BIOMEDICAL ELECTRODE ASSEMBLY

WIPO Patent Application WO/1979/000042

An electrode assembly (12) for use in a biomedical electrode unit (10) having a contact pad (20) with a hole in it for receiving the electrode assembly including: a first member (16) disposed on one side of the pad and having a stud portion (30) extending axially through the hole in the pad and having a first mating area (34); a second member (14) disposed on the other side of the pad and having an aperture (38) with a second mating area (36) for snugly engaging the first mating area (34) of the stud portion (30); and a connector member (18) extending axially through the hole in the pad and into the first (16) and second (14) members for securely connecting together the first (16) and second (14) members with the pad (20) between them.

Mercuri A.

PCT/US1978/000036

02/08/1979

07/07/1978

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Mercuri A.

A61B5/0408; A61N1/04

C≤AIMS

1. In an. electrode assembly for use in a biomedical electrode unit having a contact pad with a hole in it for receiving the electrode assembly, the improvement compris¬ ing: a first member disposed on one side of said pad and having a stud portion extending axially through the hole in said pad and having a first mating area; a second mem¬ ber disposed on the other side of said pad and having an aperture with a second mating area for snugly engaging the first mating area of said stud portion; and a connector member extending axially through the hole in said pad and into said first and second members for securely connecting together said first and second members with said pad betwe them.

2. The electrode assembly of claim 1 in which said stud portion and said aperture are mutually tapered where they engage with each other at the mating surfaces.

3. The electrode assembly of claim 1 in which said first member is a cap for receiving an electrical contact and said second member is a base which is connected to the skin.

4. The electrode assembly of claim 1 in which each of said first and second members including said mating areas are electrically conductive.

5. The electrode assembly of claim 1 in which at leas portions of the surface of each of said first and second members including said mating areas is electrically conduc tive.

6. The electrode assembly of claim 1 in which said first member and said connector member are electrically conductive and said connector member extends through said second member.

7. The electrode assembly of claim 1 in which at least a portion of the surfaces of said first member and said connector member are electrically conductive and said connector member extends through said second member.

Biomedical Electrode Assembly

FIELD OF INVENTION This invention relates to an improved electrode assem¬ bly for a biomedical electrode unit.

BACKGROUND OF INVENTION ■ Electrode assemblies for biomedical electrode units use snap fasteners commonly used on clothing or variations of such fasteners, which are relatively complex, expensive, a d difficult to assemble. Since they are made as clothing fas¬ teners they are not ideally suited for use as electrodes. When these and other fasteners are mounted on the adhesive pad which adheres to the skin, the lower and upper elec- ' trodes may either squeeze the pad too much and distort it or grip it too loosely so that the electrode can wobble rela¬ tive to the pad and is not held tightly in contact with the skin. In addition, the upper and lower parts of some fas¬ teners may not always seat tightly together; they can wiggle relative to each other and the pad between them. This in¬ stability can result in poor or intermittent contact and result in poor electrical .continuity between the upper and lower electrodes. In many constructions the base electrode, which carries a sponge disc impregnated with conductive gel for electrical interface with the skin, is hollow so that the gel can move through it to the junction of the elec¬ trodes where it can interfere with and cause corrosion of the parts.

SUMMARY OF INVENTION

It is therefore an object of this invention to provide an improved, inexpensive electrode assembly for a biomedi¬ cal electrode unit which is simple in construction and easy to assemble.

It is a further object of this invention to provide an electrode assembly which is extremely stable, firmly but gently grips the pad without squashing it, maintains,-βpsi-. _^ ?

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tive electrical interconnection through the electrode assem bly, and prevents tilting of the electrode assembly parts relative to each other and the pad.

The invention results from the realization that a truly simple, inexpensive, and easy to assemble electrode assem¬ bly can be made using first and second members secured to¬ gether by a connector member, to obtain mechanically stable, positive electrical coupling and firm gripping of the pad and which can be enhanced by the use of tapered mating por¬ tions.

The invention features an electrode assembly for use in a biomedical electrode unit having a pad with a hole in it for receiving the electrode assembly. The improvement includes a first member disposed on one side of the pad and having a stud portion which extends axially through the hole in the pad, and contains on it a first mating area. There is a second member disposed on the other side of the pad and having an aperture in it containing a second mating area which snugly engages the first mating area of the stud portion. • A connector member extends axially through the hole in the pad and into the first and second members for securely connecting together the first and second members with the pad between them and the connector member may be integral with either of the other members.

In preferred embodiments, the stud portion and the aper ture are mutually tapered at least where they engage with each other at the mating surfaces. The first member may be a cap which receives an electrical contact or lead from monitoring equipment, and the second member may be a base which is connected to the skin, either directly or through a gel-soaked disc of sponge rubber or the like. Each of the first and second members including the mating areas may be electrically conductive, or at least functional por¬ tions of the surfaces of each of those first and second members and their mating areas may be electrically conduct-

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ive. The first member and the connector member may be electrically conductive or may have at least portions of their surfaces electrically conductive, with the connector member extending from the first member through the second member to make contact with the skin directly or through a gel-soaked disc.

DISCLOSURE OF PREFERRED EMBODIMENTS

Other objects, features and advantages will occur from the following description of a preferred embodiment and the accompanying drawings, in which:

Fig. 1 is a schematic sectional view with portions re¬ moved of a biomedical unit using an electrode assembly ac¬ cording to this invention;

Fig. 2 is a more complete axonometric view on a reduced scale of the biomedical electrode unit using the electrode assembly of Fig. 1;

Fig. 3 is a schematic sectional view of an alternative embodiment of the electrode assembly shown in Fig. 1;

Fig. 4 is a schematic sectional view of an alternative construction of an electrode assembly with the connector member mounted in the base member;

Fig. 5 is a view similar to Fig. 4 with the connector member mounted in the cap member; and

Fig. 6 is a schematic sectional view of an electrode assembly with the tapered surfaces reversed with respect to those shown in Fig. 1.

The invention may be accomplished with an electrode assembly used in a biomedical electrode unit which has a contact pad with a hole in it for receiving the electrode assembly. There is a first member on one side of the pad which has a stud portion which extends axially through the hole in the pad. The stud portion carries a first mating area. A second member ^' is disposed on the other side of the pad and has an aperture with a second mating area,

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which snugly engages the first mating area of the stud por¬ tion.

The connector member extends axially through the hole in the pad and into the first and second members for secure ly connecting together the first and second members and may be integral with either of them.

Typically, each of the first and second members, includ ing their respective mating areas, are electrically conduc¬ tive, for example where the parts are all made of metal. If the parts are made of plastic with metallized conductive coating, then at least functional portions of the surfaces of each-of the first and second members, including the mat¬ ing areas, is electrically conductive to maintain electri¬ cal continuity through the electrode assembly.

The first member and the connector member may be elec¬ trically conductive or have portions of their surface made electrically conductive, such as by metal plating, so that the connector member extends through the first membeij which may be for example the cap, through the second ember which may be for example the base, to contact the skin or at least the gel-soaked disc which contacts the skin.

The stud portion and the aperture on the respective first and second members may be mutually tapered, at least where they engage with each other at the mating surfaces. This tapering insures good, solid electrical contact be¬ tween the mating surfaces where the tapers have wedged together. It also provides a self-stabilizing fitting between the two members so that they do not tend to tilt or wobble with respect to each other. Also, because of the wedging action of the tapered, interfitting mating surfaces, the spacing between the two members is fixed so that they maintain a predetermined gripping action with the intermediate pad.

There is shown in Figs. 1 and 2 a biomedical electrode unit 10 including an electrode assembly 12, including an

upper member or cap 14 with flange 15, lower ^' member or *» base 16 with flange 17, and connector member or pin 18. Held in position between cap 14 and base 16 is an adhering pad 20 which carries along its bottom surface and the bot¬ tom surface of base 16 an adhesive layer 22 for adhering to the skin of the user. A sponge-like disc 24 impreg¬ nated with a conductive gel may be placed beneath the cen¬ ter of the electrode and a removable paper sheet 26 may be used to protect the adhesive and the gel before use. Typically, an enlarged washer 28 is employed between cap 14 and pad 20 to provide a greater area of gripping so that washer 28 and base 16 have approximately the same diameter, with base 16 being typically slightly larger.

Base 16 includes an axially upstanding stud 30, which may be tapered 32 throughout its extent, but at a minimum is tapered at the mating surface 34 where stud _. 30 engages with a similar tapered mating surface 36 in aperture 38 of cap 14. The aperture 38 may also be generally tapered as at 40. Pin 18 may take various forms and may be secured to base 16 and cap 14 in various ways. In Figs. 1 and 2, pin 18 may originally have a wholly cylindrical shape as indicated by the phantom lines 42 at its upper and lower ends. Then cap 14 has a cylindrical bore 44 with a flared mouth 46; and base 16 has a similar cylindrical bore 48 with a flared mouth 50. For assembly then, pin 18 is mount¬ ed in and may be integral with cap 14 and base 16 and its ends are spread to the presently shown flared shape 52 at the upper end and 54 at the lower end, so that pin 18 is spread to fill the flared mouth 46 and 50, respectively. Alternatively, pin 18 may be installed in either the cap 14 or base 16 first, then inserted through pad 20 and washer 28, following which the flaring of the other end of pin 18 is effected in the remaining unattached one of cap 14 in base 16. The tapered area, especially at mating surfaces 34 and 36, insures a tight fit between cap 14 and base 16

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which prevents wobbling of cap 14 and base 16 with respect to each other and positively limits the spacing between them in order to properly secure pad 20. In addition, whe cap 14 and base 16 are made of electrically conductive ma¬ terial, electrical continuity is assured from an electrica connection which grips cap 14 through the positive grippin of the wedged-together starfaces 34 and 36 and then through base 16, either directly or through the gel-soaked disc 24 If pin 18 is also a conductive material, this too acts as a conductive path from cap 14 to base 16 and gel-soaked • disc 24.

Although in Figs. -1 and 2 caps 14 ^' and 16 have been ind cated as being made of electrically conductive material such as metal and pin 18 may or may not be of such a mater ial, this is not a necessary limitation. For example, as shown in Fig. 3, where as in subsequent figures like parts have been given like numbers and similar parts like num¬ bers accompanied by a successive lower case letter, cap 14 and base 16a are formed of a non-electrically conductive material. Therein cap 14a includes on at least the neces¬ sary functional portions of its surface a conductive layer 60 for connection with a lead for monitoring equipment, which conductive surface at mating area 36a connects with a similar conducting surface 62 on base 16a at mating sur¬ face 34a.

Pin 18a may be made of conductive or non-conductive material and if it is conductive material or non-conductiv material with a conductive surface and there are suitable conducting surfaces interfacing with it on cap 14a and 16a then it too acts as a conductive path in addition to the positive primary path through the mating surfaces 34a and 36a. Pin 18a may be hollow for at least a portion of its length to reduce weight and cost, as indicated in phantom at 63.

Alternatively, pin 18b, Fig. 4, may be attached at one

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end 68 to base 16b such as by mounting in bore 70 while maintaining its previously explained flared form 52b de¬ rived from the original cylindrical form 42b for mating with the flared mouth 46b of cap 14b.

Conversely, pin 18c, Fig. 5, may have end 72 fitted in bore 74 of ca 14c and may be integral therewith, with its lower end flared 54c to grip flared mouth 50c of base ; 16c .

Although thus far in each of the illustrations it is , cap 14 which contains a tapered aperture 38 and base 16 which contains a tapered stud 30, this is not a necessary limitation of the invention, for as shown in Fig. 6, cap 14d may include a stud portion 30d having a general taper 32d with a mating surface 34d that engages with mating surface 36d of general taper 40d of aperture 38d located on base 16d. Cap 14d and base 16d are held together in the usual fashion by pin 18d.

Other embodiments will occur to those skilled in the art and are within the following claims: What is claimed is: