Physiological sensor and transmitter

• US 3,949,388 A
• Filed: 03/26/1975
• Issued: 04/06/1976
• Est. Priority Date: 11/13/1972
• Status: Expired due to Term

• Current Assignee: Monitron Industries Incorporated
• Original Assignee: Monitron Industries Incorporated
• Inventors: Fuller, Charles H.
• Primary Examiner(s): Habecker, Thomas B.
• Application Number:
  US05/562,083
• Time in Patent Office: 377 Days
• Field of Search: 340/189 M, 128/2.1 A
• US Class Current: 340/870.17
• CPC Class Codes: A61B 5/0008 Temperature signals
• CPC Class Codes: Y10S 128/903 Radio telemetry

Abstract

A small self-contained sensor and transmitter assembly including a sensor for detecting physiological and bio-medical phenomena and a transmitter for transferring such data to a receiver for display and other use is disclosed. In one embodiment, the sensor is adapted to be secured within the axilla of a patient to detect his temperature by means of a thermistor arranged in heat exchange relation with the body of the patient. The thermistor modulates the pulsing rate of a blocking oscillator which generates a magnetic field, the pulsing rate being proportional to the physiological phenomenon of interest. The oscillator, power supply, antenna, and other circuit elements are mounted within corresponding compartments in a molded plastic housing, the arrangement being such that substantially all of the interconnections between circuit elements are made using only the component lead wires. The thermistor is mounted on the exterior surface of the housing and is thermally isolated from it to provide a fast response, and an adhesive is provided to secure the housing to the patient'"'"'s skin. A resilient cover on the housing provides thermal insulation and insures patient comfort. The transmitter circuitry is constructed for stable operation, fast response, and transmits data in a narrow frequency spectrum for accurate measurement.

Claims

1. In a blocking oscillator for generating a sequence of bursts of oscillations, said blocking oscillator having an amplifying device that has a control element,

a resonant circuit including an inductor and a tuning capacitor operatively connected to said amplifying device, said oscillator also including a blocking capacitor connected to said resonant circuit for developing a control bias;

means for applying said control bias to said control element to quench said oscillations when the bias attains one value and to initiate said oscillations when said bias attains another value, said control capacitor charging in one direction while said oscillator is oscillating and in the other direction when said oscillator is quiescent to change said bias;

an isolation impedence connecting said blocking capacitor between said resonant circuit and said control element, whereby intermittent switching of the amplifying element on and off precludes intermittent direct connection and disconnection of said blocking capacitor across said resonant circuit, thereby concentrating the oscillations to a narrow band of frequencies determined by said tuning capacitor and said inductor substantially independently of said blocking capacitor.

2. A blocking oscillator as defined in claim 1 wherein said isolation impedence element is a resistor.

3. In a blocking oscillator for generating a sequence of bursts of oscillations of radio frequency, including an amplifying device in the form of a solid-state element having a control electrode and an output electrode, the oscillator having a tuned circuit including an inductor and a tuning capacitor operatively connected to said electrodes, the improvement comprising:

a bias control circuit for said oscillator including an isolating resistor and a blocking capacitor connected between said tuned circuit for said control electrode for developing a control bias in accordance with the oscillations in said tuned circuit, wherein the bias on said control electrode charges in one direction while said oscillator is oscillating, finally attaining a bias which quenches said oscillations, and charges in the other direction when said oscillator is quiescent, to reach a value at which oscillations are initiated; and

high voltage means connected between said output electrode and said control electrode for stabilizing the time between successive ones of said bursts.

4. The blocking oscillator as defined in claim 3, wherein said high voltage means comprises a rectifying element and storage capacitor, the junction between said capacitor and said rectifying element being connected to said control electrode.

5. The blocking oscillator as defined in claim 3, further including temperature senstive variable impedence means connected between said high voltage means and said blocking capacitor to control the rate of charging of said blocking capacitor while said oscillator is quiescent, whereby the time between successive ones of said bursts is varied in accordance with the temperature sensed by said variable impedence.

6. In a blocking oscillator for generating a sequence of bursts of oscillations of radio frequency at a burst rate that corresponds to the value of a physiological parameter of a subject, said oscillator having an amplifying device in the form of a solid-state element having a control electrode and an output electrode and a tuned circuit including an inductor and a tuning capacitor operatively connected to said electrodes, said oscillator including a sensing element having a resistance that varies in accordance with the value of said parameter, the improvement comprising:

a storage capacitor connected to said tuned circuit for developing a control bias in accordance with the strength and duration of oscillations in said tuned circuit; and

a bias control circuit including said sensing element and a resistor connected to said control electrode and to said blocking capacitor whereby said control capacitor changes the bias on said control electrode in one direction while said oscillator is oscillating, finally reaching a bias which quenches said oscillations, and in the other direction when said oscillator is quiescent, to reach a value at which oscillations are initiated, the rate of change of bias while said oscillation is quiescent varying in accordance with the value of said sensing element.

7. The blocking oscillator of claim 6, further including means for compensating for variations in the loading of said tuned circuit, said compensating means comprising a source of high voltage connected to said blocking capacitor for maintaining constant the time between successive ones of said bursts.

8. The blocking oscillator of claim 7, further including means for maintaining a narrow spectrum of frequencies during each of said bursts of radio frequency, said last named means comprising an isolating impedance connected to said blocking capacitor.

9. The blocking oscillator of claim 8, further including power supply means for said amplifying device, said power supply means including a battery and a capacitor connected to each other and to said output electrode.

10. The blocking oscillator of claim 9, wherein said power supply means is connected to said output electrode through at least a part of said inductor.

11. The blocking oscillator of claim 9, wherein said source of high voltage comprises a storage capacitor connected to said blocking capacitor through said sensing element.

12. The blocking oscillator of claim 11, wherein said source of high voltage further includes rectifying means connected between said tuned circuit and said storage capacitor.

13. The blocking oscillator of claim 12, wherein said sensing element comprises a thermistor adapted to monitor the temperature of a subject, and wherein said inductor serves as an antenna to transmit said bursts of radio frequency oscillations.

14. The blocking oscillator of claim 13, further including housing means for receiving each element of said oscillator, said housing being dimensionally rigid to protect said elements, and means for securing said housing to said subject whereby said thermistor is brought into thermal equilibrium with said subject.

15. The blocking oscillator of claim 14, wherein said housing has receptacle means for receiving said thermistor and holding it against the surface of said subject when said housing is secured to the subject, and further including thermal insulation means between said thermistor and said housing to thermally isolate said thermistor from said housing, whereby said thermal equilibrium is achieved.

16. The blocking oscillator of claim 15, further including thermally insulating cover means for said housing, whereby said sensing element and said oscillator are thermally isolated from sudden changes in ambient temperature, but remain sensitive to changes in the temperature of said subject.

17. In a physiological testing unit to be secured to a subject:

a blocking oscillator for generating a sequence of bursts of oscillations at a burst rate that corresponds to the value of a physiological panameter of the subject, said oscillator having an amplifying device including a control electrode and an output electrode and having a resonant circuit operatively connected to said electrodes, said resonant circuit including an antenna winding adapted to emit signals corresponding to said oscillations;

a blocking capacitor connected to said resonant circuit for developing a control bias;

a bias control circuit including a sensing element responsive to said parameter connected to said control electrode and to said blocking capacitor, said bias control circuit changing the bias on said control electrode in one direction while said oscillator is oscillating, finally reaching a bias level which quenches said oscillations, and changes the bias level on said control electrode in the other direction when said oscillator is quiescent, finally reaching a bias level at which oscillations are initiated, the rate of change of bias level while said oscillator is quiescent varying in accordance with the value of the parameter detected by said sensing element whereby said burst rate varies with the value of said parameter;

a housing enclosing said oscillator;

means mounting said sensing element exteriorly of said housing; and

means for externally removably attaching said unit to the subject, said sensing element being mounted on the housing to detect a desired physiological parameter of the subject and being connected to said oscillator bias control circuit to modulate said signals in accordance with such parameter.

18. A physiological testing unit as defined in claim 17, wherein said resonant circuit is electrostatically shielded in order to reduce electrostatic radiation to and from the transmitter without substantially reducing the magnetic inductive transmission.

19. A physiological testing unit as defined in claim 17, wherein said winding encircles a powdered iron core.

20. A physiological testing unit as defined in claim 19, wherein said oscillator is powered by a battery of cylindrical configuration and wherein said iron core is in the form of a tubular cylinder that encircles said battery.

21. A physiological testing unit as defined in claim 17, wherein said sensing element comprises a thermistor which is to be placed in close proximity to the skin of the subject to detect the temperature of the subject.

22. A physiological testing unit as defined in claim 17, wherein said means for securing said assembly to the subject comprises a thin, double-faced adhesive member.

23. A physiological testing unit as defined in claim 17, wherein said housing comprises a rigid case member formed with a plurality of shaped interior cavities, an exterior switch receptacle, and an exterior receptacle for said sensing element;

said resonant circuit, said winding, said core, and said battery all being mounted in corresponding cavities within said case member for accurate placement;

a flexible cover member secured over said rigid case member; and

an adhesive member having an aperture, one side of said adhesive member being secured to the bottom of said flexible cover member and to the bottom of said case, the other side of said adhesive member being adapted to be secured to the subject said sensing element protruding through said aperture of said adhesive member and being adapted to contact the subject when the unit is in place on the subject.

24. A physiological testing unit as defined in claim 23, wherein said sensing element is a thermistor mounted in said exterior sensing element receptacle by means of a thermally insulating adhesive.

40. The physiological testing unit of claim 17, wherein said sensing element comprises means responsive to changes in the temperature of the subject.

41. The testing unit of claim 40, further including means for compensating for variations in the loading of said resonant circuit, said compensating means comprising a source of high voltage connected to said blocking capacitor for maintaining constant the time between successive ones of said bursts.

42. The testing unit of claim 41, further including means for maintaining a narrow spectrum of frequencies during each of said bursts of oscillations, said last named means comprising an isolating impedance connected to said blocking capacitor.

43. The testing unit of claim 42, further including power supply means for said oscillator, said power supply having a battery and a capacitor connected to each other and to said output electrode.

44. The testing unit of claim 43, wherein said power supply means is connected to said output electrode through at least a part of said antenna winding.

45. The testing unit of claim 41, wherein said source of high voltage comprises a storage capacitor connected to said blocking capacitor through said sensing element.

46. The testing unit of claim 45, wherein said source of high voltage further includes rectifying means connected between said tuned circuit and said storage capacitor.

47. The testing unit of claim 40, wherein said housing has receptacle means for receiving said sensing element and holding it against the surface of a subject when said housing is secured to the subject, and further including thermal insulation means between said sensing element and said housing to thermally isolate said sensing element from said housing, whereby said sensing element can attain thermal equilibrium with the subject.

48. The testing unit of claim 47, wherein said housing includes means to thermally isolate said sensing element and said oscillator from sudden changes in ambient temperature, said sensing element remaining sensitive to changes in the temperature of said subject.

25. A small, self-contained physiological testing unit to be externally secured to a patient and adapted to transmit signals corresponding to the temperature of the patient, comprising:

a thermistor adapted to be placed adjacent the surface of the patient'"'"'s skin to detect its temperature, said thermistor having a pair of electrodes;

an oscillator circuit having an antenna winding, said oscillator being controlled by the thermistor to inductively transmit signals modulated in accordance with the detected temperature;

a tubular iron core composed of powdered iron particles held together with an electrically insulating, non-magnetic binder, said winding being wound on the outside of said core;

a power supply for said oscillator circuit including a battery fitting snugly within said core;

a dimensionally rigid case member formed with a plurality of internal cavities, each cavity being formed to receive a corresponding one of said core and of said electrical components making up said oscillator circuit, said cavities locating said components in such a way that substantially all electrical connections for said oscillator circuit may be made by means of the lead wires on said components;

means for mounting said thermistor on the exterior of said case member, said thermistor electrodes being connected through said case member to said oscillator circuit;

battery cover means for securing said battery within said case member;

a flexible, flanged cover secured to said rigid case member and together with said case providing thermal insulation for said electrical components, said cover providing a pliant outer cover for the testing unit; and

a thin adhesive member having adhesive on both sides, one side of the adhesive member being secured to the bottom of the flanged cover and to said case member, said unit being adapted to be secured externally to the patient by the adhesive member with said thermistor adjacent the patient'"'"'s skin.

26. The testing unit of claim 25, wherein said means for mounting said thermistor comprises a first external receptacle on said case member, and a heat insulating adhesive securing said thermistor to said receptacle.

27. The testing unit of claim 26, wherein at least one surface of said thermistor is exposed for contact with said patient'"'"'s skin, said exposed surface being available for calibration of said unit after assembly thereof.

28. The testing unit of claim 26, further including a pair of helical coils interconnecting said thermistor electrodes and said oscillator circuit, said helical coils being bifilar to reduce the effect of said transmitted signals on said oscillator and being of thin wire to thermally isolate said thermistor from said case member and said oscillator circuit.

29. The testing unit of claim 26, further including a second external receptacle on said case member, said second receptacle receiving electrical component lead wires for said oscillator circuit from within said case, said lead wires being separated to form an open switch to prevent operation of said oscillator;

and

switch cover means adapted to engage said second receptacle and to close said switch, whereby said oscillator is activated.

30. The testing unit of claim 29, wherein said switch cover means includes means for securing said cover to said case member to prevent reopening of said switch.

31. The testing unit of claim 30, wherein said battery cover means includes flange means for preventing easy removal of said battery, said switch cover and said battery cover insuring single use of said testing unit, while permitting recycling through replacement of the battery said recalibration of said unit.

32. The testing unit of claim 25, wherein said lead lines of said electrical components are interconnected by means of an electrically conductive epoxy adhesive which cures at room temperature, whereby said electrical circuit is assembled without the application of heat.

33. The testing unit of claim 25, wherein said oscillator is a blocking oscillator for generating recurring bursts of oscillations at radio frequency, said oscillator including an amplifying device in the form of a transistor having collector and base electrodes, and a tuned circuit comprising said antenna winding and a tuning capacitor connected between said collector and base electrodes.

34. The testing unit of claim 33, wherein said oscillator further includes a bias control circuit comprising an isolating network having an isolating impedance and a blocking capacitor, said isolating network being connected between said tuned circuit and said base electrode, and high voltage means connected to said isolating network for stabilizing the time between successive bursts.

35. The testing unit of claim 34, wherein said thermistor is connected between said high voltage means and said isolating network, and between said high voltage means and said base electrode, whereby the resistance of said thermistor regulates the repetition rate of said bursts.

36. The testing unit of claim 35, wherein said high voltage means comprises rectifying means and a storage capacitor connected between said collector electrode and said thermistor.

37. For an oscillator of a radio frequency transmitter, a winding wound on a tubular magnetic core that encircles a miniature battery, said core being composed of carbonyl iron.

38. A device as defined in claim 37, wherein said core is grooved, and then etched to restore its insulative characteristics, said grooves receiving the turns of said winding.

39. A device as defined in claim 38, further including an electrostatic shield encircling said winding and covering at least one end of the winding and core assembly.

49. In a physiological testing unit to be secured to a subject:

a blocking oscillator including an amplifying device having a control element for generating a sequence of bursts of oscillations, said oscillator including a resonant circuit operatively connected to said amplifying device and including an antenna winding and a tuning capacitor adapted to emit signals corresponding to the detected physiological condition;

a blocking capacitor connected to said resonant circuit for developing a control bias;

means for applying said control bias to said control element to quench said oscillations when said bias attains one value and to initiate said oscillations when said bias attains another value, said blocking capacitor charging in one direction while said oscillator is oscillating and in the other direction when said oscillator is quiescent to change said bias;

an isolation impedance connecting said blocking capacitor between said resonant circuit and said control element whereby intermittent switching of the amplifying device on and off precludes intermittent direct connection and disconnection of said blocking capacitor across said resonant circuit, thereby concentrating the oscillations to a narrow band of frequencies determined by said tuning capacitor and said antenna winding substantially independently of said blocking capacitor;

a housing enclosing said oscillator circuit;

means for externally removably attaching said unit to the subject; and

a sensing element mounted on the housing to detect a desired physiological parameter of the subject and connected to said oscillator to modulate said emitted signals in accordance with such parameter.

50. A physiological testing unit as defined in claim 49 wherein said isolation impedance element is a resistor.

51. The testing unit of claim 49, wherein said housing includes a plurality of shaped interior cavities adapted to receive said oscillator circuit and an exterior sensing element receptacle;

a cover member securable on said housing for protecting and thermally insulating said circuit means;

means for securing said sensing element in said exterior sensing element receptacle; and

means for securing said housing to said subject so that said sensing element is capable of sensing said physiological parameter.

52. The unit of claim 51, wherein said sensing element comprises a thermistor.

53. The unit of claim 51, wherein said cover member is flexible and provides a pliant outer covering for the testing unit.

54. The unit of claim 51 wherein said means for securing said sensing element includes means for exposing at least a portion of said sensing element for contact with said subject.

55. The unit of claim 51, further including a switch receptacle on said housing, said switch receptacle receiving electrical circuit lead wires from within said housing, said lead wires forming an open switch to prevent operation of said electrical circuit;

and

switch closure means adapted to engage said switch receptacle to close said open switch and permit operation of said electrical circuit.

56. The unit of claim 55, further including means on said switch closure means for preventing reopening of said switch, whereby said electrical circuit remains in operation once activated.

57. A physiological testing unit including a transmitter having a blocking oscillator for generating a sequence of bursts or oscillations of radio frequency and including an amplifying device in the form of a solid-state element having a control electrode and an output electrode, the oscillator having a tuned circuit including a transmitter antenna and a tuning capacitor operatively connected to said electrodes;

a bias control circuit for said oscillator including an isolating resistor and a blocking capacitor connected between said tuned circuit for said control electrode for developing a control bias in accordance with the oscillations in said tuned circuit, wherein the bias on said control electrode charges in one direction while said oscillator is oscillating, finally attaining a bias which quenches said oscillations, and charges in the other direction when said oscillator is quiescent, to reach a value at which oscillations are initiated;

high voltage means connected between said output electrode and said control electrode for stabilizing the time between successive ones of said bursts;

variable impedance means connected between said high voltage means and said blocking capacitor to control the rate of charging of said blocking capacitor while said oscillator is quiescent, whereby the time between successive ones of said bursts is varied in accordance with a parameter sensed by said variable impedance;

a housing enclosing said blocking oscillator, bias control circuit and high voltage means;

means for mounting said impedance means on the exterior of said housing; and

means for securing said housing externally on a subject whose temperature is to be sensed with said impedance means in contact with said subject, whereby said testing unit transmits bursts of oscillations having a time rate which corresponds to the temperature being sensed.