# Patent

## Title
Reverse current controlling electrode

## Abstract

A medical electrode includes a moderately conductive flexible member having a top side and a bottom side with a connector and contact with a flexible member top side for establishing electrical contact with an external apparatus. A non-conductive flexible sheet covers the conductive flexible member top and the connector and a highly conductive ink pattern is disposed on a conductive flexible member bottom side. A moderately high conductive hydrogel adhesive disposed on the conductive flexible member bottom side and cover the conductive ink pattern is provided for adhering electrode to a patients' skin.

## Background
The present invention generally relates to electrodes and, more particularly, electrodes suitable for transcutaneous nerve and/or muscle stimulation and biological signal recording.
Medical electrodes must provide an even electrical distribution to a patient's skin over an entire surface of the electrode to effect proper coupling. Because of the curvaceous nature of the human body, it is apparent that medical electrodes for use thereon must be flexible not only for confirmation with a patient's skin contours, but also to accommodate relative movement of the patient's skin.
It is well known that inadequate flexing and shaping of the electrode to a patient's contour can result in an irritation of the patient's skin. Electrical “hot spots” due to uneven electrode-skin contact can result in a rash or a burning sensation. A sensation of burning may be felt by a patient within a few minutes after application of the electrical signals during nerve and/or muscle stimulation, while rash conditions generally take a longer period of time to develop.
In order to provide uniform electrical coupling, heretofore developed electrodes have utilized conductive fabrics and foils in combination with a conductive adhesive in order to uniformly couple electrical signals to and/or from an electrical lead wire, or connector. A number of electrodes have provided impedance compensation for directing electrical pulses from the lead wire uniformly throughout an electrode, such as, for example, U.S. Pat. No. 5,038,796 entitled, ELECTRICAL STIMULATION ELECTRODE WITH IMPEDANCE COMPENSATION, and U.S. Pat. No. 5,904,712 CURRENT CONTROLLING ELECTRODE to Axelgaard. U.S. Pat. No. 4,736,752 teaches the control of current density across an electrode through the use of conductive ink design areas. These patents are incorporated in their entirety herewith by this specific reference thereto.
Many prior art electrodes have compromised the flexibility of the electrode in order to provide adequate current densities over the entire contact area of the electrode. Such electrodes typically have utilized a metallic mesh, or foil, to provide conductivity and utilize a conductive gel between the electrode and the patient's skin in order to accommodate the movement therebetween. Such use of foil or mesh often cause burning or hot spots at electrode edges.
The present invention is directed to a medical electrode having a combination of conductive elements, with selected conductivities which enables assembly of the electrode in a manner hereinbefore not possible. More specifically, the present invention is directed to a medical electrode having a connector disposed on a top surface of a conductive member. This enables automated assembly of the electrode as opposed to conventional manual assembly which in turn reduces unit cost while at the same time providing for controlled and even current density.
SUMMARY OF THE INVENTION
A medical electrode in accordance with the present invention generally includes a moderately conductive flexible member having a top side and a bottom side with a highly conductive pattern, such as, for example conductive ink, printed or transferred to the member bottom side.
A conductive adhesive of moderately high conductivity is disposed on the flexible member bottom side and covering the conductive pattern for adhering the electrode to a patients' skin.
Importantly, the use of a moderately high conductivity adhesive enables the placement of a connector on the top side of the flexible member while at the same time providing uniform current distribution by the electrode. This arrangement is reverse to the configuration of prior art electrode such as set forth in U.S. Pat. No. 5,904,712 and accordingly has been named “Reverse Current Controlling Electrode”.
In controlling current density, the surface resistivity of the conductive member may be between about 102 and about 106 ohm/square, the resistivity of the conductive pattern may be between about 0.1 and about 10 ohms and the volume resistivity of the adhesive may be between about 102 and 103 ohm-cm. The conductivity of the conductive pattern can be controlled through the use of various grid designs with preselected line widths and spacing as well as thickness and ink compositions.
The connector is disposed over the conductive ink pattern and on the top side of the conductive member, whereas the ink pattern is disposed on the bottom side of the conductive member. This arrangement enables the connectors to be disposed in any selected points within a perimeter of the pattern without affecting current distribution. This flexibility of connector positioning, provided by the present invention, facilitates manufacture of the electrodes. In addition, because the lead wire is not disposed between the conductive pattern and patients' skin, there is no interference with the electrode current distribution as is the case when the lead wire is disposed between the conductive pattern and the patients' skin as is the case with some prior art electrodes.
In one embodiment of the present invention, the conductive pattern is disposed on the conductive flexible member bottom at a spaced apart distance from a perimeter of the conductive flexible member in order to establish a border between the perimeter of the conductive ink pattern and the conductive flexible member perimeter. This is important in providing controlled “roll off” of electrical current distribution. While even and uniform electrical current density across the electrode is the desired distribution, such current density should not be present at the edge of the electrode since it may cause unwanted stimulation at that site. Thus, it is most desirable to have the current density “roll off” or be reduced to zero over a short distance. The border arrangement in accordance with the present invention provides for such desired current roll off while providing uniform current distribution over the electrode from border to border.
In addition, the present invention provides for indicia, which is printed on the conductive flexible member in the border region and not contacting the conductive ink pattern, for conveying written information to a user. The indicia when disposed in the border does not affect current distribution or current “roll off” at electrode edges. Visual observation of the indicia is enhanced through the utilization of a conductive hydrogel adhesive with sufficient transparency to enable the user to read the indicia therethrough.
In yet another embodiment of the present invention, the medical electrode includes a moderately conductive flexible member having a top and a bottom side with a plurality of connectors in contact with the conductive member top side for establishing electrical contact with external apparatus, and a plurality of highly conductive patterns are disposed on the conductive flexible member bottom side.
This feature provides for the advantage of fixed electrode distances which assures proper application of the electrode for optimum patient stimulation or signal recording when multiple electrodes are utilized.
A moderately high conductive adhesive is disposed on the conductive member bottom side and covers the conductive ink patterns for adhering the electrode to a patients' skin.
It should be appreciated that the lead wire may be attached or held in place on the conductive flexible member top side in any manner, and inasmuch as the current distribution across the electrode conductive gel is controlled by the relative conductivities of the flexible member, ink pattern and the adhesive, the connector can be placed anywhere within the borders of the ink pattern as hereinabove noted.



BRIEF DESCRIPTION OF THE DRAWINGS
The present invention may be better understood with reference to the following detailed description, taken in conjunction with the accompanying drawings, in which:
FIG. 1 is an exploded cross-sectional view of a medical electrode in accordance with the present invention generally showing a moderately conductive flexible member having a top side and a bottom side, a connector in contact with the member top side, and a non-conductive flexible sheet covering the moderately conductive flexible member top side and the connector; a highly conductive pattern is disposed on the member bottom side, along with a moderately high conductive adhesive and a plastic carrier with a release layer, the carrier preventing premature and/or inadvertent contact with the hydrogel;
FIGS. 2a and 2b are plan views of two embodiments of the present invention showing different ink patterns and indicia for identifying the electrodes;
FIG. 3 is a plan view of yet another embodiment of the present invention showing several ink patterns disposed on a single conductive flexible member;
FIG. 4 is a plot of current distribution profile of the electrode shown in FIG. 1, (i.e. an electrode having a moderately conductive flexible member, a highly conductive pattern disposed on the member bottom side and a moderately high conductive adhesive;
FIG. 5 is a plot similar to FIG. 4, and included for comparison purposes, of the current distribution of an electrode having a moderately conductive flexible member, a highly conductive pattern disposed on the member bottom side and moderately conductive adhesive; and
FIG. 6 is a plot similar to FIG. 5, and included for comparison purposes, of the current distribution of an electrode with no highly conductive pattern disposed on a moderately conductive member bottom side, a moderately conductive adhesive and a connector disposed on a top side of the moderately conductive member.



DETAILED DESCRIPTION
With reference to FIGS. 1 and 2, there is shown, in exploded cross-section, a medical electrode 10 in accordance with the present invention, which generally includes a moderately conductive flexible member 12 having a top side 14 and a bottom side 16.
A connector 20, which may include a lead wire 22 and jack 24 is provided with the lead wire 22 in contact with the member top side 14.
A non-conductive flexible sheet 26 covers the conductive flexible member 12 along with the connector 20 in order to prevent inadvertent contact with the conductive member 12 and connector 20. The sheet 26 may be adhered to the flexible member 12 with any suitable adhesive 28.
The lead wire 22 may be of any inexpensive suitable conductive material.
The sheet 12 may be formed from any suitable carbon loaded elastomeric film having suitable surface resistivity of between about 102 ohm/square and about 106 ohm/square, for example, about 5000 ohm/square and a transverse resistivity of between about 103 and about 105 ohm/square, for example, about 104 ohm/square. Suitable polycarbonate polyolefin and a conductive ink pattern 30 may be printed, or otherwise transferred to the conductive member bottom side 16 with various patterns 32, 34 for embodiments 36, 38, as shown in FIGS. 2a and 2b. The ink pattern may have a resistivity of between about 0.1 and about 10 ohms.
With reference again to FIG. 1, the conductive ink pattern 30 contacts a conductive hydrogel adhesive 44, which is utilized for adhering the electrode 10 to a patients' skin, not shown. The conductive hydrogel adhesive is formulated with moderately high conductivity for example a volume resistivity between about 102 and about 103 ohm-cm, preferably about 400 ohm-cm. Suitable gels are described in U.S. 6,038,464.
A plastic, paper, or other suitable carrier 48 along with a release coating 50 may be provided in order to prevent inadvertent and/or premature adhesion of the patients' skin or other object to the hydrogel. The plastic carrier 48 and release coating 50 is removed prior to application of the electrode 10 to the patients' skin.
Shown in FIG. 3 is another electrode embodiment 54 which includes a moderately conductive flexible member 56 having a plurality of highly conductive ink patterns 60, 62, 64 disposed on a bottom side 62 of the conductive member 56. The conductive ink patterns 60, 62 and 64 may be of various shapes and grid patterns in order to customize the electrical conductivity of the electrode 54 beneath the pattern 60, 62, 64. The adhesive, not shown in FIG. 3, is of moderately high conductivity as hereinabove described.
The spaced apart pattern 60, 62 and 64 act as separate electrodes and communicate with lead wires 72, 74, 76 respectively, which are attached to a top side (not shown in FIG. 3) of the conductive member 56 as illustrated in FIG. 1 with the description of the electrode embodiment 10.
The advantage of utilizing a common conductive member 56 with spaced apart ink patterns 60, 62, 64 is the uniformity of spacing between the independent electrodes effected by the pattern 60, 62, 64 to insure proper electrode placement on a patients' skin.
It should be appreciated that, as shown in FIG. 3, the connector 72, 74, 76 are in placed over the ink patterns 60, 62, 64. The lead wires 72, 74, 76 can be placed anywhere between the borders 80, 82, 84 of the ink patterns 60, 62, 64 since the current distribution across the electrode gel 44 is independently controlled as hereinabove noted.
Referring again to FIGS. 2a and 2b, indicia, which may or may not be conductive ink, may be printed on borders 96, 98 and do not interfere with the current density of the electrode 10 if no contact is made with the patterns 32, 34. The borders 96, 98 are created when the conductive ink patterns 32, 34 are disposed on the flexible member bottom side 16 at a spaced apart distance from a perimeter 102, 104 of the conductive member 12. That is, a perimeter 106, 108 of the ink patterns 32, 34 is spaced apart from the perimeters 102, 104.
FIG. 4 shows the current distribution profile for the electrodes shown in FIG. 2 utilizing a flexible conductive member having a surface resistivity of about 200 ohm/square, a conductive ink pattern having resistivity of about 1 ohm and a hydrogel such as set forth in U.S. Pat. No. 6,038,464 with a volume resistivity of about 400 ohm-cm. This patent is incorporated by this reference thereto in its entirety for describing this type of gel in general electrical configuration which ihay be used to advantage in accordance with the present invention.
As shown in FIG. 4, the conductivity of a 2-inch (50 mm) square electrode is very uniform over almost the entire electrode surface with very little edge effects, i.e. perimeter edges in which non-uniform conductivity occurs, typical with prior art electrodes. In FIG. 4, the green area represents high current density or current transfer by the electrode, the red area represents low or no current density and the yellow area represents a sharp roll off of current density. Because of the rapid roll off in current density, the efficiency of the electrode is enhanced since most of the electrode is utilized for providing uniform current density without burning edge effects.
The current density plot of FIG. 4 shows a vastly improved current density over the electrode in FIG. 5 which is identical except for the use of a moderately conductive adhesive (about 1100 ohm-cm) instead of a moderately high conductive adhesive (about 400 ohm-cm).
It should be clear that the current density shown in FIG. 5 is considerably more non-uniform than the current density shown in FIG. 4. Accordingly, the electrode efficiency in coupling current to a patent (not shown) is severly diminished.
FIG. 6 is a plot of current density of an electrode as constructed similar to the electrode of FIG. 5 with a moderately conductive flexible member and a moderately conductive adhesive but with the lead wire disposed on top of the flexible member and no conductive pattern on the bottom side. The current density shown in FIG. 6 (which is representative of prior art electrodes) is by far inferior to the current densities shown in FIGS. 4 and 5 and illustrates that the unique combination of elements collectively provides an electrode having unexpectedly improved current density.
The difference in conductivity or resistivity between the sheet 12 and the lines 30 as well as the adhesive 44 enables precise control of current distribution which cannot be achieved, for example, with a non-conductive sheet or a highly conductive sheet. The conductivity of the adhesive is selected to be moderately high in order to enable the lead wire 20 to be disposed on top of the sheet 12 instead of in contact with the pattern as with prior art electrode. This effect of adhesive conductivity was heretofore not known and is an unexpected result. In addition, the ink pattern may be of varied conductivity in order to tailor the current through the conductive sheet which may have a thickness of up to about 10 mils, for example, about 1 mil.
Although there has been hereinabove described a specific reverse current-controlling electrode in accordance with the present invention for the purpose of illustrating the manner in which the invention may be used to advantage, it should be appreciated that the invention is not limited thereto. That is, the present invention may suitably comprise, consist of, or consist essentially of the recited elements. Further, the invention illustratively disclosed herein suitably may be practiced in the absence of any element which is not specifically disclose herein. Accordingly, any and all modifications, variations or equivalent arrangements which may occur to those skilled in the art, should be considered to be within the scope of the present invention as defined in the appended claims.

## Claims

1. A medical electrode comprising:
a conductive flexible member having a top side and a bottom side, said conductive flexible member having a surface resistivity of between about 102 and about 106 ohm/square;
a plurality of discrete conductive pattern electrodes disposed spaced apart from one another on the conductive flexible member bottom side, the conductive pattern electrodes having resistivities of between about 0.1 and about 10 ohms the conductive flexible member being operational to insure proper electrode placement on a patient's skin;
a plurality of connectors in contrast with the conductive flexible member top side opposite a corresponding pattern electrode for establishing electrical contact with an external apparatus; and
a conductive adhesive disposed on the conductive flexible member bottom side and covering said conductive patterns, for adhering the electrode to a patient's skin, said conductive adhesive having a volume resistivity of between about 102 and about 103 ohm-cm.

2. The electrode according to claim 1, wherein each of said conductive patterns are disposed on the conductive flexible member bottom side at a spaced apart distance from a perimeter of said conductive flexible member to establish a border between a perimeter of each of said conductive patterns and the conductive flexible member perimeter for providing controlled roll off of electrical distribution of the electrode.