Measuring and testing – Liquid analysis or analysis of the suspension of solids in a... – Viscosity
Reexamination Certificate
1999-09-23
2001-11-06
Kwok, Helen (Department: 2856)
Measuring and testing
Liquid analysis or analysis of the suspension of solids in a...
Viscosity
C073S054250, C073S054410, C073S024050, C073S03200R
Reexamination Certificate
active
06311549
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to apparatus and methods for the accurate determination of viscosity, density or both of very small volumes of fluids.
2. Prior Art
The atomic force microscope (AFM) was first demonstrated by Binnig and co-workers at IBM in Switzerland. In the AFM, the tip of a flexible cantilever stylus is rastered over the surface of a sample and the movement of the tip of the cantilever is monitored as a measure of minute forces characteristic of surfaces at the atomic level. Demonstration of this principle led to rapid development of microcantilevers [(Albrecht et al.,
J. Vac. Sci. Technol,
8, 3386 (1990)]. The concept of micromechanical and microelectromechanical detection devices has been developed for a number of analytical uses. Wachter et al., U.S. Pat. No. 5,445,008 describes the use of vibrated microcantilevers having a chemical coating as a detector for the presence of specific chemical entities. Thundat, et al. in
Appliance Manufacturer, April
1997, 57 (1997) and
Microscale Thermophysical Engineering
1, 185 (1997) describe developments of the microelectromechanical sensors (MEMS) for the measurement of chemicals and physical phenomena including the use of sensors to determine concentrations of glycerol in water based on viscosity.
U.S. Pat. No. 5,719,342 to Thundat et al., addresses additional methods for analysis using MEMS devices particularly directed to induced stress in the microcantilever.
U.S. Pat. No. 5,130,257 to Bear et al., discloses a viscosity sensor fabricated using a surface transverse wave device for use in the measurement of viscosity.
Oden et al.,
Appl. Phys. Lett.,
68, 3814 (1996) discloses method for the measurement of viscosity using microfabricated cantilevers in a confined medium. The frequency of vibration of an isolated vibrating cantilever is measured in different solutions.
U.S. Pat. No. 5,494,639 to Grzegorzewski discloses a disposable biosensor which uses a vibrating member beneath a cell to accurately measure blood coagulation time as a function of viscosity.
The foregoing methods are attempts to find an alternative to the instruments most currently used to measure viscosity of both liquids and gases. These are instruments which perform the analysis by a comparison with a “control fluid.” For this reason, measurements are still routinely done using instruments such as the Redwood viscometer, the Couette or rotational concentric-cylinder viscometer (MacMichael or Stormer viscometer), the Rotating Sphere viscometer, the Sayboult Falling Body viscometer, the Vibrating String viscosity meter and the thickness-shear mode resonators. All of these methods require comparatively large volumes and bulky equipment. The need remains for a small reliable and inexpensive instrument which can measure the viscosity or specific density of small amounts of a liquid or gas and which can be used in difficult-to-access locations.
BRIEF SUMMARY OF THE INVENTION
It is an object of this invention to provide a microminiaturized instrument for the measurement of viscosity and density in liquids and gases. It is a further object of this invention to provide such an instrument which is reliable and inexpensive in comparison with other instrumentation available.
It is a further object to provide a means for profiling the viscosity in a non-inhomogeneous fluid.
It is a further object of this invention to provide means for detecting viscosity and density of very small sample volumes of fluids; to determine viscosity and density of fluids in small confined spaces; to determine kinetics of chemical, biological, and physical reactions by measuring viscosity and density; and, to determine the completeness of chemical, biological, and physical reactions by measuring the viscosity and density.
These and other objects are met by using microcantilevers having typical dimensions of 50-200 &mgr;m in length, 10-40 &mgr;m in width, and 0.3-3 &mgr;m in thickness. When such a microcantilever is driven into resonance, the resonance frequency, amplitude and Q-value varies with the viscosity and the density of the medium surrounding the cantilever. More particularly, according to this invention, the cantilever is excited into resonance by an external means for a finite amount of time until a stable resonance amplitude is established. After that period, the external excitation is switched off and the transient behavior (decay) of the vibration is recorded. The resonance frequency, amplitude and Q factor are determined from the transient spectrum. The decay in amplitude of vibration can be used to determine the density of the material. Numerous methods for measuring the vibration of the cantilever are available and a multiplicity of cantilevers can be used for the determination of a wide range of densities.
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Albrecht et al., Microfabrication of Cantilever Styli for the Atomic Force Microscope, J of Vacuum Science & Technology A, 8, 3386- (1990).
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Finot Eric Laurent
Oden Patrick I.
Thundat Thomas G.
Warmack Robert J.
Hardaway/Mann IP Group
Kwok Helen
Nexsen Pruet Jacobs & Pollard LLC
O'Toole J. Herbert
U T Battelle LLC
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