# US 9,038,443 B1 · Microfabricated resonant fluid density and viscosity sensor > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 9,038,443 B1 - Document ID: US9038443B1 - Status: Granted - Kind: B1 - Application number: 13/708,969 - Filed: 2012-12-08 - Granted: 2015-05-26 - Earliest claimed: 2011-12-14 - Applicants: Maria Esther Pace; Eric Anthony Perozziello - Inventors: Maria Esther Pace; Eric Anthony Perozziello - Web page: https://patentgrep.com/patent/US9038443B1 ## CPC - G01H 13/00: Measuring resonant frequency - G01N 9/002: {using variation of the resonant frequency of an element vibrating in contact with the material submitted to analysis (G01N9/34 takes precedence)} - G01N 11/16: by measuring damping effect upon oscillatory body - G01N 29/022: {Fluid sensors based on microsensors, e.g. quartz crystal-microbalance [QCM], surface acoustic wave [SAW] devices, tuning forks, cantilevers, flexural plate wave [FPW] devices (microdevices per se B81B)} - G01N 29/036: by measuring frequency or resonance of acoustic waves - G01N 2291/02818: Density, viscosity - G01N 2291/0426: Bulk waves, e.g. quartz crystal microbalance, torsional waves - G01H: MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES - G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q) ## Abstract Determination of fluid properties is important in a variety of research and industrial applications. Real-time measurements in operating fluidic systems are performed for monitoring, diagnosis, and feedback-control. A simplified, microfabricated resonant sensor for separate density and viscosity measurements of a fluid with a common sensor is disclosed. The sensor is micron-scale, so as to produce a minimum of perturbation to the fluid under test, and may be arrayed to probe viscosity and density across a flowstream or vessel. Measurement is performed at resonance peaks, and geometry or operating conditions of sensor are varied to produce different resonance responses useful for separate sensing of density and viscosity of a fluid. Another embodiment includes a method for reducing quiescent in-plate elastic strain in a plate or membrane so as to allow bending-stiffness dominated behavior of a resonator. ## Claims ### Claim 1 A sensor for measuring physical properties of a fluid comprising: a substrate having a principal surface; at least one support placed onto said principal surface of said substrate; at least one plate suspended from said support and in communication with said fluid wherein said plate is substantially free to oscillate in a direction normal to said plate; a driver for exciting said plate into mechanical resonance at a plurality of distinct resonant frequencies; a detector for determining said distinct resonant frequencies of said plate; a computer for matching said physical properties of said fluid to said distinct resonant frequencies; a tensioner for providing variable in-plane elastic strain in said plate; whereby said plate is acted on by said fluid and said resonant frequencies are detected and said physical properties of said fluid are determined. ### Claim 2 (depends on 1) The sensor recited in claim 1 wherein said tensioner is an electrostatic potential applied between a lower electrode and said plate. ### Claim 3 (depends on 2) The sensor recited in claim 2 wherein said plate has an aspect ratio greater than 500. ### Claim 4 (depends on 2) The sensor recited in claim 2 wherein said plate is composed of graphene having a thickness of approximately 0.2 to 0.5 nanometer. ### Claim 5 (depends on 4) The sensor recited in claim 4 wherein said in-plane elastic strain is varied from 2×10−8 to 2×10−3. ### Claim 6 (depends on 1) The sensor recited in claim 1 wherein said driver excites a plurality of said plates having different geometric dimensions. ### Claim 7 (depends on 1) The sensor recited in claim 1 wherein said tensioner provides a displacement of at least one said support. ### Claim 8 (depends on 1) The sensor recited in claim 1 wherein said support is substantially compliant providing reduced quiescent in-plane elastic strain in said plate. ### Claim 9 (depends on 1) The sensor recited in claim 1 wherein said driver excites a plurality of distinct modes of vibration of said plate. ### Claim 10 (depends on 1) The sensor recited in claim 1 wherein said fluid is in communication with a top surface of said plate and said fluid is in communication with a bottom surface of said plate. ### Claim 11 (depends on 1) The sensor recited in claim 1 wherein said fluid is in communication with a top surface of said plate and wherein a bottom surface of said plate is in communication with a second fluid characterized by a second density and a second viscosity, said second fluid having a predictable effect on said resonant frequencies of said plate. ### Claim 12 (depends on 1) The sensor recited in claim 1 wherein said plate has a suspended shape selected from the group consisting of disks, squares, rectangles, beams, and cantilevers. ### Claim 13 (depends on 1) The sensor recited in claim 1 wherein said driver is electrostatic. ### Claim 14 (depends on 13) The sensor recited in claim 13 wherein said driver further comprises a plurality of electrodes. ### Claim 15 (depends on 1) The sensor recited in claim 1 wherein said detector is capacitive. ### Claim 16 (depends on 15) The sensor recited in claim 15 wherein said detector further comprises a plurality of electrodes. ### Claim 17 A system for measuring physical properties of a fluid comprising: at least one resonator in communication with said fluid; a driver for exciting said resonator in one or more modes of vibration at a plurality of distinct resonant frequencies; a tensioner for varying in-plane elastic strain in said resonator; a detector for determining said plurality of distinct resonant frequencies of said resonator; a computer for receiving said plurality of distinct resonant frequencies data from said detector; a computer program for instructing said computer in calculating a best-fit for matching said physical properties of said fluid to said plurality of distinct resonant frequencies, whereby said physical properties of said fluid can be determined from said plurality of distinct resonant frequencies. ### Claim 18 A method for measuring density and viscosity of a fluid comprising: providing at least one resonator in communication with said fluid; exciting said resonator into mechanical resonance at a plurality of distinct resonant frequencies; tensioning said resonator for variable in-plane elastic strain in said resonator; detecting said plurality of distinct resonant frequencies of said resonator; comparing said plurality of distinct resonant frequencies to a model or database; calculating a best numerical fit of said plurality of distinct resonant frequencies to said model; obtaining said density and viscosity values describing said fluid from said best numerical fit.