Electromagnetic sensors for biological tissue applications and methods for their use

• US 20030036674A1
• Filed: 07/26/2002
• Published: 02/20/2003
• Est. Priority Date: 07/26/2001
• Status: Active Grant

• Current Assignee: Bayer Healthcare LLC (Bayer AG)
• Original Assignee: Medrad Incorporated (Bayer AG)
• Inventors: Bouton, Chad Edward
• Granted Patent: US 7,591,792 B2
• Time in Patent Office: Days
• US Class Current: 600/12
• CPC Class Codes: A61B 2562/02 Details of sensors specially adapted for in-vivo measurements
• CPC Class Codes: A61B 2562/046 in a matrix array
• CPC Class Codes: A61B 2562/143 for coupling microwaves
• CPC Class Codes: A61B 5/05 Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves impedance plethysmography A61B5/0295; measuring movement of the entire body or parts thereof A61B5/11; detecting, measuring or recording bioelectric or biomagnetic signals of the body or parts thereof A61B5/24
• CPC Class Codes: A61B 5/0507 using microwaves or terahertz waves
• CPC Class Codes: A61B 5/0537 Measuring body composition by impedance, e.g. tissue hydration or fat content
• CPC Class Codes: A61B 5/411 Detecting or monitoring allergy or intolerance reactions to an allergenic agent or substance
• CPC Class Codes: A61B 5/4878 Evaluating oedema
• CPC Class Codes: A61M 5/16836 by sensing tissue properties at the infusion site, e.g. for detecting infiltration detecting tissue temperature for diagnostic purposes A61M39/0247
• CPC Class Codes: H01Q 1/273 Adaptation for carrying or wearing by persons or animals
• CPC Class Codes: H01Q 1/40 Radiating elements coated with or embedded in protective material
• CPC Class Codes: H01Q 13/18 the slot being backed by, or formed in boundary wall of, a resonant cavity longitudinally slotted cylinder H01Q13/12 ; Open cavity antennas
• CPC Class Codes: H01Q 21/06 Arrays of individually energised antenna units similarly polarised and spaced apart
• CPC Class Codes: H01Q 21/065 Patch antenna array
• CPC Class Codes: H01Q 21/20 the units being spaced along or adjacent to a curvilinear path slotted waveguide arrays H01Q21/005; circularly or helically slotted waveguides H01Q21/0062
• CPC Class Codes: H01Q 9/0407 Substantially flat resonant element parallel to ground plane, e.g. patch antenna dipole H01Q9/285; monopole H01Q9/40
• CPC Class Codes: H01Q 9/0414 in a stacked or folded configuration

Abstract

Tissue sensors house one or more sensor elements. Each element has a housing mounted substrate and a superstrate with a planar antenna between. A transitional periphery (TP) of a superstrate outer surface interconnects a base to a plateau. At least some of the TP has a generally smooth transition. Plural elements are spaced by the housing. Alternately, the superstrate TP is flat, the housing extends to the outer superstrate surface and a shield surrounds the element. The housing is flush with or recessed below the superstrate and defines a TP between the housing and superstrate. A method converts a reference signal to complex form; plots it in a complex plane as a reference point (RP); converts a measurement signal to complex form; plots it in the complex plane as a measurement point (MP); determine a complex distance between the MP and the RP; and compares complex distance to a threshold.

Claims

1. A sensor element for injecting and/or receiving electromagnetic waves into body tissue, said sensor comprising:

a housing;

a substrate mounted within said housing;

a superstrate mounted to said substrate and having a base facing said substrate and an outer surface extending away from said substrate, said outer surface having a transitional periphery interconnecting said base to an outer surface plateau extending over at least a central portion of said superstrate; and

a generally planar antenna element accommodated by and mounted between said substrate and said superstrate, wherein at least a portion of said transitional periphery of said outer surface of said superstrate has a generally smooth transition from said base to said surface plateau.

2. A sensor element as claimed in claim 1 wherein said transitional periphery is generally linear so that said outer surface forms a truncated pyramid.

3. A sensor element as claimed in claim 1 wherein said transitional periphery is curvilinear.

4. A sensor element as claimed in claim 1 wherein said housing comprises a resilient material.

5. A sensor element as claimed in claim 4 wherein said resilient material comprises polyurethane.

6. A sensor element as claimed in claim 1 wherein said planar antenna element comprises a rectangular electrically conductive patch.

7. A sensor element as claimed in claim 6 wherein said planar antenna element is square and is electrically contacted adjacent a corner of said element to generate circularly polarized electromagnetic wave signals.

8. A sensor element as claimed in claim 1 wherein said planar antenna element comprises a generally circular electrically conductive patch.

9. A sensor element as claimed in claim 1 wherein said portion of said transitional periphery of said outer surface of said superstrate having a generally smooth transition from said base to said surface plateau directs electromagnetic waves toward said portion.

10. A sensor element as claimed in claim 1 further comprising an electrically conductive shield around at least a portion of said substrate to form an electrically conductive cavity.

11. A sensor element as claimed in claim 10 wherein a resonance mode of said antenna element is matched to a resonance mode of said cavity so that said antenna element and said cavity resonate together.

12. A sensor element as claimed in claim 11 wherein said antenna element and said cavity are rectangular, said resonance mode of said antenna element corresponds to a diagonal measurement of said antenna element and said resonance mode of said cavity corresponds to a side dimension of said cavity.

13. A sensor element as claimed in claim 12 wherein said antenna element and said cavity are congruent squares.

14. A sensor element as claimed in claim 1 wherein said antenna element is mounted to said substrate and said superstrate is removably mounted to said substrate.

15. A sensor element as claimed in claim 14 wherein said outer surface of said superstrate includes adhesive for securing said sensor element to said body tissue.

16. A sensor element as claimed in claim 1 wherein said outer surface of said superstrate includes adhesive for securing said sensor element to said body tissue.

17. A sensor element as claimed in claim 1 wherein said substrate and said superstrate comprise a high permittivity, low loss material.

18. A sensor element as claimed in claim 17 wherein said superstrate comprises a ceramic material.

19. A sensor element as claimed in claim 17 wherein said superstrate comprises a material with an intrinsic impedance substantially the same as the surface impedance of tissue into which electromagnetic waves are to be injected and/or from which electromagnetic waves are to be received.

20. A sensor element as claimed in claim 17 wherein said material comprises magnesium calcium titanium dioxide.

21. A sensor element as claimed in claim 1 wherein said generally planar antenna element is secured to said substrate.

22. A sensor element as claimed in claim 21 wherein said base of said superstrate includes an indentation sized to receive said generally planar antenna element.

23. A sensor element as claimed in claim 22 wherein said indentation in said substrate is formed to accommodate an electrical connection to said generally planar antenna element.

24. A sensor comprising at least two sensor elements each sensor element comprising:

a substrate;

a superstrate mounted to said substrate and having a base facing said substrate and an outer surface extending away from said substrate, said outer surface having a transitional periphery interconnecting said base to an outer surface plateau extending over at least a central portion of said superstrate; and

a generally planar antenna element accommodated by and mounted between said substrate and said superstrate, wherein at least a portion of said transitional periphery of said outer surface of said superstrate has a generally smooth transition from said base to said surface plateau.

25. A sensor as claimed in claim 24 further comprising a housing supporting said at least two sensor elements.

26. A sensor as claimed in claim 25 wherein said housing comprises a resilient material.

27. A sensor as claimed in claim 26 wherein said resilient material comprises polyurethane.

28. A sensor as claimed in claim 25 wherein said housing is shaped and said sensing elements are positioned within said housing to permit visual observation and palpation of body tissue interposed between said at least two sensor elements.

29. A sensor as claimed in claim 28 wherein said housing is shaped like a bowtie having two expanded portions interconnected by a portion more narrow than said expanded portions, each of said two expanded portions having at least one sensor element housed therein.

30. A sensor as claimed in claim 28 wherein said housing having first and second elongated portions interconnected by a third elongated portion, each of said first and second elongated portions having at least one sensor element housed therein.

31. A sensor as claimed in claim 30 wherein said third elongated portion is positioned at one end of said two elongated portions so that said sensor housing is generally U-shaped to permit visual observation and palpation of body tissue interposed within the open end of said U-shaped housing.

32. A sensor as claimed in claim 30 wherein said portion of said transitional periphery of at least one of said at least two sensor elements is positioned to provide directional transmission and/or receipt of electromagnetic wave energy.

33. A sensor as claimed in claim 32 wherein said transitional periphery of at least two of said at least two sensor elements are positioned to be directed toward one another.

34. A sensor as claimed in claim 24 comprising at least four sensor elements, said at least four sensor elements defining at least two electromagnetic wave transmitters and at least two of said sensor elements defining at least two electromagnetic wave receiver elements, said at least two electromagnetic wave transmitters being positioned opposite said at least two electromagnetic wave receivers.

35. A sensor as claimed in claim 34 wherein said portions of said transitional periphery of said at least two electromagnetic wave transmitters is positioned toward said at least two electromagnetic wave receivers.

36. A sensor as claimed in claim 35 wherein said portions of said transitional periphery of said at least two electromagnetic wave receivers is positioned toward said at least two electromagnetic wave transmitters.

37. A sensor as claimed in claim 24 wherein said at least two electromagnetic wave transmitters are separated from said at least two electromagnetic wave receivers by body tissue to be monitored by electromagnetic waves.

38. A sensor as claimed in claim 24 wherein said planar antenna elements of said at least two sensor elements are square and are electrically contacted adjacent inner corners of said elements.

39. A sensor comprising at least two sensor elements each sensor element comprising:

a first substrate;

a second substrate; and

a generally planar antenna element accommodated by and mounted between said first substrate and said second substrate, wherein said antenna element is structured to emit electromagnetic waves from an edge of the antenna and said at least two sensors are angularly oriented relative to and directed toward each other.

40. A sensor as claimed in claim 39 wherein said angular orientation of said at least two sensors is approximately 120°

relative to each other.

41. A sensor as claimed in claim 39 wherein said angular orientation of said at least two sensors is adjustable relative to each other.

42. A method for evaluating a measurement signal against a reference signal comprising the steps of:

converting a reference signal having magnitude and phase to a complex form;

plotting said complex form reference signal in a complex plane to form a reference point;

converting a measurement signal into a complex form;

plotting said complex form measurement signal in said complex plane to form a measurement point;

determining complex distance between said measurement point and said reference point; and

comparing said complex distance to a threshold.

43. A method as claimed in claim 42 further comprising the step of generating said reference signal by taking a reference measurement.

44. A method for evaluating measurement signals against reference signals comprising the steps of:

taking measurements at a plurality of frequencies to generate a plurality of reference signals;

converting said plurality of reference signals having magnitude and phase to a complex form;

plotting said complex form reference signals in a complex plane to form a plurality of reference points;

taking measurements at said plurality of frequencies to generate a plurality of measurement signals;

converting said plurality of measurement signals into a complex form;

plotting said complex form measurement signals in said complex plane to form a plurality of measurement points;

determining a plurality of complex distances between said measurement points and corresponding ones of said reference points; and

comparing said plurality of complex distances to a corresponding plurality of thresholds.

45. A method as claimed in claim 44 further comprising the step of:

normalizing said reference signals by multiplying all reference signals by a normalization factor so that the maximum reference signal becomes one; and

multiplying all measurement signals by said normalization factor.

46. A method as claimed in claim 44 wherein said plurality of thresholds vary as a function of frequency.

47. A method as claimed in claim 46 wherein said plurality of thresholds vary as a function of frequency such that lower threshold values are used at frequencies where sensor performance is higher.

48. A method for evaluating measurement signals against reference signals comprising the steps of:

taking measurements at a plurality of frequencies to generate a plurality of reference signals;

converting said plurality of reference signals having magnitude and phase to a complex form;

plotting said complex form reference signals in a complex plane to form a plurality of reference points;

taking measurements at said plurality of frequencies to generate a plurality of measurement signals;

converting said plurality of measurement signals into a complex form;

plotting said complex form measurement signals in said complex plane to form a plurality of measurement points;

determining a plurality of complex distances between said measurement points and corresponding ones of said reference points;

determining a threshold based on said plurality of reference points;

determining a complex distance curve based on said plurality of complex distances; and

comparing the area under said complex distance curve to said threshold.

49. A sensor comprising at least two sensor elements each sensor element comprising:

a substrate;

a superstrate mounted to said substrate and having a base facing said substrate and an outer surface extending away from said substrate;

a generally planar antenna element accommodated by and mounted between said substrate and said superstrate; and

a housing supporting said at least two sensor elements to maintain a predetermined distance between said at least two sensor elements.

50. A sensor as claimed in claim 49 wherein said housing comprises a resilient material.

51. A sensor as claimed in claim 49 wherein said resilient material comprises polyurethane.

52. A sensor as claimed in claim 49 wherein said housing is shaped and said sensing elements are positioned within said housing to permit visual observation and palpation of body tissue interposed between said at least two sensor elements.

53. A sensor as claimed in claim 52 wherein said housing is shaped like a bowtie having two expanded portions interconnected by a portion more narrow than said expanded portions, each of said two expanded portions having at least one sensor element housed therein.

54. A sensor as claimed in claim 52 wherein said housing having first and second elongated portions interconnected by a third elongated portion, each of said first and second elongated portions having at least one sensor element housed therein.

56. A sensor as claimed in claim 49 comprising at least four sensor elements, said at least four sensor elements defining at least two electromagnetic wave transmitters and at least two of said sensor elements defining at least two electromagnetic wave receiver elements, said at least two electromagnetic wave transmitters being positioned opposite said at least two electromagnetic wave receivers.

57. A sensor as claimed in claim 49 wherein said at least two electromagnetic wave transmitters are separated from said at least two electromagnetic wave receivers by body tissue to be monitored by electromagnetic waves.

58. A sensor as claimed in claim 49 wherein said planar antenna elements of said at least two sensor elements are square and are electrically contacted adjacent inner corners of said elements.

55. A sensor as claimed in claim 55 wherein said third elongated portion is positioned at one end of said two elongated portions so that said sensor housing is generally U-shaped to permit visual observation and palpation of body tissue interposed within the open end of said U-shaped housing.

59. A sensor element for injecting and/or receiving electromagnetic waves into body tissue, said sensor comprising:

a housing;

a substrate mounted within said housing; and

a superstrate mounted to said substrate and having a base facing said substrate and an outer surface facing away from said substrate; and

a generally planar antenna element accommodated by and mounted between said substrate and said superstrate, wherein said housing extends to said outer surface of said superstrate and an electrical shield surrounds said sensor element except for said outer surface of said superstrate.

60. A sensor element as claimed in claim 59 wherein said housing is flush with said outer surface of said substrate.

61. A sensor element as claimed in claim 59 wherein said housing is recessed below said outer surface of said superstrate and defines a transitional periphery interconnecting said housing to said outer surface of said superstrate, wherein at least a portion of said transitional periphery has a generally smooth transition from said base to said surface plateau.