Pressure sensor with conductive laminate membrane

• US 20060225494A1
• Filed: 05/30/2006
• Published: 10/12/2006
• Est. Priority Date: 10/18/2004
• Status: Active Grant

• Current Assignee: Precision Mechatronics Pty Ltd
• Original Assignee: Silverbrook Research Pty Limited
• Inventors: Silverbrook, Kia, Mallinson, Samuel George
• Granted Patent: US 7,350,417 B2
• Time in Patent Office: Days
• US Class Current: 73/146
• CPC Class Codes: B60C 23/0408 transmitting the signals by non-mechanical means from the wheel or tyre to a vehicle body mounted receiver
• CPC Class Codes: G01L 13/00 Devices or apparatus for measuring differences of two or more fluid pressure values
• CPC Class Codes: G01L 17/00 Devices or apparatus for measuring tyre pressure or the pressure in other inflated bodies
• CPC Class Codes: G01L 19/04 Means for compensating for effects of changes of temperature , i.e. other than electric compensation
• CPC Class Codes: G01L 9/0072 using variations in capacitance
• CPC Class Codes: G01L 9/0073 using a semiconductive diaphragm
• CPC Class Codes: G01L 9/0075 using a ceramic diaphragm, e.g. alumina, fused quartz, glass
• CPC Class Codes: G01L 9/125 with temperature compensating means non electric temperature compensating means G01L19/04

Abstract

A pressure sensor (30) for sensing a fluid pressure in harsh environments such as the air pressure in a tire, by using a chamber (58) partially defined by a flexible membrane (50), the flexible membrane (50) is a laminate having at least two layers wherein at least one of the layers is at least partially formed from conductive material, and the chamber (58) containing a fluid at a reference pressure, such that the flexible membrane (50) deflects from any pressure difference between the reference pressure and the fluid pressure; and,

associated circuitry (34) for converting deflection of the flexible membrane (50) into an output signal indicative of the fluid pressure.

Forming the membrane from a number of separately deposited layers alleviates internal stress in the membrane (50). The layers can be different materials specifically selected to withstand harsh environments.

Claims

1. A pressure sensor for sensing a fluid pressure, the pressure sensor comprising:

a chamber partially defined by a conductive membrane having a laminate structure;

fluid at a reference pressure sealed within the chamber such that the conductive membrane deflects from pressure differences between the reference pressure and the fluid pressure; and

,

associated circuitry incorporating the conductive membrane to convert its deflection into an output signal indicative of the fluid pressure.

2. A pressure sensor according to claim 1 wherein the laminate structure has layers formed from the deposition of different metal ceramics.

3. A pressure sensor according to claim 2 wherein the metal ceramics are metal nitrides or mixed metal nitrides.

4. A pressure sensor according to claim 2 wherein the metal ceramics are titanium nitride, titanium aluminium nitride, tantalum silicon nitride, titanium aluminium silicon nitride, tantalum aluminium silicon nitride.

5. A pressure sensor according to claim 4 wherein one or more of the layers of the laminate is metal.

6. A pressure sensor according to claim 5 wherein the metal is titanium, tantalum or vanadium.

7. A pressure sensor according to claim 1 wherein, the chamber, the conductive membrane and the associated circuitry are formed on a silicon wafer substrate using lithographically masked etching and deposition techniques.

8. A pressure sensor according to claim 1 wherein the membrane is less than 0.1 grams.

9. A pressure sensor according to claim 1 wherein the pressure sensor is adapted to sense the air pressure within a pneumatic tire.

10. A pressure sensor according to claim 1 wherein the membrane is non-planar.

11. A pressure sensor according to claim 10 wherein the membrane is corrugated.

12. A pressure sensor according to claim 11 wherein, the membrane corrugations have a period of between 5 microns and 15 microns.

13. A pressure sensor according to claim 1 wherein, the membrane is substantially circular and the corrugations are annular.

14. A pressure sensor according to claim 10 wherein the corrugations have a substantially square-shaped cross-sectional profile.

15. A pressure sensor according to claim 14 wherein the flexible corrugated membrane has a corrugation factor of 8.

16. A pressure sensor according to claim 15 wherein the sensor has a linear response up to about 1 MPa.

17. A pressure sensor according to claim 1 wherein the sensor is powered by a long-life battery.

18. A pressure sensor according to claim 1 wherein the sensor is powered by radio waves transmitted from a remote source.

19. A pressure sensor according to claim 1 wherein the sensor is a capacitative sensor having:

a conductive layer deposited in the chamber to form a first capacitor electrode; and

, the conductive membrane forms a second capacitor electrode;

such that,

deflection of the membrane changes the capacitance which the associated circuitry converts to the output signal;

wherein,

the conductive layer is arranged such that deflection of the membrane towards the conductive layer can displace the fluid from between the membrane and the conductive layer.

20. A pressure sensor according to claim 1 further comprising a second chamber with a second membrane, the second chamber being sealed from the fluid pressure and the second membrane deflecting from a predetermined pressure difference in the second chamber;

wherein,

the associated circuitry converts the deflection of the second membrane into an adjustment of the output signal to compensate for the temperature of the sensor.