A replaceable, prefilled electrode enclosed in a plastic seal and suitably adapted for attachment to a reusable, washable cap having snaps thereon is disclosed. The apparatus is particularly adapted for quick positioning of electrodes to obtain an EEG. The individual electrodes are formed of a sponge body which is filled with a conductive electrolyte gel during manufacture. The sponge body is adjacent to a base formed of a conductive plastic material. The base has at its center a male gripper snap. The cap locates the female snap to enable the electrode to be positioned. The electrode can be stored and used quickly by attaching to the female gripper snap. The snap is correctly positioned and located by mounting it in a stretchable cap. The cap is reusable with new electrodes for each use. The electrolyte gel serves as the contact electrode to achieve a good ohmic contact with the scalp

Frost, J. D., Jr.

Hillman, C. E., Jr.

English

NASA Technical Reports Server

United States Patent [191 
Fletcher et al. 
[I11 4,033,334 
[451 July 5, 1977 
[54] SNAP-IN COMPRESSIBLE BIOMEDICAL 
ELECTRODE 
[ 761 Inventors: James C. Fletcher, Administrator of 
the National Aeronautics and Space 
Administration, with respect to an 
invention of; James D. Frost, Jr., 
Houston; Carl E. Hillman, Jr., 
Bellaire, both of Tex. 
[22] Filed: Dec. 3, 1975 
[21] Appl. No.: 637,269 
[52] U.S. CI. ............................ 128/2.1 E; 128/410; 
128/DIG. 4 
[5 1 J Int. CL2 ........................................... A61B 5/04 
[58] Field of Search ........... 128/2.06 E, 2.1 R, 404, 
128/410, 41 1, 416, 417, 418, DIG. 4, 2.1 B 
[561 References Cited 
UNITED STATES PATENTS 
3,279,468 10/1966 LeVine .............................. 128/410 
3,490,439 1/1970 Rolston ........................... 128/2.1 E 
3,508,541 4/1970 Westbrook et al. ............ I28/2.1 B 
3,659,614 5/1972 Jankelson .......................... 128/410 
3,669,l 10 6/1972 Low ................................ 128/2.1 E 
3,830,229 8/1974 Johnson ........................ 128/2.06 E 
3,976,055 8/1976 Monter ......................... 128/2.06 E 
3,998.21 3 12/1976 Price ............................... 128/2.1 B 
FOREIGN PATENTS OR APPLICATIONS 
1,489,708 5/1969 Germany ........................... 128/410 
OTHER PUBLICATIONS 
Hanly et al., “Electrode Systems for Recording The 
EEG in Active Subjects”, Bio Med. Electrode Technol- 
ogy, Academic Press, 1974, pp. 283-313. 
Primary Examiner-Robert W. Michell 
Assistant Examiner-Lee S. Cohen 
Attorney, Agent, or Firm-Edward K. Fein; John R. 
Manning; Marvin F. Matthews, 
[571 ABSTRACT 
A replaceable, prefilled electrode enclosed in a plastic 
seal and suitably adapted for attachment to a reusable, 
washable cap having snaps thereon is disclosed. The 
apparatus is particularly adaptled for quick positioning 
of electrodes to obtain an EEG. The individual elec- 
trodes are formed of a sponge body which is filled with 
a conductive electrolyte gel during manufacture. The 
sponge body is adjacent to a base formed of a conduc- 
tive plastic material. The base has at its center a male 
gripper snap. The cap locates the female snap to enable 
the electrode to be positioned. The electrode can be 
stored and used quickly by attaching to the female 
gripper snap. The snap is correctly positioned and lo- 
cated by mounting it in a stretchable cap. The cap is 
reusable with new electrodes for each use. The electro- 
lyte gel serves as the contact electrode to achieve a 
good ohmic contact with the scalp. 
6 Claims, 1 Drawing Figure 
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U.S. Patent July 5 ,  1977 
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4,03 3,3 34 
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scalp to obtain a good signal with controlled contact 
DESCRIPTION OF THE DRAWING 
The single drawing is a sectilonal view through the 
disposable electrode of the present invention disclosing 
details of construction and showing how it is affixed to 
a cap by use of male and female gripper snaps. 
10 DESCRIPTION OF THE PREFERRED 
SNAP-IN COMPRESSIBLE BIOMEDICAL resistance. 
ELECTRODE 
ORIGIN OF THE INVENTION 
The invention described herein was made in the Per- 
formance of work under a NASA contract and is sub- 
ject to the provisions of Section 305 of the National 
Aeronautics and Space Act .of 1958, Public Law 
85-568 (72 Stat. 435; 45 U.S.C. 2457). 
PRIOR ART U.S. Pat. No. 3,669,110 
BACKGROUND OF THE INVENTION 
5 
EMBODIMENT 
Attention is directed to the single drawing where the 
numeral 10 identifies the disposable electrode of the 
The referenced patent is directed to a previously present invention. The disposable electrode is adapted 
developed disposable EEG recording cap containing l 5  to be used with a reusable cap 12. The cap 12 is typi- 
Permanently athched compressible bhnedical elec- cally formed of a stretchable material such as lycra. It 
trades. It has served quite adequately. It is however is sized to fit a range of heads with the stretch of the 
somewhat expensive to use. The major expense results material accommodating slight variations in size and 
from the high manufacturing cost Of the cap and at- 2o shape. The cap includes with it a plug or socket which 
tached connector, not de- enables all of the conductors for several electrodes to 
able amplification and recording apparatus. The cap attached electrodes is disposed of after use. 
the electrode disclosed herein can be used with a reus- the one indicated at 14. They are located so that the able cap, thereby achieving a significant economic 25 cap, when it has been placed on the head of the subject, advantage. The fit of the cap, which is made of a positions the gripper snaps 14 at the desired locations stretchable material, accomplishes correct positioning 
of the electrodes against the scalp. The stretching of for obtaining a suitable EEG signal. The electrodes are 
the cap at the time of the positioning of the electrodes required to be positioned at selected locations to obtain 
accommodates Some variations in head size. Through 30 the Correct Signals. If they are incorrectly positioned, 
the use of three or four basic cap sizes, most head sizes the data which 
can be accommodated. Skilled technician time is re- The cap l2 thus has the gripper snap 14 installed 
duced. The cap incorporates a set of snaps which en- where a portion of it is on the interior of the cap and a 
able the electrodes to be positioned for reliable data Portion is on the exterior of the cap. The gripper snap 
collection for the EEG. The cap itself incorporates the 35 14 has a wire 16 welded to it and the wire 16 is adjacent 
wiring harness with the necessary conductors grouped to the cap and connects to a suitable plug or socket. 
and connected through a suitable plug or socket to The female gripper snap 14 has an exposed receptacle 
enable the cap, when positioned on the user, to be for mating with a male gripper snap 18. The two are 
connected directly to the strip chart recorder. affixed by pushing them together. They are released by 
When the EEG has been obtained, the electrodes are 40 pulling them apart. The gripper snap assembly is the 
quickly unsnapped and can be thrown away. The cap is sort typically found on children’k clothing and the like. 
stored for reuse. The sanitary Purposes, it is Preferably The electrode of the present invention incorporates a 
washed after each use. It can be stored and subse- sponge-like body 20, The body 20 is formed of a 
VentlY reused on the head of a Person of approxi- rous, foamed silicone rubber compound, or other suit- 
mateb’ the Same size- An inventory Of three Or four 45 able communicating pore sponge material. It is shaped 
different sized caps enables practically all test subjects to define a lower flat face. The body of the electrode is 
an inverted cone having a tab at the upper end. The tab to be accommodated. 
SUMMARY OF THE INVENTION 22 is a filling and sealing tab. The lower face of the 
electrode is a disc 26 of conductive plastic material. A 
This invention is directed to a disposable electrode 50 suitable mixture is about 30% carbon in the form of 
ticularly adapted for use with a cap having a female The material is shaped by injection molding tech- gripper snap installed at a selected location. The female niques. This percentage of carbon defines an electrode gripper snap is connected to a wire which transfers the which is fairly conductive. If the concentration of car- signal to suitable recording equipment. The disposable 55 
electrode of the present invention includes a funnel bon is increased, electrical conductivity is improved, 
with an electrolyte gel. It is preferably enclosed within been determined that the ratio of about 30% carbon to 
a leakproof coating such as vinyl. The body has a lower 70% PolYethYlene is suficient flor most purposes. 
flat face which is formed of a conductive plastic mate- 60 The body of the electrode 10 is coated with a thin 
rial. A suitable material is formed of readily moldable vinyl coating at 24. It covers the filling tab 22 and the 
plastic impregnated with carbon black. The male grip- Conk surface. In addition, the vinyl coating 24 covers 
per snap is located in the center of the lower face. The the h v e r  face of the Plastic disc 26. The male gripper 
entire apparatus is coated with a vinyl coating to cap- snap 18 is embedded in the plastic disc 26. However, it 
ture the gel during storage to prevent evaporation. At 65 is not covered over by the vinyl coating 24. The vinyl 
the time of use, the vinyl coating is punctured to enable coating is relatively thin, typically in the range of three 
the electrolyte gel to seep from storage in the sponge to eight mils. It can be even thinner, but this sometimes 
and to saturate the immediate area of contact with the makes it a bit too fragile. 
by the recording procedure, together with the be routed through the socket for connection to a suit- 
with the present apparatus, it is that has strategically located female gripper snaps such as 
obtained may not be useful. 
for Obtaining EEG from a test subject* It is par- particulate graphite mixed in about 70% polyethylene. 
shaped absorbent sponge body which has been filled but generally becomes more difficult. It has 
4,033,334 
3 4 
The electrode of the present invention functions in 
the following manner. The cap 12 is held by the user 
who affixes the electrode 10 by simply mating the male 
an electrically conductive plastic base member at- 
tached to said sponge-like body, said base member 
having a generally planar surface; 
and female gripper snaps. The tab 22 is then cut. When an electrolyte gel said sponge-1ike body; 
it is cut, this enables the electrolyte to flow freely to 5 electrically conductive snap connector em- 
bedded into said base member and extending out- 
ward therefrom; 
sponge-like body and said plastic base member 
except for an area immediately surrounding said 
snap connector means extending outward there- 
from, said coating means providing a leakproof 
barrier for said electrolyte gel; 
cap means formed of stretchable material for posi- 
tioning in a predetermined pattern a plurality of 
said sponge-like bodies at desired locations about 
the head of a subject for obtaining EEG signals; 
and 
moisten the area near the electrode. The electrode 
snaps 14 2nd 18 assembled together in ohmic contact 
with the scalp of the user and the recording device. The ,o  
cap and attached electrode are placed on the head of 
the subject such that the electrodes contact the scalp. 
Contact with the scalp is ordinarily very poor, but when 
the scalp is moistened with the electrolyte, the contact 
becomes much better. When in use, the contact with 15 
the scalp is quite good, enabling the electrode to obtain 
signals in the range of microvolts. At this juncture, the 
entire area of the scalp near the electrode is moistened 
is electrically connected through the gripper plastic coating surrounding completely said 
in the electrolyte solution which maintains good con- 
ductivity, thereby stablizing and reducing the ohmic 2' 
electrically conductive snap connector at- 
for releasably connecting tached to said cap 
both electrically and mechanically to one or more 
of said sponge-like bodies through corresponding 
snap connector means embedded into said base 
members thereof. 
2. The apparatus of claim 1 wherein said electrically 
conductive plastic base member comprises a plastic 
material and an electrically conductive material in a 
ratio which will permit molding and transmittance of 
the desired EEG signal. 
3. The apparatus of claim 2 wherein said electrically 
conductive material is carbon. 
4. The apparatus Of claim 3 wherein the ratio Of said 
is about 30 percent carbon to about 70 per- 
contact resistance to a minimum and preventing fluctu- 
ation in this value, thereby avoiding variations as a 
result of scalp contact. 
detached, and the electrode 10 is readily thrown away. 
Its replacement cost is minimal. The cap itself remains 
intact and is able to be used again. Preferably, it is 
washed to remove any traces of electrolyte gel from it. 
after the vinyl coating 24 has been placed on the 
When the device has been the gripper snaps are 25 
The electrolyte gel is preferably injected by syringe 30 
sponge-like body 20. The syringe is inserted through 
the vinyl coating. This leaves a small perforation which 
can be readily sealed by applying a drop of liquid vinyl 
evaporates, the hole has been resealed. 
ment of the electrode of the present invention, but the 
scope is determined by the claims which follow. 
cent plastic 
body is conically shaped, and further includes filling 
and sealing tab means at the apex thereof for easy 
sponge-like body. 
6. The apparatus of claim 1 wherein said cap means 
further includes electrical conductor means attached to 
said snap connector means of said cap means for trans- 
ferring the EEG signal to suitable recording equipment. 
or other suitable solvent to the tab. When the solvent 35 5* The apparatus Of 'Iaim wherein said sponge-1ike 
The foregoing is directed to the preferred embodi- cutting to enable said electrolyte gel to flow from said 
40 
We claim: 
1. A biomedical electrode assembly for use in obtain- 
ing EEG signals from a subject comprising: 
a resilient sponge-like body; * * * * *  
45 
50 
55 
60 
65 


Snap-in compressible biomedical electrode

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