High resolution solid state pressure sensor

• US 20050148884A1
• Filed: 10/08/2004
• Published: 07/07/2005
• Est. Priority Date: 10/10/2003
• Status: Active Grant

• Current Assignee: Covidien LP (Medtronic Plc)
• Original Assignee: Covidien LP (Medtronic Plc)
• Inventors: Parks, Thomas R., Son, Jae S.
• Granted Patent: US 9,078,570 B2
• Time in Patent Office: Days
• US Class Current: 600/488
• CPC Class Codes: A61B 5/0215 by means inserted into the body catheters A61M25/00
• CPC Class Codes: A61B 5/037 Measuring oesophageal pressure
• CPC Class Codes: A61B 5/6852 Catheters
• CPC Class Codes: A61M 2025/0002 with a pressure sensor at the distal end

Abstract

A pressure sensor and pressure-sensing catheter in which a deformable pressure sensing membrane is separated from an inner metalized surface on a rigid support by an air gap. An input allows a voltage to be applied to an electrode on the sensing membrane and an output allows reading of the signal modulation from the support surface. An outer sleeve overlays the membrane and a wire bus transmits the signals to a terminal connector. The catheter may include a vented air gap, a multiplexing wire bus, and an internal cable to maintain tension.

Claims

1. A pressure sensing catheter comprising:

a plurality of pressure sensors having a deformable outer membrane with an electrically conductive inner surface, spaced apart from a rigid inner, electrically conductive surface by a gap, said pressure sensors spaced along a support cable, wherein each pressure sensor may produce an electrical signal in response to pressure external to the assembly; and

a signal bus extending through the plurality of sensors and electrically connected to each of the electrical conductive inner surface of each pressure sensor and each of the rigid inner electrically conductive surface of each pressure sensor, said signal bus extending to terminal connectors.

2. The apparatus of claim 1 wherein said pressure sensors are capacitive transducers.

3. The apparatus of claim 2 wherein said pressure sensors include a deformable membrane and a rigid metalized surface separated from said deformable membrane by an air gap.

4. The apparatus of claim 1 wherein said signal bus comprises a first group of input lines and a second group of output lines.

5. The apparatus of claim 4 wherein said first group of input lines are connected to a first terminal of the pressure transducers and said second group of output lines are connected to a second terminal of the pressure transducers.

6. The apparatus of claim 5 wherein the input lines supply a voltage as an A.C. signal.

7. The apparatus of claim 6 wherein said A.C. signal has a frequency below 250 kHz.

8. The apparatus of claim 1 wherein said signal bus is carried in a flexible wire harness.

9. The apparatus of claim 1 further including a non-rigid support tube.

10. The apparatus of claim 9 wherein said silicone sleeve is 0.050 to 0.001 inch thick.

11. The apparatus of claim 1 including pressure sensors spaced 1 cm center to center.

12. The apparatus of claim 1 wherein the pressure sensors have a coaxial tubular deformable outer electrode having a plurality of longitudinal lengthwise slits.

13. The apparatus of claim 4 wherein said input lines and said output lines are both disposed on a single, shielded ribbon cable.

14. A tubular capacitive pressure sensor comprising:

a pair of spaced apart, co-axially aligned surfaces including an outer tubular, deformable, electrically conductive membrane surface, and an inner axially aligned non-deformable electrically conductive surface separated from the deformable membrane by an air gap having a characteristic gap dimension; and

electrical signal leads positioned proximate to said membrane surface, making separate contact with the deformable conductive membrane surface and the non-deformable conductive surface, whereby when a signal source having a frequency establishing a measurable capacitive impedance across the electrical signal leads, the capacitive impedance varies as pressure changes the dimension of the gap.

15. The sensor of claim 14 wherein said inner surface is a surface on a spool, said spool having annular raised structures for positioning said outer surface.

16. The sensor of claim 15 wherein said outer surface is comprised of a polyamide membrane having a patterned conductive area.

17. The sensor of claim 16 wherein the electrical signal leads are positioned on an arm that extends from a side of the spool.

18. The sensor of claim 14 wherein the deformable outer membrane has a plurality of longitudinal slits.

19. The sensor of claim 17 further including a ground on said sensor, said ground electrically joined to said spool.

20. A pressure sensing device comprising:

a longitudinally extending tube, said support tube having an internal lumen and an external wall;

a plurality of solid state pressure sensors inside said support tube, each pressure sensor having an input and an output; and

an interconnect bus connecting each sensor input and output to an input line and an output line, wherein (m×

n) sensors connect in a m×

n matrix to m input lines and n output lines.

21. The catheter of claim 20 further comprising an axially rigid support cable extending through the support tube at least as far as the most distal pressure sensor.

22. The catheter of claim 21 wherein said support cable is mechanically joined to said pressure sensors.

23. The catheter of claim 20 wherein said pressure sensors are air gap pressure sensors.

24. The catheter of claim 23 wherein said air gap pressure sensors include an air gap region in gas communication with a vent tube, said vent tube venting to atmospheric pressure.

25. The catheter of claim 20 wherein said plurality of pressure sensors includes 36 pressure sensors.

26. The catheter of claim 20 wherein six sensors share an input line and six sensors share an output line.

27. The catheter of claim 25 wherein said pressure sensors are spaced at one centimeter intervals.

28. The catheter of claim 20 wherein said input lines and output lines are disposed on a ribbon.

29. An elongate pressure sensing device including:

a longitudinally extending non-rigid external tube;

a plurality of capacitive pressure sensors inside said tube; and

a multiplexing means for providing an input and an output to each sensor and transmitting said output to a terminal connector.

30. The device of claim 29, wherein said device is a catheter.

31. The pressure sensor of claim 29, wherein said pressure sensors are capacitive transducers.

32. A circumferential pressure sensor comprising:

a pair of spaced apart co-axially aligned surfaces including an outer deformable tubular membrane, and an inner axially aligned surface separated from the deformable membrane by an air gap having a characteristic dimension; and

a means for transducing a deformation of said deformable membrane into an electrical signal that indicates pressure from outside said sensor.

33. A pressure sensing catheter comprising:

an a longitudinally extending non-rigid external sleeve;

a plurality of solid state pressure sensors positioned inside said sleeve such that pressure from outside of said sleeve may be measured by said pressure sensors; and

an axial load bearing cable positioned coaxially inside said pressure sensors, said cable allowing bending of areas between said sensors while bearing an axial load.

34. A pressure sensor comprising:

an outer, flexible member;

an outer electrode positioned on an inside surface of said flexible membrane;

a rigid mounting structure onto which said outer flexible membrane is annularly mounted;

an inner electrode positioned on an surface of said rigid mounting structure such that said outer electrode and said inner electrode are coaxial such that said outer electrode and said inner electrode are separated by an air gap; and

wherein said outer electrode and inner electrode do not extend to either side of said rigid mounting structure, said rigid mounting structure acting to shunt axial and bending loads.

35. A capacitive pressure sensing catheter comprising:

a plurality of pressure sensors, each pressure sensor having an input and an output; and

a flexible ribbon cable extending through said pressure sensors, said flexible ribbon cable containing a plurality of wires, said input and output from each sensor connected to at least one wire in said cable.

36. A pressure sensor comprising:

an outer, flexible member;

an outer electrode positioned on an inside surface of said flexible membrane;

a rigid mounting structure onto which said outer flexible membrane is annularly mounted;

an inner electrode positioned on an surface of said rigid mounting structure such that said outer electrode and said inner electrode are coaxial such that said outer electrode and said inner electrode are separated by an air gap; and

a vent extending though said rigid mounting structure into an internal space in said sensor, said vent allowing connection to a vent line to vent said air gap to an external pressure.

37. A pressure sensing catheter comprising:

a plurality of solid state pressure sensors;

a wire bus electronically connected to each pressure sensor such that said bus may provide an input signal to each sensor and an out put signal from each sensor, said wire bus extending from a most distal pressure sensor to a terminal connector; and

a disposable sheath extending over said plurality of sensors.

38. A pressure sensing catheter comprising:

a plurality of solid state pressure sensors;

a wire bus electronically connected to each pressure sensor such that said bus may provide an input signal to each sensor and an out put signal from each sensor, said wire bus extending from a most distal pressure sensor to a terminal connector; and

an outer compliant sleeve extending over said plurality of sensors.

39. A capacitive pressure sensor comprising:

an outer sensing membrane;

an inner rigid structure supporting said outer sensing membrane;

a first conductive trace leading to a deformable outer electrode;

a second conductive trace allowing connection to an underlying second electrode surface.

40. A capacitive pressure sensor comprising:

an outer deformable membrane;

an input on said deformable membrane to allow a voltage to be introduced onto an electrode on said outer deformable membrane;

a rigid inner structure;

a metalized surface on said rigid structure, said metalized surface coaxial with an electrode on said outer deformable membrane; and

a ground on said rigid structure, said ground allowing connection to a ground wire to allow shielding of said sensor from ambient dielectric charges.