ELECTRODE ARRANGEMENT
United States Patent 3841312
This is an electrode arrangement particularly useful in providing a reliable electrical contact to be made to the skin of a person or animal in order to permit, for example, an electroencephalogram or electrocardiogram reading to be made by means of an EEG or ECG system connected to the electrode arrangement. The electrode arrangement utilizes an elongated post and an apertured ring having a plurality of tabs for making a strong mechanical attachment to the post. Also disclosed is a combined electrode arrangement and adhesive pad assembly. A feature of this combination is the use of the electrode arrangement described above in combination with the use of a pair of electrically conductive irregular shaped gel pads with the gel pads being located on opposite sides of the flange associated with the post of the electrode arrangement. The gel pad configuration provides a short electrical contact path to be created between the skin of the animal or person that is being monitored and the electrode post.
US Patent References:
Therapeutic appliance
Sullivan - December 1936 - 2065295
Electric applicator
Dobes - March 1953 - 2632447
Rectifier stack
Vanderhoof - September 1953 - 2652522
Body electrode
Berman - April 1963 - 3085577
Nonlatching resilient fastening arrangement
Wiley - November 1964 - 3155808
Therapeutic appliance
Sullivan - December 1936 - 2065295
Electric applicator
Dobes - March 1953 - 2632447
Rectifier stack
Vanderhoof - September 1953 - 2652522
Body electrode
Berman - April 1963 - 3085577
Nonlatching resilient fastening arrangement
Wiley - November 1964 - 3155808
Application Number:
05/346154
Publication Date:
10/15/1974
Filing Date:
03/29/1973
View Patent Images:
Export Citation:
Assignee:
Consolidated Medical Equipment Inc. (Utica, NY)
Primary Class:
Other Classes:
600/394, 600/397
International Classes:
A61B5/0408; A61B5/0416; A61B5/04
Field of Search:
128/2.6E,2.1E,DIG.4,416-418,404,410-411 339/258A,257,214,95S,11,253R
US Patent References:
Primary Examiner:
Gaudet, Richard A.
Assistant Examiner:
Cohen, Lee S.
Attorney, Agent or Firm:
Larson, Taylor And Hinds
Claims:
I claim
1. An electrode arrangement for use as a probe for sensing heart beats comprising, in combination, an electrode including a generally circular base flange and a solid integral upstanding central post, said base flange and solid integral upstanding central post being coated with conductive silver, gel pad means covering the bottom surface of the base flange and extending outwardly beyond the outer periphery of said flange, an adhesive pad having a central aperture receiving said central post, said adhesive pad being disposed adjacent the upper surface of said base flange, and retainer means having a central aperture receiving said central post and retaining said adhesive pad on said electrode below said retainer means and above said base flange, said gel pad being maintained in contact with the base flange of said electrode by adherence between the outer peripheral portions of the gel pad and the adhesive pad, the adhesive pad extending peripherally outwardly beyond the gel pad for adherence with the skin of a patient, the upper end of said central post being electrically exposed on the upper end portion thereof above said retainer means so as to be adapted to be directly connected with the electrode connector of an EEG or ECG system.
2. An electrode arrangement according to claim 1 wherein said retainer means includes a plurality of tabs extending inwardly towards said central aperture.
3. An electrode arrangement according to claim 1 wherein said retainer means includes four tabs spaced 90° apart in a circular configuration, said tabs being angularly displaced with respect to the plane of said retainer means by said central post.
4. An electrode arrangement according to claim 1 wherein said central post includes a knob shaped portion on the upper end to provide means for connecting said central post with an electrode connector of an EEG or ECG system.
5. An electrode arrangement according to claim 1 wherein said circular base flange and said solid integral upstanding central post are made of a material forming a base for an adherent silver encapsulating coating whereby said silver coating provides electrical connection with said gel pad and with an electrode connector of an EEG or ECG system.
1. An electrode arrangement for use as a probe for sensing heart beats comprising, in combination, an electrode including a generally circular base flange and a solid integral upstanding central post, said base flange and solid integral upstanding central post being coated with conductive silver, gel pad means covering the bottom surface of the base flange and extending outwardly beyond the outer periphery of said flange, an adhesive pad having a central aperture receiving said central post, said adhesive pad being disposed adjacent the upper surface of said base flange, and retainer means having a central aperture receiving said central post and retaining said adhesive pad on said electrode below said retainer means and above said base flange, said gel pad being maintained in contact with the base flange of said electrode by adherence between the outer peripheral portions of the gel pad and the adhesive pad, the adhesive pad extending peripherally outwardly beyond the gel pad for adherence with the skin of a patient, the upper end of said central post being electrically exposed on the upper end portion thereof above said retainer means so as to be adapted to be directly connected with the electrode connector of an EEG or ECG system.
2. An electrode arrangement according to claim 1 wherein said retainer means includes a plurality of tabs extending inwardly towards said central aperture.
3. An electrode arrangement according to claim 1 wherein said retainer means includes four tabs spaced 90° apart in a circular configuration, said tabs being angularly displaced with respect to the plane of said retainer means by said central post.
4. An electrode arrangement according to claim 1 wherein said central post includes a knob shaped portion on the upper end to provide means for connecting said central post with an electrode connector of an EEG or ECG system.
5. An electrode arrangement according to claim 1 wherein said circular base flange and said solid integral upstanding central post are made of a material forming a base for an adherent silver encapsulating coating whereby said silver coating provides electrical connection with said gel pad and with an electrode connector of an EEG or ECG system.
Description:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to the field of electrode arrangements and, more particularly, relates to the field of electrode arrangements useful for EEG and ECG systems.
2. Description of the Prior Art
In the past, various electrode arrangements were developed for use with electrocardiogram systems in order to permit electrocardiograms to be made that are sensitive to the heart beat of a person or animal.
One of these prior art electrode arrangements utilized a two piece "post" and "stud" arrangement. The stud was the male, and the post was the female portion of the electrode which fitted over the stud and provided electrical contact between the post and the stud due to the physical metal contact between the metal post and the metal stud. A number of disadvantages were associated with this prior art type of electrode arrangement. For example, one disadvantage was that the stud, which had a flange portion to provide a means for making electrical contact to the skin of a person or animal would not always make good electrical contact to the post due to the location or trapping of dielectric material between the post and stud which frequently occured because the post and stud were mechanically and electrically connected together after the stud was forced through a dielectric adhesive pad.
Another disadvantage associated with the stud of the prior art is that it was generally difficult to uniformly electroplate this element with silver because it utilized a hollow stud member which was less expensive to manufacture. However, the inner portion of the hollow stud member could not be easily silverplated which resulted in it being a source of contamination for the electrode gel material that found its way into the hollow portion of the stud. Additionally, the post and the stud arrangement of the prior art electrode device utilized in EEG or ECG systems frequently came apart in an electrical sense and did not maintain a good stable electrical contact due to the failure to hold a good electrical contact fit between the post and stud.
A need existed for a reliable, low cost, disposable electrode arrangement that could be utilized for EEG and ECG systems which would consistently provide a good electrical contact to the skin of the person or animal being tested, and which would maintain this good electrical contact despite natural or accidental movements in areas around the electrode arrangement when attached to the person or animal being tested.
A need also existed for providing a combined electrode arrangement and adhesive pad assembly which could both provide a reliable electrical contact to the skin of the person or animal being tested and a low resistance, short electrical path between the skin and the electrode arrangement.
SUMMARY OF INVENTION
An objective of this invention is to provide an improved electrode arrangement.
It is another object of this invention to provide an improved electrode arrangement for use in making contact to the skin of a person or animal.
It is a still further object of this invention to provide a combination electrode arrangement and adhesive pad assembly for use in insuring good, low resistance electrical contact to be made to the skin of a person or animal being tested.
BRIEF DESCRIPTION OF THE FIGURES
FIG. 1 is an exploded elevational view in cross section of the post and stud electrode arrangement of the prior art with the post and stud separated from each other prior to assembly of the post onto the stud.
FIG. 2 is a view similar to FIG. 1 with the post and stud connected together to provide complete electrode arrangement.
FIG. 3 is a sectional view in elevation showing the one piece stud and an apertured ring in mechanical contact with the stud in a manner which permits the one piece stud to provide direct electrical connection to an electrode associated with the electrical system EEG or ECG connected to the electrode arrangement.
FIG. 4 is a top view showing the metal ring of FIG. 3.
FIG. 5 is a side elevational view in cross section showing the raised or angularly displaced tabs of the metal ring of FIG. 4.
FIG. 6 is a cross section view, in elevation, showing a gel pad mounted on the stud of FIG. 3.
FIG. 7 is a view similar to FIG. 6 showing the stud and gel pad after the stud has been inserted through an opening in an adhesive pad that is applied to the skin of the person or animal being tested.
FIG. 8 is a view similar to FIG. 7 showing the apertured metal ring in place over the stud and serving the function of holding together, between the flange of the stud and the metal ring, the gel pad and the adhesive pad.
FIG. 9 is a view similar to FIG. 8 showing a second gel pad placed over the flange portion of the stud and in electrical contact with the gel pad located on the other side of the flange portion of the stud.
FIG. 10 is a bottom view of the complete assembly of FIG. 9 showing the adhesive pad, both gel pads, and the flange of the stud (shown in dotted form).
Referring to the Prior Art electrode arrangement of FIG. 1, a stud 20 is shown having a flange 22 and an extension member 24 having a hollow inner portion 26. Post 28 contains a flange 30 and a hollow, door knob shaped element 32 which serves to provide both mechanical and electrical contact to the electrode connector associated with an EEG or ECG electronic system.
Referring to FIG. 2, the stud 20 and post 28 are shown mechanically and electrically connected together in order to provide electrical contact between the outer portion of the extension member 24 of the stud 20 and the inner portion of the hollow, door knob shaped element 32 of the post 28. Dielectric material caught between the stud 20 and and the post 28 prevented a good reliable electrical contact to be made between these two elements.
FIG. 3 is an elevational view, in section, showing the electrode arrangement of this invention wherein a single, solid, unitary stud 34 is shown having a flat flange 36 and a solid elongated extension member 38 which together with the flange 36 are formed as a one piece element. A door knob shaped portion 40 associated with the extension member 38 of the stud 34 is used for the purpose of providing a good electrical contact to the connecting electrode of the EEG or ECG system similar in function as the door knob shaped portion of the post of the prior art electrode arrangement of FIGS. 1 and 2. An apertured metal ring 42 is shown in mechanical contact with the elongated extension member 38 of the stud 34.
With reference to the apertured metal ring 42, FIG. 4 is a top view showing the metal ring 42 without the stud 34. As can be seen from FIG. 4, the metal ring 42 contains an aperture configured in a manner which provides for metal tabs 44. Any number of tabs can be used, however, in the arrangement of FIG. 4, four metal tabs spaced 90° apart from each other has been found to be ideally suited to providing a good metal fastening attachment to be made between the apertured metal ring 42 and the stud 34. While a metal ring 42 is preferred, other materials can be used to form the apertured ring 42.
Referring to FIG. 5, the metal ring 42 is shown in cross section from the side to emphasize the angular displacement of the metal tabs 44 from the plane of the ring 42. The angle displacement of the metal tabs 44 is to provide essentially a spring loaded connection between the elongated member 38 of the stud 34 and the metal ring 42 in order to prevent the metal ring 42 from becoming accidentally disengaged or removed from the stud due to forces exerted on the metal ring 42 or the stud 34. Particularly useful to maintain the ring 42 on the stud 34 is the flat edged contact portions of the metal tabs 44 which dig in and securely grip the stud 34 to prevent accidental disengagement between the stud 34 and the ring 42.
FIG. 6 is a view showing the first step in the process of assembling the electrode arrangement of the invention onto an adhesive pad which is to be attached to the skin of a person or animal being tested or monitored with an EEG or ECG system. In FIG. 6 through FIG. 10, the same reference numerals used in FIG. 3 and FIG. 4 are repeated in order to maintain clarification of the description of the invention. With reference to FIG. 6, an electrically conductive gel pad 46 is mounted on the flange 36 of the stud 34. The extension member 38 is pushed preferably through the central portion of the gel pad 46 to provide the arrangement shown in FIG. 6. The gel pad 46 is made of material that is commonly known in the industry as containing an electrically conductive solution so that the pad performs the function of providing a good, low resistance, electrical contact to be made to the flange 36 of the stud 34.
Referring to FIG. 7, this figure shows the assembly after the extension member 38 of the stud 34 has been inserted through opening 47 in an adhesive pad 48. The adhesive pad 48 is used to provide a good adhesive contact of the electrode arrangement of this invention to the skin of a person or animal being tested. The adhesive pad 48 has a strongly adherent coating located on the bottom portion 49 which is the surface portion of the pad 48 that contacts the skin of the person or animal.
Referring to FIG. 8, this figure illustrates the electrode arrangement containing the apertured metal ring 42 with its metal tabs 44 shown in contact with the elongated extension member 38 of the stud 34 in combination with the adhesive pad 48 and the gel pad 46. Accordingly, the apertured metal ring 42 provides a very firm and strong mechanical connection to the elongated extension member 38 of the stud 34, thereby holding securely in place the adhesive pad 48 and the electrically conductive gel pad 46 between the flange of the apertured metal ring 42 and the flange 36 of the stud 34.
Referring to FIG. 9, this is a view similar to that of FIG. 8 with the addition of a second gel pad 50 shown covering the exposed flat, bottom surface portion of the flange 36 of the stud 34. As can be seen with reference to FIG. 9, the electrically conductive gel pad 50 is in electrical contact with the bottom surface portion of the flange 36 and is also in electrical contact with the electrically conductive gel pad 46 located on the other side of the flange 36 of the stud 34. Thus, in the event of movement of the person or animal being tested with the electrode arrangements of this invention, the flange 36 may move directly out of contact with the gel pad 50. However, electrical contact is continuously made to the flange 36 by means of the electrical contact between the gel pad 50 and the gel pad 46 in the circular overlapping region located around the outer portion of the flange 36 of the stud 34.
With reference to FIG. 10, the gel pads 50 and 46 are shown to contain four arms (a four star configuration) with each of the arms of gel pad 50 being located out of phase (interleaved) with the arms of gel pad 46. A dotted circle 52 defines the outer portion of the flange 36 of the stud 34 which is located behind the gel pad 50 and between the gel pad 50 and the gel pad 46. The use of the interleaved or out of phase arrangement shown in FIG. 10 for the gel pads 50 and 46 provides an excellent low resistance contact path to be made between the skin of the person or animal being tested or probed with the electrode arrangement of this invention. Regardless of whether the flange 36 of the stud 34 retreats or moves away from the gel pad 50, the gel pad 50 can still provide electrical contact between the skin of the person or animal being tested because of electrical contact to the gel pad 46.
In this manner, since the overlap or contact regions between the gel pads 46 and 50 are much closer to the flange 36 of the stud 34, the skin of the person or animal being tested is closer to the probe or electrode flange position of the stud 34. This is due to the non-circular configurations of the pads 46 and 50 which permits the skin to be positioned closer to the center of the pads 46 and 50 than could otherwise be achieved by using circular pads which would not provide the recess portion provided by the areas that are not overlapped between the gel pads 46 and 50. These star shaped gel pads assure a short low resistance, electrically conductive path to be made from the skin to the electrode stud. Preferably, the stud 34 is made of a brass material such as one containing nickel like a product of Anaconda called Nickel Silver. It has been found that this material provides a good base for a silver plating operation and is also very resistant to erosion.
Although the invention has been described with reference to a particular embodiment, it is to be understood that this embodiment is merely illustrative of the application of the principles of the invention. Numerous modifications may be made therein and other arrangements may be devised without departing from the spirit and scope of the invention.
1. Field of the Invention
This invention relates generally to the field of electrode arrangements and, more particularly, relates to the field of electrode arrangements useful for EEG and ECG systems.
2. Description of the Prior Art
In the past, various electrode arrangements were developed for use with electrocardiogram systems in order to permit electrocardiograms to be made that are sensitive to the heart beat of a person or animal.
One of these prior art electrode arrangements utilized a two piece "post" and "stud" arrangement. The stud was the male, and the post was the female portion of the electrode which fitted over the stud and provided electrical contact between the post and the stud due to the physical metal contact between the metal post and the metal stud. A number of disadvantages were associated with this prior art type of electrode arrangement. For example, one disadvantage was that the stud, which had a flange portion to provide a means for making electrical contact to the skin of a person or animal would not always make good electrical contact to the post due to the location or trapping of dielectric material between the post and stud which frequently occured because the post and stud were mechanically and electrically connected together after the stud was forced through a dielectric adhesive pad.
Another disadvantage associated with the stud of the prior art is that it was generally difficult to uniformly electroplate this element with silver because it utilized a hollow stud member which was less expensive to manufacture. However, the inner portion of the hollow stud member could not be easily silverplated which resulted in it being a source of contamination for the electrode gel material that found its way into the hollow portion of the stud. Additionally, the post and the stud arrangement of the prior art electrode device utilized in EEG or ECG systems frequently came apart in an electrical sense and did not maintain a good stable electrical contact due to the failure to hold a good electrical contact fit between the post and stud.
A need existed for a reliable, low cost, disposable electrode arrangement that could be utilized for EEG and ECG systems which would consistently provide a good electrical contact to the skin of the person or animal being tested, and which would maintain this good electrical contact despite natural or accidental movements in areas around the electrode arrangement when attached to the person or animal being tested.
A need also existed for providing a combined electrode arrangement and adhesive pad assembly which could both provide a reliable electrical contact to the skin of the person or animal being tested and a low resistance, short electrical path between the skin and the electrode arrangement.
SUMMARY OF INVENTION
An objective of this invention is to provide an improved electrode arrangement.
It is another object of this invention to provide an improved electrode arrangement for use in making contact to the skin of a person or animal.
It is a still further object of this invention to provide a combination electrode arrangement and adhesive pad assembly for use in insuring good, low resistance electrical contact to be made to the skin of a person or animal being tested.
BRIEF DESCRIPTION OF THE FIGURES
FIG. 1 is an exploded elevational view in cross section of the post and stud electrode arrangement of the prior art with the post and stud separated from each other prior to assembly of the post onto the stud.
FIG. 2 is a view similar to FIG. 1 with the post and stud connected together to provide complete electrode arrangement.
FIG. 3 is a sectional view in elevation showing the one piece stud and an apertured ring in mechanical contact with the stud in a manner which permits the one piece stud to provide direct electrical connection to an electrode associated with the electrical system EEG or ECG connected to the electrode arrangement.
FIG. 4 is a top view showing the metal ring of FIG. 3.
FIG. 5 is a side elevational view in cross section showing the raised or angularly displaced tabs of the metal ring of FIG. 4.
FIG. 6 is a cross section view, in elevation, showing a gel pad mounted on the stud of FIG. 3.
FIG. 7 is a view similar to FIG. 6 showing the stud and gel pad after the stud has been inserted through an opening in an adhesive pad that is applied to the skin of the person or animal being tested.
FIG. 8 is a view similar to FIG. 7 showing the apertured metal ring in place over the stud and serving the function of holding together, between the flange of the stud and the metal ring, the gel pad and the adhesive pad.
FIG. 9 is a view similar to FIG. 8 showing a second gel pad placed over the flange portion of the stud and in electrical contact with the gel pad located on the other side of the flange portion of the stud.
FIG. 10 is a bottom view of the complete assembly of FIG. 9 showing the adhesive pad, both gel pads, and the flange of the stud (shown in dotted form).
Referring to the Prior Art electrode arrangement of FIG. 1, a stud 20 is shown having a flange 22 and an extension member 24 having a hollow inner portion 26. Post 28 contains a flange 30 and a hollow, door knob shaped element 32 which serves to provide both mechanical and electrical contact to the electrode connector associated with an EEG or ECG electronic system.
Referring to FIG. 2, the stud 20 and post 28 are shown mechanically and electrically connected together in order to provide electrical contact between the outer portion of the extension member 24 of the stud 20 and the inner portion of the hollow, door knob shaped element 32 of the post 28. Dielectric material caught between the stud 20 and and the post 28 prevented a good reliable electrical contact to be made between these two elements.
FIG. 3 is an elevational view, in section, showing the electrode arrangement of this invention wherein a single, solid, unitary stud 34 is shown having a flat flange 36 and a solid elongated extension member 38 which together with the flange 36 are formed as a one piece element. A door knob shaped portion 40 associated with the extension member 38 of the stud 34 is used for the purpose of providing a good electrical contact to the connecting electrode of the EEG or ECG system similar in function as the door knob shaped portion of the post of the prior art electrode arrangement of FIGS. 1 and 2. An apertured metal ring 42 is shown in mechanical contact with the elongated extension member 38 of the stud 34.
With reference to the apertured metal ring 42, FIG. 4 is a top view showing the metal ring 42 without the stud 34. As can be seen from FIG. 4, the metal ring 42 contains an aperture configured in a manner which provides for metal tabs 44. Any number of tabs can be used, however, in the arrangement of FIG. 4, four metal tabs spaced 90° apart from each other has been found to be ideally suited to providing a good metal fastening attachment to be made between the apertured metal ring 42 and the stud 34. While a metal ring 42 is preferred, other materials can be used to form the apertured ring 42.
Referring to FIG. 5, the metal ring 42 is shown in cross section from the side to emphasize the angular displacement of the metal tabs 44 from the plane of the ring 42. The angle displacement of the metal tabs 44 is to provide essentially a spring loaded connection between the elongated member 38 of the stud 34 and the metal ring 42 in order to prevent the metal ring 42 from becoming accidentally disengaged or removed from the stud due to forces exerted on the metal ring 42 or the stud 34. Particularly useful to maintain the ring 42 on the stud 34 is the flat edged contact portions of the metal tabs 44 which dig in and securely grip the stud 34 to prevent accidental disengagement between the stud 34 and the ring 42.
FIG. 6 is a view showing the first step in the process of assembling the electrode arrangement of the invention onto an adhesive pad which is to be attached to the skin of a person or animal being tested or monitored with an EEG or ECG system. In FIG. 6 through FIG. 10, the same reference numerals used in FIG. 3 and FIG. 4 are repeated in order to maintain clarification of the description of the invention. With reference to FIG. 6, an electrically conductive gel pad 46 is mounted on the flange 36 of the stud 34. The extension member 38 is pushed preferably through the central portion of the gel pad 46 to provide the arrangement shown in FIG. 6. The gel pad 46 is made of material that is commonly known in the industry as containing an electrically conductive solution so that the pad performs the function of providing a good, low resistance, electrical contact to be made to the flange 36 of the stud 34.
Referring to FIG. 7, this figure shows the assembly after the extension member 38 of the stud 34 has been inserted through opening 47 in an adhesive pad 48. The adhesive pad 48 is used to provide a good adhesive contact of the electrode arrangement of this invention to the skin of a person or animal being tested. The adhesive pad 48 has a strongly adherent coating located on the bottom portion 49 which is the surface portion of the pad 48 that contacts the skin of the person or animal.
Referring to FIG. 8, this figure illustrates the electrode arrangement containing the apertured metal ring 42 with its metal tabs 44 shown in contact with the elongated extension member 38 of the stud 34 in combination with the adhesive pad 48 and the gel pad 46. Accordingly, the apertured metal ring 42 provides a very firm and strong mechanical connection to the elongated extension member 38 of the stud 34, thereby holding securely in place the adhesive pad 48 and the electrically conductive gel pad 46 between the flange of the apertured metal ring 42 and the flange 36 of the stud 34.
Referring to FIG. 9, this is a view similar to that of FIG. 8 with the addition of a second gel pad 50 shown covering the exposed flat, bottom surface portion of the flange 36 of the stud 34. As can be seen with reference to FIG. 9, the electrically conductive gel pad 50 is in electrical contact with the bottom surface portion of the flange 36 and is also in electrical contact with the electrically conductive gel pad 46 located on the other side of the flange 36 of the stud 34. Thus, in the event of movement of the person or animal being tested with the electrode arrangements of this invention, the flange 36 may move directly out of contact with the gel pad 50. However, electrical contact is continuously made to the flange 36 by means of the electrical contact between the gel pad 50 and the gel pad 46 in the circular overlapping region located around the outer portion of the flange 36 of the stud 34.
With reference to FIG. 10, the gel pads 50 and 46 are shown to contain four arms (a four star configuration) with each of the arms of gel pad 50 being located out of phase (interleaved) with the arms of gel pad 46. A dotted circle 52 defines the outer portion of the flange 36 of the stud 34 which is located behind the gel pad 50 and between the gel pad 50 and the gel pad 46. The use of the interleaved or out of phase arrangement shown in FIG. 10 for the gel pads 50 and 46 provides an excellent low resistance contact path to be made between the skin of the person or animal being tested or probed with the electrode arrangement of this invention. Regardless of whether the flange 36 of the stud 34 retreats or moves away from the gel pad 50, the gel pad 50 can still provide electrical contact between the skin of the person or animal being tested because of electrical contact to the gel pad 46.
In this manner, since the overlap or contact regions between the gel pads 46 and 50 are much closer to the flange 36 of the stud 34, the skin of the person or animal being tested is closer to the probe or electrode flange position of the stud 34. This is due to the non-circular configurations of the pads 46 and 50 which permits the skin to be positioned closer to the center of the pads 46 and 50 than could otherwise be achieved by using circular pads which would not provide the recess portion provided by the areas that are not overlapped between the gel pads 46 and 50. These star shaped gel pads assure a short low resistance, electrically conductive path to be made from the skin to the electrode stud. Preferably, the stud 34 is made of a brass material such as one containing nickel like a product of Anaconda called Nickel Silver. It has been found that this material provides a good base for a silver plating operation and is also very resistant to erosion.
Although the invention has been described with reference to a particular embodiment, it is to be understood that this embodiment is merely illustrative of the application of the principles of the invention. Numerous modifications may be made therein and other arrangements may be devised without departing from the spirit and scope of the invention.