Electrowetting, active self-cleaning surface

Abstract

There is provided an optical element having an outer surface, the optical element comprising: a coating on the outer surface for forming any fluid thereon into fluid droplets; a plurality of independently activated electrodes, each having a plurality of interdigitated fingers, the plurality of interdigitated fingers being positioned proximate the outer surface and extending across a region of the outer surface; and a driving circuit for selectively applying a signal to the plurality of electrodes. The AC signals applied to the electrodes with adjacent fingers each have a phase shift such that fluid droplets are continuously swept across the outer surface in a predetermined direction. The electrode fingers may be arranged at a uniform pitch, where the pitch is the distance between the centers of the electrodes, and the pitch is less than or equal to 750 [mu] m. The electrode fingers may be arranged in a single plane with a gap therebetween.

Description

Technical Field

[0001] Embodiments of the present invention relate generally to self-cleaning surfaces, and more particularly to self-cleaning surfaces for shedding fluids for vehicles. Summary of the invention

[0002] In one aspect of the present invention, an optical element is provided, the optical element comprising: a substrate having an outer surface on which a droplet of a fluid can be formed; N independently activated electrodes, each of the electrodes can be identified by a sequence reference n (where n=1 to N), each electrode having a plurality of electrode fingers, the plurality of electrode fingers being positioned proximate to the outer surface and extending across an area of ​​the outer surface, the electrode fingers being arranged in a repeating sequential order from 1 to N; and a drive circuit for selectively applying a phase modulated AC signal to the electrode, the drive circuit generating the phase modulated AC signal by applying N phase modulated signals to an AC signal, wherein the N phase modulated signals are equal to the N independently activated electrodes, each phase modulated signal can also be identified by the sequence reference n (where n=1 to N) to correspond to a corresponding electrode, wherein each phase modulated signal is T w The phase shift is imposed on the AC signal periodically between the in-phase state and the anti-phase state, wherein the phase shift in each phase modulation signal n is delayed in time by a time step t relative to the phase shift in the sequentially preceding phase modulation signal n-1. s , so that the droplet is continuously swept across the outer surface in a predetermined direction.

[0003] In another aspect of the present invention, an optical element is provided, comprising: a substrate having an outer surface on which droplets of a fluid can be formed; a plurality of independently activated electrodes, each of the electrodes having a plurality of fingers, the plurality of fingers being positioned proximate to the outer surface and extending across an area of ​​the outer surface; and a drive circuit for selectively applying signals to the plurality of electrodes, wherein the electrode fingers are arranged at a uniform pitch, wherein the pitch is the distance between the centers of the electrodes, and the pitch is less than or equal to 750 μm.

[0004] In another aspect of the present invention, an optical element is provided, comprising: a substrate having an outer surface on which droplets of a fluid can be formed; a plurality of independently activated electrodes, each of the electrodes having a plurality of fingers, the plurality of fingers being positioned proximate to the outer surface and extending across an area of ​​the outer surface; and a drive circuit for selectively applying signals to the plurality of electrodes, wherein the electrode fingers are arranged at uniform spacings, wherein the electrode fingers are arranged in a single plane with gaps therebetween.

[0005] These and other features, advantages and objects of the present device will be further understood and appreciated by those skilled in the art through a study of the following specification, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Embodiments will now be described with reference to the following drawings, in which:

[0007] Figure 1 is an electrical diagram in block form of an optical device of an embodiment described herein;

[0008] Figure 2 yes Figure 1 a graphical illustration of a cross-sectional view of the optical device shown in with a water droplet thereon;

[0009] Figure 3 is a graphical illustration of an enlarged cross-sectional view showing polar molecular alignment due to the presence of an electric field within a water droplet;

[0010] Figures 4A-4C is a series of graphical illustrations showing the aggregation of water droplets over time;

[0011] Figures 5A-5C is a series of graphical illustrations showing the sweep of a water droplet over time;

[0012] Figures 6A-6C is a series of photographs showing the aggregation of water droplets and the force of gravity pulling down larger droplets over 2.5 second intervals;

[0013] Figures 7A-7C is a series of photographs showing a water droplet being swept at one-second intervals;

[0014] Figure 8 is a graphical representation of an example of a row of electrode fingers;

[0015] Fig. 9 is shown for modulating an AC signal to produce a Figure 8 A first timing diagram of a phase modulated signal of a phase modulated signal of each of the interdigital electrode fingers shown in;

[0016] Fig.10 is shown for modulating an AC signal to produce a Figure 8 a second timing diagram of a phase modulated signal of a phase modulated signal of each of the interdigital electrode fingers shown in;

[0017] Fig.11 is a third timing diagram showing electrical signals delivered to each of the interdigitated electrode fingers;

[0018] Fig.12is a fourth timing diagram illustrating electrical signals delivered to each of the interdigitated electrode fingers;

[0019] Fig.13A and 13B is a pair of graphical representations of the electric field imposed on a water droplet with and without the use of a floating or grounded electrode;

[0020] Fig.14A and 14B are side and top views of multiple water droplets bridging the gap between electrodes;

[0021] Fig.15A and 15B is a pair of graphical representations of the electric field imposed on a water droplet with and without the use of a floating / grounded / common / neutral / HiZ electrode;

[0022] Fig.16A and 16B are a pair of graphical representations of the charge imposed on a water drop after sweeping it;

[0023] Fig.17 is a top view of a pattern of zigzag electrode fingers;

[0024] Fig.18 is a graphical illustration of an example of a layered in-plane geometry IDE with an isolated ground plane underneath;

[0025] Fig.19 is a graphical illustration of an example of a layered parallel geometry;

[0026] Fig. 20 is a top view of the layered hash pattern of the electrode fingers;

[0027] Fig.21 is a top view of the overlapping pattern of electrode fingers;

[0028] Fig. 22 is a graphical illustration of an optical device used as a capacitive touch surface;

[0029] Fig.23A and 23B is a pair of graphical representations of the electric field imposed on small water droplets with large and small separations;

[0030] Fig.24A and 24B is a pair of graphical representations of the electric field imposed on a large water droplet with different numbers of independent electrodes N = 2 and N = 8;

[0031] Fig.25A is a top view of the active area of ​​the eWash surface with 8 independent electrodes;

[0032] Fig.25B yes Fig.25A Photograph of water droplets on the active area of ​​the eWash surface shown;

[0033] Fig.26A is a top view of the active area of ​​the eWash surface with 64 independent electrodes;

[0034] Fig.26B yes Fig.26A Photograph of water droplets on the active area of ​​the eWash surface shown;

[0035] Fig. 27 is a top view of the active area of ​​the eWash surface showing how the 7 groups (AG) of tiled electrodes are connected;

[0036] Fig.28 is shown for modulating an AC signal to produce a Fig. 27 a third timing diagram of a phase modulated signal of a phase modulated signal of each of the interdigital electrode fingers shown in;

[0037] Fig.29 is a side view of a diagram showing the electric field imposed on a droplet propelled by the electric field;

[0038] Fig.30 is a photograph of a top view of a droplet propelled by an electric field;

[0039] Fig.31 is a photograph of a droplet at the edge of the active area of ​​the eWash surface; and

[0040] Fig.32 is a plan view of the active region of the eWash surface with the connection of the electrode fingers and also with the region of the extended first and last electrode fingers. DETAILED DESCRIPTION

[0041] For the purpose of this description, the terms "upper", "lower", "right", "left", "rear", "front", "vertical", "horizontal" and their derivatives will be used in conjunction with the present invention. Figure 2 Unless otherwise specified, the term "front" shall refer to the surface of the element that may be exposed to water, and the term "rear" shall refer to the surface of the element that is farther from the front surface. However, it should be understood that the present invention may adopt various alternative orientations except that the opposite direction is explicitly specified. It should also be understood that the specific devices and processes illustrated in the drawings and described in the following description are merely exemplary embodiments of the inventive concepts defined in the appended claims. Therefore, unless the claims explicitly state otherwise, the specific dimensions and other physical characteristics related to the embodiments disclosed herein should not be considered restrictive.

[0042] The terms "comprises", "includes" or any other variation thereof are intended to cover non-exclusive inclusions, such that a process, method, article or apparatus comprising a list of elements includes not only those elements, but may also include other elements not explicitly listed or inherent to such process, method, article or apparatus. Without further constraints, an element preceded by "comprises..." does not exclude the presence of additional identical elements in the process, method, article or apparatus comprising the element.

[0043] As used herein, the term "and / or" when used in a list of two or more items means that any one of the listed items can be used alone, or any combination of two or more of the listed items can be used. For example, if a composition is described as containing components A, B, and / or C, the composition can contain: A only; B only; C only; a combination of A and B; a combination of A and C; a combination of B and C; or a combination of A, B, and C.

[0044] As optical and electromagnetic imagers and sensors become ubiquitous, such as in advanced driver assistance systems and autonomous vehicles, self-cleaning external surfaces become important for reliable operation of these sensors and imagers. Sensors and imagers operating in the field are subject to environmental elements that leave contaminants or water droplets on the first surface of the sensing device. In order to keep the field of view unobstructed, it is preferred to remove contaminants on the first surface as quickly and efficiently as possible.

[0045] Mechanical wipers have been a conventional method of removing fluid from windshields and cleaning surfaces as well as the first surface of various sensors and imagers. As future technology moves toward advanced driver assistance and unmanned systems, multiple sensors must be installed at several strategic locations on the vehicle. Clear signals on these sensors require unobstructed viewing through optical elements, such as optical or sensor devices' first surfaces. Although effective, wipers may block the view of sensors during operation, and too many of these mechanical wipers will increase the weight of the vehicle, the possibility of mechanical failure, and power requirements.

[0046] Adding wipers to self-cleaning surfaces, such as bathrooms or building surfaces, can be an eyesore.

[0047] Self-cleaning devices that apply severe mechanical vibrations to a surface have been proposed to clean vehicles. An example of such a device is disclosed in commonly assigned U.S. Patent No. 8,899,761. Although the vibrations can eject fluid and debris vertically off a surface, in a moving vehicle, unless blown to the side, the debris is likely to be propelled back onto the surface by the airflow. The droplets sweep along the surface like a conventional wiper. If designed and oriented to sweep in the same direction, external forces such as gravity and airflow will assist and increase the efficiency of the surface cleaning.

[0048] Another approach is to use a surface dewetting device using an electrical signal on a surface having patterned electrodes, which will hereinafter be referred to as an electrowetting, organically clean hydrophobic (eWASH) surface. An example of an eWash surface is disclosed in U.S. Pat. No. 8,172,159 B2, which uses a DC voltage applied to patterned electrodes.

[0049] The present disclosure relates to improved eWASH surfaces. The improved eWASH surfaces of the present disclosure are non-obstructive, robust, non-mechanical solutions for cleaning surfaces. These improved eWASH surfaces can be made of transparent materials that are not noticeable to the naked eye.

[0050] The improved eWash surface enables the movement of multiple fluid droplets, with multiple droplet sizes ranging from about tens of microns to millimeters, which can be extended to large areas and is suitable for any application. The improved eWash surface does not necessarily only remove or clean the surface, but more generally, the surface moves droplets, which can be used for other purposes, such as actively collecting water in a coastal desert where it is always foggy but not raining at a certain time of the day. For water collection applications, water can be actively swept into a collection pool before it evaporates or even before condensation / accumulation reaches the volume threshold of gravity to overcome static friction and affect the movement of droplets. It should be noted that depending on weather conditions, the droplet size required for gravity to move droplets may not be achieved. However, using this technology, water droplets can be moved without waiting for the droplet size to become large enough for gravity to control.

[0051] The novel feature of this eWASH surface cleaning device not found in self-cleaning surfaces is to induce the movement of droplets through electrowetting, gravity or other mechanisms to efficiently sweep fluid from the surface. The eWASH system can gather small droplets of water, common solvents and cleaning fluids into larger droplets, and allow external forces such as gravity to cause the droplets to fall off. Simultaneously and / or at various time points and areas on the surface, the self-cleaning device can actively and continuously sweep fluid droplets in one or more directions suitable for the application.

[0052] like Figure 1 and 2As shown, the embodiments described below relate to an optical element 10 having an outer surface 15, the optical element 10 comprising: an optional hydrophobic (or super-hydrophobic) coating 20 on the outer surface 15, the optional hydrophobic coating being used to form any fluid thereon into fluid droplets 5; a dielectric layer 25 on which the hydrophobic coating 20 is disposed; a plurality of interdigitated electrodes 30, 40, 60, 70 positioned on the dielectric layer 25, the plurality of interdigitated electrodes being proximate to the outer surface 15 and extending across an area of ​​the outer surface 15; and a drive circuit 50 for selectively applying an AC signal to the plurality of electrodes 30, 40, 60, 70, wherein the AC signals applied to adjacent electrodes each have a phase shift relative to each other in such a manner as to continuously sweep the fluid droplets 5 across the outer surface 15 in a predetermined direction.

[0053] According to one embodiment, the plurality of electrodes may include a first electrode 30 positioned close to the outer surface 15, the first electrode 30 having a plurality of first fingers 32 extending across an area of ​​the outer surface 15; and a second electrode 40 positioned close to the outer surface 15, the second electrode 40 having a plurality of second fingers 42 extending across an area of ​​the outer surface 15 and intersecting the plurality of first fingers 32 in a spaced-apart relationship.

[0054] The plurality of electrodes may further include an optional third electrode 60 having a plurality of third fingers 62 extending across the area of ​​the outer surface 15 and intersecting the plurality of first fingers 32 and the plurality of second fingers 42 in spaced relationship, and an optional fourth electrode 70 having a plurality of fourth fingers 72 extending across the area of ​​the outer surface 15 and intersecting the plurality of first fingers 32, the plurality of second fingers 42, and the plurality of third fingers 62 in spaced relationship. As explained below with respect to further embodiments, a greater number of electrodes may be provided.

[0055] The drive circuit 50 may be further configured to selectively apply a voltage potential between the first electrode 30 and the second electrode 40 (and optionally between the third electrode 60 and the fourth electrode 70 ) in a manner that causes fluid droplets to coalesce into larger fluid droplets and / or sweep fluid droplets across a surface.

[0056] The optical element 10 can be used in a variety of applications. One example is a transparent cover for a camera or imager of a vehicle, wherein the transparent cover includes the optical element 10. Other non-limiting examples include: lens cover glass; lens first surface; windshield; car window; building window; solar cell; mirror; any self-cleaning surface (family car); cover lens of a lidar or radar; and camera cover.

[0057] Figure 2 The basic structure of the eWASH system on the surface 15 or substrate 12 according to the first embodiment is shown. The electrode array layer (32, 42 and optionally 62 and 72), the dielectric layer 25 and the hydrophobic, superhydrophobic and / or oleophobic layer 20 can each be made of multiple layers of the same or different materials. The hydrophobicity and / or oleophobicity of the topmost layer 20 in contact with the fluid is characterized by the contact angle (θ) of the fluid on the surface 15. C ). The dielectric layer 25 and the hydrophobic layer 20 can be made of different material layers or made of one and the same layer. The substrate 12 itself can be one and the same layer as the dielectric layer 25, or can be a separate layer different from the dielectric layer 25. Further, the substrate 12 itself or the dielectric layer 25 itself can have hydrophobic properties, thereby not requiring a separate coating 20. Conductive electrodes 30, 40, 60 and 70 and / or their fingers 32, 42, 62 and 72 can be placed on the bottom surface of the dielectric layer 25. On the active area, the individual electrodes 30, 40, 60 and 70 are not necessarily in electrical contact with each other, but the fingers 32, 42, 62 and 72 can be grouped together via contacts outside the active area. The overall pattern of the electrodes 30, 40, 60 and 70 will vary depending on the embodiment or application. One or more electrodes 30, 40, 60 and 70 can be directly exposed to the environment or placed on the first surface 15. The gaps between the electrodes 30, 40, 60 and 70 do not need to be uniform. Electrodes 30, 40, 60 and 70 may be opaque or transparent. Although outer surface 15 is preferably hydrophobic, the embodiments described below will work with surfaces that may not be considered hydrophobic (ie, where the contact angle is less than 90 degrees).

[0058] This eWASH surface will effectively dehumidify water. Other fluids and solvents can also be cleaned, such as water-alcohol mixtures, salt water, etc. The degree of efficacy for various fluids depends on the interaction of the fluid with the hydrophobic coating 20 and the polarizability of the fluid. The power or voltage level applied to the electrodes 30, 40, 60 and 70 by the driver circuit can be tuned to be more efficient for fluids or solvents other than water.

[0059] Nonpolar, polar, or electrolytic fluids can be polarized to varying degrees in the presence of an electric field. For example, applying an electric field to a nonpolar molecule such as isopropyl alcohol causes the electron cloud to displace, thereby inducing a dipole moment. Water, on the other hand, is polar and consists of molecules that have a net permanent dipole due to their molecular charge distribution. As long as an electric field is present, these water molecule dipoles will align along the field (see Figure 3 ).

[0060] Dielectric phenomena are often the principle referred to when explaining the dynamics of a system due to the forces on this polarized dielectric or water droplet 5. A brief description of the phenomena is provided below. These neutral fluid droplets are affected by electric forces due to the polarization of the fluid's permanent dipoles or induced dipoles. For example, in the presence of a gradient in the electric field, the energy of the induced droplet dipole is minimized,

[0061]

[0062] This creates the driving force. Figure 3 With the electrode geometry and droplet positioning shown, the electric force will flatten the droplet 5. The equation also tells that polarized droplets are attracted toward areas of increased electric field. With the appropriate electrode geometry to produce a dynamic field pattern, the droplet flattening effect and attractive forces can be used to cause droplets to coalesce and / or sweep droplets off a surface.

[0063] An equivalent way to view the electrowetting phenomenon is in terms of the dynamic change in the induced contact angle of a fluid 5 on a surface. When there is an inhomogeneous field between the gaps or in a region with differential pressure, a water droplet is attracted to the electrode gap or wets the region while exhibiting a reduced contact angle. Once the voltage difference is removed, the contact angle increases.

[0064] As described above, droplets can be removed by either gathering or sweeping. In addition, a combination of gathering and sweeping can be used. These three cleaning modes are discussed below.

[0065] First, refer to Figures 4A-4C The aggregation mode is described, which shows parallel or interdigitated electrodes (IDE) 30, 40, 60 and 70, which can have an AC voltage at the same time, or any voltage can be applied to the individual fingers at different times and sequences. When a differential voltage is applied between the electrode fingers 32, 42, 62 and 72, an electric field is generated. The field distribution and intensity lead to the flattening of the droplets 5. The flattened droplets 5 contact other flattened droplets 5 and merge to form larger droplets 5. Large droplets 5 slide out more efficiently via external forces such as gravity and airflow.

[0066] Passive aggregation can also be achieved by cleverly patterning hydrophobic and hydrophilic regions of the surface. This is discussed separately below.

[0067] Another novel idea is the process of actively removing fluid droplets 5 from the eWASH surface 15 by sequentially sweeping the field present across the surface 15. The sweeping pattern is shown in FIG5. As previously discussed, the droplets 5 are attracted toward the region having pairs of electrode fingers 32, 42, 62, and 72 that have a differential voltage in the presence of an inhomogeneous electric field. Thus, when pairs or groups of electrode fingers 32, 42, 62, and 72 are formed, the droplets 5 are attracted toward the region having pairs of electrode fingers 32, 42, 62, and 72 that have a differential voltage in the presence of an inhomogeneous electric field. Figures 5A-5CWhen power is applied sequentially as shown, a droplet 5 of fluid that can cross over to the next electrode is moved in the direction of the electrical sweep. The profiles for electrical sweeping, sweep directions and geometries are described below.

[0068] Figures 6A-6C 7A-7C show a glass substrate, indium tin oxide (ITO) electrodes 30, 40, 60 and 70, SU8 photoresist as a dielectric 25, and AF are exemplary results of the hydrophobic layer 20 . Figures 6A-6C Examples of accumulation (vertical orientation) and shedding (gravity along the finger) are shown. Figures 7A-7C An example of a sweep without gravity assistance (horizontal orientation) is shown.

[0069] Efficient dehumidification and surface cleaning may involve both focusing and sweeping droplets during the cleaning procedure. Power distribution, focusing, or sweeping may be done in any order, or may occur simultaneously at different areas of the sample.

[0070] There are various ways to sweep the electrodes by sequentially powering the electrode groups 30, 40, 60 and 70. The novel idea is to be able to continuously and sequentially power the electrodes 30, 40, 60 and 70 without having to power each electrode independently. Figure 8 It is helpful to describe the execution of the idea. Initially, a manageable number of electrodes 30, 40, 60 and 70 that can be powered independently are needed, for example, four electrode fingers 32, 42, 62 and 72 numbered 1-4 one after the other. These groups of four electrode fingers can be repeated to add up to however many electrode fingers are desired. In this example, there will be three groups (or tiles) of fingers 32, 42, 62 and 72 labeled R, G and B, respectively, as shown in FIG. Figure 8 As shown, there are a total of 12 electrode fingers. The electrode fingers 32R, 32G and 32B numbered 1 on all three groups are physically connected (the connection method is described below), and the same is true for the electrode fingers 42R, 42G and 42B numbered 2; the electrode fingers 62R, 62G and 62B numbered 3; and the electrode fingers 72R, 72G and 72B numbered 4. Therefore, when electrode number 1 (30) is powered, all fingers 32R, 32G and 32B numbered 1 on all other groups are also powered. In other words, fingers 32R, 32G and 32B receive the same signal with the same phase from the driver circuit 50. Therefore, these electrode fingers are regarded as interdigitated and arranged in the block. In other words, the multiple interdigitated fingers 32, 42, 62 and 72 are arranged in multiple tiles R, G and B, wherein each tile R, G and B includes one finger 32, 42, 62 and 72 of each of the multiple electrodes p30, 40, 60 and 70 arranged in a sequential order, wherein the sequential order is repeated for each tile R, G and B.

[0071] To produce an effective continuous sweep across all electrodes, the driver circuit 50 can be configured so that the signal period or power supply period on the fingers 32, 42, 62, and 72 is equal to the period of one group of sweeps. Once this scheme is applied sequentially to all groups, the fluid droplets positioned on the first group are swept as if continuously as they move along all groups of electrodes 30, 40, 60, and 70. The continuous sweep effect is as follows: Fig. 9 and 10 This is demonstrated in the example timing diagram shown.

[0072] With respect to sweeping geometry or direction, electrodes 30, 40, 60, and 70 can, for example, be oriented so that their fingers 32, 42, 62, and 72 extend horizontally perpendicular to the direction of gravity, so that the sweeping direction can be parallel or anti-parallel to the direction of gravity's pull. The ability to orient the electrode fingers 32, 42, 62, and 72 and direct the sweep with appropriate electrode power sequencing plus focus opens up an unlimited number of directions in which fluid droplets can be swept (novel electrode geometries are discussed below).

[0073] A non-exhaustive list of sweep geometries and directions includes: up-down sweep; left-right sweep; sweep outward from the center; sweep inward from the center to induce focus; sweep toward one or more focus points; radial sweep (inward or outward); and diagonal and arbitrary angle sweeps.

[0074] A droplet staging / initiation zone can be created for a snowballing effect. The idea here is to provide a head start for gathering and / or sweeping outside the active area so that by the time the droplets reach the active area, they have snowballed to a size that more efficiently cleans the active area or has reached a volume that is more susceptible to dewetting and external forces.

[0075] The difference in field between electrodes / fingers can be achieved by applying an AC voltage signal with various waveforms (square, sinusoidal, etc.). The frequency, waveform, phase and voltage can be optimized according to the details of the geometry (finger width, gap width, layer thickness) and the electrical properties of the materials (substrate, dielectric coating, hydrophobic coating).

[0076] Each electrode 30, 40, 60 and 70 can be switched between a charged state, a grounded state, a floating state or continuously flipped between the states during operation. Intermittently grounding all electrodes 30, 40, 60 and 70 will give droplets time to not be electrically attracted to the surface and can help to efficiently allow external forces such as gravity and / or wind to sweep the droplets and contaminants. Fig.11 An example of such a method is shown in .

[0077] The signal applied to the electrodes may be phase modulated. A uniform waveform may be applied to all electrodes 30, 40, 60, and 70. A differential voltage is achieved by applying a phase difference in the waveform between the electrodes 30, 40, 60, and 70. The out-of-phase regions may then be sequentially swept across the finger to achieve a sweep of a fluid droplet. Fig.12 An example is shown in FIG.

[0078] Amplitude and phase modulation can be applied at different times, or both can be applied simultaneously at separate regions of the active region. The phase difference of a gap relative to another gap can be fixed, or the phase in a series of gaps can be changed continuously or arbitrarily. The amplitude of the voltage difference can also be adjusted by tuning the phase difference between electrodes 30, 40, 60 and 70. The driver circuit 50 can connect a two-phase or multi-phase output signal source to a separate electrode. Multi-pole or multi-throw switching between available signals and separate fingers 32, 42, 62 and 72 can then toggle or waveform selection between different signals to produce an appropriate voltage sweep profile.

[0079] Various novel geometries can be used for electrodes 30, 40, 60 and 70. While parallel or interdigitated electrodes (IDE) are the simplest patterns that can be achieved for electrowetting and self-cleaning features, many other electrode pattern variations are possible. One such example is floating fingers 82. Depending on the self-cleaning mode of operation, focusing and / or sweeping, the direction of the IDE can be oriented parallel or perpendicular to the shedding / sweeping direction. For example, if the fingers 32, 42, 62 and 72 have an alternating high voltage and a low voltage (see Fig.13A and 13B ), it will be difficult for the droplet 5 to pass through the next gap due to the orientation of the electric field on the next gap. In this case, if the IDE is aligned along the direction of gravity or other external forces, the self-cleaning on the surface will be more efficient, which avoids the dilemma of the water droplet having to pass through a gap with opposing fields or opposing forces.

[0080] A useful trick for making the droplet expand and traverse the gap is to place an electrically insulated or floating conductive electrode finger 82 between the two electrode fingers 32 and 42 with a voltage difference. If the droplet 5 is large enough, the droplet 5 can stretch all the way between the two charged electrode fingers 32 and 42 (see Fig. 13B ). There will also be no opposing fields between the charged electrode fingers 32 and 42. The field around the gap of the floating electrode finger 82 will always be in the same direction. This has the additional benefit that the droplets within the active electrode fingers 32 and 42 are attracted to each other.

[0081] The floating electrode fingers 82 also prevent the droplets 5 from being electrostatically attracted to the electrode fingers 32 and 42. Fig.14A and 14BWhen the dielectric 25 is very thin (dielectric thickness << gap width), the probability of leaving residual charge on the electrode fingers 32 and 42 and electrostatic polarization of the water droplet 5 is high (see Fig.15A and 15B ).

[0082] The floating fingers 82 are neutral and insulated. Therefore, the net charge is constant or always balanced. Regardless of the charge separation that occurs when the device is powered, the floating fingers are lost once the device is powered off.

[0083] Having exposed electrodes / fingers 92 may be useful because the exposed electrode fingers 92 can transfer charge through ionization of contacting water droplets. Fig.16A and 16B An interdigitated exposed electrode 92 is shown on the surface 15 of interest. Additional insulated electrodes 90a and 90b are placed in the periphery above the dehumidifying surface 15, and the insulated interdigitated electrode fingers 32, 42 and 62 are located below the surface 15. The first step of the process is to apply a voltage difference between the exposed electrode fingers 92 and the peripheral electrodes 90a and 90b. Charge transfer occurs between the exposed electrode fingers 92 and the water droplet. The second step involves sweeping the droplet 5 over the insulated interdigitated electrode fingers 32, 42 and 62 with an appropriate sequence of power supply and potential. The electrophoresis phenomenon is a principle that appropriately describes the resulting force on the charged water droplet 5.

[0084] like Fig.17 As shown, the electrode fingers may also be zigzag shaped. Fingers without clear lines increase the density of gap lines, the number of gaps, the effective length of gap lines, or the area where droplets are attracted. The spikes on the electrode fingers also help to create an uneven electric field, thereby creating an unbalanced force that may propel the water droplet 5. The droplet 5 will stop moving at the boundary, and if the boundary is sharp, the droplet will continue to be pulled to the end of the spike, which in some zigzag designs can pull the droplet 5 to the beginning of the next electrode, thus preventing the droplet 5 from getting stuck.

[0085] The size of the fingers 32, 42, 62, and 72 and the gap width may also be gradually changed. This may improve the efficiency of the droplet sweeping. For example, the sweep may start from a narrower finger / gap to a larger finger / gap to more efficiently sweep the droplet 5 because the droplet starts small and becomes larger as it continues to move across the fingers and gaps.

[0086] Individual fingers 32, 42, 62 and 72 may also be combined / grouped to effectively create larger fingers. More and more individual fingers may be powered together simultaneously / identically to efficiently move droplets as they grow or "snowball" along the electrode fingers.

[0087] Thin film transistors (TFTs) are an option for creating active electrode patterns on the surface of a support substrate 12 such as glass or transparent polyimide. The electrode pattern can be pixelated, and a differential voltage can be applied between a pair or group of pixels to move a droplet in any direction. TFTs allow for integrated circuits on substrates, which enables applications requiring large areas or high channel counts. TFTs can also be used to reduce the number of contacts required.

[0088] It is also possible to use a layered geometry of the electrode fingers 32, 42, 62 and 72. An example of a layered geometry is an in-plane geometry IDE with an isolated ground plane 95 underneath, such as Fig.18 As shown. Additional electrode fingers 32, 42, 62 and 72 or conductive planes 95 may also be placed in different layers on the surface separated by insulating material or dielectric 25. For example, Fig.18 A non-planar geometry is shown. A conductive plane 95 is placed below the interdigitated electrodes. An inhomogeneous field to which the droplets are attracted is created by powering individual electrodes with opposite polarity to the conductive plane 95 and leaving their neighboring electrodes floating.

[0089] Another example of a layered geometry is a layered parallel geometry. When power is applied, the electrode fingers 32 may have regions of zero field or uniform field, such as in the middle of the electrode fingers or in the middle of the gap, respectively. Therefore, droplets located in those regions may not experience gathering or sweeping forces. A method for minimizing those regions where field non-uniformity is small is to add another lower layer of electrode fingers 42 offset from the first pattern, such as Fig.19 shown.

[0090] Still another example of a layered geometry is a layered hash. The additional lower electrode fingers 62 and 72 need not be parallel to the first layer pattern of electrode fingers 32 and 42. Fig. 20 As shown, the interdigitated layers can be orthogonal to each other. This "hashed" pattern allows multi-directional sweeping of the droplet.

[0091] Another geometry that can be used is the reverse coated geometry. The last layer is covered with electrodes, flipped over, and then bonded to the substrate with the electrodes sandwiched between the last layer and the substrate. Electrodes, such as ITO, PDOT, graphene can be coated on the back side of the first layer (e.g., glass, parylene).

[0092] Other geometries include: stacked IDE (IDE|dielectric|IDE); stacked IDE with a slight angular offset between them; and tiled agglomeration (tile IDE), which avoids larger capacitance.

[0093] Various geometries of the electrodes have been described, and now various forms of connection of the electrodes are described. One such connection is an overlapping connection or a bypass crossing electrode. Electrodes can be grouped together by short - circuiting the overlaps and thereby providing an overlapping connection. Electrical insulation crossing, bypass crossing between electrodes can be achieved by placing a layer of material with high dielectric strength between the overlapping electrodes. These are useful ways of grouping or bypassing electrode fingers 32, 42, 62, and 72 having a helical or overlapping geometry, as Fig.21 shown. Other connections can be made through vias or an anisotropic conductive film (ACF).

[0094] The heater can be used in combination with electrowetting. This can be useful if surface 15 is exposed to snow and ice such that the heater melts the snow and ice, converting it to water, which can then be removed using the methods described above.

[0095] Moreover, it can be desirable to utilize the capacitance sensing and triggering capabilities of the device. The IDE is essentially a capacitor. Contaminants and droplets on the surface of the electrowetting device change the effective capacitance measured in the device through capacitive coupling and also change the effective dielectric constant due to the additional layer of water and contaminants. Fig. 22 Examples are shown in. This inherent capacitance sensing ability of eWASH can be used to trigger voltage sweeps or water spraying, air suction, and other complementary or supplementary cleaning procedures of the device. The capacitance sensing ability can be used to trigger internal and external processes inside and outside the eWASH surface. In other words, the plurality of interdigitated fingers provide capacitance sensing of droplets on the outer surface, and the drive circuit is configured to apply a signal to the plurality of electrodes in response to capacitance sensing of droplets on the outer surface.

[0096] In the following embodiments, the electrodes are arranged in a single plane and there are gaps between the electrodes. In this arrangement, the following metric allows for actively and efficiently sweeping various droplet sizes.

[0097] Spacing < droplet diameter < N * spacing,

[0098] where N is the number of electrode fingers independently activated for each tile, and the spacing is the distance between the centers of adjacent electrode fingers, which are of uniform size and spacing. Fig.23A and 23B shows the effect of the spacing on the small droplet 5. In Fig.23A , the spacing between adjacent electrodes is greater than the diameter of droplet 5. In this case of large spacing, it may be difficult to move droplet 5. In Fig. 23B , the spacing is smaller and thus it is easier to sweep the small droplet 5. In Fig.24A , a larger droplet 5 is shown, and its spacing is the same as that in Fig. 23B but less than the diameter of the droplet. Fig.24AThe example shown in has two independently activated electrodes 30 and 40 (N=2), each having fingers 32 and 42, respectively. Thus, there are two electrode fingers 32 and 42 per tile. Since the tile size is relatively small compared to the droplets 5, moving larger droplets 5 can be a challenge. Fig. 24B , for the eight electrode fingers 32, 42, 62, 72, 82, 92 of each tile, the number of independently activated electrodes is N=8, with the phase changing once every 4 electrode fingers. Larger tile sizes are more effective in moving larger droplets 5. However, to move smaller droplets, it is beneficial to perform a sweep as described further below.

[0099] The inventors have found that a smaller pitch is better because it can move smaller droplets more efficiently, and still move larger droplets, particularly when the group of electrode fingers is grouped together using the "tiling" concept. Therefore, the pitch can be equal to or less than 750 μm, or more preferably equal to or less than 200 μm, or even more preferably equal to or less than 100 μm.

[0100] Tiling, or creating a finite number (N) of replicas of active individual electrodes, is a novel technique for building larger active areas from a small number of individual electrodes. Tiling makes the technique scalable to large areas. Tiling is accomplished by connecting groups of electrode fingers (see Fig. 27 The voltage set on any single electrode finger (e.g., electrode finger 1 of group A) is replicated on the remaining electrode fingers 1 of electrode group BG by tiling. In the case of tiling, the sweeping of the active area 17 of the outer surface 15 occurs simultaneously on multiple sweep fronts. Fig.25A , 25B , 26A and 26B show the sweeping motion of the shaded and non-shaded parts (or tiles). The droplets are attracted to the boundary between the shaded and non-shaded segments where the electric field exists.

[0101] Although the tiling causes the segments of the active area 17 to be mirror images of the other segments, a novel sequential voltage operation is produced on the electrodes so that the droplets 5 act by being pulled continuously across the area of ​​the active area 17, even though what is happening on each segment is the same as on the other segments. One key to producing an effective continuous sweep across all electrodes is to make the voltage signal period or power supply period on the electrode fingers an integer multiple of the time it takes for the entire sweep signal / pattern to spatially traverse a group of electrode fingers. Once this scheme is applied to all groups, the sweep is positioned on the fluid droplets 5 corresponding to the segments on the first group, as if continuously because the fluid droplets move along the electrode fingers of all groups. The continuous sweep effect is caused by Fig.28The timing diagram shown in , which shows a phase modulation signal for each electrode to modulate the phase of the AC signal, so that the phase modulated AC signal is applied to each electrode. Fig.28 In the example, the modulation signal is low or high, indicating in-phase and out-of-phase, respectively. For descriptive purposes, each electrode may be identified by a sequential reference n (where n=1 to N, and N is the total number of individually activated electrodes). Each electrode has a plurality of electrode fingers, inheriting the reference number of its electrode. The electrode fingers are arranged in a repeating sequential order from 1 to N for each tile A, B, C, ... Each electrode 1-N is driven by a corresponding phase modulated AC signal. For example, each phase modulated AC signal is generated by a single AC signal, which is generated using Fig.28 The corresponding N phase modulation signals shown are phase modulated individually for each electrode. Therefore, each phase modulation signal can also be identified by a sequential reference n (where n=1 to N) to correspond to the corresponding electrode. Each phase modulation signal is T w The phase shift is imposed on the AC signal periodically between an in-phase state (e.g., 0°) and an anti-phase state (e.g., 180°) with a period of t. The phase shift in each phase modulation signal n is delayed in time by a time step t relative to the phase shift in the preceding phase modulation signal n-1. s , so that the droplet is continuously swept across the outer surface in a predetermined direction.

[0102] exist Fig. 27 In the example shown, twelve independently controlled electrode fingers (N=12) are provided for each electrode group (or tile) AG, and the phase modulated AC signal applied to each finger is the same, but in a manner such as by Fig.28 The phase modulation signal for each electrode is shown to determine the in-phase state or the anti-phase state. In order to provide continuous sweeping, for any N independently activated electrodes, the time step t s will be t s =T w / N. t s and T w The value of can change over time. Therefore, continue to sweep the droplet from the Nth finger in tile A to the 1st finger in tile B. If the time criterion (t s =T w / N), then this "switching" between tiles is like a sweeping discontinuity. As an example, the frequency of the AC signal can be 500 Hz, the number of independently activated electrodes N is 12, and the phase modulation signal can have a period T of 24 milliseconds. w In this case, the time step t sFor a square wave phase modulated signal that imposes a 0° or 180° phase on the AC signal at any instant in time, the 0° / 180° phase shift advances every t s The 0° / 180° phase shift is used to shift the finger pairs from one pair to the next pair (e.g., 2 milliseconds). The additional benefit of the in-phase / anti-phase (0° / 180° phase) option is that it allows twice the effective voltage while minimizing the voltage supplied by the driver. The higher the voltage of the driver, the higher the complexity and cost. Taking N=12 and 0° or 180° phase shift as an example, the following table shows the time required for a period T w Within the time interval t s Phase shift of the AC signal applied to each of the 36 electrode fingers (3 electrode fingers per electrode):

[0103]

[0104]

[0105] The combination of agglomeration cycles and sweeping cycles is a novel idea. Sweeping may be more efficient by agglomerating smaller droplets into larger ones.

[0106] A focused cycle is when the voltage is applied so that the total voltage pattern does not move in a particular direction on average. A swept cycle is a voltage pattern that is spatially displaced in one direction in time. In the case of a swept cycle, the instantaneous or average velocity can be defined as the total voltage pattern. During a focused cycle, there may be motion in individual parts of the pattern, but the total voltage pattern in the active area does not shift in space.

[0107] In the present application, both the focusing cycle and the sweeping cycle can be used for clearing and cleaning the fluid droplets. The sweeping cycle has been described above and is described in Fig. 27 and 28 The focusing period is where an AC or DC field is applied by applying a voltage difference across two electrodes or across a group of electrodes. Recall that droplets are attracted to the area where the differential voltage is produced. The focusing period allows multiple droplets to be attracted to the area with a differential voltage, and the droplets can become larger by aggregating or combining with each other. For focusing, all other electrode fingers can be in opposite phases, and thus only two channels may be required. For sweeping, more independent channels are better, and this arrangement can still perform focusing.

[0108] AC sweeping is different from a DC voltage swept across electrodes or voltage channels. AC sweeping means that the polarity of each electrode has been flipped once or more before the sweeping pattern moves spatially to the next electrode. It should be noted that the next electrode does not necessarily mean the adjacent electrode. AC sweeping is more effective in: (1) avoiding charge accumulation on the electrodes, which may cause pinning, (2) moving droplets away from pinning points due to droplet vibrations during AC sweeping, and (3) pushing droplets and attracting droplets. It should also be noted that briefly shorting an electrode that has been driven with a DC voltage may not be sufficient to remove accumulated charge from the outer surface. However, when an AC voltage is used, the voltage changes from positive to negative, and there is no net charge on the surface, so the average voltage is zero.

[0109] Droplets can be pushed in case of AC sweep. Pushing / repelling droplets instead of attracting them is a novel idea. When the field or voltage is at DC, a droplet with a fixed dipole orientation reorients with the nearby DC, where the dipole moment is antiparallel or angled to the field. In case of AC voltage or AC field sweep, part of the droplet can reorient its dipoles, but each reorientation causes an instantaneous increase in the total potential energy within the droplet. The increase is associated with a repulsive force on the induced dipole on the droplet. Here, as Fig.29 and 30 As shown, ground (GND) is a voltage level between the low voltage and the high voltage. By using an intermediate ground voltage to push the droplet 5, the field generated by the ground electrode is not as strong as the field generated by the voltage difference across the high and low voltage electrodes. This means that the field across the high and low voltages is strong enough to keep the dipole orientation fixed, while the electric field from the ground electrode provides a push, but is not enough to flip the dipole orientation.

[0110] There are clear advantages to extending the area of ​​the first electrode 16 and the last electrode 19 so that droplets are not repelled on the first electrode or the last electrode (depending on the direction of the sweep). Fig.31 An example of droplet rejection at the end of the last electrode or from outside the active area is shown.

[0111] The explanation for this is similar to the droplet push effect. Here, the region outside the electrode is grounded so that the field from outside the active region to the end electrode opposes the dipole induced in the water droplet. Fig.32 To avoid repulsion at the end of the sweep, the area of ​​the last electrode (or the first electrode, depending on the sweep direction) can be extended. This creates an equipotential surface outside the active area so that during operation the forces due to the electric field do not prevent the droplets from sliding beyond the active area.

[0112] In addition to or as an alternative to the extended first electrode 16 and last electrode 19, these areas may also be coated with a hydrophilic material so as to expel the droplet 5 from the active area 17. In other words, the hydrophilic coating may be positioned close to the edge of the outer surface of the swept droplet.

[0113] It should be noted that the outer surface layer need not be merely hydrophobic. It may be superhydrophobic. Oil and other droplets may also be moved, for example, ice droplets or snowflakes. With various patterns of hydrophobic or hydrophilic droplets, the droplets may collect from the reservoir or sink to locations within or outside the active area.

[0114] The driver circuit 50 can be configured to variably adjust the frequency of the AC signal to change the speed at which the droplet is swept across the outer surface. For example, the sweep speed can be adjusted between about 20-40 mm / sec by changing the frequency between about 400 Hz and 1 KHz. The period of the AC signal can be selected so that each period causes the droplet to be moved the distance of one electrode finger. The speed at which the droplet is swept can be adapted to the terminal velocity of the droplet.

[0115] Another way to control water droplets on a surface is by using patterned hydrophobicity. If a water droplet lands on a boundary between a more hydrophobic area and a less hydrophobic area, the droplet will generally move toward the less hydrophobic area. This can be used to passively direct the droplet (or induce it to condense) into a smaller area to force the droplets to merge, which helps to form larger droplets in addition to aggregation or sweeping. For example, there can be alternating stripes of more hydrophobic layers and less hydrophobic layers. If the less hydrophobic area is too hydrophilic, the effect is not ideal because the water will then seep out too much and not bead up and fall off / be driven off the glass, or it may affect sweeping. Another embodiment would be a checkerboard pattern with more hydrophobic and less hydrophobic areas, or less hydrophobic "spots" on a more hydrophobic background. In each case, the goal will be an alternative method to get more drops to merge. Hydrophobic patterning can be used independently of electrowetting or in combination with it.

[0116] A hydrophobicity gradient is a continuous version of hydrophobicity patterning, which can be viewed as adjacent areas or true gradients with more finely varying hydrophobicities. The idea is that a droplet will move more easily in the direction of lower hydrophobicity, and so this can be exploited to help the droplet move in the desired direction. A gradient can also be created by a binary combination of two hydrophobicities, but the scale of the pattern is much smaller than the droplet, so the effective hydrophobicity is a gradient. The different hydrophobicities can be two spatially patterned coatings of different materials, removal of a single applied material, or surface patterning of a single substrate or coating material.

[0117] The hydrophobic layer 20 can be sprayed, coated or manufactured by microstructuring and / or nanostructuring the surface. Possible hydrophobic materials include AF, Optool UD120, Parylene AF4, Optool DSX, CYTOP, PDMS, Polyisobutylene (PIB), Rare Earth Ceramic Oxides, and Aquapel.

[0118] Substrate 12 may be made of any type of glass or plastic and may be rigid or flexible.

[0119] The electrodes can be made of indium tin oxide as a transparent ceramic conductor or PEDOT as a transparent polymer conductor.

[0120] The dielectric 25 may be made of: SU-8 (a photoresist polymer); a polymer-ceramic oxide composite; ultra-thin glass; a ceramic oxide or nitride (such as Al2O3, SiO2, Si3N4); or polyparaxylene.

[0121] Although two to twelve electrodes are described above, it should be understood that any number of electrodes may be used.

[0122] The above list of materials is not exhaustive in terms of what can be used. The material requirements are that the electrodes are preferably sufficiently conductive (there is no specific value for this property as far as is known), the dielectric preferably does not allow surface water to reach the electrodes (and is electrically insulating), and the hydrophobic layer is preferably sufficiently hydrophobic. By definition, hydrophobic means a water contact angle > 90 degrees. In some cases, both the hydrophobic and dielectric functions can be achieved by a single layer of material.

[0123] Unless otherwise stated in the claims, one of ordinary skill in the art will understand that the described invention and the construction of other components are not limited to any specific materials. Unless otherwise described herein, other exemplary embodiments of the invention disclosed herein may be formed from a variety of materials.

[0124] For purposes of this disclosure, the term "coupling" (in all its forms, coupling, coupling, coupled, etc.) generally means the direct or indirect (electrical or mechanical) engagement of two components with one another. Such engagement may be stationary in nature or movable in nature. Such engagement may be achieved using the two (electrical or mechanical) components and any additional intermediate members that are integrally formed as a single entity with each other or with the two components. Unless otherwise stated, such engagement may be permanent in nature or may be removable or releasable in nature.

[0125] It is also worth noting that the construction and arrangement of the elements of the present invention as shown in the exemplary embodiments are merely illustrative. Although only a few embodiments of the present innovation are described in detail in the present disclosure, it should be easily understood by those skilled in the art who review the present disclosure that many modifications are possible (e.g., changes in the size, dimensions, structure, shape and proportion, parameter values, installation arrangements, use of materials, colors, orientations, etc. of various elements) without substantially departing from the novel teachings and advantages of the stated subject matter. For example, an integrally formed element may be constructed of a plurality of elements, or an element shown as a plurality of elements may be integrally formed, the operation of the interface may be reversed or otherwise changed, the length or width of the structure and / or the components or connectors or other elements of the system may be changed, and the nature or number of the adjustment positions between the elements may be changed. It should be noted that the elements and / or assemblies of the system may be composed of any of a wide variety of materials that provide sufficient strength or durability, and may be in any of a wide variety of colors, textures, and combinations. Therefore, all such modifications are intended to be included within the scope of the present innovation. Other substitutions, modifications, changes, and omissions may be made in the design, operating conditions, and arrangements of desired and other exemplary embodiments without departing from the spirit of the present innovation.

[0126] It should be understood that any described process or step within the described process can be combined with other disclosed processes or steps to form a structure within the scope of the present invention. The exemplary structures and processes disclosed herein are for illustrative purposes and should not be construed as limiting.

[0127] It will also be understood that changes and modifications may be made to the structures and methods described above without departing from the concepts of the inventive apparatus and that such concepts are intended to be covered by the appended claims unless the language of such claims expressly states otherwise.

[0128] The above description is to be regarded as a description of the illustrated embodiment only. Those skilled in the art and those skilled in the art of making or using the device may make modifications to the device. Therefore, it should be understood that the embodiments shown in the drawings and described above are for illustrative purposes only and are not intended to limit the scope of the device, which is defined by the appended claims interpreted in accordance with the principles of patent law (including the doctrine of equivalents).

Claims

1. An optical element, comprising: a substrate having an outer surface on which droplets of a fluid may be formed; N independently activated electrodes, each identifiable by a sequential reference n (where n=1 to N), each electrode having a plurality of electrode fingers positioned proximate to and extending across an area of ​​the outer surface, the electrode fingers arranged in a repeating sequential order from 1 to N; and A drive circuit for selectively applying a phase modulated AC signal to the electrodes, the drive circuit generating the phase modulated AC signal by applying N phase modulated signals to the AC signal, wherein the N phase modulated signals are equal to the N independently activated electrodes, each phase modulated signal can also be identified by the sequence reference n (where n=1 to N) to correspond to the corresponding electrode, wherein each phase modulated signal is T w The phase shift is imposed on the AC signal periodically between the in-phase state and the anti-phase state, wherein the phase shift in each phase modulation signal n is delayed in time by a time step t relative to the phase shift in the sequentially preceding phase modulation signal n-1. s , so that the droplet is continuously swept across the outer surface in a predetermined direction. 2 . The optical element according to claim 1 , wherein the electrode fingers are arranged in a single plane with gaps therebetween. 3 . The optical element according to claim 1 , wherein the electrode fingers are arranged at a uniform pitch, wherein the pitch is a distance between centers of the electrodes, and the pitch is less than or equal to 750 μm.

4. The optical element of any one of claims 1 to 3, wherein the drive circuit is further configured to selectively apply voltage potentials between adjacent fingers in a manner that causes the fluid droplets to aggregate into larger fluid droplets.

5. The optical element according to any one of claims 1 to 4, wherein the time step t s Equal to T w / N.

6. An optical element according to any one of claims 1 to 5, wherein the drive circuit is configured to variably adjust the frequency of the AC signal to change the speed at which the droplet is swept across the outer surface.

7. An optical element according to any one of claims 1 to 6, wherein a last electrode finger of the plurality of electrode fingers is positioned close to an edge of the outer surface onto which the droplet is swept, wherein the last electrode finger of the plurality of electrode fingers is larger than the other electrode fingers.

8. An optical element according to any one of claims 1 to 7, and further comprising a hydrophilic coating located proximate to the edge of the outer surface where the droplet is swept.

9. An optical element according to any one of claims 1 to 8, wherein the plurality of electrode fingers provide capacitive sensing of droplets on the outer surface, and wherein the drive circuit is configured to apply the phase-modulated AC signal to the electrodes in response to the capacitive sensing of droplets on the outer surface.

10. An optical element according to any one of claims 1 to 9, wherein the plurality of electrode fingers are arranged in a plurality of tiles, wherein each tile comprises one finger of each of the plurality of electrodes arranged in a sequential order, wherein the sequential order is repeated for each tile.

11. An optical element, comprising: a substrate having an outer surface on which droplets of a fluid may be formed; a plurality of independently activated electrodes, each of the electrodes having a plurality of fingers positioned proximate to the outer surface and extending across an area of ​​the outer surface; and a driving circuit for selectively applying a signal to the plurality of electrodes, The electrode fingers are arranged at a uniform pitch, wherein the pitch is a distance between centers of the electrodes, and the pitch is less than or equal to 750 μm. 12 . The optical element according to claim 11 , wherein the pitch is less than or equal to 200 μm.

13. The optical element according to claim 12, wherein the pitch is less than or equal to 100 μm.

14. The optical element according to any one of claims 11 to 13, wherein the drive circuit is configured to selectively apply a phase modulated AC signal to the plurality of electrodes.

15. The optical element of claim 14, wherein the phase modulated AC signals applied to electrodes having adjacent fingers are identical but have a time step t in phase shift relative to each other in such a way as to continuously sweep the fluid droplet in a predetermined direction across the outer surface. s time delay.

16. The optical element according to any one of claims 11 to 16, wherein the electrode fingers are arranged in a single plane with gaps therebetween.

17. An optical element according to any one of claims 11 to 16, wherein the drive circuit is further configured to selectively apply voltage potentials between adjacent fingers in a manner that causes the fluid droplets to coalesce into larger fluid droplets.

18. An optical element according to any one of claims 11 to 17, wherein a plurality of interdigitated fingers provide capacitive sensing of droplets on the outer surface, and wherein the drive circuit is configured to apply the signal to the plurality of electrodes in response to the capacitive sensing of droplets on the outer surface.

19. An optical element according to any one of claims 11 to 18, wherein the plurality of interdigitated fingers are arranged in a plurality of tiles, wherein each tile comprises one finger of each of the plurality of electrodes arranged in a sequential order, wherein the sequential order is repeated for each tile.

20. An optical element, comprising: a substrate having an outer surface on which droplets of a fluid may be formed; a plurality of independently activated electrodes, each of the electrodes having a plurality of fingers positioned proximate to the outer surface and extending across an area of ​​the outer surface; and a driving circuit for selectively applying a signal to the plurality of electrodes, The electrode fingers are arranged in a single plane with gaps between them.

21. The optical element of claim 20, wherein the drive circuit is configured to selectively apply a phase modulated AC signal to the plurality of electrodes.

22. The optical element of claim 21, wherein the phase modulated AC signals applied to electrodes having adjacent fingers are identical but have a time step t in phase shift relative to each other in such a way as to continuously sweep a fluid droplet in a predetermined direction across the outer surface. s time delay. 23 . The optical element according to claim 20 , wherein the electrode fingers are arranged at a uniform pitch, wherein the pitch is a distance between centers of the electrodes, and the pitch is less than or equal to 750 μm.

24. An optical element according to any one of claims 20 to 23, wherein a plurality of interdigitated fingers provide capacitive sensing of droplets on the outer surface, and wherein the drive circuit is configured to apply the signal to the plurality of electrodes in response to the capacitive sensing of droplets on the outer surface.

25. An optical element according to any one of claims 20 to 24, wherein the plurality of interdigitated fingers are arranged in a plurality of tiles, wherein each tile comprises one finger of each of the plurality of electrodes arranged in a sequential order, wherein the sequential order is repeated for each tile.

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