Method and apparatus for measuring viscosity

• US 20010045122A1
• Filed: 05/28/2001
• Published: 11/29/2001
• Est. Priority Date: 05/26/2000
• Status: Active Grant

• Current Assignee: Dieter Knoll, Henning Zinke, Karl-Ernst Ehwald, Rudolf Ehwald, Wolfgang Winkler
• Original Assignee: Dieter Knoll, Henning Zinke, Karl-Ernst Ehwald, Rudolf Ehwald, Wolfgang Winkler
• Inventors: Ehwald, Karl-Ernst, Knoll, Dieter, Winkler, Wolfgang, Zinke, Henning, Ehwald, Rudolf
• Granted Patent: US 7,284,413 B2
• Time in Patent Office: Days
• US Class Current: 73/54.23
• CPC Class Codes: A61B 5/14532 for measuring glucose, e.g. by tissue impedance measurement
• CPC Class Codes: G01N 11/16 by measuring damping effect upon oscillatory body
• CPC Class Codes: G01N 13/02 Investigating surface tension of liquids
• CPC Class Codes: G01N 2011/008 optical properties
• CPC Class Codes: G01N 2203/0094 Visco-elasticity

Abstract

An apparatus for measuring the viscosity of a fluid having a first rigid member extending from a body of semiconductor material and provided with a first conductive path and a second resiliently flexible member provided with a second conductive path and arranged in cantilever fashion over the rigid member. At least one of the conductive paths may be selectively energized to brig about relative movement between the rigid and flexible member. Subsequent deenergization of the path causes the resiliently flexible member to return to its initial position, the rate of return being measured to derive a signal representative of the viscosity. Also described are methods of carrying out the measurement and of fabricating the apparatus.

Claims

1. An apparatus for measuring viscosity with a micromechanical measuring facility and electronic systems for measuring, transducing and analyzing signals, with the following features:

a measuring zone implemented on a mechanically stable substrate is freely accessible or enclosed within a measuring chamber with pores or openings for diffusive or convective mass transport, the measuring zone containing two or several closely spaced conductors of which at least one is connected to a controllable current source or HF voltage source and of which at least one is completely or partially cantilevered within the measuring zone, the position of the cantilevered conductor(s) being defined within the measuring zone by the resiliency of the bracket or their/its own resiliency and by voltage-dependent or current-dependent electrical or magnetic attraction or repelling forces, which can be changed by means of said HF voltage sources or current sources, and the measuring zone containing an implemented measuring set up for detection of the viscosity-dependent position change of the conductor(s) in response to changes of said attraction or repelling forces.

2. The apparatus of

claim 1

, wherein the substrate consists of a semiconductor material and contains implemented circuits for detecting the position respectively position change of the cantilevered movable conductor(s) and/or for the signal transduction and/or the signal export and/or for the controllable current or HF voltage sources.

3. The apparatus of

claim 1

, wherein a tightly implemented loop or flat coil and a cantilevered movable conductor forming a loop are arranged on the substrate at the place of the measuring zone, this cantilevered movable conductor being fixed to the substrate at two or more points within the measuring zone.

4. The apparatus of

claim 1

, wherein the substrate is formed as bar-shaped thin tip at the place of the measuring zone.

5. The apparatus of

claim 4

, wherein the measuring zone is connected with the outer medium by a dialysis membrane, the resulting measuring chamber being filled with a macromolecular sensitive fluid, the components of which cannot penetrate the dialysis membrane and the viscosity of which is determined by reversible affinity bonds between polymer substances and can be changed by the concentration of one or several analyte molecules for which the dialysis membrane is permeable, wherein at any point the sensitive fluid volume being bordered by the dialysis membrane and the substrate is not remote from the dialysis membrane by more than 0.5 mm.

6. The apparatus of

claim 5

, wherein the bar-shaped thin tip with the measuring zone is arranged in the lumen of a dialysis hollow fiber but not completely filling out this lumen, so that the region between hollow fiber membrane and substrate acts as a measuring chamber.

7. The apparatus of

claim 6

, wherein the movable conductor(s) which is (are) cantilevered in the measuring zone consist(s) of thin metal wires and wherein the resilient resistance of the movable conductor(s) against the field-induced force is mainly based on the torsion of said wires.

8. The apparatus of

claim 7

, wherein the cantilevered movable conductor(s) are arranged in the field of a permanent magnet in such a way, that this field is directed perpendicularly to the movable conductor(s) and to their/its main direction of movement and wherein the movable conductors are connected to a controllable current source.

9. A method of measuring viscosity with a device according to

claim 8

, wherein the position change of the cantilevered movable conductor(s) referring to the substrate or one other conductor being induced by a change of the electrical HF field or of the magnetic field intensity and the viscosity dependent velocity or extent of this position change being established by means of a preferably high frequency capacity or impedance measurement or by means of the frequency-shift of an HF-oscillator.

10. The method of measuring viscosity of

claim 9

, wherein the viscosity-dependent amplitude of the measured position change of the cantilevered movable conductor(s) is evaluated at a suitable modulation or switching frequency of the HF field affecting the conductors or of the current flowing in the conductor(s) or as function of the modulation or switching frequency.

11. The method of measuring viscosity of

claim 9

, wherein the intensity or direction of the magnetic force or the intensity of the electrostatic force to the cantilevered movable conductor(s) is abruptly changed by the control of the current- or HF voltage source(s) and subsequently the viscosity-dependent position change of the conductors is measured as a function of time.

12. A method of making a device for measuring viscosity according to claims 8, wherein after completion of all active and passive components of the viscosity sensor on a suitable semiconductor substrate (including the implemented leading paths) but before separation of the chips jointly generated on the semiconductor substrate (wafer), an additional photolithographically structured soft mask is applied to enable a localized isotrope insulator etching process on the parts of the upper conducting path layer being provided in the completed sensor as cantilevered movable conductors and wherein these parts of the upper conducting path layer are undercut by etching and completely separated from the corresponding sections of the insulating base in the localized isotrope insulator etching process.

13. The method of

claim 12

, wherein the intermediate layer between the uppermost conductor path and the lower conductor is dielectric and consists of at least two layers of different chemical compounds, and wherein the lower part of the interlayer is not affected by the etching agent used for the isotropic undercutting of the upper conductor path.

14. The method of

claim 13

, wherein the upper partial layer of the intermediate layer consists of silicon dioxide or silicate glass and one of the lower partial layers consists of Si₃N₄.

15. An apparatus for measuring the viscosity of a fluid, comprising:

a substantially rigid support;

an extension protruding from the support and provided with a first conductive path;

a cantilever member comprising a second conductive path extending over the first conductive path and resiliently biased to a first position spaced therefrom;

means for cyclically energizing at least one of the first and second conductive paths for moving the cantilever member to a second position;

means for detecting the rate of return of the cantilever member to its first position to derive a value representative of the viscosity.

16. The apparatus of

claim 15

, wherein the length and width of the extension are about 1 mm and 300 μ

m, respectively.

17. The apparatus of

claim 16

, wherein the extension and the cantilever member are mounted in a chamber formed by a membrane of predetermined permeability.

18. The apparatus of

claim 17

, wherein the membrane is a dialysis membrane and wherein the layout of the chamber is such that the distance between any point in the chamber and a permeable portion of the membrane does not exceed 0.3 mm.

19. The apparatus of

claim 18

, wherein the dialysis membrane has a molecular weight cut-off of about 10 kDa.

20. The apparatus of

claim 19

, wherein the chamber contains lyophized components of a fluid sensitive to glucose.

21. The apparatus of

claim 15

, wherein the at least one of the first and second conductive paths is adapted to be energized by direct current.

22. The apparatus of

claim 15

, wherein the at least one of the first and second conductive paths is adapted to be energized by high frequency voltage.

23. The apparatus of

claim 22

, wherein the high frequency voltage is in the Ghz range.

24. A method of measuring the viscosity of a fluid, comprising the steps of:

providing a substantially rigid member with a first conductive path therein;

providing a resiliently flexible member having a second conductive path therein biased into a first position spaced from the first conductive path;

subjecting the rigid and flexible members to the fluid;

energizing at least one of the first and second conductive paths to move the flexible member to a second position;

measuring the rate of movement of the flexible member to derive therefrom a value representative of the viscosity.

25. The method of

claim 24

, wherein the at least one conductive path is energized by high frequency voltage and wherein the rate of movement is measured by the capacitance between the first and second conductive paths.

26. The method of

claim 24

, wherein the at least one conductive path is energized by direct current and wherein the rate of movement is measured by rate of relaxation of the resilient member.

27. The method of

claim 24

, wherein the rigid and resiliently flexible members are disposed in a measuring chamber formed by a membrane of predetermined permeability and wherein the chamber further contains a fluid sensitive to the fluid for measuring the viscosity thereof by affinity.

28. A method of fabricating an apparatus for measuring the viscosity of a fluid, comprising an elongate rigid member extending from a substrate of a semiconductor material for supporting a first conductive path and a second member supporting a second conductive path and mounted for oscillations relative to the first member, wherein the second member is formed by depositing on the parts of the substrate provided with second conductive path an additional photolithographic lacquer mask for undercutting by localized isotropic insulator etching.

29. The method of

claim 28

, wherein an intermediate layer comprising at least two superposed layers of different chemical compounds is provided between the first and second conductive paths and wherein the etching step is performed on an upper one of the layers.

30. The method of

claim 29

, wherein the etching step is performed with an etching agent removing layers of one of silicon dioxide and silicate glass and immune to lower layers of Si₃Ni₄.