Pressure sensor with a deformable electrically resistive membrane
A pressure sensing element has at least a housing containing a fluid. The housing has at least two moveable surfaces in contact with the fluid in the housing; There is a first moveable surface comprising a pressure application surface which, when moved towards, away from, into or out of the fluid, creates a change in fluid pressure and a second moveable surface in contact with the fluid in the housing comprising a membrane which, when deformed by pressure changes in the fluid, alters its electrical resistance. The membrane has two electrodes attached to deformable material in the membrane. The membrane my have an elastomer having conductive particles distributed therein. The elastomer may be a dielectric and the particles are conductive nanoparticles.
1. A pressure sensing element comprising:
a housing defining a tubular fluid chamber containing a fluid therein;
a pressure application surface operably coupled to a moveable piston positioned proximal to a first end of the tubular fluid chamber and in contact with the fluid, the piston configured to shift relative to the housing when an external pressure is applied to the pressure application surface, thereby affecting a change in fluid pressure; and
a deformable piezoresistive membrane in contact with the fluid, wherein the deformable piezoresistive membrane comprises an elastomer having conductive carbon nanoparticles distributed therein, and is configured to change in electrical resistance when deformed by pressure changes in the fluid.
2. The pressure sensing element of claim 1 wherein the deformable piezoresistive membrane has the two electrodes attached to deformable material in the membrane.
3. The pressure sensing element of claim 2 wherein the conductive carbon nanoparticles are conductive nanotubes.
4. The pressure sensitive element of claim 3 wherein the deformable piezoresistive membrane comprises an elastic body of a silicone rubber containing a loading of between 0.5% and 3%, by total weight of conductive nanotubes.
5. The pressure sensing element of claim 2 wherein the fluid in the housing comprises a gas.
6. The pressure sensing element of claim 2 wherein the fluid in the housing comprises a liquid.
7. The pressure sensing element of claim 2 wherein the pressure application surface comprises a film at one end of the housing.
8. The pressure sensitive element of claim 7 wherein the two electrodes of the deformable piezoresistive membrane are in communication with both a power source and a processor.
9. The pressure sensing element of claim 2 wherein the pressure application surface is separate from the deformable piezoresistive membrane by a distance within the fluid of between 0.1 and 20 mm.
10. The pressure sensing element of claim 2 wherein the pressure application surface is separate from the deformable piezoresistive membrane by a distance within the fluid of between 0.1 and 5 mm.
11. The pressure sensing element of claim 2 wherein the pressure application surface is separate from the deformable piezoresistive membrane by a distance within the fluid of between 0.1 and 2 mm.
12. The pressure sensing element of claim 2 wherein the housing comprises a tubular wall defining the tubular fluid chamber, with the pressure application surface positioned proximal to a first end of the tubular fluid chamber and the deformable piezoresistive membrane positioned proximal to a second end of the tubular fluid chamber.
13. The pressure sensitive element of claim 12 wherein the two electrodes of the deformable piezoresistive membrane are in communication with both a power source and a processor.
14. The pressure sensitive element of claim 2 wherein the deformable piezoresistive membrane has a thickness of between 4 and 50 microns.
15. The pressure sensitive element of claim 2 further comprising a source of voltage between 0.01 and 10 volts applied to one electrode and a current sensor on the second electrode.
16. The pressure sensitive element of claim 2 wherein the at least two electrodes of the deformable piezoresistive membrane are in communication with both a power source and a processor.
17. The pressure sensitive element of claim 2 wherein a separation of at least 0.01 mm is maintained between the pressure application surface and the deformable piezoresistive membrane when a weight of 5 grams is applied to the pressure application surface.
18. The pressure sensitive element of claim 17 wherein the two electrodes of the deformable piezoresistive membrane are in communication with both a power source and a processor.
19. A method of detecting pressure comprising providing a current into a first of the electrodes of the two electrodes of the pressure sensitive element of claim 2 , comprising:
providing a voltmeter or ammeter to a second of the two electrodes;
applying a pressure to the pressure application surface to cause a change in the current or voltage measured by the voltmeter or ammeter; and
comparing the change in the current or voltage to a lookup table to identify a magnitude of the pressure applied to the pressure application surface.
20. A method of detecting pressure comprising providing a current into a first of the electrodes of the two electrodes of the pressure sensitive element of claim 2 , comprising;
providing a voltmeter or ammeter to a second of the two electrodes;
applying a pressure to the pressure application surface to cause a change in the current or voltage measured by the voltmeter or ammeter;
forwarding a signal indicating the change in the current or voltage to a processor; and
executing a code to indicate a magnitude of the pressure applied to the pressure application surface.
21. The pressure sensitive element of claim 1 wherein the deformable piezoresistive membrane comprises an electrically conductive silicone rubber composite comprised of a liquid silicone rubber with a multi-wall carbon nanotube loading of between 1%-3% by weight and a hardness between 10 and 60 Asker C hardness.