Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to an electrical
detector to fix to the skin surface, for use in biometrical
observations and in particular for electrocardiographic, e.g.
electroencephalographic examinations.
The electrode incorporated in the detector has the
task of picking up and transferring the potential appearing on
the skin surface without any change there. Since in the body we
can speak of the second kind-transfer that is of ion transfer,
the electrode transforms substantially the transfer of the second
kind to a transfer of the first kind (to electron transfer). The
most important requirement for the electrodes is the stability
over a period of time of the potential of the electrode, i.e.
prevention of the substantial polarization of the electrode. This
can be achieved, as is known, by means of silver silver-chloride
electrodes in conjunction with an electrolyte containing Cl ions.
Besides the primary requirement, that is the stability
of potential the electrode must possess between the electrolyte
and the electron transferring outlet minimum contact resistance
and the entire surface of the electrode must be equipolar. The
electrolyte containing Cl ion located between the electrode
surface and the skin surface must not irritate the skin surface
even during extended use, e.g. 48 - 72 hours and it must maintain
essentially its initial concentration.
With the development of medical techniques, disposable
medical appliances, including electrical detectors are gaining
popularity at a steadily growing rate, due to their simple
manoeuvrability and quick, hygienic applicability. Disposability
sets another requirement for the electrical detectors. In the
interests of quick and simple manipulation it is desirable that
the electrode should be all ready for use with the electrolyte
necessary for its proper functioning, and with means for ensuring
its proper connection to the skin surface.
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In a conventional electrode, the material of the
electrode consists of fine-grained compressed silver silver-
chloride mixture to which an electrical outlet is connected by
soldering. The surface of the electrode formed this way will not
be equi-potential, since the individual silver grains are in
contact with each other only through silver chloride which is a
bad electrical conductor. The currents flowing through the ele-
ctrode which are of very low value produce voltage drops at
different places on the electrode surface which have a disturbing
effect on the measurements. Leading out the current from a
soldered joint can be the source additional problems, since in
the presence of the electrolytic substance the soldering material
may cause disturbing potentials, and the developing corrosion may
disadvantageously influence the contact quality.
In another construction of the silver silver-chloride
electrode an electrolytic silver-chloride coating is applied on
the surface of a silver plate. The disadvantage of this con-
struction is that firstly the high specific resistance of the
solid silver-chloride increases the resistance of the electrode,
and secondly the silver-chloride does not adhere well on the
surface of the silver and in aqueous substances, especially during
extended examination periods particles of the silver chloride
may separate, thus causing fluctuations in the potential. A
further disadvantage of the plain-surface electrode is that in
comparison with electrodes of porous surface it has a surface
smaller by several orders, therefore it is not well suited for
examinations over extended periods, e.g. of 4~ - 72 hours. The
constantly increasing popularity of disposable electrical detectors
is mainly due to their simple and quick applicability. The
special requirements necessitated by disposability and in partic-
ular the ease of manufacturing required have not been satisfied
by the conventional electrical detectors.
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According to the present invention therefore there is
provided an electrical detector to fix to the skin for biometri-
cal observations, comprising an electrically conductive housing
defining a cavity having an open side and having a silver inner
surface, a coherent porous body of silver grains compressed in
said housing substantially filling the cavity and having cohesive
bonds between contacting silver surfaces of said grains and
between said grains and said housing surface, and a coating of
silver chloride on the surfaces of substantially all of said
grains other than said contacting surfaces.
In accordance with the present invention the electrical
detector, which can be fixed to the skin for biometrical obser-
vations comprises a silver silver-chloride electrode housed in a
casing with an outlet, and a biologically harmless ion conducting
gel arranged between the skin surface and the electrode, the
electrode having a porous structure containing silver grains
desirably of less than 800 ~m linear size and with a density
desirably falling between 2 and 8 g/cm , the surfaces of the
individual silver grains being bound by surface adhesion without
the use of an adhesive to the surface of adjacent silver grains
and/or to the surface of the outlet which is also silver, the
free surfaces of the silver grains being coated by the known
silver-chloride layer.
The terms "adhesion bond" and "adhesive bonding" as
- used herein refer to the individual silver grains which have been
pressed together under sufficient pressure to provide surface
cohesion forces between the adjacent silver surfaces. There is
no adhesive substance but pure surface adhesion between these
surfaces. This kind of connection provides for the extra good
electrical conductivity and for the equipotential properties of
the resulting porous structure. The silver-chloride layer covers
only those surface areas which do not participate in this kind of
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adhesion bonding.
The silver grains being bonded to each other provide
for good conductivity of the electrode material and by this for
i the equipotential character. This formation of the electrode
further maintains the very advantageous large homogeneous surface,
which reduces polarisation and ensures the stability of potential.
Since the ou~;let is also made of silver, and the adjacent silver
grains are bonded to it, a stable and safe electrical contact is
obtained between the material of the electrode and the outlet.
The outlet can also be made of silver wire, which can
be placed between the silver grains of the electrode.
Preferably, the outlet is a silver cup, which surrounds
the electrode on three sides and there exists an adhesive bond
between the inner surface of the cup and the silver grains of
the electrode adjacent to the cup. The outlet can also form the
housing of the electrode at the same time.
The ion transferring gel soaks into the pores of an
elastic disc of porous structure and the disc extends from the
electrode so that it is compressed when the electrode surface
and the skin surface are in contact.
The cup with the electrode placed in it, and the disc
soaked by the ion transferring gel may be surrounded by a disc of
closed cell foam; a plastic annulus can be fastened between the
disc of the closed cell foam and the exterior of this cup. The
surface of the closed cell foam disc in contact with the skin
surface can be coated by a biologically harmless adhesive layer.
A bell can be fixed to the external surface of the
silver cup and the disc of closed cell foam will be held between
the bell and the plastic annulus.
When the detector is adapted to be used only once, the
adhesive coated surface of the disc of closed cell foam is suitably
made of polyethylene and covered by a protective paper of silicon
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lining. The protective paper hermetically seals the disc soaked
by the conductive gel, thus protecting it from drying. Before
use the paper cover must be removed from the surface of the disc.
The electrical detector rnay be placed in a hermetically sealed
container containing saturated water vapour.
The present invention will be further illustrated by
way of the accompanying drawings in which:
Figure 1 represents the scheme of the electrode struc-
ture connected to the outlet,
Figure 2 is a simplified sectional drawing of a dis-
posable electrode.
In Figure 1, the grain structure of the electrical
detector (transducer) according to one embodiment of the invention
is shown. Electrode 4 is formed by silver grains 1 connected to
each other and silver grains 13 connected also to the outlet. Due
to the porous structure of the electrode, only specific parts of
the surfaces of the silver grains 1 and 13 are connected to each
other. The silver grains 1 have edge portions 2 along which the
silver grains are connected to each other by adhesive bonding.
Silver grains 13 adjacent to the outlet are connected along edge
portions 14, also by adhesive bonding, to the outlet made of
silver. The size of silver grains 1 and 13 is less than 800 ~m
and the density of the material of the electrode in this embodi-
ment was 3.5 g/cm3. The free surfaces of silver grains 1 and 13
are coated by a silver-chloride layer.
In Figure 2, an embodiment of the electrical detector
according to the invention is shown, which has been designed to
be used once and then discarded. In this case the outlet of the
electrode 4 is a cup 6 made of silver, which surrounds the elec-
trode 4 on three sides. The external flange of cup 6 joints tothe inner surface of a plastic annulus 7 and this annulus 7 also
forrns the seat for an annulus disc 8 of porous plastic foam. A
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metallic bell 12 is attached by solid bindin~ to the outside of
cup 6. In the space between bell 12 and annulus 7 an annulus
plastic foam disc 8 of closed cell structure is located. On the
surface of the annulus plastic foam disc 8 which will be in
contact with the skin, a conventional adhesive coat 9, which will
not dissolve in water, is put on so that the electrode can be
attached to the skin. In this embodiment the annulus plastic foam
disc 8 of closed cell structure is made of polyurethane with a
diameter of 50 mm and a thickness of 3 mm. The adhesive coating
9 applied to the disc 8 can be any glue which is not harmful to
the human organism and is soluble in water, for instance glue
having a polyisobutylene base.
A gel containing plastic foam disc 5 is placed in the
interior of annulus 7 and its thickness exceeds the depth of the
recess in annulus 7 and consequently the external surface of the
disc 5 protrudes beyond th~ external flange of annulus 7. The
disc 5 is soaked in a gel containing Cl ions and is harmless to
the human organism. The gel utilized can contain, for example,
1~ of Cl , 6~ of glycerine, and 1~ of carboxymethylcellulose.
The other components of the gel can be various perfume substances,
e.g. lemon oil, further distilled water.
Before use, the surface coated by the layer 9 of the
annulus disc 8 is protected by a multi-layered protective paper
10, the surface of the paper in contact with the layer 9 being
for instance a silicon lining, which will not adhere to the glue.
The electrode is placed in a hermetically sealed multi-
layer bag containing saturated water vapour and this bag has at
least one polythene layer and one aluminium foil layer. The ion
conducting gel contained in the gel containing disc 5 and stored
in the bag containing saturated water vapour does not dry out for
a long time.
When the electrode is to be used, the bag is opened
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and protectiVe paper 10 is removed from the annulus plastic foam
disc 8, thereafter the electrical detector is placed on the skin
surface to be examined, and is held ~here by the adhesive layer
1 9. When placed on the skin, the gel containing plastic foam
disc 5 is compressed and the ion conducting gel stored in it
establishes a safe electrical contact between the skin surface
and the electrode 4. Since the ion conducting gel is encircled
by a hermetically sealed surface it cannot evaporate and, once in
place, the electrode provides for an excellent connection for
several days.
Electrical connection between the detector according
to the invention and the examining device can be established by
a contactor of suitable design attached to the external surface
of bell 12. Due to its advantageous properties the electrode
according to the invention is outstanding among the detectors of
known designs: its stability of potential, contact resistance,
stability in time is remarkably better than those of the electrode~
known up to now. From the simple design it is also evident, that
the production costs of the detector are moderate too.
