US 3572323 A
Description (OCR text may contain errors)
March 23, 1971 YUAN 3,572,323
' DISPOSABLE ELECTRODE WITH A METALLURGICALLY-BONDED,
SILVER-SILVER CHLORIDE SENSING ELEMENT Filed Jan. 5, 1969 fFP/W/K 4. run/v BY AAQ4-LE K MTM ATTORNEYS United States Patent DISPOSABLE ELECTRODE WITH A METALLURGI- CALLY-BONDED, SILVER-SILVER CHLORIDE SENSING ELEMENT Frank L. Yuan, Wayland, Mass., assignor, to Becton, Dickinson and Company, East Rutherford, NJ. Filed Jan. 3, 1969, Ser. No. 788,828 Int. Cl. A61b 5/04 U.S. Cl. 1282.06 6 Claims ABSTRACT OF THE DISCLOSURE A disposable electrode is provided for biological and medical use comprising a sensing element housing formed of an insulating material and having surfaces thereon adapted to receive and retain a sensing element and a sensing element. The sensing element comprises a uniformly thick flat layer of silver to which a uniformly thick fiat layer of silver chloride is metallurgically bonded.
BACKGROUND OF THE INVENTION Electrodes find extensive use in the medical and related fields to transform biopotentials into electrical signals which may be monitored for a variety of functions, such as electrocardiographs, electroencephalographs, or electromyograms. Such electrodes are usually placed on the skin of the patient whose function is to be monitored with an interposed layer of a suitable electrolyte, generally in gel form. Ion flow passes through the subjects skin and the electrolyte to react with the electrode and generate an electrical signal which is then monitored.
One electrode construction which affords relative stability, low impedance, and low offset voltage, and is therefore particularly well suited for medical purposes utilizes a silver-silver chloride sensing element. Heretofore, such silver-silver chloride electrodes were generally formed either by compressing a mixture of silver and silver-chloride powders, occasionally with small quantities of a binder such as bentonitic clay added, or by mechanically coupling sheets of silver and silver-chloride to one another.
Although such electrodes have generally performed well from a technical point of view, in most applications, the high cost associated with their construction has prevented their extensive use, particularly where electrode contamination is a problem and disposability is desirable or required. Further, the impedance of such prior art electrodes is higher than required or desired for most applications and the effectiveness of the mechanical bond between the silver and silver chloride molecules may vary with movement of the patient, thereby varying the electrode impedance resulting in variations in the accuracy of the electrode readout. Also, the electrical characteristics of these prior art electrodes usually varied considerably from electrode to electrode and hence interchangeability was not possible unless the monitoring equipment was recalibrated for each electrode.
SUMMARY OF THE INVENTION It is, therefore, the principal object of the present invention to provide an improved disposable electrode having acceptable electrical characteristics including low impedance and polarization voltage which is lightweight, reliable, compact, sufiiciently inexpensive to reasonably permit single use, and which is interchangeable with other similarly manufactured electrodes.
These and other beneficial objects and advantages are attained in accordance with the present invention by providing an electrode comprising a sensing element housing including a generally flat member formed of an insulating ice material and having a depressed center portion integral with a raised peripheral portion, and a sensing element disposed within the depression. The sensing element comprises a first, uniformly thick, flat layer of silver to which a uniformly thick, flat layer of silver-chloride is metallurgically bonded. An intermediate layer is interposed between the silver and silver-chloride layers and is coextensive therewith and forms a zone wherein difiusion of the silver and silver-chloride molecules occurs while preventing any slippage between the silver and silverchloride layers. The sensing element is disposed within the housing depression with the silver layer abutting the rear surface of the depression. An electrically conductive lead having one end in electrical contact with the silver layer and the other end adapted to be coupled to the monitoring equipment is also provided. The raised peripheral portion of the housing also includes a continuous double sided adhesive adapted to facilitate adhering the electrode to the subject.
BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings:
FIG. 1 is a top plan view of the electrode of the present invention;
FIG. 2 is a side elevational sectional view taken along reference line 2-2 of FIG. 1; and
FIG. 3 is a fragmentary diagrammatic view of portions of the sensing element of the electrode of the present invention greatly magnified.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Reference is now made to the drawings wherein like parts are designed by similar reference numerals throughout the several views. In FIG. 1, the electrode 10 of the present invention is depicted as comprising a housing 12, a sensing element 14 disposed within the housing, an electrical lead 16 extending between the sensing element 14 and a terminal portion 18, and a.terrninal portion 18 which includes a connector 20 which in this preferred embodiment, is a snap-fit female connector adapted to be snapped into place about a suitable male connector.
The housing 12 is formed of an insulating material such as polyethylene or polypropylene which is readily moldable into the desired shape. .In this case, the housing comprises a generally flat member having a depressed center portion 22- and a peripheral portion 24 raised with respect to the center portion 22 and spaced from the center portion by the conical frustum Wall member 26 'which extends between the two portions of the housing.
The inner surfaces 28 and 30 of wall member 26 and depressed center portion 22, respectively, thus define an open ended chamber 32- the opening 34 of which is further defined by the inner edge 36 of the raised peripheral portion 24. In this regard, and as best seen in FIG. 2, the raised peripheral portion 24 comprises, in essence, an annular disc and the raised edge 36 is defined by the inner radius of the disc.
A double sided adhesive strip 38 is disposed about the outer face of the raised peripheral portion 24. One side of adhesive 38 adheres to the outer face of the housing and the other side is adapted to be adhered to the body of the subject under observation, thereby forming means for coupling the electrode to the subject. In this regard, a backing strip 40 is disposed about the free face of the double sided adhesive to protect the tackiness of the adhesive prior to use. A tab 42 extends from the outer peripheral edge of the backing strip to facilitate its removal and the application of the electrode to the subject.
The inner surface 30 of the depressed center portion of the housing 12 is further defined by a circular recessed section 44 into which the sensing element 14 is fitted.
A hole 46 extends through the center of recess 44 to the outer surface of the housing and the conductive wire 48 of electrical lead 16 extends through hole 46 to make electrical contact with the rear of the sensing element 14. After the sensing element is positioned within recess 44 and the electrical contact is established between the sensing element 14 and lead 16 as by soldering, a suitable potting compound, as for example epoxy, is applied to the rear of the housing filling hole 46 and thereby serving to form bead 50 which protects the electrical contact between the lead and sensing element and also serves to secure the sensing element 14 within the housing 12.
The sensing element .14 comprises agenerally circular disc, the diameter of which is substantially the same as that of recess 44 having raised side walls 52 which are substantially equal to the depth of the recess. The sensing element comprises a first flat layer 54 of silver to which a layer of silver chloride 56 has been metallurgically bonded as for example, by the process disclosed in US. Letters Patent No. 3,059,331 for Method of Making Composite Stock which issued on Oct. 23, 1962 and is assigned to the Texas Instruments Corporation. The metallurgical bond between the silver and silver-chloride layers 54 and 56, respectively, results in the formation of an interposed diffused third layer 58 comprising both silver and silver-chloride molecules. The cross-sectional configuration of the sensing element =14 is depicted in FIG. 3 in exaggerated diagrammatic form. In a successful practice of the present invention, the thickness of the sensing element was two mils with the silver chloride portion comprising of the total composite or approximately .3 mil. The individual sensing elements 14 are formed by properly stamping or cutting a sheet of composite stock. Since the thicknesses of the silver and silver chloride layers of the composite material may be accurately maintained throughout the stock and also since a firm metallurgical bond is maintained between the composite layers, the electrical characteristics of two such electrodes will be substantially identical, thus penmitting the interchangeability of the electrodes.
The sensing element 14 is positioned within housing 12 with the silver layer 14 abutting the housing and making electrical contact with the conducting lead 48 and the silver chloride layer 56* directed toward the housing opening 34. That is, when viewing the front of electrode 10, all that will be seen is the silver chloride surfaces 56 of the sensing element 14.
In use, the open ended chamber 32 is filled to the brim with an electrolyte such as a salt gel whereafter the backing strip 42 is removed from the face of adhesive 38 and the electrode is appropriately positioned on the subject. The terminal portion 18 of the electrode is then connected to suitable monitoring equipment with the connector 20 coupled to a mating connector associated with the monitoring equipment. Electrical signals transmitted from the subject will be transmitted through the electrolyte to the sensing element and then to the monitoring equipment. After use, the electrode may be disposed of and in this regard, it will be economically feasible to discard an electrode produced in accordance with the present invention after a single use.
Having thus described my invention, what I claim is:
1. A disposable electrode comprising: a sensing element housing formed of an insulating material and having first surfaces adapted to be mounted to the subject being monitored and second surfaces spaced apart from said first surfaces to receive and retain the sensing element; a sensing element mounted to said housing second surfaces and comprising a uniformly thick fiat layer of silver and a uniformly thick flat layer of silver-chloride coextensive with said first layer and metallurgically bonded thereto; and, an electrically conductive lead in electrical contact with said silver layer of said sensing element and adapted to be coupled to associated monitoring equipment.
2. The invention in accordance with claim -1 wherein said sensing element further includes an intermediary layer interposed between said silver layer and said silver chloride layer and coextensive therewith wherein diffusion of silver and silver chloride molecules occurs in said intermediate layer whereby to effect said metallurgical bond.
3. The invention in accordance with claim 1 wherein said housing comprises a molded plastic material.
4. The invention in accordance with claim 3 wherein said housing comprises a generally flat member having a depressed center portion defining said housing second surfaces integral with a raised peripheral portion defining said housing first-surfaces and said sensing element is mounted at the base of said depressed portion with said silver chloride layer directed toward said raised peripheral portion.
5. The invention in accordance with claim 1 further comprising a double faced adhesive disposed about said first surfaces.
6. The invention in accordance with claim 1 wherein said silver layer is substantially two mils in thickness and said silver-chloride layer is substantially .3 mil in thickness.
References Cited UNITED STATES PATENTS 3,420,223 1/1969 Day et a1 1282.06
WILLIAM E. KAMM, Primary Examiner