US4896098A — Turbulent shear force microsensor

Claim 1

Independent Claim 81 words

A wall shear stress microsensor comprising: a microndiminsioned shear-sensitive plate; a plurality of supporting arms which suspend the plate above a substrate and define a cavity between the plate and the substrate, the cavity being so small that it dampens movement of the plate normal to the plane of the plate through viscous forces generated within the cavity; and readout means for providing an indication of the deflection of the plate and thereby a measurement of the shear stress of interest.

Claim 2

Dependent Claim 81 words

A wall shear stress microsensor comprising: a microndiminsioned shear-sensitive plate; a plurality of supporting arms which suspend the plate above a substrate and define a cavity between the plate and the substrate, the cavity being so small that it dampens movement of the plate normal to the plane of the plate through viscous forces generated within the cavity; and readout means for providing an indication of the deflection of the plate and thereby a measurement of the shear stress of interest.

Claim 3

Dependent Claim 61 words

A wall shear stress microsensor as claimed in Claim 1 wherein the microndimensions of the plate cause environmental pressures to be uniformly felt throughout an entire top surface of the plate such that the plate in combination with the damping effect of the cavity renders the sensor substantially insensitive to pressures, and shear lateral forces are sensed substantially independent of pressure.

Claim 4

Dependent Claim 67 words

A wall shear stress microsensor as claimed in claim 2 wherein the microndimensions of the plate include a top surface area which is greater than an end surface area lying in a plane perpendicular to the plane in which the top surface area lies, and said top surface area is an order of magnitude smaller than an area in which the smallest eddy of interest is uniform.

Claim 5

Dependent Claim 99 words

A wall shear stress microsensor as claimed in claim 2 wherein the microndimensions of the plate include a dimension along a length of the top surface no bigger than about 5L* to about 10L* and a total height or protrusion above a target surface no higher than about 2L* to about 3L* where L* is a relevant length scale in turbulent flow such that L*=ν/u* where ν is a kinematic viscosity equal to μ/ρ and u* is friction velocity equal to ##EQU6## where μ is absolute viscosity of the target fluid, ρ is density and τ is shear stress.

Claim 6

Dependent Claim 41 words

A wall shear stress microsensor as claimed in claim 2 wherein the plate has a lateral dimension along a length of its top surface of about 1000 microns or less and is suspended about 10 microns or less above the substrate.

Claim 7

Dependent Claim 43 words

A wall shear stress microsensor as claimed in claim 5 wherein a longitudinal dimension of the cavity between the plate and substrate is less than a longitudinal dimension of the supporting arms between the substrate and a top surface of the supporting arms.

Claim 8

Dependent Claim 36 words

A wall shear stress microsensor as claimed in claim 1 wherein the readout means for providing an indication of the deflection of the plate and measurement of the shear stress includes an integrated differential capacitance circuit.

Claim 9

Dependent Claim 155 words

A wall shear stress microsensor as claimed in claim 7 wherein the integrated differential capacitance circuit comprises: a conducting layer attached to the plate; three conductors attached to the substrate, two positioned to the outside of the third, the third conductor being in the middle, the conducting layer of the plate being aligned within the two outer positioned substrate conductors, the conducting layer being capacitively coupled with the conductors attached to the substrate; and means for sensing a change in capacitive coupling between the conductive layer and the outer positioned substrate conductors where lateral motion of the plate changes the capacitive coupling between the conducting layer and the outer positioned substrate conductors, one outer positioned substrate conductor experiencing a lowered coupling, the other outer positioned substrate conductor experiencing an increased coupling, said sensing means sensing the change in coupling and producing a signal indicative of the deflection of the plate and thereby sensed shear stress.

Claim 10

Dependent Claim 111 words

A wall shear stress microsensor as claimed in claim 8 wherein the means for sensing a change in capacitive coupling includes: two sensing nodes, one for each outer positioned substrate conductor, each sensing node sensing the change in coupling experienced by its respective substrate conductor; and two field effect transistors (FET's) one for each sensing node, where each sensing node senses a change in coupling of its respective outer positioned substrate conductor and places charge on its respective FET, the FET's connected to a differential amplifier circuit which is sensitive to the difference in current from the two FET's and therefrom provides an output signal indicative of the sensed wall shear.

Claim 11

Dependent Claim 18 words

A wall shear stress microsensor as claimed in claim 9 wherein the two FET's are essentially the same.

Claim 12

Dependent Claim 63 words

A wall shear stress microsensor as claimed in claim 9 wherein the differential amplifier circuit is off chip and comprises two amplifiers, one connected to one FET, the second connected to the other FET, the FET's changing current flow to each respective amplifier such that said amplifiers produce signals which are differentially compared to provide an output signal indicative of sensed wall shear.

Claim 13

Dependent Claim 110 words

A wall shear stress microsensor as claimed in claim 8 wherein said circuit is integrated into the microsensor by micro-fabrication of films on the substrate by the process of: depositing a sacrificial film on the substrate, the substrate fabricated with the conductors of the integrated circuit; depositing a second film onto the sacrificial film such that said second film is connected to the conducting layer and patterned to form the plate and supporting arms; and removing only the sacrificial film leaving the plate defined by the second film connected to the conducting layer and suspended above the substrate by the supporting arms, and leaving the conductors connected to the substrate.

Claim 14

Dependent Claim 35 words

A wall shear stress microsensor as claimed in claim 8 wherein an array of shear-sensitive plates with said support arms and said integrated differential capacitance circuits is repeated on one substrate to provide multi-point measurements.

Claim 15

Dependent Claim 18 words

A wall shear stress microsensor as claimed in claim 1 wherein the readout means includes optical readout means.

Claim 16

Dependent Claim 63 words

A wall shear stress microsensor as claimed in claim 14 wherein said optical readout means include: a window in the substrate; a distinguishing optical feature associated with the plate and open to the window; where the distinguishing optical feature moves with the plate and is viewed through the window to provide an indication of the amount of plate deflection and thereby shear stress.

Claim 17

Dependent Claim 78 words

A wall shear stress microsensor as claimed in claim 15 wherein said optical readout means further include an optical scale associated with the window, said scale enabling a user to measure the amount of deflection of the plate and thereby shear stress by viewing through the window the change in position of the optical distinguishing feature of the plate relative to said scale where the optical distinguishing feature moves with the plate and the scale remains relatively stationary.

Claim 18

Dependent Claim 34 words

A wall shear stress microsensor as claimed in claim 1 wherein the plate is suspended within a recess in the substrate and the cavity is formed between the plate and base of the recess.

Claim 19

Dependent Claim 43 words

A wall shear stress microsensor as claimed in claim 17 wherein the plate has a lateral top surface which is flush with the surface of the substrate, said plate top surface being open to the turbulent flow creating the shear stress of interest.

Claim 20

Dependent Claim 40 words

A wall shear stress microsensor as claimed in claim 18 wherein said plate has lateral dimension along a length of the top surface which is n order of magnitude smaller than a length dimension of the smallest eddy of interest.

Claim 21

Dependent Claim 92 words

A wall shear stress microsensor as claimed in claim 18 wherein the microndimensions of the plate include a length dimension no bigger than about 5L* to about 10L* and a total height or protrusion above a target surface no higher than about 2L* to about 3L* where L* is a relevant length scale in turbulent flow such that ##EQU7## where ν is kinematic viscosity equal to μ/ρ and u* is friction velocity equal to ##EQU8## where μ is absolute viscosity of the target fluid, ρ is density and τ is shear stress.

Claim 22

Dependent Claim 49 words

A wall shear stress microsensor as claimed in claim 18 wherein said plate has a lateral dimension along a length of its top surface of less than about 1000 microns and the cavity is less than about 10 microns in height between the plate and base of the recess.

Claim 23

Dependent Claim 20 words

A wall shear stress microsensor as claimed in claim 17 wherein the readout means includes an integrated differential capacitance circuit.

Claim 24

Dependent Claim 159 words

A wall shear stress microsensor as claimed in claim 22 wherein the integrated differential capacitance circuit comprises: a conducting layer connected to the plate; three conductors connected to the substrate, two of the three conductors positioned on the outside of the third, the third being in the middle, said conducting layer of the plate being aligned within the two outer positioned substrate conductors, the conducting layer being capacitively coupled with the conductors connected to the substrate; and means for sensing a change in capacitive coupling between the conducting layer and the two outer positioned substrate conductors where lateral motion of the plate changes the capacitive coupling between the conducting layer and the outer positioned substrate conductors, one outer positioned substrate conductor experiencing a lowered coupling, the other outer positioned substrate conductor experiencing an increased coupling, said sensing means sensing the change in coupling and producing a signal indicative of the deflection of the plate and thereby sensed shear stress.

Claim 25

Dependent Claim 111 words

A wall shear stress microsensor as claimed in claim 23 wherein the means for sensing a change in capacitive coupling includes: two sensing nodes, one for each outer positioned substrate conductor, each sensing node sensing the change in coupling experienced by its respective substrate conductor; two field effect transistors (FET's) one for each sensing node where each sensing node senses a change in coupling of its respective outer positioned substrate conductor and places charge on its respective FET, the FET's connected to a differential amplifier circuit which is sensitive to the difference in current flowing from the two FET's and therefrom provides an output signal indicative of the sensed wall shear.

Claim 26

Dependent Claim 18 words

A wall shear stress microsensor as claimed in claim 24 wherein the two FET's are substantially the same.

Claim 27

Dependent Claim 62 words

A wall shear stress microsensor as claimed in claim 24 wherein the differential amplifier circuit is off-chip and comprises two amplifiers, one connected to one FET, the second connected to the other FET, the FET's changing current flow to their respective amplifier such that said amplifiers produce signals which are differentially compared to provide an output signal indicative of sensed wall shear.

Claim 28

Dependent Claim 121 words

A wall shear stress microsensor as claimed in claim 23 wherein said circuit is integrated into the microprocessor by microfabrication of films in the recess of the substrate by the process of: depositing a sacrificial film in the substrate recess, the base of the recess fabricated with the three conductors of the circuit; depositing a second film over the sacrificial film such that said second film is connected to the conducting layer and is patterned to form the plate and supporting arms; and removing only the sacrificial film and leaving the plate defined by the second film connected to the conducting layer and suspended within the recess by the support arms, and the conductors connected to the base of the recess.

Claim 29

Dependent Claim 35 words

A wall shear stress microsensor as claimed in claim 22 wherein an array of shear-sensitive plates with said arms and said integrated differential capacitance circuits is repeated on one substrate to provide multiple point measurements.

Claim 30

Dependent Claim 18 words

A wall shear stress microsensor as claimed in claim 17 wherein the readout means includes optical readout means.

Claim 31

Dependent Claim 69 words

A wall shear stress microsensor as claimed in claim 29 wherein said optical readout means include: a window in the base of the recess; and a distinguishing optical feature on the plate open to the window where the distinguishing optical feature moves with the plate and is viewed through the window to provide an indication of the amount of plate deflection and thereby the amount of detected shear stress.

Claim 32

Dependent Claim 80 words

A wall shear stress microsensor as claimed in claim 30 wherein said optical readout means further include an optical scale associated with the window, said scale enabling a measurement of the amount of deflection of the plate and thereby shear stress to be obtained by viewing through the window the change in position of the distinguishing optical feature of the plate relative to said scale where the distinguishing optical feature moves with the plate and the scale remains relatively stationary.

Claim 33

Dependent Claim 48 words

A wall shear stress microsensor as claimed in claim 1 further comprising mounting means to position said shear-sensitive plate, arms and readout means in a target flow substantially flush with a target wall such that said target flow is not disturbed by said plate, arms and readout means.

Claim 34

Dependent Claim 87 words

A wall shear stress microsensor as claimed in claim 32 wherein said mounting means includes a holding plate into which are evenly and smoothly fitted one or more substrates on which the shear-sensitive plate, arms and readout means are fabricated, where said holding plate fits into a matching slot and is adhered in place in a support structure in the target wall which covers a large surface area of the target wall compared to the size of a substrate and which is smooth with the target wall.

Claim 35

Dependent Claim 85 words

A sheer stress sensor having a bridge shape of microndimensions which render it substantially insensitive to pressure and sensitive to lateral forces independent of pressure, by the microndimensions causing the effects of pressure to be uniform throughout both an entire top surface and a bottom surface of the sensor and the microndimensions defining a passageway under the sensor so small that a damping effect of geometrically normal movement of the sensor under effects of vibrational forces is produced by a viscous drag within that passageway.

Claim 36

Dependent Claim 85 words

A sheer stress sensor having a bridge shape of microndimensions which render it substantially insensitive to pressure and sensitive to lateral forces independent of pressure, by the microndimensions causing the effects of pressure to be uniform throughout both an entire top surface and a bottom surface of the sensor and the microndimensions defining a passageway under the sensor so small that a damping effect of geometrically normal movement of the sensor under effects of vibrational forces is produced by a viscous drag within that passageway.

Claim 37

Dependent Claim 26 words

A shear stress sensor as claimed in claim 34 wherein the microdimensions are an order of magnitude less than dimensions of the smallest eddies of interest.

Claim 38

Dependent Claim 90 words

A shear stress sensor as claimed in claim 34 wherein the microndimensions include a dimension along a length of the top surface no larger than about 5L* to about 10L* and protrusion above a target surface no more than about 2L* to about 3L* where L* is a relevant length scale in turbulent flow defined by L*=ν/u* where ν is kinematic viscosity equal to μ/ρ and u* is frictional velocity equal to ##EQU9## where μ is absolute viscosity of the target fluid, ρ is density and τ is shear stress.

Claim 39

Dependent Claim 39 words

A shear stress sensor as claimed in claim 34 wherein said dimensions include: a dimension along a length of the top surface less that about 1000 microns, and a height under the sensor of less than about 10 microns.

Claim 40

Dependent Claim 87 words

A shear stress sensor as claimed in claim 34 wherein said microndimensions are generated by microfabrication of two films on a substrate by the process of: depositing a sacrificial film on the substrate; depositing onto the sacrificial film a second film and patterning said second film to form a microndimensioned top surface; and removing the sacrificial film leaving the microdimensioned top surface defined by the second film suspended above the substrate at the very small height and leaving a cavity where the sacrificial film was previously deposited.

Claim 41

Dependent Claim 77 words

A shear stress sensor as claimed in claim 38 wherein said second film is further deposited over the whole surface of the substrate leaving an undeposited area for access to the sacrificial film on one side of the defined top surface and leaving another area for allowance for lateral deflection on an opposite side of the top surface, said further deposited second film being made to a thickness which is greater than the height under the sensor.

Claim 42

Dependent Claim 109 words

A bridge-shaped structure having a top surface exposed to environmental effects and an opposite surface facing a plane on which legs of the bridge structure stand, the bridge structure being of micron dimensions which render it substantially insensitive to pressure and sensitive to lateral forces independent of pressure, by the micron dimensions causing the effects of pressure to be uniform throughout the entire top surface of the bridge-shaped structure and the micron dimensions defining a space between the opposite surface and the plane under the bridge structure so small that a damping effect of normal movement of the bridge-shaped structure is produced by a viscous drag within the space.

Claim 43

Dependent Claim 109 words

A bridge-shaped structure having a top surface exposed to environmental effects and an opposite surface facing a plane on which legs of the bridge structure stand, the bridge structure being of micron dimensions which render it substantially insensitive to pressure and sensitive to lateral forces independent of pressure, by the micron dimensions causing the effects of pressure to be uniform throughout the entire top surface of the bridge-shaped structure and the micron dimensions defining a space between the opposite surface and the plane under the bridge structure so small that a damping effect of normal movement of the bridge-shaped structure is produced by a viscous drag within the space.

Claim 44

Dependent Claim 28 words

A bridge structure as claimed in Claim 40 wherein the micron dimensions are an order of magnitude less than smallest eddies to which the bridge structure is exposed.

Claim 45

Dependent Claim 89 words

A bridge structure as claimed in claim 40 wherein the micron dimensions include a lateral dimension of the top surface no larger than about 5L* to about 10L* and a protrusion above a target surface no more than about 2L* to about 3L* where L* is a relevant length scale in turbulent flow defined by L*=ν/u* where ν is kinematic viscosity equal to μ/ρ and u* is friction velocity equal to ##EQU10## where μ is absolute viscosity of the target fluid, ρ is density and τ is shear stress.

Claim 46

Dependent Claim 35 words

A bridge structure as claimed in claim 58 wherein said dimensions include: a top surface lateral dimension less than about 1000 microns and a height under the bridge structure of less than about 10 microns.

Claim 47

Dependent Claim 89 words

A bridge structure as claimed in claim 40 wherein said micron dimensions are generated by microfabrication of two films on a substrate by the process of: depositing a sacrificial film on the substrate; depositing onto the sacrificial film a second film and patterning and said film to form a micron dimensioned top surface; and removing the sacrificial film leaving the micron dimensioned top surface defined by the second film suspended above the substrate at the very small height and leaving a cavity where the sacrificial film was previously deposited.

Claim 48

Dependent Claim 77 words

A bridge structure as claimed in claim 44 wherein said second film is further deposited over the whole surface of the substrate leaving an undeposited area for access to the sacrificial film on one side of the defined top surface and leaving another area for allowance for lateral deflection on an opposite side of the top surface, said further deposited second film being made to a thickness which is greater than the height under the bridge structure.

Claim 49

Dependent Claim 94 words

A micron dimensioned sensor for sensing lateral movement, the sensor comprising: a micron dimensioned plate; a plurality of supporting arms which suspend the plate above a substrate and define a cavity between the plate and the substrate, such that the plate is sensitive to lateral forces independent of pressure by the cavity being so small that it dampens movement of the plate normal to the plane of the plate through viscous forces generated within the cavity; and means for providing an indication of deflection of the plate and thereby a measurement of lateral movement.

Claim 50

Dependent Claim 94 words

A micron dimensioned sensor for sensing lateral movement, the sensor comprising: a micron dimensioned plate; a plurality of supporting arms which suspend the plate above a substrate and define a cavity between the plate and the substrate, such that the plate is sensitive to lateral forces independent of pressure by the cavity being so small that it dampens movement of the plate normal to the plane of the plate through viscous forces generated within the cavity; and means for providing an indication of deflection of the plate and thereby a measurement of lateral movement.

Claim 51

Dependent Claim 60 words

A micron dimensioned sensor as claimed in claim 46 wherein the micron dimensions of the plate cause environmental pressures to be uniformly felt throughout an entire top surface of the plate such that the plate in combination with the damping effect of the cavity renders the sensor substantially insensitive to pressures, and lateral forces are sensed substantially independent of pressure.

Claim 52

Dependent Claim 67 words

A micron dimensioned sensor as claimed in claim 46 wherein the micron dimensions of the plate include a top surface area which is greater than an end surface area lying in a plane perpendicular to the plane in which the top surface area lies, and said top surface area if an order of magnitude smaller than an area in which the smallest eddy of interest is uniform.

Claim 53

Dependent Claim 40 words

A micron dimensioned sensor as claimed in claim 46 wherein the plate has a lateral dimension along a length of its top surface of about 1000 microns or less and is suspended about 10 microns or less above the substrate.

Claim 54

Dependent Claim 23 words

A micron dimensioned sensor as claimed in claim 46 wherein the means for providing an indicating of deflection provides a measurement of acceleration.

Claim 55

Dependent Claim 251 words

A shear stress microsensor comprising: a plate having one surface open to shear force of interest and a surface opposite the one surface, the one surface having a lateral dimension of less than about 1000 microns such that the smallest eddies of interest are uniformly felt across the one surface of the plate; four microndimensioned support arms, one end of each arm connected to the plate, an opposite end of each arm connected to a substrate such that said arms suspend the plate above the substrate at a height of less than about 10 microns with said plate surface opposite the one surface facing the substrate where a cavity is formed there between, the cavity dampening movement of the plate normal to the substrate by generating a viscous drug; a conducting layer connected to the plate and capacitively coupled with three conductors attached to the substrate, two conductors positioned one on one side of the third conductor and the second on an opposite side of the third conductor, the third conductor connected to generator means, the conducting layer aligned between longitudinal axes along which the two conductors are respectively positioned on the opposite sides of the third conductor; and means for sensing a change in capacitive coupling of the conducting layer and the three conductors, said change in coupling being indicative of lateral deflection of the plate and thereby sensed shear stress, the lateral deflection being detected substantially independent of pressure affects and movement of the plate normal to the substrate.

Claim 56

Dependent Claim 251 words

A shear stress microsensor comprising: a plate having one surface open to shear force of interest and a surface opposite the one surface, the one surface having a lateral dimension of less than about 1000 microns such that the smallest eddies of interest are uniformly felt across the one surface of the plate; four microndimensioned support arms, one end of each arm connected to the plate, an opposite end of each arm connected to a substrate such that said arms suspend the plate above the substrate at a height of less than about 10 microns with said plate surface opposite the one surface facing the substrate where a cavity is formed there between, the cavity dampening movement of the plate normal to the substrate by generating a viscous drug; a conducting layer connected to the plate and capacitively coupled with three conductors attached to the substrate, two conductors positioned one on one side of the third conductor and the second on an opposite side of the third conductor, the third conductor connected to generator means, the conducting layer aligned between longitudinal axes along which the two conductors are respectively positioned on the opposite sides of the third conductor; and means for sensing a change in capacitive coupling of the conducting layer and the three conductors, said change in coupling being indicative of lateral deflection of the plate and thereby sensed shear stress, the lateral deflection being detected substantially independent of pressure affects and movement of the plate normal to the substrate.

Claim 57

Dependent Claim 68 words

A shear-stress microsensor as claimed in claim 51 wherein said means for sensing a change in capacitive coupling includes to matching on-chip field effect transistors, one transistor coupled to a first sensing node for sensing change in capacitive coupling of the conducting layer and one conductor, the second transistor coupled to a second sensing node for sensing change in capacitive coupling of the conducting layer and another conductor.

Claim 58

Dependent Claim 51 words

A shear-stress microsensor as claimed in claim 51 further comprising mounting means to position said plate, arms and means for sensing a change in capacitive coupling, in a target flow substantially flush with a target wall such that said target flow is not disturbed by said plate, arms and readout means.

Claim 59

Dependent Claim 82 words

A shear-stress microsensor as claimed in claim 53 wherein said mounting means includes a holding plate into which are perfectly fitted one or more wafers on which the plate, arms and sensing means are fabricated, where said holding plate fits into a matching slot and is adhered in place in a support structure in the target wall which covers a large surface area of the target wall compared to the size of a wafer and which is smooth with the target wall.

Annuity Stage	Window Opens	Payment Deadline	Surcharge Period Until	Estimated Fee	Status
3.5 Years (Year 4)	1993-01-22	1993-07-24	1994-01-23	$2000.00	Window Closed / Lapsed
7.5 Years (Year 8)	1997-01-22	1997-07-24	1998-01-23	$3760.00	Window Closed / Lapsed
11.5 Years (Year 12)	2001-01-22	2001-07-24	2002-01-23	$7700.00	Window Closed / Lapsed

Turbulent shear force microsensor

Abstract

Inventors

Bibliographic Details

Claims Analysis

References Cited (Backward Citations)

USPTO Annuity & Maintenance Windows

Assigned Categories & Tags

Assign Category Tag