Micro slit viscometer with monolithically integrated pressure sensors

• US 20050183496A1
• Filed: 03/11/2005
• Published: 08/25/2005
• Est. Priority Date: 10/31/2001
• Status: Active Grant

• Current Assignee: RheoSense, Inc.
• Original Assignee: RheoSense, Inc.
• Inventors: Baek, Seong-Gi
• Granted Patent: US 7,290,441 B2
• Time in Patent Office: Days
• US Class Current: 73/54.90
• CPC Class Codes: G01N 11/08 by measuring pressure required to produce a known flow

Abstract

An improved micro slit viscometer includes a combined micrometer depth rectangular slit flow channel with monolithically integrated multiple pressure sensors in the flow channels and a pumping system that injects a test sample to the channel at a desired flow rate. Pressure sensing diaphragm of the monolithically integrated pressure sensors is smooth to minimize the flow disturbance thereby measuring accurate local pressures. With the measurement of the pressures at various locations of the channel the true viscosity of test sample can be calculated. The viscometer may consist of multiple flow channels and thus the true viscosity at multiple shear rates can be measured simultaneously for a given flow rate thereby obtaining a full viscosity curve as a function of shear rate of non-Newtonian liquids in a much faster manner. The viscometer needs only a miniscule amount of sample, which minimizes a waste of test material. The flow channels and the monolithically integrated pressure sensors are fabricated using microfabriaction processes on wafers and combined, which greatly reduce the production costs.

Claims

1. A slit rheometer for determining the viscosities of liquids comprising:

a channel substrate with at least one flow channel contained by three side walls, at least one flow entrance, and at least one flow exit;

a monolithic sensor plate having at lease two independent pressure sensors at two different locations sufficiently away from the entrance and exit along the longitudinal direction in each flow channel of the at least one flow channel so that a pressure drop of fully developed flow can be measured;

the channel substrate and the sensor plate being combined so that the sensor plate surface becomes a side wall that enables full containment along with the three side walls of the channel substrate of the liquids during flow along the channel except at areas of liquid entrance and exit.

2. A slit rheometer according to claim 1, additionall including means to force a liquid to flow through a channel at a known volumetric flow rate.

3. A slit rheometer according to claim 1, wherein the flow channel has a width and a depth and wherein the width of the flow channel is at least about ten times larger than the depth of the flow channel in each of the at least one flow channels.

4. A slit rheometer according to claim 1, wherein the sensor plate has at least one temperature sensor for each of the at least one flow channels located to measure the temperture of the liquid flowing through the flow channel.

5. A slit rheometer according to claim 1, wherein there are at least two flow channels connected in series.

6. A slit rheometer according to claim 5, wherein the at least two flow channels are different in channel depth.

7. A slit rheometer according to claim 1, wherein the at least two flow channels are different in channel width.

8. A slit rheometer according to claim 1, wherein there are at least two channels in parallel.

9. A slit rheometer according to claim 1, where the at least one channel is on the order of a micrometer in depth.

10. A slit rheometer according to claim 9, where the at least one channel is at least about ten micrometers in width.

11. A slit rheometer according to claim 10 where the at least one channel has a length of at least about one hundred micrometers.

12. A slit rheometer according to claim 1 where the pressure sensors are capacitive pressure sensors.

13. A slit rheometer comprising:

a body;

a plurality of recesses in the body each having different dimensions and being connected together in series to form a flow channel through the body; and

a plurality of pressure sensors associated with each recess to provide indications of pressure exerted by liquid flowing through the recess against the recess at the location of each of the pressure sensors associated with the recess.

14. A slit rheometer according to claim 13, wherein there are at least two recesses.

15. A slit rheometer according to claim 13, wherein there are at least two pressure sensors associated with each recess.

16. A slit rheometer according to claim 13, wherein the recesses each have a different depth.

17. A slit rheometer according to claim 13, wherein the recesses each have a different width.

18. A method of manufacturing slit rheometers comprising:

etching at least two cavities in a micro-fabrication wafer;

combining the etched micro-fabrication wafer with a substrate to create a pressure sensor plate with pressure sensors formed in the cavities; and

combining the pressure sensor plate with another substrate to create a flow channel through which liquid can flow, the flow channel passing over the pressure sensors in the pressure sensor plate.

19. A method of manufacturing slit rheometers according to claim 18 where the at least two wells are etched using chemical etching.

20. A method of manufacturing slit rheometers according to claim 18 where the at least two wells are etched using plasma etching.

21. A method of manufacturing slit rheometers according to claim 18 where the at least two wells are etched using a combination of chemical and plasma etching.

22. A method of manufacturing slit rheometers according to claim 18 where the pressure sensors are capacitor type sensors.

23. A method of manufacturing slit rheometer according to claim 18 where the pressure sensors are piezoresistive type sensors.