupled to a discrete external source to provide a plurality of individually selective independent contact areas, within the concepts disclosed herein. Either one or more electrodes 20 may be conveniently disposed on a single insulated support member such as strap 34 (see FIG. 6) to effect the releasable positional retention of said electrodes adjacent a preselected area of the body.