MICROFLUIDIC DEVICE AND METHOD OF OPERATION

Abstract

A microfluidic device and method for assessing properties of a fluid. The device includes a base supported by a substrate and a tube extending from the base and spaced apart from the substrate surface. The tube has an internal passage, first and second portions adjacent the base and defining, respectively, an inlet and outlet of the passage, and a distal portion. A drive electrode is located on the substrate surface adjacent the distal portion of the tube. Sensing electrodes are located on the substrate surface adjacent the first and second portions of the tube, and are adapted for sensing deflections of the first and second portions when vibrated with the drive electrode and from which the fluid property is determined. A pair of electrodes is located on the substrate surface between the drive and sensing electrodes, and are operated to enhance the performance of the microfluidic device, such as by supplementing the drive or sensing electrodes.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 are perspective and cross-sectional views, respectively, of a microfluidic device with a resonating micromachined tube through which a fluid flows in accordance with the prior art.

FIG. 3 is a plan view of a microfluidic device with a resonating micromachined tube in accordance with a first embodiment of this invention.

FIG. 4 is a plan view of a microfluidic device with a resonating micromachined tube in accordance with a second embodiment of this invention.

Claims

1. A microfluidic device for determining at least one property of a fluid, the device comprising: a substrate;a structure comprising a base supported by the substrate and a tube extending from the base and spaced apart from a surface of the substrate so as to be capable of vibrating in a plane normal to the surface of the substrate, the tube having a continuous internal passage, a first portion adjacent the base and defining a fluid inlet of the passage, a second portion adjacent the base and defining a fluid outlet of the passage, and a distal portion relative to the base;a drive electrode on the surface of the substrate, adjacent the distal portion of the tube, and adapted for vibrating the tube;sensing electrodes on the surface of the substrate, adjacent the first and second portions of the tube, adapted for sensing deflections of the first and second portions of the tube when vibrated with the drive electrode, and adapted for producing outputs corresponding to the sensed deflections;a pair of electrodes adjacent the tube and on the surface of the substrate between the drive electrode and the sensing electrodes; andmeans for determining the property of the fluid from the outputs of the sensing electrodes.

2. The microfluidic device according to claim 1, wherein the pair of electrodes are means for vibrating the tube in addition to the drive electrode.

3. The microfluidic device according to claim 1, wherein the pair of electrodes are means for sensing deflections of the tube in addition to the sensing electrodes.

4. The microfluidic device according to claim 3, wherein the sensing electrodes sense amplitudes of the deflections of first and second portions of the tube, and the pair of electrodes sense a phase difference in the deflections of the first and second portions of the tube.

5. The microfluidic device according to claim 1, further comprising means for applying a bias to the pair of electrodes and balancing the tube to counter a twist in the tube.

6. The microfluidic device according to claim 1, further comprising means for operating the pair of electrodes as additional drive electrodes if a damped condition is detected by the sensing electrodes while the tube is vibrated with the drive electrode.

7. The microfluidic device according to claim 1, wherein each of the sensing electrodes is spaced about 0.1 to about 4 micrometers from the tube.

8. The microfluidic device according to claim 7, wherein each of the sensing electrodes is closer to the tube than the pair of electrodes.

9. The microfluidic device according to claim 7, wherein each of the sensing electrodes is closer to the tube than the pair of electrodes and the drive electrode.

10. The microfluidic device according to claim 1, wherein each of the sensing electrodes extends less than half a distance from the base to the distal portion of the tube.

11. The microfluidic device according to claim 1, further comprising means for altering the operation of the determining means if a damped condition is detected while the tube is vibrated with the drive electrode.

12. The microfluidic device according to claim 1, further comprising means for triggering a high pressure pulse in the fluid if a damped condition is detected while the tube is vibrated with the drive electrode.

13. The microfluidic device according to claim 1, further comprising means for sensing time and temperature during operation of the microfluidic device and applying a frequency offset to the outputs of the sensing electrodes based on the sensed time and temperature.

14. The microfluidic device according to claim 1, wherein the tube has a C-shaped configuration.

15. The microfluidic device according to claim 1, wherein the base is between the first and second portions of the tube and the first and second portions are coaxial.

16. The microfluidic device according to claim 1, wherein the microfluidic device is installed in a system chosen from the group consisting of chemical concentration sensors, fuel cell systems, and drug delivery systems.

17. A method of operating a microfluidic device to sense the density of a fluid, the method comprising: causing a structure of the microfluidic device to vibrate as the fluid flows through a microchannel within the structure;producing a series of outputs corresponding to the vibration frequency of the vibrating structure; anddetermining the density of the fluid flowing through the microchannel of the vibrating structure on the basis of at least a first set of the outputs and performing at least one of: excluding from the determination any outputs altered by a second phase in the fluid; andoffsetting the density for any film build-up within the microchannel.

18. The method according to claim 17, wherein the method comprises only one of the excluding and offsetting steps.

19. The method according to claim 17, wherein the method comprises each of the excluding and offsetting steps.

20. The method according to claim 17, wherein the excluding step is performed for any outputs produced while the peak gain or quality factor of the vibrating structure falls outside a predetermined threshold therefor.

21. The method according to claim 17, wherein the offsetting step comprises sensing time and temperature of the fluid while the fluid is flowing and offsetting the density based on the sensed time and temperature.

22. The method according to claim 17, further comprising the step of triggering a high pressure pulse in the fluid if the peak gain or quality factor of the vibrating structure falls outside a predetermined threshold therefor.