US3791377A

US3791377A - Radio capsule battery

Info

Publication number: US3791377A
Application number: US00158294A
Authority: US
Inventors: C Rogers; T Norby
Original assignee: Individual
Current assignee: Individual
Priority date: 1971-06-30
Filing date: 1971-06-30
Publication date: 1974-02-12
Anticipated expiration: 1991-02-12

Abstract

A battery for an active radio capsule wherein one of the electrodes, a silver-silver chloride electrode, functions as the reference electrode for a sensor by means of an electrolytic path from the battery chamber to the solution external to the capsule. The reference electrode, which is stable and insensitive to foreign ions, is disposed in a closed chamber filled with an electrolyte which is immobilized by an absorptive powder. One or more fibrous plugs form an electrical connection between the chamber and the surrounding medium. The reference electrode is designed to have a low, stable internal impedance and has a high current capability.

Description

Waited States Eatent n91 Norby et a1.

[4 1 Feb. 12, 1974 1 1 RADIO CAPSULE BATTERY [76] Inventors: Thomas E. Norby, 3617 Allendale Dr.; Charles H. Rogers, 3724 Arrowhead Dr., both of Raleigh,

[22] Filed: June 30, 1971 [21] Appl. No.: 158,294

[52] US. Cl 128/2 1?, 136/177 [51] int. Cl A611) 5/07 [58] Field of Search 128/2 P, 2 R, 2.1 R, 419 R;

[56] References Cited UNITED STATES PATENTS 3,133,537 5/1964 Muth 128/2 P 3,033,911 5/1962 Duddy 136/177 3,190,285 6/1965 Muth 128/2 P FOREIGN PATENTS OR APPLICATIONS 1,202,435 10/1965 Germany '128/2 P Primary ExaminerWilliam E. Kamm- Attorney, Agent, or Firm-William J. Simmons, Jr.

[5 7 ABSTRACT A battery for an active radio capsule wherein one of 14 Claims, 3 Drawing Figures PAFENIED FEB 1 21914 COIL ' INVEN TORS.

mas E. Norby Charles H. Rogers 1 RADIO CAPSULE BATTERY BACKGROUND OF THE INVENTION This invention relates to a radio capsule of the type utilized in a telemetering system for transmitting physi' ological information from within the human body, and more particularly, it relates to an improved battery for an active radio capsule.

Telemetering systems for transmitting information such as temperature, potential difference, pressure and specific ion activity such as pH, pK and the like include a radio capsule which can be swallowed by a patient. Conventional active radio capsules comprise a sensor or transducer, a power supply and a modulator and transmitter. Due to the nature of the use to which a radio capsule is put, i.e., it is swallowed by a patient and transmits information from within the gastrointestinal tract, some severe design limitations are placed on the components thereof. The number of components must be kept to a minimum due to the small space available, the sensor, battery and transmitter being packaged within a housing having a length of about three-fourths in. and a diameter of about five-sixteenths in. Also inert materials must be used to avoid injury to the human body.

A radio capsule power source should provide a stable voltage supply to the transmitter during its entire lifetime. However, due to the limitations imposed on size and materials, capsule batteries are generally of the type that provide a low voltage which decreases with usage. Although the volume of the power supply should be as small as possible, some capsule batteries, the volume of which are more than 40 percent of the entire capsule, have been developed in an attempt to prevent voltage drift. Such batteries have not been acceptable since they increase the size of the capsule beyond acceptable limits.

Other capsules have included discrete miniature batteries such as mercury cells, but dangers arising from toxic chemical substances cannot be fully avoided by encapsulation of the battery. Leakage due to selfcorrosion and due to biting on capsules must be considered. Non-toxic batteries are disclosed in US. Pat. Nos. 3,340,886 and 3,323,513, issued to H. J. Noller and M. Gnadke, respectively. Poor voltage stability exists in these batteries since the electrodes thereof are wetted by ambient gastric or intestinal fluid which acts as the electrolyte. Capsule batteries having a self-contained electrolyte are disclosed in US. Pat. Nos. 3,133,537 and 3,190,285 issued to H. Muth. Due to the type of electrode construction and the type of semi-permeable connection between the battery electrolyte and the fluid outside the capsule, the voltage produced by the Muth batteries is not adequately stabilized.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a small, stable, radio capsule battery, one electrode of which functions as a reference electrode for a sensor. Another object is to provide a radio capsule battery wherein the reference electrode has a stable internal impedance and a relatively high current capability. Still another object is to provide a radio capsule battery having a silver-silver chloride reference .electrode which exhibits uniform physical and electrical characteristics during a relatively long period of battery usage.

Briefly, the battery of the present invention is of the type that is adapted to be used in a radiov capsule for. investigating a condition of a region that is readily accessible only by wireless probes. Such capsules generally comprise a sensor for providing a voltage, the value of which is determined by the investigated condition. An oscillator in the capsule generates an rf signal, the frequency of which is determined by the sensor voltage. The radio capsule battery is adapted to be activated by an electrolyte prior to use, such batteries having two electrodes for providing an operating voltage for the oscillator, one of the electrodes also functioning as the reference electrode for the sensor. The battery of the present invention is characterized in that it comprises means defining a chamber in the capsule and means defining at least one hole in the chamber defining means, a mass of low porosity material being disposed in the hole for permitting only an extremely limited diffusion of electrolyte to or from the chamber. One of the battery electrodes is a consumable electrode, and the other of the electrodes comprises a silver portion and a silver chloride portion contacting the silver portion, a part of the silver portion being exposed so that it is free to contact the electrolyte. That portion of the silver chloride which contacts the silver is thin in cross section so that the impedance of the electrode is relatively low.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a cross-sectional view of a radio capsule which incorporates the battery of the present invention.

FIG. 2 is an enlarged, front view of the silver-silver chloride electrode, the side view of which is shown in FIG. 1.

FIG. 3 is an oblique view of another silvensilver chloride electrode that can be utilized in the battery of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The radio capsule illustrated in FIG. 1 comprises a battery chamber 1 1 a sensing electrode 12 and an oscillator circuit 13, oscillator coil 14 functioning as the transmitting antenna. A description of ion sensing electrode 12 can be found in copending' application Ser. No. 158,293, entitled Glass Electrode Structure for Radio Capsules, filed on even date herewith, which discloses an electrode structure that is accurate and stable over long periods of time.

The battery chamber 11 comprises a cylindrically shaped side wall 16 and elastic cap 17 made of urethane, viton rubber, or the like and a wall 18 which separates the battery from the circuit 13. The

walls

16 and 18 may be made of a non-conductive material such as epoxy, plastic, or the like. A silver-silver chloride electrode 19 and a consumable electrode 20 made of zinc, magnesium or the like are disposed in chamber 11. Circuit 13 comprises a plurality of discrete components arranged in a so-called cord wood fashion between two disk shaped

circuit boards

22 and 23. Zinc electrode 20, which may be in the form of a bent wire or plate is affixed to one side of circuit board 22, whereas silver wire 24, which forms a part of electrode 19 extends through circuit board 22 and contacts circuit board 23 and forms an electrical connection between these two 3 circuit boards. ion sensitive electrode 12 is connected to the oscillator circuit by a lead 26.

It is well known that one of the battery electrodes may be used as the reference electrode for the sensor circuit. The advantageous properties of an accurate and stable sensor can only be fully realized if a reference electrode of comparable stability and insensitivity to foreign ions is employed. in accordance with the present invention, both the design of the silver-silver chloride reference electrode 19 and the external path between the reference electrode and the ion sensing electrode structure 12 are designed to provide a stable reference voltage for the ion sensing circuit. Reference electrode 19 is disposed in a closed electrolyte chamber 11 in which the electrolyte, which may consist of a -10 percent sodium chloride solution, is immobilized by an absorptive powder 28, i.e. powder 28 prevents varying exposure of battery parts when the capsule changes orientation and a small electrolyte void is present. For the sake of clarity only a portion of the absorptive powder is illustrated. The absorptive powder may consist of grains of synthetically produced crystalline metal alumino-silicates that have been activated by removing their water of hydration. These materials are crystalline zeolites having a basic formula of ll TQQG Al OQ- xSiOQ who where M is a cation of n valence. A preferred type of absorptive powder was prepared by crushing commerically available pellets of an aluminum sodium silicate. The crushed material was graded to size by passing it over suitable 3O screens. All pieces which passed through a 0.025 in. mesh but failed to pass through a 0.015 in. mesh were used. in addition to providing a porous absorbing medium for the electrolyte, absorptive powder 28 reduces the chance of a large bubble forming and lodg-, ing in the chamber 11 when the battery is activated and also prevents separation of the electrolyte from the sonsumable electrode 20 if hydrogen is evolved.

One or more fibrous plugs 30 are disposed in holes 31 to form a wetted electrical path or connection between the electrolyte in the chamber 11 and the surrounding medium. The electrical path through the fibrous plugs must remain conductive in a variety of unusual media such as stomach juice, food, commercial anticids and digestive materials. It must also remain conductive without the aid ofa positive flushing action which is used in some liquid junctions. Regardless of the different ionic concentrations which may exist in the electrolyte and in the media in which the radio capsule is disposed, the potential across the fibrous plugs should remain so small that it is insignificant. Fibrous junctions or plugs in which the fibers were oriented parallel to the direction of flow were best suited for this application. Such an orientation, wherein the fibers are substantially parallel to the axis of the hole permits at least some of the fibers to extend from chamber 11 to that region which is external to the capsule. While providing an electrical connection between the electrolyte and the surrounding media, the fibrous plugs can still be of low porosity, thus limiting the diffusion of materials from the electrolyte within chamber 11 to the surrounding media or vice versa. A good electrical connection was obtained by using a single birch wood cylinder 0.03 in. in diameter and 0.05 in. long, the fibers thereof being parallel to the longitudinal axis of the cylinder. Although wood, asbestos. and porous ceramic plugs have been used, wood is the preferred material.

In a self-contained active radio capsule it is convenient to combine the reference electrode of the sensing circuit with one electrode of the internal battery. in such a situation, however, the reference electrode may be required to carry much more current than conventional electrodes are designed to supply. For example, in a radio capsule designs for the remote readout of pH, the reference electrode was required to carry as much as 10 ampere, a factor of 10 more than conventional reference electrodes are designed to supply. Since the accuracy of the measured ion activity depends on the stability of the reference potential, it is important that the reference electrode maintain a nearly constant potential while supplying 10 ampere to operate the transmitting circuitry. There are three important factors in the design of a reference electrode having high current capability. First, the electrode should have a stable internal impedance. Secondly, the surrounding electrolyte should not change in its chloride ion concentration with time. Finally, the interface between the silver and the silver chloride should exhibit uniform physical electrical characteristics as the silver chloride is reduced to silver.

A stable internal impedance was obtained by keeping the internal impedance as low as possible. A low internal impedance was maintained by causing the metallic silver portion of the electrode to directly contact the electrolyte and by keeping the silver chloride thin in cross-section in that portion thereof which contacts the silver electrode portion. 1f the silver chloride is too thick at the silver-silver chloride interface, an undesirable voltage drop will exist since the silver chloride is an insulator. A preferred electrode embodiment having these characteristics is illustrated in FIGS. 1 and 2. The portion of the silver wire 24 extending beyond wall 18 into chamber 11 consists of a portion 32 which is bent in a first plane and a portion 34 which is bent in a second plane to form a loop or closed figure such as the rectangular shape illustrated. The volume within loop 34 and portion 32 is filled with silver chloride which may be applied to the silver wire by inserting the wire into a pool of molten silver chloride. As the chemical reaction proceeds during battery usage, wherein the silver chloride is reduced to silver, the physical area of the interface between the silver and silver chloride remains nearly constant and electrically similar to the originally formed interface. Although there is an i.r. voltage drop near the silver chloride, it is substantially constant.

FIG. 3 illustrates another design which may be utilized for the silver-silver chloride electrode. in this embodiment the interface between the silver and silver chloride is formed by melting a uniform coating of silver chloride 33 onto a piece of silver foil 40. This can be done by applying a thin layer of powdered silver chloride to the surface of foil'40 and thereafter fusing the particles. The foil 40 which may be U-shaped as i1- lustrated in FIG. 3, is bonded to a silver wire 42 by soldering or the like. In this embodiment the internal impedance is made small by causing the metallic silver to directly contact the electrolyte and by keeping the silver chloride thin in cross section. Also, the physical area of the interface between the silver and silver chloride remains substantially constant as the chemical reaction reduces the silver chloride to silver during battery operation.

Since the silver chloride evolves chloride ions at a rate proportional to the current being supplied by the battery, it is necessary to either actively control the concentration of the electrolyte or begin with a volume which is not appreciably affected by the release of these chloride ions. In a battery having an electrolyte volume of 7.2 X cu. in. the chloride ion concentration was not appreciably affected by the release of chloride ions. Moreover, the use of the wooden plugs 30 to maintain a liquid interface between the battery chamber and the media being measured did not permit a rapid diffusion of ions between the battery electrolyte and the surrounding medium. Thus the chloride ion concentration of the electrolyte did not appreciably vary during use. A 5-10 percent sodium chloride solution provided best electrode performance. At this concentration level, initial stable potentials were established at a satisfactory rate, and in the time period of capsule operation desired, i.e. 18 hours, the most stable reference potentials could be maintained.

The battery chamber lll may be filled with porous powder and electrolyte so that the capsule can be tested. Thereafter, the chamber 11 can be emptied of absorptive powder and electrolyte, and the capsule can be stored for ultimate use. To activate the battery, the user adds absorptive powder and electrolyte to the chamber ill and affixes cap 37. Alternatively, the absorptive powder could be stored in chamber ll while the capsule is on the shelf. The user could inject electrolyte through cap 17 by means of a syringe. The battery described herein has an indefinite shelf life and has an operating lifetime of at least 50 hours.

A battery containing radio capsule has been described herein as being capable of measuring hydrogen ion activity in the human alimentary canal. Such capsules can also be used to determine specific ion activity and other information in animals or inanimate objects such as chemical reaction or storage vessels, where the need to fully enclose the system for purposes of sterility or confinement of reaction products because of poisonous gas generation, presence of radio active materials, and the like, makes a wireless telemetry system advantageous.

We claim:

1. In a radio capsule for investigating a condition of a region that is readily accessible only by wireless probes, said capsule being of the type comprising a sensor for providing a voltage, the value of which is determined by said investigated condition,

an oscillator for generating an rf signal modulated by said sensor voltage, and

a battery adapted to be activated by an electrolyte prior to use, said battery having two electrodes for providing an operating voltage for said oscillator, one of said electrodes also functioning as the reference electrode for said sensor, said battery being characterized in that it comprises means defining a chamber in said capsule, said two electrodes being disposed'in said chamber,

means defining at least one hole in said chamber defining means,

a plug of fibrous material disposed in said hole for permitting only an extremely limited diffusion of electrolyte to or from said chamber, the fibers of 6 one of said electrodes being a consumable electrode,

and

the other of said electrodes comprising a silver portion and a silver chloride portion contacting said silver portion, a part of said silver portion being exposed so that it is free to contact said electrolyte, that portion of said silver chloride which contacts said silver being thin in cross section so that the impedance of the electrode is relatively low.

2. A radio capsule in accordance with claim 1 wherein said fibrous material is wood.

3. A radio capsule in accordance with claim 2 wherein said chamber is substantially filled with a porous powder, said electrolyte being disposed within the voids between adjacent grains of said powder and within the pores thereof.

4. A radio capsule in accordance with claim 3 wherein said other of said electrodes comprises a silver wire which is bent at one end in the form of a substantially closed loop, said silver chloride filling the space within said loop and contacting that portion of said silver wire disposed on the inner surface of said loop.

5. A radio capsule in accordance with claim 4 wherein said loopis disposed in a first plane, thatpon tion of said silver wire immediately adjacent to said loop being bent in a U-shaped manner in a second plane which intersects said first plane the volume within said loop and said U-shaped portion being filled with said silver chloride.

6. A radio capsule in accordance with claim 3 wherein said other of said electrodes comprises a sheet of silver foil, a thin layer of silver chloride disposed on one surface of said silver foil, and a silver wire bonde to said silver foil.

7. A radio capsule in accordance with claim 6 wherein said silver foil-silver chloride composite is U- shaped. 1

8. A radio capsule in accordance with claim 1 wherein said chamber has an open end, said capsule further comprising an elastic cap disposed over said open end. i

9. A radio capsule in accordance with claim 1 wherein said other of said electrodes comprises a silver wire which is bent at one end in the form of a substantially closed loop, said silver chloride filling the space within said loop and contacting that portion of said silver wire disposed in the inner surface of said loop.

10. A radio capsule in accordance with claim 9 wherein said loop is disposed in a first plane, that portion of said silver wire immediately adjacent to said loop being bent in a U-shaped manner in a second plane which intersects said first plane the volume within said loop and said U-shaped portion being filled with said silver chloride.

1 l, in a radio capsule for investigating a condition of a region that is readily accessible only by wireless probes, said capsule being of the type comprising a sensor for providing a voltage, the value of which is determined by said investigated condition,

an oscillator for generating an rf signal modulated by said sensor voltage, and

a battery adapted to be activated by an electrolyte prior to use, said battery having two electrodes for providing an operating voltage for said oscillator, one of said electrodes also functioning as the reference electrode for said sensor,

said battery being characterized in that it comprises posed so that it is free to contact said electrolyte, that portion of said silver chloride which contacts said silver being thin in cross section so that the impedance of the electrode is relatively low. 12. A radio capsule in accordance with claim 11 wherein said porous powder is a crystalline zeolite.

13. A radio capsule in accordance with claim 12 wherein the voids between the grains of porous powder and the pores thereof are filled with an electrolyte.

14. A radio capsule in accordance with claim 13 wherein said electrolyte consists of a 5 to 10 sodium chloride solution.

Claims

2. A radio capsule in accordance with claim 1 wherein said fibrous material is wood.
3. A radio capsule in accordance with claim 2 wherein said chamber is substantially filled with a porous powder, said electrolyte being disposed within the voids between adjacent grains of said powder and within the pores thereof.
4. A radio capsule in accordance with claim 3 wherein said other of said electrodes comprises a silver wire which is bent at one end in the form of a substantially closed loop, said silver chloride filling the space within said loop and contacting that portion of said silver wire disposed on the inner surface of said loop.
5. A radio capsule in accordance with claim 4 wherein said loop is disposed in a first plane, that portion of said silver wire immediately adjacent to said loop being bent in a U-shaped manner in a second plane which intersects said first plane the volume within said loop and said U-shaped portion being filled with said silver chloride.
6. A radio capsule in accordance with claim 3 wherein said other of said electrodes comprises a sheet of silver foil, a thin layer of silver chloride disposed on one surface of said siLver foil, and a silver wire bonded to said silver foil.
7. A radio capsule in accordance with claim 6 wherein said silver foil-silver chloride composite is U-shaped.
8. A radio capsule in accordance with claim 1 wherein said chamber has an open end, said capsule further comprising an elastic cap disposed over said open end.
9. A radio capsule in accordance with claim 1 wherein said other of said electrodes comprises a silver wire which is bent at one end in the form of a substantially closed loop, said silver chloride filling the space within said loop and contacting that portion of said silver wire disposed in the inner surface of said loop.
10. A radio capsule in accordance with claim 9 wherein said loop is disposed in a first plane, that portion of said silver wire immediately adjacent to said loop being bent in a U-shaped manner in a second plane which intersects said first plane the volume within said loop and said U-shaped portion being filled with said silver chloride.
11. In a radio capsule for investigating a condition of a region that is readily accessible only by wireless probes, said capsule being of the type comprising a sensor for providing a voltage, the value of which is determined by said investigated condition, an oscillator for generating an rf signal modulated by said sensor voltage, and a battery adapted to be activated by an electrolyte prior to use, said battery having two electrodes for providing an operating voltage for said oscillator, one of said electrodes also functioning as the reference electrode for said sensor, said battery being characterized in that it comprises means defining a chamber in said capsule, said two electrodes being disposed in said chamber, said chamber being substantially filled with a porous powder, means defining at least one hole in said chamber defining means, means having low porosity disposed in said hole for permitting only an extremely limited diffusion of electrolyte to or from said chamber, one of said electrodes being a consumable electrode, and the other of said electrodes comprising a silver portion and a silver chloride portion contacting said silver portion, a part of said silver portion being exposed so that it is free to contact said electrolyte, that portion of said silver chloride which contacts said silver being thin in cross section so that the impedance of the electrode is relatively low.
12. A radio capsule in accordance with claim 11 wherein said porous powder is a crystalline zeolite.
13. A radio capsule in accordance with claim 12 wherein the voids between the grains of porous powder and the pores thereof are filled with an electrolyte.
14. A radio capsule in accordance with claim 13 wherein said electrolyte consists of a 5 to 10 sodium chloride solution.