1/27 Precision PositioningCapacitive Distance Sensors for Wijnand Harmsen, PME – Mechatronic...

1/27

Precision PositioningCapacitive Distance Sensors for

Wijnand Harmsen, PME – Mechatronic System Design

June 28th , 2010

The Excessive Humidity Effect on

Challenge the future

DelftUniversity ofTechnology

2/27

Precision Positioning

Position sensor• Contactless • Resolution • Accuracy • Sensor volume

Introduction

3/27

22mm

Capacitive Distance Sensor

Introduction

Electrode spacing d 50 µm

transmitting electrode

sensing electrode

readout

Resolution: <1 nm, Accuracy: <10 nm

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The Excessive Humidity Effect

Introduction


sensing electrode

readout

Resolution: <1 nm, Accuracy: <10 nm

200-800 nm

5/27

To find a relation between the change in humidity and the readout of the capacitive sensor and to find how this relation depends on the adsorption of water on the capacitive electrodes.

Research Goal

Introduction

?

6/27

Outline

• Water layers • Measurement setup

• Humidity response

• Conclusions & recommendations

Water layers / Setup / Humidity response / Conclusions

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Water layersAdsorption


sensing electrode

0.6 nm

0.3 nm www.nasa.gov

8/27

Water layersAdsorption

sensing electrode



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Indirect• Weight 6 nm• Polarization 1 nm• Attraction force 100 nm• Capacitive (el. field) 200-800 nm

Water layersMeasurement


Schwartz, 1994 Motschmann & Teppner, 2001 Worldpress.comWang & Kido, 2003

Max. water layer thickness

10/27

25°C50% RH

35°C50% RH

Measurement SetupRequirements


• Offset / gain error• Relative / absolute humidity• Thickness of 1-800 nm

Multiple distances Different temperatures 1 nm resolution 1 nm stability

Double measurement setup

Transmitting electrode

Sensing el.

Requirement

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Measurement SetupCapacitive measurement


Transmitting electrode

Sensing el.

Insulator

Conductor

Multiple distances Different temperatures 1 nm resolution 1 nm stability 50

µm

12/27

Measurement SetupCapacitive measurement



Insulator

Conductor

13/27

d

Laser

Camera

Measurement SetupReference measurement



14/27

Measurement SetupDouble measurement setup


Laser

Camera


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Optical Capacitive




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0 2 4 60

1

2

3

4

5

6

dist

ance

mea

sure

d [

m]

exitation distance [m]

capacitiveoptical



Laser

Camera


17/27

Humidity responseInput


0 2 4 6

20

40

60

80

time [h]hu

mid

ity [

%]

6 8 10 12

20

40

60

80

time [h]

hum

idity

[%

]

0 2 4 6

20

40

60

80

time [h]

hum

idity

[%

]

6 8 10 12

20

40

60

80

time [h]hu

mid

ity [

%]

18/27

0 5 10 15 20 25

20

40

60

80

time [h]

hum

idity

[%

]Humidity responseMeasurements


0 5 10 15 20 25

-40

-20

0

20

time [h]m

easu

red

dist

ance

[nm

]

capacitiveoptical

19/27

Humidity responseMeasurements


0 2 4 6

20

40

60

80

time [h]

hum

idity

[%

]

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• Water • Measurement distance• Temperature

• Optical measurement• Time response

Humidity responseWater layer presence


• Water

• Optical measurement• Time response

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Humidity responseOptical measurement


0 5 10 15 20 25

-40

-20

0

20

time [h]

mea

sure

d di

stan

ce [

nm]

capacitiveoptical

• Water• Optical measurement• Time response

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Humidity responseOptical measurement



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0 20 40 60 80 100 120-2

0

2

4

6

time [min]

d wat

er [

nm]

0 20 40 60 80 100 120-2

0

2

4

6

time [min]

d wat

er [

nm]

modelmeasured

Humidity responseTime response



0 20 40 60 80 100 120

40

42

44

46

time [min]

hum

idity

[%

]

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Humidity responseTime response


0 2 4 6

20

40

60

80

time [h]

hum

idity

[%

]

1 2 3 4 5 6

0

100

200

300

400

time [min]

d wat

er [

nm]

modelmeasured


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• Humidity - Capacitive sensor readout• Humidity - Water adsorption

Conclusions


• Capacitive precision measurements will be even more precise

26/27

• Different materials• Water layer influence on optical measurement• Nonlinear time dependency

ConclusionsRecommendations


27/27

Questions

28/27

0 1 2 3 4 5

0

100

200

300

time [h]

d wat

er [

nm]

modelmeasured

0 2 4 6

0

100

200

300

400

time [h]

d wat

er [

nm]

modelmeasured

29/27

Marek & Straub, 2001

30/27Water layers / Setup / Humidity response / Conclusions

32/27

Water layersDisturbance

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Measurement SetupReference measurement



• Material type • Surface roughness • Contamination


16 18 20

35

40

45

50

55

time [h]

hum

idity

[%

]

16 18 20-110

-100

-90

-80

-70

-60

-50

time [h]

mea

sure

d di

stan

ce [

nm]

capacitiveoptical

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Wang & Kido 2003


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0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

x 104

35

40

45

50

55

Rel

ativ

e H

umid

ity [

%]

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

x 104

1.1278

1.128

1.1282

1.1284x 10

-4

mea

sure

d di

stan

ce [

m]

time [s]

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

x 104

35

40

45

50

55

Rel

ativ

e H

umid

ity [

%]

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

x 104

1.1278

1.128

1.1282

1.1284x 10

-4

mea

sure

d di

stan

ce [

m]

time [s]

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0 5 10 15 20 25-50

-40

-30

-20

-10

0

10

time [h]

d

[nm

]

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0

2

4

6

8

10

12

14

16

20 30 40 50 60

chan

ge in

diff

eren

ce b

etw

een

capa

citi

ve a

nd o

ptic

al

mea

urem

ent

for

a hu

mid

ity

chan

ge o

f 5 %

[nm

]

initial humidity level [%]

60µm 21°C

50µm 24°C

55µm 25°C

55µm 30°C

50µm 30°C

40/27

0

2

4

6

8

10

12

14

16

20 30 40 50 60

chan

ge in

diff

eren

ce b

etw

een

capa

citi

ve a

nd o

ptic

al

mea

urem

ent f

or a

hum

idity

ch

ange

of 5

% [n

m]

initial humidity level [%]

trend 20-30°C

50µm 35°C

50µm 35°C

95µm 30°C


0

2

4

6

8

10

12

14

16

0 100 200 300

chan

ge in

diff

eren

ce b

etw

een

capa

citi

ve a

nd o

ptic

al

mea

urem

ent

for

a hu

mid

ity

chan

ge o

f 5 %

[nm

]

initial humidity level [kPa]

60µm 21°C

50µm 24°C

95µm 30°C

50µm 35°C

50µm 35°C

42/27

Humidity response


Electrode spacing [μm]

Temperature

[°C]

Initial humidity level

[%]

Final humid

ity level

[%]

Difference

between both

sensors Δd [nm]

Settling time [h]

50 24 60 88 300 5100 26 53 90 380 5.5220 25 57 88 340 450 26 70 88 200 650 35 42 85 280 6

43/27

Drinks:

Next Friday 21:00

“De Ruif”

1/27 Precision PositioningCapacitive Distance Sensors for Wijnand Harmsen, PME – Mechatronic...

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