The Excessive Humidity Effect on Capacitive Distance Sensors

The Excessive Humidity Effect on Capacitive Distance Sensors for Precision Positioning June 28 th , 2010 Delft University of Technology Challenge the future Wijnand Harmsen, PME – Mechatronic System Design 1/27

Precision Positioning Position sensor • Contactless • Resolution • Accuracy • Sensor volume Introduction 2/27

Capacitive Distance Sensor 22 mm transmitting electrode Electrode spacing d 50 µm sensing electrode readout Resolution: <1 nm, Accuracy: <10 nm Introduction 3/27

The Excessive Humidity Effect transmitting electrode 200 -800 nm sensing electrode readout Resolution: <1 nm, Accuracy: <10 nm Introduction 4/27

Research Goal 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. ? Introduction 5/27

Outline • Water layers • Measurement setup • Humidity response • Conclusions & recommendations Water layers / Setup / Humidity response / Conclusions 6/27

Water layers Adsorption 0. 6 nm 0. 3 nm www. nasa. gov sensing electrode Water layers / Setup / Humidity response / Conclusions 7/27

Water layers Adsorption transmitting electrode sensing electrode Water layers / Setup / Humidity response / Conclusions 8/27

Water layers Measurement Indirect • Weight • Polarization • Attraction force • Capacitive (el. field) Schwartz, 1994 Max. water layer thickness 6 nm 100 nm 200 -800 nm Motschmann & Teppner, 2001 Water layers / Setup / Humidity response / Conclusions Worldpress. com Wang & Kido, 2003 9/27

Measurement Setup Requirements • Offset / gain error • Relative / absolute humidity • Thickness of 1 -800 nm Double measurement setup Requirement Ø Multiple distances Ø Different temperatures Ø 1 nm resolution Ø 1 nm stability Transmitting electrode Sensing el. 35°C 25°C 50% RH Water layers / Setup / Humidity response / Conclusions 10/27

Measurement Setup Capacitive measurement Ø Ø Transmitting electrode Multiple distances Different temperatures 1 nm resolution 1 nm stability 50 µm Sensing el. Insulator Conductor Water layers / Setup / Humidity response / Conclusions 11/27

Measurement Setup Capacitive measurement Ø Ø Multiple distances Different temperatures 1 nm resolution 1 nm stability Insulator Conductor Water layers / Setup / Humidity response / Conclusions 12/27

Measurement Setup Reference measurement Camera Ø Multiple distances Ø Different temperatures Ø 1 nm resolution Ø 1 nm stability Laser d Water layers / Setup / Humidity response / Conclusions 13/27

Measurement Setup Double measurement setup Camera Ø Ø Multiple distances Different temperatures 1 nm resolution 1 nm stability Laser Water layers / Setup / Humidity response / Conclusions 14/27

Measurement Setup Double measurement setup Ø Ø Multiple distances Different temperatures 1 nm resolution 1 nm stability Optical Water layers / Setup / Humidity response / Conclusions Capacitive 15/27

Measurement Setup Double measurement setup Camera Ø Ø Multiple distances Different temperatures 1 nm resolution 1 nm stability Laser Water layers / Setup / Humidity response / Conclusions 16/27

Humidity response Input Water layers / Setup / Humidity response / Conclusions 17/27

Humidity response Measurements Water layers / Setup / Humidity response / Conclusions 18/27

Humidity response Measurements Water layers / Setup / Humidity response / Conclusions 19/27

Humidity response Water layer presence • Water • Measurement distance • Temperature • Optical measurement • Time response Water layers / Setup / Humidity response / Conclusions 20/27

Humidity response Optical measurement • Water • Optical measurement • Time response Water layers / Setup / Humidity response / Conclusions 21/27

Humidity response Optical measurement • Water • Optical measurement • Time response Water layers / Setup / Humidity response / Conclusions 22/27

Humidity response Time response • Water • Optical measurement • Time response Water layers / Setup / Humidity response / Conclusions 23/27

Humidity response Time response • Water • Optical measurement • Time response Water layers / Setup / Humidity response / Conclusions 24/27

Conclusions • Humidity - Capacitive sensor readout • Humidity - Water adsorption • Capacitive precision measurements will be even more precise Water layers / Setup / Humidity response / Conclusions 25/27

Conclusions Recommendations • Different materials • Water layer influence on optical measurement • Nonlinear time dependency Water layers / Setup / Humidity response / Conclusions 26/27

Questions 27/27

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Marek & Straub, 2001 29/27

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

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Water layers Disturbance 32/27

Measurement Setup Reference measurement Water layers / Setup / Humidity response / Conclusions 33/27

Material type • Surface roughness • Contamination • Water layers / Setup / Humidity response / Conclusions 34/27

Water layers / Setup / Humidity response / Conclusions 35/27

Wang & Kido 2003 Water layers / Setup / Humidity response / Conclusions 36/27

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Water layers / Setup / Humidity response / Conclusions 41/27

Humidity response Electrode spacing [μm] 50 100 220 50 50 Temperat ure [°C] 24 26 25 26 35 Initial Final humidity humidit level [%] y level [%] 60 53 57 70 42 88 90 88 88 85 Difference between both sensors Δd [nm] 300 380 340 200 280 Water layers / Setup / Humidity response / Conclusions Settling time [h] 5 5. 5 4 6 6 42/27

Drinks: Next Friday 21: 00 “De Ruif” 43/27