Dry electrode design with wire sandwiched between two flexible conductive discs for monitoring physiological response

Ramme, F. B.

English

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PATENTED DEC 1 51970 
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INVENTOR 
FRANK B. RAMME 
ATTORNEYS 
Inventors T. 0. Paine 
Deputy Administrator of the National 
Aeronautics and Space Administration with 
Respect to an Invention of; 
Frank B. Ramme, Lancaster, Calii. 
Appl. No. 760,389 
Filed Aug. 29,1968 
Patented Der. 15,1970 
3,029,808 4/1962 Kagan .......................... 128/2.06 
3,170,459 2/1965 Phippsetal. ................. 128/2.06 
3,426,746 2/1969 Seamans, Jr .................. 128/2.06 
3,464,404 9/1969 Mason .......................... 12812.06 
Primary Examiner-William E. Kamm 
Attorney-Monte F. Mott, J. H. Warden and G. T. McCoy 
FLEXIBLE CONDUCTIVE DISC ELECTRODE 
4 Claims, 6 Drawing Figs. 
U.S. CI. ....................................................... 128/2.06 
Int. CI. ........................................................ A61b 5/04 
Field of Search ............................................ 12812.06, 
2.1,362,379-383,390-404,410,411, 
416-418 
References Cited 
UNITED STATES PATENTS 
128141 6 1,989,282 1/1935 Kimble et a1 .................. 
ABSTRACT: A dry, electrode featuring a wire sandwiched 
between two discs cut from sheets of a flexible conductive 
material. The electrodes are made by mixing silver powder 
with a cement, diluting the mixture with a suitable solvent for 
the cement and applying it in a thin layer to a surface from 
which it can be removed as a film when dry; cutting or shaping 
the dried film to form the size electrodes desired; placing a 
wire lead on the cut film piece; applying a small amount of sol- 
vent to the film surface having the wire thereon; and pressing a 
second piece of the dried film thereto to form the electrode of 
the invention. 
23 
t 
then sprayed on a sheet of inert material such as polyethylene 
to a desired thickness. After drying, the conductive cement is 
detached from the plastic sheet and placed upon a sheet of 
The invention described herein was made in the per- material such as rubber SO that discs can be punched from the 
formance of work under a NASA contract and is subject to the 5 cement. Utilizing a conventional punch, discs of any chosen 
provision of Section 305 of the National Aeronautics and diameter can then be provided from the dried sheet of con- 
Space Act of 1958, Public Law 83-568 (72 stat. 435; 42 USC ductive cement. To form the completed electrode a wire hav- 
2457). ing a stripped end is placed on one disc resting on a sheet of 
inert plastic, a drop or two of acetone or other suitable solvent 
BACKGROUND OF THE INVENTION lo for the cement is then placed on the disc, and a second disc 
immediately then pressed over the wire to the underlying first 
disc lo form a sandwich about the wire. The product is again 
allowed to dry. The final dry dectrode thus has two discs sand- 
15 wiched about the lead wire. The two discs, of course, are held 
2. Description of the Prior Art together by the adhesive action due to the action of the sol- 
Prior to the herein invention there have been developed dry vent and can then be readily applied to the subject by wiping a 
electrodes for application to individuals. The electrodes were desired section of the subject’s body with acetone and pressing 
for physiological monitoring, such as for electrocardiograms the dried disc on that area, leaving it there until the acetone 
and electroencephalograms. This work is described in NASA 20 evaporates. It is believed the invention will be better un- 
Technical Note D-34 14, May 1966, “Dry Electrodes for derstood from the following detailed description and drawings 
Physiological Monitoring,” by Charles W. Patten, Frank B. in which: 
Ramme and James A. Roman. This prior method involved FIGS. la-Id schematically depict the steps of forming the 
forming a solution of conductive electrode material to be dry electrode of this invention; 
sprayed on to the individual. The solution was comprised of 25 FIG. 2 is a top view ofa dry electrode ofthe invention; 
powdered silver in a cement, such as Duco cement made by FIG. 3 is a sectional view taken along line 3-3 of FIG. 2. 
the DuPont Company, which is cellulose nitrate dissolved in a 
suitable solvent. The viscosity was controlled by adding more DESCRIPTIoN OF THE PREFERRED 
solvent for the cement such as acetone, so that the mixture 
could be readily sprayed through an atomizer. Upon evapora- 
tion of the solvent from the sprayed mixture, a dry conductive 
electrode of the silver disposed in the cement would reside on 
the person sprayed. 
In  the practice of this prior technique, a small amount of 
conventional electrode jelly was wiped on the area of the skin 
to which the electrode was to be applied. The lead wire util- 
ized was Teflon insulated copper wire that had a pin connec- 
tor on one end for eventual connection to the readout instru- 
ment, while the other end of the wire was stripped with a small 
epoxy ball fastened to the end tip. The stripped end of the wire 
with the ball thereon was placed against the nozzle of the 
spray gun utilized. The nozzle was then placed against the skin 
and centered over the jelly coat. A coating of the conductive 
cement mixture was then sprayed onto the skin to form about 
a half-dollar size electrode and capture the lead wire in the ce- 
ment. The same spray gun was then utilized by a valve control 
to spray air only against the dried electrode to rapidly dry it. 
Care had to be taken to withdraw the gun about two 
seconds after the start of the air dry to prevent the gun from 
adhering to the sprayed area on the skin. The aforegoing steps 
were repeated for each electrode to be applied to the in- 
dividual. Normally three different electrodes are applied, for 
example, in taking electrocardiograms. Additionally, for best 
results, the wire should not contact the skin. Thus, a thin coat 
of the conductive mixture is preferably sprayed and dried be- 
fore the wire is pressed onto the skin, then the spraying con- 
tinued to place a further coat over it and the wire. As can be 
seen the aforegoing is a fairly time consuming process with 
certain critical steps. Additionally, the equipment to spray the 
conductive mixture is relatively expensive and is subject to 
fouling or clogging and the like. Thus, though the concept of 
forming electrodes in situ on the body would appear to be ex- 
peditious and advantageous, there are several drawbacks. 
Thus, an object of this invention is to provide a dry elec- 
trode which is prefabricated prior to application to subject. 
Another object of this invention is to provide a dry elec- 
trode which is readily and easily applicable to a subject. 
ORIGIN OF INVENTION 
1. Field of the Invention 
The invention is in the field of dry electrodes. More pafiicu- 
larly the invention is in the field of dry electrodes for use in 
physiological monitoring of individuals. 
SUMMARY OF THE INVENTION 
The herein invention comprises mixing a suitable cement, 
such as a cellulose nitrate type cement, with silver powder in 
about a 50 : 50 weight ratio, together with enough solvent to 
provide a fluid mixture to be sprayed. The solvent preferably 
used is an organic material such as acetone. The mixture is 
30 
35 
40 
45 
Turning now to the drawing there is seen in FIG. la,  a sheet 
of plastic I t  with a nozzle 13 from an atomizer or like as- 
sembly disposed adjacent thereto. The nozzle 13 sprays a con- 
ductive cement on the plastic 11. The conductive cement can 
be of a variety of materials. It has been found Fhat the metal 
portion of the cement should be preferably silver powder. The 
metal should be conductive. However, it should not readily 
oxidize since this interfeces with the electrical properties. For 
this reason, silver is preferable over a material such as copper. 
Another metal that could be used is platinum. However, it is 
considerably more expensive. 
The metal powder is initially mixed with a cement material 
which should be fast drying and adherent to the skin. It is ap- 
parent that the basic cement material should also be inert to 
the body so that it will not irritate or cause discomfort. Addi- 
tionally, it is important that after the cement has dried it can 
be readily redissolved at its surface so that one can easily and 
subsequently attach the formed electrode to the body. Thus, 
various organic cements such as cellulose nitrate, cellulose 
acetate, polyvinyl acetate and various acrylic resin adhesives 
50 are contemplated. These materials all possess the foregoing 
adhesive qualities and can be readily and easily dissolved in an 
organic solvent which will evaporate readily. 
The organic solvent which serves the purpose of decreasing 
the viscosity of the cement so that it can be easily sprayed 
55 from the atomizer head 13, should also, of course, be a materi- 
al that will be tolerated by the body as well as rapidly 
evaporating. Acetone is found to be preferable as a solvent 
material to serve the aforegoing purposes. However, other or- 
Bo ganic materials such as methyl ethyl ketone, butyl acetate, 
amyl acetate, and the‘like can be utilized in addition to or in 
place of acetone. 
To form the initial mixture, silver or other metal used is 
added to the cement on the weight ratio of 90 to 110 percent 
65 of silver to the amount of cement present. The amount of 
acetone or other suitable solvent added to the mixture de- 
pends solely upon the spay  apparatus utilized. Only enough 
acetone should be used so that an adequate spray can be ob- 
tained. Too fluid a material i s  not readily handled, and the 
70 thickness cannot be easily controlled when applied to the 
plastic sheet 11. The plastic sheet 21 should be of a material 
that I s  inert to the cement 90 it will not adhere to it. For exam- 
ple, a typical plastic would be polyethylene plastic. 
To control the thickness of the conductive cement applied 
75 to the plastic sheet 41, one can maintain the surface area of a 
portion of the sheet at a given size, and vary the amount of 
material applied to that surface. Thus, by applying twice the 
quantity of the conductive cement to a given surface area, one 
will double the thickness of the final product. The thickness is 
not critical. The cement product can vary from about 7 mils to 
one that is several times as thick. 
After the conductive cement has been sprayed onto the sur- 
face 11, it is allowed to dry. This can be aided by means of a 
fan to circulate air over the surface, aiding in the evaporation 
of the solvent used. Upon completion of the drying, the con- 
ductive cement I5 is then peeled, as in FIG. Pb, from the base 
11. This produces a continuous sheet of a desired thickness of 
conductive cement. 
The dried sheet of conductive cement 15, after it is peeled 
as shown in FIG. Zb, is then placed as seen in FIG. IC, on a mat 
17 of hard rubber or the like. A punch 19 is then used to cut 
disc elements from the sheet IS as seen at the remaining holes 
21. The discs removed are preferably the size of a half-dollar 
but can obviously be of any suitable diameter. 
To form the complete electrode element, two discs, as 
shown in PIG. Id, are utilized. A first disc 23 has a drop or two 
of solvent applied to its surface. The lead wire 25 is then laid 
upon the disc as shown. A second disc 27 is then placed on top 
of the first disc 23, sandwiching the wire there between, and 
pressed upon the first disc 23. The solvent rapidly evaporates, 
leaving a solid electrode member. The last operation can be 
performed while the bottom disc 23 is once again resting on a 
sheet of plastic material similar to or the same as the sheet 
used in the initial spraying step shown in FIG. Pa. 
FIOS. 2 and 3 combined show a completed unit. The insu- 
lated lead wire 25 preferably is exposed along the portion 29 
that extends between the two discs 23 and 27, and is silver 
plated thereat to provide a nonoxidative surface in this region, 
as well as improve the conductivity from the conductive ce- 
ment to the wire. The wire 25 is then capable of being con- 
nected to a suitable plug which can also receive the other elec- 
trodes utilized. The plug in turn can be attached to a line fed 
into an electrocardiogram apparatus or the like. 
To use the completed dry electrode as shown in FIGS. 2 and 
3. a portion of the body to which the electrode is to be applied 
is wiped or dabbed with the solvent used for the cement, such 
as, for example, acetone. The electrode is also wetted with sol- 
vent, then immediately pressed upon the wet area of the body 
and held for a second or two until the electrode has started to 
adhere. It has been found that the cement is not conductive 
when wet with solvent. Thus, one of the advantages of the 
herein invention as compared to the prior art spraying device 
is that the electrode when applied is basically dry. This small 
layer of solvent is absorbed into the skin as well as the dry 
electrode at an extremely rapid rate. Thus, the electrode is 
ready for use much sooner than in the spray-on device which 
takes longer to dry. 
In order to remove the electrode from the body, one can 
simply peel it off in the manner of an adhesive bandage, or al- 
ternatively, where the area might be covered with hair or the 
like, the entire electrode can be dissolved when wiped with the 
liquid solvent. The invention will be fully understood from the 
Following example. 
EXAMPLE 
To form a conductive cement mixture capable of being 
sprayed, 43 grams of Duco household cement, manufactured 
by E. 1. DuPont de Nemours & Company, which is a cellulose 
nitrate cement, containing acetone and butyl acetate as sol- 
vents therefor together with a high boiling ester plasticizer, 
I o  was mixed with 43 grams of silver powder and 100 milliliters 
of acetone. The mixture waa sprayed onto a sheet of 
polyethylene plastic over a square area of 6 by 6 inches. This 
produced a thickness of approximately 7 mils over that area. 
The conductive layer was then permitted to dry into a pliable 
nontacky solid surface on the plastic sheet. The conductive 
layer was then peeled off of the underlyin plastic and laid 
upon a sheet of neoprene rubber. Discs of kree-fourths inch 
diameter were then cut with a punch from the sheet of con- 
ductive cement. To form the completed electrode, a cut disc 
20 was then laid upon a sheet of polyethylene. Two drops of 
acetone were placed on the top exposed surface of the disc 
and a lead wire, which was silver plated in the region of con- 
tact with the disc, was laid upon it. Immediately, a second disc 
a was then placed on top ofthe first one sandwiching the wire 
25 therebetween. Pressure was applied to the two discs for a 
second or two to allow the acetone solvent to thoroughly 
blend the two discs together about the wire. The electrode 
together with its lead wire was then ready to be attached to a 
suitable plug for eventual connection to a readout apparatus. 
It should be apparent that the invention can be practiced 
with obvious modifications to the process described. For ex- 
ample, the initial mixture of conductive cement can be applied 
by methods other than spraying. It can be rolled onto a base or 
applied through a dipping. In other words, various techniques 
35 can be used to obtain a dry film of the conductive cement to 
be cut into discs. 
Additionally, the conductive cement does not have to be 
removed from the base prior to punching the discs. It is just 
believed to facilitate the separation of the cement from the 
40 plastic sheet if it is accomplished before the discs are punched. 
I claim: 
1. A dry electrode for application to the body comprising: 
two discs of cement that is soluble in an organic solvent, 
said cement having sufficient metal powder dispersed 
therethrough to provide electrical conductivity; 
an electrical lead wire; and 
means securing said discs to each other sandwiching one 
2. The electrode of claim I, wherein said means for securing 
50 said discs comprises an amount of solvent for said discs suffi- 
cient only to soften a surface layer of said discs. 
3. The electrode of claim 1 wherein said cement is selected 
from the group consisting of cellulose nitrate and cellulose 
acetate, and wherein said metal powder is silver. 
4. The device of claim 3 wherein the portion of said wire 
sandwiched between said discs is silver plated. 
30 
45 
end of said wire therebetween. 
55 
60 
65 
IO 
75 


Flexible conductive disc electrode Patent

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