Abstract:
A stimulation or recording electrode with varying impedances includes a plurality of layers that are compressed together with varying compressions forces, with at least a first compression force used at the perimeter of the electrode and a second compression force used towards the center of the electrode, with the first force being lesser than the second force, thereby creating a greater measured impedance at the perimeter of the electrode than at the center of the electrode.

Description:
CROSS-REFERENCE TO RELATED PATENTS 
     The present U.S. Utility Patent Application claims priority as a continuation-in-part of application Ser. No. 13/020,392 (now U.S. Pat. No. 8,569,935), filed Feb. 3, 2011, which is a continuation-in-part of application Ser. No. 12/835,972, filed Jul. 14, 2010, now abandoned, which is a continuation-in-part of application Ser. No. 12/559,061, filed Sep. 14, 2009, now abandoned, which claims benefit of U.S. Provisional Application Ser. No. 61/347,963, filed May 25, 2010, all of which are incorporated by reference herein and made part of the present U.S. Utility Patent Application for all purposes. 
     This present U.S. Utility Patent Application claims priority to both U.S. Provisional Application Ser. No. 61/788,575, entitled, “SYSTEM AND METHOD FOR A DRY ELASTOMER ELECTRODE,” filed Mar. 15, 2013 and U.S. Provisional Application Ser. No. 61/819,574, entitled, “SYSTEM AND METHOD FOR A DRY ELASTOMER ELECTRODE,” filed May 4, 2013, all of which are incorporated by reference herein and made part of the present U.S. Utility Patent Application for all purposes. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable. 
     INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     Technical Field of the Invention 
     This invention relates generally to medical electrodes, and in particular to a low impedance dry stimulation and recording electrode with at least one layer having an elastomeric surface. 
     Description of Related Art 
     In the medical field, electrodes are utilized to establish electrical contact with the skin of a patient, and are commonly used for the administration of electrical signals to the patient as well as for receiving electrical signals generated in the body of the patient. 
     Contact between the electrode and the skin of the patient is typically made through the use of conductive gels, pastes or creams. The conductive gels, pastes or creams are typically applied directly to the surface of the skin of the patient. As can be appreciated, the use of these conductive products can be problematic, as they may produce bridging artifacts, may cause the electrode displacement, i.e., the electrode may slide away from the desired position, or may even dry out rendering the electrode useless and any recording impossible (pertaining mostly to prolonged intraoperative monitoring). The conductive gels, pastes or creams are messy and often irritate the skin of the patient. Another disadvantage of the conductive gels, pastes and creams is that they leave a residue on the skin of the patient subsequent to the removal of the electrode therefrom, thereby requiring additional cleaning of the patient when finished, thus extending the preparation and testing time. 
     Accordingly, there is a need for systems and methods for providing a dry elastomer electrode that can be utilized in the medical industry without the need for applying conductive gels, pastes or creams to the patient. Dry biocompatible elastomer electrodes are durable, and re-usable. Can be incorporated into fabrics and clothing and can be worn for long periods of time. The rubbery surface of the electrode provides a smooth and uniform contact surface with the skin. Silicon rubber traps moisture (sweat) which helps to reduce the skin-to-electrode impedance, and thereby reduces electrode susceptibility to motion artifacts and noise. On the other hand, traditional wet gel electrodes will not work on the skin of a diaphoretic patient. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1 a    is an exploded side view of an embodiment of a dry elastomer electrode in accordance with the present invention; 
         FIG. 1 b    is an exploded top perspective view of another embodiment of a dry elastomer electrode in accordance with the present invention; 
         FIG. 1 c    is an exploded top perspective view of an embodiment of a dry elastomer electrode as similarly shown in  FIG. 1 a    in accordance with the present invention; 
         FIG. 2  in an exploded top perspective view of another embodiment of a dry elastomer electrode in accordance with the present invention; 
         FIG. 3  is a top view of an embodiment of a dry elastomer electrode in a bar electrode in accordance with the present invention; 
         FIG. 4  is a side view of an embodiment of a dry elastomer electrode in a bar electrode as similarly shown in  FIG. 3  in accordance with the present invention; 
         FIG. 5  is a cross-sectional side view taken along line  5 - 5  of  FIG. 3 ; 
         FIG. 5 a    is an exploded perspective view of the cross-sectional view as similarly shown in  FIG. 5 ; 
         FIG. 5 b    is an exploded perspective view of an embodiment of a dry elastomer electrode in a bar electrode as similarly shown in  FIGS. 3 and 4  in accordance with the present invention; 
         FIG. 6  is a cross-sectional side view taken along line  6 - 6  of  FIG. 3 ; 
         FIG. 7  is a top view of a digital ring electrode with portions enlarged; 
         FIG. 8  is a top view of an another embodiment of a digital ring electrode with a clip; 
         FIG. 8 a    is a perspective view of a digital ring electrode with a clip as similarly shown in  FIG. 8  with the clip in an open position; 
         FIG. 8 b    is a top view of the digital ring electrode a similarly shown in  FIG. 8   a;    
         FIG. 8 c    is a side view of the digital ring electrode as similarly shown in  FIG. 8 ; 
         FIG. 9  is a partial cross-sectional view of an electrode with a disc as a backing layer where the electrode conforms to the convex shape of the disc; and 
         FIG. 10  is a partial cross-sectional view of an electrode with a disc as a backing layer where the electrode conforms to the convex shape of the disc providing uniform contact with the skin. 
         FIG. 11  illustrates a graph of skin to electrode impedance for an embodiment of a Hydrogel Electrode. 
         FIG. 12  illustrates a graph of skin to electrode impedance for another embodiment of a Hydrogel Electrode. 
         FIG. 13  illustrates a graph of skin to electrode impedance for an embodiment of an Ag/AgCl Electrode. 
         FIG. 14  illustrates a graph of skin to electrode impedance of another embodiment of a Hydrogel Electrode. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the figures, wherein various elements depicted therein are not necessarily drawn to scale and wherein, through various views and figures, like elements may be referenced with identical reference numerals, there are illustrated embodiments of a dry elastomer electrode according to the principles of the present invention. 
       FIGS. 1 a - c    and  FIG. 2  illustrate embodiments of a dry elastomer electrode. The electrodes  1400  ( FIGS. 1 a  and 1 c   ),  1600  ( FIG. 1 b   ), and  1800  ( FIG. 2 ) may be a transcutaneous medical electrode for stimulating nerves and/or muscles by generating electricity that could be used in different parts of the body. The electrodes  1400 ,  1600 , and  1800  may be employed for other uses as well. In an embodiment, the electrodes  1400 ,  1600 , and  1800  include a substantially dry body comfortable, biocompatible, electrically conductive interfacing layer of a metal-integral conductive silicon rubber sheet. The dry elastomer electrodes  1400 ,  1600 , and  1800  are employed for similar uses as adhesive electrodes or gel electrodes or where such electrodes may not be appropriate or desirable. For example, the electrodes  1400 ,  1600 , and  1800  may replace an adhesive electrode, e.g. where allergic reaction may be possible. 
       FIGS. 1 a  and 1 c    illustrate the electrode  1400  which includes in an embodiment at least an upper/first sheet  1401  of metal integral conductive silicon rubber (or elastomer) which, by way of example and not limitation, may be a gold, silver, silver plated copper, or other conductive metal plated material filled silicon. Electrode  1400  further includes a second layer  1403  which may be a conductive adhesive gel layer to adhere to the first sheet  1403 , a third sheet  1405  of a conductive carbon film to adhere to the second layer  1403 , and a fourth sheet  1407  which may be a conductive metal sheet and the metal may be silver or other appropriate metals. An electrical lead  1409  is positioned and secured between the fourth sheet  1407  and the fifth sheet  1411 . The electrical lead  1409  facilitates the delivery of energy to the electrode  1400  from a power source (not shown). Fifth sheet  1411  may be a dielectric/non-conducting flexible backing sheet. 
       FIG. 1 b    illustrates the electrode  1600  which includes two layers  1401  and  1411 . Electrode  1600  includes an upper/first sheet  1401  of metal integral conductive silicon rubber (or elastomer) which, by way of example and not limitation, may be a gold, silver, silver plated copper, or other conductive metal plated material filled silicon. Electrode  1600  further includes an electrical lead  1409  which is positioned and secured between the first sheet  1401  and the bottom sheet  1411 . The electrical lead  1409  facilitates the delivery of energy to the electrode  1600  from a power/recording source (not shown). The bottom sheet  1411  may be a dielectric/non-conducting flexible backing sheet. 
       FIG. 2  illustrates another embodiment of an electrode  1800  which includes four layers  1401 ,  1403 ,  1417  and  1411 . The first or top layer  1401  is the interfacing layer and is a silver filled silicone rubber (or elastomer) skin interface. The second layer  1403  is a conductive adhesive layer is positioned in-between first layer  1401  and third layer  1417 . The third layer  1417  is an Ag/AgCl film and is positioned between second layer  1403  and fourth layer  1411 . The fourth layer  1411  is a dielectric backing layer and is positioned below third layer  1417 . An electrical lead  1409  is positioned and secured between the third layer  1417  and the fourth layer  1411 . The electrical lead  1409  facilitates the delivery of energy to the electrode  1800  from a power/recording source (not shown). 
     Though the interfacing or upper layer is described as including the metal integral conductive silicon rubber (or elastomer), other layers may also include the elastomer covering, e.g. conductive inks, or other materials which may facilitate the prevention of corrosion. In addition, one or more other interfacing or upper layers may be added on top of the metal integral conductive silicon rubber (or elastomer) for interfacing with the skin. In another embodiment a plurality of metal integral conductive silicon rubber (or elastomer) layers may be used. 
     The elastomer is preferably a conductive material with low volume resistivity, such as silicone rubber. 
     In an embodiment, a dry and flexible electrode is prepared by stacking the desired layers as described herein and pressing them. For the interfacing or top layer  1401 , an electrically conductive silicone elastomer containing silver fillers is utilized. Then a pressure is applied to the electrode. The amount of pressure applied to the electrode layers depends upon the desired operating parameters for the electrode for a particular user. 
       FIG. 11  illustrates a graph of skin to electrode impedance for an embodiment of a Hydrogel Electrode.  FIG. 12  illustrates a graph of skin to electrode impedance for another embodiment of a Hydrogel Electrode.  FIG. 13  illustrates a graph of skin to electrode impedance for an embodiment of an Ag/AgCl Electrode.  FIG. 14  illustrates a graph of skin to electrode impedance of another embodiment of a Hydrogel Electrode. For example, in an embodiment, the pressure was approximately 429 PSI for a 5 cm (diameter) electrode and as high as approximately 2684 PSI for a 2 cm electrode and at approximately 11914 PSI for a 1 cm electrode though other pressures may facilitate optimal operation as well, as evidenced by the reduced electrode-skin impedance values. In an embodiment, lower electrode-skin impedance values were found as shown in  FIGS. 11-14 .  FIGS. 11-14  illustrate how compression after laminating changes impedance of elastomer electrodes. 
     As seen in  FIGS. 11-14 , different values of impedance are observed, with pressure applied to an electrode, at different frequency ranges. In an embodiment, the pressure applied to an electrode is adjusted during manufacture to try to achieve a certain impedance for a desired frequency range. For example, as shown in  FIG. 14 , a 5 cm elastomer-hydrogel electrode with pressure applied has a lower impedance than similar hydrogel electrode, only at lower frequencies, and a much lower impedance than elastomer-hydrogel electrode that has been laminated but not pressed, across the entire frequency range. Similarly, as shown in  FIG. 11 , for a 1 cm elastomer-hydrogel electrode operating at a lower frequency range, more pressure may be applied during manufacture to the elastomer-hydrogel electrode to obtain a lower impedance value for that frequency range while less pressure is applied to a lcm elastomer-hydrogel electrode that is operating in a higher frequency range. Thus, pressure applied during manufacturing of an electrode is adjusted to attempt to optimize performance of the electrode at a required or desired frequency value. 
     In an embodiment, to mitigate the “edge effect” and to provide even current density distribution across the electrode, a given electrode is pressed concentrically, where increasingly higher force is applied from the periphery toward the center of the electrode, and thus creating a “segmented impedance” electrode or a varying impedance electrode with the higher impedance at the periphery of the electrode and the lowest resistance in the center of the electrode. For example with an electrode having at least 2.5 cm radius, the following could be utilized to create a “segmented impedance” electrode: 
     i. 2.5 cm radius is pressed with 500 PSI, then 
     ii. 2.0 cm radius is pressed with 2000 PSI, then 
     iii. 1.5 cm radius is pressed with 4000 PSI, then 
     iv. 1.0 cm radius is pressed with 8000 PSI, then 
     v. 0.5 cm radius is pressed with 12000 PSI. 
     Other radii and/or pressures applied to the electrode may be implemented in addition to or alternatively to those shown above. In an embodiment, the electrode has the physical structure of the electrode described herein. In another embodiment, the concentrically applied pressure may be used with an electrode having similar or other physical structures and shapes as well. 
     Although illustrated hereinabove in the various embodiments as circular shaped electrodes, it is contemplated that the present invention is not limited to circular shaped electrodes, rather the electrodes of the present invention could be of virtually any shape and size with the applied pressure varying from the outer most perimeter to the middle portions so as to provide a selected performance for a particular user. 
       FIGS. 3-10  illustrate various embodiments of form factors for use of the multilayered dry elastomer electrode as described herein above with respect to  FIGS. 1 a , 1 b , 1 c   , and  2 . Although  FIGS. 3-10  are illustrated with a single embodiment of the electrode, it is contemplated that any of the electrode embodiments described herein could be utilized and be within the scope of this invention. It is further contemplated to be within the scope of this invention that other form factors and embodiments may also employ the multilayered dry elastomer electrode. 
     Referring now to  FIGS. 3-6 , there is illustrated an embodiment of a bipolar stimulator bar electrode  3000  utilizing multilayered dry elastomer electrodes described hereinabove. Typically bar electrodes are attachable to a stimulator device or electromyographic (EMG) device (not shown) and are utilized for skin or surface stimulation of peripheral nerves. It can be configured with to perform both as a stimulation electrode and a recording electrode, to record nerve and muscle action potentials and to provide electrical stimulation. 
     Bar electrode  3000  includes an elongated body  3010  having a top  3012  and a bottom  3014 . Two cylindrical shape posts  3016  having convex upper surfaces extend up from bottom  3014 . Each of posts  3016  have a slot  3018  extending there-across. An electrode, such as described herein above,  1800   a  and  1800   b  are placed across the top surfaces of posts  3016  and are positioned between top  3012  and bottom  3014 . Electrodes  1800   a  and  1800   b  conform to the convex shape of the top surfaces of posts  3016 . Holes in top  3012  that are positioned in alignment of posts  3016  in top  3012  permit at least a portion of the electrodes  1800   a  and  1800   b  to extend above top  3012  (see  FIGS. 4 and 5 ). 
     The slots  3018  of each of the posts  3016  are configured in shape to receive the leads  1409   a  and  1409   b  of electrodes  1800   a  and  1800   b , respectively. This facilitates the leads  1409  to extend from the bar electrode and ultimately be connected to the stimulator device (not shown). 
     Referring now to  FIGS. 7-8   c , there are illustrated examples of digital ring electrodes employing multilayered dry elastomer electrodes in accordance with the principles of the present invention as described herein. It is contemplated that the embodiments of the digital ring electrodes illustrated in  FIGS. 7-8   c  may be the same with the exception that the embodiment disclosed in  FIG. 8  may employ a clip or cord lock as discussed in more detail herein below. As can be appreciated, digital ring electrodes are often used for sensory nerve stimulation or recording from the fingers and toes of patients. 
     Referring now to  FIG. 7 , there is illustrated an embodiment of noose type digital ring electrodes  7000 . The ring electrode portion  7800  is a multilayered dry elastomer electrode as similarly described herein, with the inner most layer  1401  being silver filled silicone rubber. The next layer  1403  is a conductive adhesive layer, while the third layer  1417  is an Ag/AgCl film, while the outer layer  1411  is a dielectric backing layer. Layer  1401  has a gap or plurality of gaps preventing delaminating while adjusting either the radius or diameter to the given size. 
     Referring now to  FIGS. 8, 8   a ,  8   b  and  8   c , there is illustrated another embodiment of another digital ring electrode  8000 . The ring electrode portion  8800  is a multilayered dry elastomer electrode as described in the various electrode embodiments herein. Digital ring electrode  8000  includes a clip  8010  (or cord lock—not shown) which facilitates the adjustment of the size of the electrode portion  8800 . When in the clip  8010  (or cord lock—not shown) is in the open position ( FIGS. 8 a  and 8 b   ), the inner diameter of the electrode  8800  can be adjusted to facilitate the placement of the electrode  8800  onto a finger or toe of a patient and then adjusted to the proper size to secure the electrode  8800  in place. When clip  8010  (or cord lock—not shown) is in the closed position ( FIG. 8 ), the size of the inner diameter of the electrode  8800  cannot be adjusted, thereby keeping the electrode  8800  in place the testing of the patient. 
     Referring now to  FIGS. 9 and 10 , there is illustrated an embodiment of disc electrode  9000  employing multilayered electrodes in accordance with the principles of the present invention as described herein, such as, but not limited to electrode  1400 ,  1600 , and  1800 . As illustrated disc electrode  9000  includes a disc  9002  having a convex outer surface  9004 , a cylindrical wall  9012  and a flange  9010 . An electrode  1800  is attached to the convex surface  9004  of disc  9002  for placement providing uniform contact against the patient&#39;s skin  9080 . An adhesive  9020  can be utilized to secure the disc electrode  9000  to the patient during use. 
     The specification has described, at least in part, one or more embodiments. The one or more embodiments described are used herein to illustrate the present invention, an aspect thereof, a feature thereof, a concept thereof, and/or an example thereof. A physical embodiment of an apparatus, an article of manufacture, a machine, and/or of a process that embodies the present invention may include one or more of the aspects, features, concepts, examples, etc. described with reference to one or more of the embodiments discussed herein. Further, from figure to figure, the embodiments may incorporate the same or similarly named functions, steps, modules, etc. that may use the same or different reference numbers and, as such, the functions, steps, modules, etc. may be the same or similar functions, steps, modules, etc. or different ones. 
     While particular combinations of various functions and features of the present invention have been expressly described herein, other combinations of these features and functions are likewise possible. The present invention is not limited by the particular examples disclosed herein and expressly incorporates these other combinations.