Wireless capacitance pressure sensor

• US 7,181,975 B1
• Filed: 09/13/2005
• Issued: 02/27/2007
• Est. Priority Date: 09/13/2005
• Status: Expired due to Fees

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Bradley, Alistair D., Shiffer, Stephen R.
• Primary Examiner(s): Lefkowitz; Edward
• Assistant Examiner(s): Jenkins; Jermaine
• Application Number:
  US11/226,085
• Time in Patent Office: 532 Days
• Field of Search: 73700-756, 3612831-2834
• US Class Current: 73/724
• CPC Class Codes: A61B 5/0002 Remote monitoring of patients using telemetry, e.g. transmission of vital signals via a communication network A61B5/07 takes precedence; transmission systems for measured values G08C; transmission H04B; transmission of digital information H04L; wireless communication networks H04W
• CPC Class Codes: A61B 5/0215 by means inserted into the body catheters A61M25/00
• CPC Class Codes: G01L 9/0072 using variations in capacitance

Abstract

A wireless pressure sensor system has a pressure sensing capacitor and an inductor mounted on a common housing. The pressure sensing capacitor has a conductive diaphragm, a dielectric layer and a fixed electrode separated at least in part from the diaphragm by a gap formed in the housing. The electrode is arranged with a protrusion such that displacement of the diaphragm varies the area of capacitive contact with the electrode by rolling along the protrusion. The inductor coil and pressure sensing capacitor are connected to form a passive inductive-capacitive (LC) tank circuit. A remote interrogation circuit, inductively coupled to the pressure sensor inductor coil can be utilized to detect the resonant frequency of the LC tank which varies as a function of pressure sensed by the diaphragm.

Claims

1. A pressure sensor, comprising:

a pressure sensing capacitor comprising;

a housing defining a cavity,

a diaphragm, supported on said housing and separating said cavity from an external pressure region, said diaphragm comprising a conductive material,

an electrode disposed on said housing inside said cavity and facing said diaphragm so as to define a gap between at least part of said diaphragm and at least part of said electrode, wherein said electrode is arranged such that said diaphragm can roll against said electrode in capacitive contact therewith so as to vary the contact area upon displacement of said diaphragm;

an insulating layer disposed between said electrode and said diaphragm to provide a dielectric layer between said electrode and said diaphragm, and

an inductor, formed on said housing, electrically connected to said pressure sensing capacitor so as to form an LC tank circuit,

wherein said gap varies as a function of a pressure differential applied to said diaphragm such that the capacitance of said pressure sensing capacitor varies, and

whereby, an electromagnetic signal can be applied to the pressure sensor to detect the resonant frequency of said LC tank to determine said pressure differential.

2. The system of claim 1, wherein said electrode is shaped such that a portion of said electrode projects towards said diaphragm, said diaphragm rolling against said projecting portion in capacitance therewith upon displacement of the diaphragm.

3. The system of claim 2, wherein said projecting portion has a curved or rounded shape apex.

4. The system of claim 1, wherein said electrode has an inner region and an outer region surrounding said inner region, said outer region being substantially planar and said inner region projecting towards said diaphragm such that said diaphragm can roll against said inner region in capacitive contact therewith.

5. The system of claim 1, wherein the inductor comprises an inductor coil disposed on said housing.

6. The system of claim 5, further comprising first and second metal interconnects formed on or in said housing for electrically connecting said inductor coil to said pressure sensing capacitor, said first metal interconnect connecting one end of said coil to said electrode and a second metal interconnect connecting the other end of said coil to said diaphragm.

7. The system of claim 1, wherein said housing is formed with a portion projecting towards said diaphragm, said electrode

being disposed contiguous with said housing projecting portion such that said electrode-projects towards said diaphragm.

8. The system of claim 1, wherein said diaphragm is supported on said housing such that, when zero differential pressure is applied to said diaphragm, said diaphragm is partially rolled over said electrode projecting portion.

9. The system of claim 1, including an interrogation circuit for transmitting an electromagnetic signal to said inductor and for analyzing the resonant frequency of said pressure sensor LC (tank) circuit.

10. The system of claim 1, wherein said diaphragm comprises a polymer with low modulus of elasticity having a metallized layer formed thereon.

11. A pressure sensor, comprising:

a pressure sensing capacitor comprising;

a housing having a bottom wall and at least one side wall defining a cavity,

a diaphragm, supported on the said side wall(s), separating said cavity from an external pressure region, said diaphragm comprising a conductive material,

an electrode disposed inside said cavity, adjacent said diaphragm, so as to define a gap between at least part of said diaphragm and at least part of said electrode, wherein said electrode is shaped to form a protuberance or protrusion such that said diaphragm can roll against said protuberance or protrusion in capacitive contact with said electrode upon displacement of said diaphragm;

an insulating layer disposed between said electrode and said diaphragm to provide a dielectric layer between said electrode and said conductive material of said diaphragm, and

an inductor coil, formed on or in the bottom wall of said housing, electrically connected to said pressure sensing capacitor so as to form an LC tank circuit,

wherein said gap varies as a function of pressure differential applied to said diaphragm such that the capacitance of said pressure sensing capacitor varies, and

whereby, when an electromagnetic signal is applied to the pressure sensor, changes in resonant frequency of said LC tank are detectable in order to determine said pressure differential.

12. The system of claim 11, wherein said bottom wall comprises an inner region and an outer region surrounding said inner region, said outer region being substantially planar in form and said inner region being shaped also to form a protuberance or protrusion, and

wherein said electrode is formed as a layer contiguous with the inside of said bottom wall such that said electrode is shaped to form said electrode protuberance or protrusion.

13. The system of claim 12, wherein the apex of said protuberance or protrusion has a hemispherical or rounded shape.

14. The system of claim 11, wherein said inductor coil is disposed on the outside of said bottom wall about said outer region in a plane substantially parallel to the plane of said diaphragm.

15. The system of claim 14, further comprising first and second metal interconnects formed on or in said housing, said first metal interconnect connecting the inner end of said coil to said electrode via a through hole located about the centre of the bottom wall inner region and said second metal interconnect connecting the outer end of said coil to said diaphragm via a through-hole located about said bottom wall outer region.

16. The system of claim 11, further comprising locating pins distributed on said side wall(s), said diaphragm having corresponding location holes at the periphery thereof for locating on said sidewall locating pins to locate said diaphragm on said housing.

17. The system of claim 16, further comprising a frame for attaching on the periphery of said metal sheet, said frame having corresponding locating holes for locating on said housing locating pins to securely fix said diaphragm between said frame and said sidewall(s) of said housing.

18. A method of manufacturing a pressure sensor comprising the steps of

providing a housing having a bottom wall and at least one sidewall, said bottom and sidewall(s) forming a cavity,

forming a diaphragm on said sidewall(s) so as to separate said cavity from an external pressure region, said diaphragm comprising a conductive material,

arranging an electrode to form a protuberance or protrusion inside said cavity such that said diaphragm can roll against said protuberance or protrusion in capacitive contact with said electrode so as to vary said gap upon displacement of said diaphragm,

forming an insulating layer between said conductive material of said diaphragm and said electrode,

forming an inductor coil on the bottom wall,

forming an electrical interconnect between one end of said inductor coil and said electrode,

forming an electrical interconnect between the other end of said inductor coil and said diaphragm.

19. The method of claim 18, further comprising

shaping said bottom wall of said housing to form a protuberance or protrusion, and

wherein arranging said electrode in said cavity comprises forming a conductive layer contiguous with the inside of said bottom wall.