The present invention generally relates to electrodes and, more particularly, electrodes suitable for transcutaneous nerve and/or muscle stimulation. Nerve and muscle cells are excitable because they are able to discharge action potentials and, accordingly, electrical stimulation of nerve and muscle membranes can evoke such action potential, hi order for an action potential to be evoked, the stimulus intensity and pulse duration must be sufficient to pass a threshold. In this regard, muscle membranes require longer pulse durations due to their higher capacitance.

Thus, in order to meet this threshold, transcutaneous electrodes must not only be properly placed on the skin, but coupled thereto in order to provide sufficient current density to a particular cross-sectional body area. This is a very important factor in controlling the reaction of biological tissue to stimulation. As a rule, the greater the current density, the greater the resulting reaction on the tissue.

Earlier electrodes, such as set forth in U.S. Patent No. 4,736,752, teach the control of current density across an electrode through the use of a conductive ink design area. As hereinabove noted, electrodes must provide an even electrical coupling to a patient's skin over an entire surface of the electrode to effect proper interfacing. 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.

Electrode placement is another factor that influences current density and, accordingly, tissue response. This is due to the fact that the impedance of skin, bone, and adipose tissue vary, and, accordingly, placement of electrodes over these tissues will have significant effect on current flow in the surrounding tissues. In addition, orientation of the electrodes can also significantly affect the response of underlying tissue. For example, muscle tissue is nearly four times more conductive in the longitudinal direction of their fibers than in the transverse direction. 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. Patent No. 5,038,796 entitled, ELECTRICAL STIMULATION ELECTRODE WITH IMPEDANCE COMPENSATION, to Axelgaard. This patent teaches the use of an electrical shunt interconnected with the lead wire for causing more uniform resistance between equally spaced apart points in the electrode. Without tills shunt, 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. These 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. Contact between the lead wire and the metallic mesh, or foil, is typically a point contact. Because of this, electrode contacts to medical electrodes have typically been made on a top side thereof, that is, a side opposite a side of the electrode having a conductive adhesive thereon for application to a patient.

The present invention is directed to an electrode system which features control of current density utilizing multiple electrodes and/or shunt systems. SUMMARY OF THE INVI

A field controlling electrode in accordance with the present invention for providing transcutaneous nerve and/or muscle stimulation generally includes a conductive flexible member having a top side and a bottom side.

An electrically driven master electrode is provided for generating a current distribution in the conductive flexible member and an electrically undriven slave electrode is disposed in a spaced apart relationship with the master electrode for focusing or controlling the generated current distribution.

Preferably, the master electrode is disposed on the conductive flexible member top side and a slave electrode is disposed on the conductive member bottom side. In addition, at least one of the master electrode and slave electrode may be a grid, preferably a conductive ink pattern.

In one embodiment of the present invention, the master and slave electrode have different planar shapes and in yet another embodiment of the present invention, multiple sla ve electrodes are provided. Multiple slave electrodes may be of differing sizes and/or shape.

For both identification of the electrode and obscuring construction of the electrode, an opaque non-conductive sheet may be disposed over the conductive flexible member top side and master electrode thereby enabling visualization only of the slave electrode, or electrodes, including the shape and/or placement thereof.

In addition, in order to further control the current distribution, the slave electrode may include a graded conductive ink pattern with varying line width and distance between lines of the pattern. Further, an electrode shunt in electrical connection wi th both or either of the lead and master electrode may be provided to further enhance and control current distribution generated in the conductive flexible member. BRIEF DESCRIPTION OF THE DRAWINGS

The advantages and features of the present invention will be better understood by the following description when considered in conjunction with the accompanying drawings, in which:

Figure 1 is an exploded cross sectional view of a field controlling electrode in accordance with the present invention generally showing a conductive flexible member with an. electrically driven master electrode disposed on the top side of the flexible member and electrically undriven slave electrod e disposed on a bottom side of the flexible member;

Figure 2 is a plan view of the top side of the field controlling electrode shown in Figure 1 showing the driven master electrode as being formed by a conductive ink pattern;

Figure 3 is a bottom plane view of an electrode in accordance with the present invention i llustrating the use of multiple slave electrodes;

Figure 4 is a view of an electrode similar to that shown in Figure 2 with a different placement of a lead wire;

Figure 5 is a bottom view of an electrode in accordance with the present invention illustrating multiple slave electrodes each having different conductive ink patterns with different planar shapes; Figure 6 is a top view of another embodiment of the present invention illustrating a circular electrically driven master electrode;

Figure 7 illustrates a bottom view of yet another embodiment of the present invention illustrating multiple undriven slave electrodes having varying line widths and distance between lines of an ink pattern of the electrodes;

Figure 8 is a top view of still another embodiment of the present invention illustrating various electrically driven master electrode shapes;

Figure 9 is a ian view of the bottom of an electrode illustrating additional variation and placement of multiple undriven slave electrodes;

Fi gure 10 is a plan view of an electrode top utilizing an opaque non-conductive sheet disposed over a conductive flexible member top side;

Figure 11 is a plan view of an electrode top illustrating transverse placement of a shunt; and Figure 12 is a plan view of an electrode top illustrating longitudinal placement of a shunt.

DETAILED DESCRIPTION With reference to Figure I, there is shown a field controlling electrode 10, in accordance with the present invention which generally includes a conductive flexible member 14 having a top side 16 and a bottom side 18. As shown in Figure 1 , an electrically driven master electrode 22 is disposed on the conductive flexible member for generating a current distribution in the conductive flexible member 14.

An electrically undriven slave electrode 26 is disposed in a spaced apart relationship with the master electrode 22 for focusing or controlling the generated current distribution over an area of a user's body (not shown). In this instance, the undriven slave electrode 26 is disposed on the bottom side 18 of the flexible member 14, The master electrode 22 is connected via a lead 30 to external electrical apparatus (not shown).

A non-conductive flexible sheet 34 is disposed over the conductive flexible member 14 top side 16, master electrode 22, and lead 30 and adhered thereto by an adhesive layer 36,

It should be appreciated that any suitable master electrode 22 or slave electrode 26 may be utilized ; however, preferably each of the master electrode 22 and slave electrode 26 is in the form of a grid, which comprises a conductive ink pattern. Such ink patterns are disclosed in U.S. Patent No. 4.736,752, which is incorporated herewith in its entirety for the purpose of teaching the use of conductive ink design. The conductive flexible member may be formed from carbon and PVC or any other suitable material.

A suitable conductive hydrogel adhesive 40 is utilized for adhering the electrode 10 to a patient's skin (not shown).

A plastic earner 46 along with a silicone coating 44 for easy release may be provided in order to prevent inadvertent and/or premature adhesion to a patient (not shown) or other object to the hydrogel 40 with the carrier 46 being removed prior to application of the electrode 10 to the patient (not shown). With reference to Figures 2 and 3, top and bottom views of the electrode 10 are shown respectively, This embodiment illustrates not only thai the master electrode 22 and slave electrode 26 have different planar shapes, but further multiple slave electrodes 26, in this case three, may be utilized in order to focus or control the generated current distribution in the conductive flexible member 14 by the master electrode 22,

An alternative embodiment electrode 54 is illustrated in Figures 4 and 5 with common reference characters representing identical or similar elements as shown in Figures 1 -3 describing the electrode 10, in this field controlling electrode 54, with the top and bottom side respectively being shown in Figures 4 and 5, two slave electrodes 56, 58 are provided illustrating various arrays of grid patterns suitable for use for providing transcutaneous nerve and/or muscle stimulation to a user's body (not shown),

Another embodiment of a field controlling electrode 62, in accordance with the present invention, is illustrated in Figures 6 and 7, with Figure 6 showing a top side and Figure 7 showing a bottom side with common reference characters hereinabove described in conjunction with the electrodes 10 and 54. in the case of electrode 62, the electrically driven master electrode 66 has a circular shape and three slave electrodes 68, 70, 72 are provided. The electrode 62 illustrates slave electrodes 68, 70, 72 having graded conductive ink patterns with varying line width and distance between lines of the pattern useful for focusing or controlling the generated current distribution in the flexible member 14 and the user's body (not shown) by the electrically driven master electrode 66.

Turning now to Figures 8 and 9, there is shown yet another embodiment of a field controlling electrode 78 showing a .master electrode 82 incorporating various grid designs and a planar shape and, as shown in Figure 9, four slave electrodes 86. 88, 90, 92 with various planar shapes in grid configurations, This electrode 78 may be useful for stimulating the muscles proximal to a user's knee (not shown), With reference to Figure 10, an electrode 96 in accordance with the present invention may include an opaque non-conductive sheet 100 disposed over a conductive flexible member top side and master electrode, not seen in Figure 10 to enable visualization only of a slave electrode (not shown in Figure 10). In this marmer, construction of the electrode is concealed yet the electrode is identifiable by the number and shape of slave electrodes 26, 56,58,68,70, 72, 86, 88, 90, and 92, This visualization enables proper selection of the electrode by the user with the slave electrodes 26, 56, 58, 68, 70, 72, 86, 88, 90, and 92 facilitating proper placement of the electrode 10, 54, 62, 78 on an area (not shown) of a user's body (not shown). As shown in Figures 11 and 12, respectively, electrodes 104 and 108 illustrate the use of an electric shunt 112, 1 14, which may be in electrical communication with both or either of the lead 30, grid 22, and flexible member 14, The common reference numerals in Figures 11 and 12 represent identical or substantially similar elements as hereinabove discussed. Various positions of the shunt of various sizes, or a plurality of shunts (not shown), may be utilized in various positions in order to further control current distribution that is generated in the conductive flexible member 14 by the master electrode 22, Figure 11 represents a transverse placement of a shunt 112 and Figure 12 illustrates a longitudinal placement of a shunt 1 14 with respect to the lead 30. The shunt may be of any suitable type such as a conductive pattern or discrete wires. The fi gures are merely representative of the shunt placement and the invention is not limited thereto. The shunt in combination with the dual-sided electrode provides greater current, distribution than heretofore possible. Although there has been hereinabove described a specific dual-sided 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 disclosed 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.