Biomedical electrode assembly

An electrode assembly for use in a biomedical electrode unit having a contact pad with a hole in it for receiving the electrode assembly including: a first member disposed on one side of the pad and having a stud portion extending axially through the hole in the pad and having a first mating area; a second member disposed on the other side of the pad and having an aperture with a second mating area for snugly engaging the first mating area of the stud portion; and a connector member extending 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.

FIELD OF INVENTION 
This invention relates to an improved electrode assembly 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, and difficult to assemble. Since they are 
made as clothing fasteners 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 electrodes may either 
squeeze the pad too much and distort it or grip it too loosely so that the 
electrode can wobble relative to the pad and is not held tightly in 
contact with the skin. In addition, the upper and lower parts of some 
fasteners may not always seat tightly together; they can wiggle relative 
to each other and the pad between them. This instability 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 electrodes 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 biomedical 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 positive electrical interconnection through the 
electrode assembly, 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 assembly can be made using 
first and second members secured together 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 portions. 
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 aperture 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 like. Each of the first and second members including the 
mating areas may be electrically conductive, or at least functional 
portions of the surfaces of each of those first and second members and 
their mating areas may be electrically conductive. 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.

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, which snugly engages the first mating area of the stud 
portion. 
The 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 and may be integral with either of them. 
Typically, each of the first and second members, including their respective 
mating areas, are electrically conductive, 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 mating areas, is 
electrically conductive to maintain electrical continuity through the 
electrode assembly. 
The first member and the connector member may be electrically conductive or 
have portions of their surface made electrically conductive, such as by 
metal plating, so that the connector member extends through the first 
member, which may be for example the cap, through the second member, 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 between 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 bottom surface of base 16 an 
adhesive layer 22 for adhering to the skin of the user. A sponge-like disc 
24 impregnated with a conductive gel may be placed beneath the center 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 flare mouth 46; 
and base 16 has a similar cylindrical bore 48 with a flared mouth 50. For 
assembly then, pin 18 is mounted 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 and base 16. The 
tapered area, especially at mating surfaces 34 and 36, insures a tight fit 
between cap 14 and base 16 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, when cap 14 and base 16 
are made of electrically conductive material, electrical continuity is 
assured from an electrical connection which grips cap 14 through the 
positive gripping of the wedged-together surfaces 34 and 36 and then 
though 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 indicated as being made 
of electrically conductive material such as metal and pin 18 may or may 
not be of such a material, 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 numbers accompanied by 
a successive lower case letter, cap 14a and base 16a are formed of a 
non-electrically conductive material. Therein cap 14a includes on at least 
the necessary 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 surface 34a. 
Pin 18a may be made of conductive or non-conductive material and if it is 
conductive material or non-conductive 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 end 68 to base 16b 
such as by mounting in bore 70 while maintaining its previously explained 
flared form 52b derived 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 cap 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: