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11-13 May 2011, Aix-en-Provence, France Large Area Adaptative Fluidic Lens Solon Mias [1,2], Aurélien Bancaud [1,2], Henri Camon [1,2] 1 CNRS-LAAS, 7 avenue du colonel Roche, F-31077 Toulouse 2 University of Toulouse; UPS; INSA; INP; ISAE; LAAS; F-31077 Toulouse, France Abstract- We have developed a large area (30mm diameter) adaptive fluid-lens using simple fabrication procedures that do not require elaborate micro-fabrication techniques. The lens structure consists of a 2mm thick liquid reservoir which is sandwiched between a solid borosilicate glass substrate, a thick PDMS-elastomer side-wall spacer and a more flexible PDMScoated PET membrane. The reservoir is connected via a 0.3 mm tube to a commercially available micro-pump used to alter the pressure within the reservoir, thus altering the surfacecurvature of the PET membrane and at the same time the optical power of the lens. The lens focal length can be changed from infinity to 0.5m. I. INTRODUCTION Ophthalmic glasses are one of the oldest portable devices. Even so, they have remained mostly the same over hundreds of years consisting of a rigid structure with fixed focal length. Recently, lenses with variable focal distances (bifocal and progressive lenses) have been developed particularly for people suffering from presbyopia [1]. Presbyopia is a condition mostly occurring due to aging of the human eye and where the eye’s ability to accommodate is reduced [2]. Other recent developments include the creation of microstructures on a lens in order to produce a customized lens [3]. Even so, the above structures are rigid and their focal length and wavefront correction abilities are determined by the fabrication. Adaptive lenses on the other hand have the ability to tune their focal length according to the needs of the user. Many such devices have been developed using a variety of technologies such as liquid crystal devices [4-11], electrowetting devices [12, 13] and micro-fluidic devices [14-17]. Liquid crystal adaptive lenses rely on the birefringence of the liquid crystal mixtures used in order to create a refractive index modulation within the lens which then translates into a phase change of the propagating light. These lenses are limited by the birefringence and the thickness of the liquid crystal layer. In addition, they exhibit diffraction effects due to the electrodes used to spatially address the liquid crystal layer. Different electrode shapes [18] and variable resistivities [6] have been developed in order to reduce the diffraction effects but in the expense of greater fabrication complexity. Finally, the greatest problem with liquid crystal lenses is their polarization sensitivity. Therefore two liquid crystal layers are required in order to modulate all light-polarizations and this increases fabrication complexity even further, particularly due to the need of fine alignment between corresponding pixels on each layer. Electrowetting devices on the other hand do not suffer from polarization sensitivity. Two companies have been recently involved in the fabrication of electrowetting lenses, namely Varioptic [13] and Philips [12]. Both companies use two non miscible liquids; an aqueous conducting solution along with insulating oil of the same density. The liquids are inserted within a closed cell with appropriately placed electrodes. The use of two liquids instead of one (e.g. water in air) is necessary for suppressing any optical distortion of the gravity on the liquid-liquid interface. The angle of the conducting fluid with the cell wall changes when an electric field is applied to the cell. Hence, as the voltage changes, the curvature of the interface between the two liquids is also changed. Hence a lens is formed which can be tuned from convex to concave using appropriate voltage levels. Unfortunately, devices produced are limited to small active areas due to distortions on the interface between the two liquids. Therefore both Varioptic and Philips lenses are mostly destined for the mobile phone industry rather than ophthalmic optics. Fluid-lens devices are also polarisation insensitive. The tuning of their focal length is achieved by altering the pressure within a liquid reservoir which has at least one wall made out of a flexible membrane (usually PDMS). When the pressure inside the cell is below the atmospheric pressure, the device turns into a concave lens. As the pressure increases above the atmospheric pressure then the lens turns into a convex lens. The change of the pressure within the lens can be tuned using a micro-pump, a syringe or a volume changing material [15]. The diameter of the lenses produced are relatively small (200µm [19] to 20mm [17]). The uniformity of the devices can be a problem. For example, PDMS non-uniformity during the membrane fabrication can cause defects of up to 4µm [19]. Also if the membrane of the lens is too flexible then the weight of the liquid can distort the normally-spherical shape of the membrane when the lens is used in a non-horizontal position. In this publication we describe the fabrication of a large area adaptive fluid-lens using simple fabrication procedures that do not require elaborate micro-fabrication techniques. The membrane of the lens is made out of PDMS-coated 241
11-13 May 2011, Aix-en-Provence, France PET layer which is solid relative to a single PDMS PDMS membrane of the same thickness. Therefore the lens membrane exhibits good uniformity despite its large area. spacer wall II. DEVICE FABRICATION Across section of the produced adaptive lens is shown in Fig.1. Firstly a 2mm thick PDMS layer is fabricated using a mixture of PDMS base 184 from Dow Corning and crosslinking agent at a mass ratio of 10 to 1. The largest part of the mixture is degassed within a cylindrical tank and leave more than one hour to allow a natural spread by gravity of the material into the tank. Thus we can get a very flat surface. Then the material is cured for an hour at 70°C within the cylindrical container for reticulation. The thickness is calculated by knowing the diameter of the cylindrical tank and the weight difference before and after filling. After reticulation the PDMS is removed from the container. A circular hole of 30mm is then opened through the spacer to form the reservoir side-walls. A 6mm channel long is also formed from the inner to the outer wall of the spacer in order to accommodate two tubes as shown in Fig.1(a). The tubes have inner diameter of 0.3mm and outer diameter of 1.5mm. These manufacturing steps can be easily enhanced by the completion of a resin mold (in SU-8 for example) on a silicon or glass wafer. The remaining non-cured PDMS mixture is also degassed and then spin coated on to a 75µm thick PET layer at a speed of 1200 rpm for 20 seconds. (PDMS thickness on PET 50 µm) The PDMS-coated PET is also placed at 70°C for an hour in order to cure the PDMS coating. The reason for using the PET layer is for increasing the rigidity of the flexible membrane of the lens. This eliminates any non-uniformity on the membrane surface due to the fabrication and due to the weight of the liquid as the lens is placed vertically. The PDMS coating of the PET is used for adhesion purposes. To elaborate further, the PDMS spacer and the PDMS-coated PET are etched using oxygen plasma. The oxygen plasma of PDMS results in the creation of free radicals on the PDMS surface. After the plasma etching, the PDMS spacer is placed on top of the PDMS-coated PET so as to be in contact with the spin-coated PDMS layer. The present of the free radicals ensures a strong adhesion between the two PDMS surfaces. The Young’s modulus of PDMS is in the range of MPa (0,2 Mpa more precisely) while that of PET is about 3000 Mpa, ie three decade above. As the thicknesses have the same order of magnitude (50 µm for PDMS and 75 µm for PET), the deformation is overwhelmingly governed by the properties of PET. The sealed reservoir is then filled with de-ionized water using a commercially available micro-pump, produced by Bartels Mikrotechnik GmbH. The micro-pump is connected to one of the two tubes and the second tube is used for allowing the air to exit from the sealed reservoir. The introduction of the liquid in the reservoir is shown in Fig.2. Fig.2 (d) shows that no air remains within the reservoir at the end of the process. The internal dimensions of the system are large enough not to ask problems due to capillary forces. Glass Substrate PDMS coating PDMS spacer wall Glass Substrate Tubes (a) Liquid reservoir PET (b) Liquid reservoir Fig. 1. (a) Top view of the fabricated fluid-lens. (b) Cross-section of the fluid-lens along the dotted line (a) (c) (b) (d) Fig. 2. The introduction of DI-water in the sealed reservoir. The DI-water is pumped out of a bottle (shown at the bottom-left of the images) using a micro-pump. The water is introduced into the reservoir using the one of the two tubes (water inlet tube) while the air already present inside the reservoir is allowed to exit the lens via the second tube (air outlet tube). Images (a) to (d) show the reservoir being progressively filled with DIwater. Image (d) shows that no air remains into the reservoir. III. DEVICE OPERATION AND CHARACTERIZATION After the spacer and the membrane have been bonded together, the combined spacer/membrane layer is again etched using oxygen plasma along with a borosilicate glass substrate. After the plasma etching, the tubes are placed within the 6mm channel and the spacer/membrane layer is then bonded onto the glass-substrate thus forming the liquid reservoir. Non-cured PDMS mixture is then used to fill the gaps between the channel and the tubes and the complete device is then heated at 70°C for an hour in order to cure the PDMS and seal the channel - and thus the reservoir. The adaptive fluid-lens was used under different operational modes. In the first mode the micro-pump was activated in order to raise the water pressure inside the reservoir. The air-outlet tube was left open and hence water was allowed to exit through the outlet tube. In this mode of 242
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COLLECTION OF PAPERS PRESENTED AT T
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III
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V
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Table of Contents Wednesday 11 May
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PANEL DISCUSSION TEXTILE MICROSYSTE
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Friday 13 May SESSION C4: APPLICATI
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SPECIAL SESSION OF BIO-MEMS/NEMS a
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suspended membrane can be pulled to
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most likely due to not yet consider
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that detectors may measure the diff
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2) Cavity width effect To verify th
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Fig.9. Capacitive sensor output, Va
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The anode and cathode are connected
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! TABLE 3 SUMMARY OF SELECTIVITIES
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The fabrication of optical Cap-Wafe
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the glass is polished down in a cos
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Fig. 14. Time history of the envelo
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We assume that 11-13 May 2011, Aix
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Y X Fig. 1. Scanning electron mic
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10 3 11-13 May 2011, Aix-en-Proven
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Intenstiy (counts/second) Fig. 1. X
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etween x 2 to L (remember that x 2
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piezoelectric displacement transduc
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Figure 7 Displacement conditions of
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protect the corners from undercut.
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A. Continuous domain Starting from
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Fig. 8. Central finite difference m
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700 11-13 May 2011, Aix-en-Provenc
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o o o o o o o o Check applicability
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C. Identification Results The ident
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The proposed solution for this prob
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teen wire segments of a coil, as in
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As the metallization is too reflect
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B. Implemented die overview A die c
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IN CLK OUT Fig. 16. Probe setup for
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adhesive material with 30μm thickn
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B. Dynamics of Energy Flows For a l
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80˚C. Additionally, we looked into
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The XRD shows a peak above the 2θ
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fibers which define the electric co
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Figure 15. Key board input system.
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ρ = h 2∆α∆T + + E 1h 3 1 +E 2
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In recent years, the pipe flow moni
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As the speed of the rotor increases
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inches silicon wafers which have th
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samples tested in different vacuum
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l c 11-13 May 2011, Aix-en-Provence
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Vp (V) 3,5 3,0 2,5 2,0 1,5 1,0 0,5
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II. MATHEMATICAL MODEL AND NUMERICA
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fluids travel along a curved channe
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measured mixing indices are depicte
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length, which enables them to focus
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however, a rotation for coincidence
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excludes the nature of the fixed bo
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Page 230 and 231: electrocardiogram. • The heart be
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Presently, the microfabrication pro
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[6] C. Richard, A. Renaudin, V. Aim
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NA sinθ c 11-13 May 2011, Aix-en-
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the waveguide on the fused silica,
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microphone diaphragm. The chosen CM
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TABLE V MICROPHONE CHARACTERISTICS
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Figure 7b shows the effect of a par
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over the temperature range (i.e. th
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given. This allows a CTM model to b
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the magic-Tee, and the coherent sig
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After analyzing the two conditions
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IV. MICRO FABRICATION For fabricati
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IV. A. Simulation and Sensitivity A
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grown to sub-confluence were washed
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Clamps rotation [21] Clamps transla
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Layout Total dimensions of the grip
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focusing increased both as the stre
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Time of diffusion (hr) 1200 1000 80
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Chip Magnet Light source Hot plate
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above, they would move to upward an
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This phenomenon is now reaching the
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C. Proof mass displacement Moreover
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The VerilogA block code is : 11-13
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Author Index Abi-Saab D. 81 Aimez V
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Nussbaum Dominic 273 O’Hara T. 35
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